250 Top End On A Cbr 150

[Hog Head]

Will a Honda 250 top end fit on a CBR 150 case? Just looking at it would suggest so but I would like to know a bit more before bring in the bits.

If so what is the preferred model, what else is required besides carb, pipe, ignition etc.

Anyone done this?

[dave_boo]

Supposedly the last generation of 250 from Australia is a drop on fit. I'd mostly be worried about the added stresses to the CBR-150R's bottom end.....

[jackcorbett]

Supposedly the last generation of 250 from Australia is a drop on fit. I'd mostly be worried about the added stresses to the CBR-150R's bottom end.....

I blew the transmission of a 1992 Mazda Miata at 140,000 miles. Transmissions don't normally go out on a Mazda Miata. Here's how I managed it.

First off I put an after market exhaust on it...good for 5 more horsepower. Then I put a header on the little car...good for even more horsepower. Then I added a Sebring supercharger and that alone increased my horsepower by at least 40 %. Then to get more cool air into the engine I put an air scoop on. Let's see, oversized wheels and larger tires. Now that was the berries. I felt a huge increase in torque at all rpm levels and the power came on instantaneous unlike the case would have been had ai turbocharged it. The car behaved as if I had put a V-8 in it. I could get 139 miles an hour out of it before the rev limiter cut in. I think it would have done 150 without the rev limiter. My zero to sixty miles an hour times dropped from about 9.1 seconds to around 6.5 seconds. Let's see. I blew my first engine while trying to get more miles per hour out of the car. I can't remember exactly but probably 6000 rpms was good for about 118 miles an hour and that's about what the stock engine on a 1992 Miata was good for having just enough power to drive 2200 pounds at 6000 rpms in fifth gear for 118 miles per hour. But now with the vast increase in power that little engine could push the same 2200 pounds through all that air resistance in fifth gear way way past its previous limitations. The Rev limiter would cut in at about 7200 rpms which equated to 139 miles an hour. Thinking about it after the blow out I reasoned that the car was holding at over 7000 rpms for periods of time exceeding 30 seconds...an altogether different situation to shifting quickly at 7000 rpms to a higher gear and dropping the rpms when all I wanted to do was to accelerate quickly. So then I decided not to drive at speeds over 120 miles an hour. But then I blew engine number 2. The reason was the engine was burning lean now on account of the supercharger. After that I blew engine number three and that's when I took the supercharger off. Suddenly the car once again became typically Mazda Miata reliable. And I drove it all over the U.S. and about the only thing that ever happened to it after that is I wore out a fan belt causing the engine to overheat a little so I just spent the night in a hotel somewhere out West and the next day I had a shop replace the belt and I was on my way.

My long term solution after the transmission went out (that's because I essentially dropped a V-8 into a car that was engineered for only four cylinders which must have been like hitting the transmission with huge sledgehammers) was to buy a brand new special edition 2002 Mazda Miata with a 6 speed transmission that would drop the engine's rpms at cruising speeds. The car was only good for zero to sixty times of around 7.9 seconds but when I'd take it out West for long cruises and where the speed limits were 75 miles and hour but not enforced very much, I'd simply set the cruise control for about 85 to 90 miles an hour and I'd really be able to get down the road in a hurry eating up hundreds of miles at a clip. I think the car would have easily lasted 200,000 miles or more with hardly a problem.

So what does this have to do with souping up bikes? I think a lot. But each to his own. One more thing.....the new Miatas now have a lot more horsepower than my 2002 model had, and I'll bet they have much beefier transmissons too. Oh, and one more thing.......out on a lot of those roads I was driving on in the Western states there weren't any Thai motorcyle taxi drivers full of too much testocerone. In fact, there wasn't too much of anything out on a lot of those roads so the greatest danger was falling asleep at the wheel.

Edited January 26, 2008 by jackcorbett

[submaniac]

Fast, reliable, cheap. Choose any TWO.

Actually Jack, did you ever check out the Mazdaspeed Miata with the FACTORY turbo? I never did drive one, but was always curious at how that thing would go. I mean the Miata is so light, and I LOVE turbos, especially when they are factory. When you get into aftermarket FI, you will get some 'reliability issues'.

Anyways, back to the original post, it is supposed that the 250 heads will fit on the CBR 150, but I do not know, and do not know anyone that has ever done it. But my thoughts are that it probably would work, and it's not like parts for a CBR 150 are expensive or anything. Also, I wouldn't worry about the bottom end not withstanding the power of a 250cc. 1) Manufacturers generally make the bottom end stronger than it needs to be to avoid having to fix bikes under warranty 2) Honda is known for building super tough engines 3) a 100cc difference is unlikely to put that much additional stress to the bottom end and 4) supposedly the 150cc is the same engine as the 250cc but with a smaller cylinder head.

Actually what I have been thinking for a while is why doesn't any one talk about engine swaps in this country. In the states, it is standard fare with lil' Asian boys swapping an Acura engine into a civic. Everyone is always talking about getting larger displacement bikes in this country, so I don't know why people haven't done it.

The 150 sportbikes, be it Honda, Yamaha, Kawasaki, etc., seem to be based upon the 1 cylinder dirtbike engines. (The proviso is I am NOT a mechanic, but looking at the engines makes me think they are the dirtbike engines.) If you are talking the CBR, it seems to me that the engine from the CRF would work, and I think the idea of a CBR with a 450 cc thumper engine producing 55 hp seems very intriguing: http://www.powersportstv.com/2007/Honda/CR...torcycle/23190/

I also *think* the CBR 150 engine is the same as the CRF 150 engine (once again I am NOT a mechanic, so get more information before spending $$--AND I do not own a Honda so haven't looked into it very much), and there are tons of big bore kits for the CRF 150: http://www.xr100.com/crf150.htm

Does anyone know really what engine is in the CBR 150? Like the engine model? I am 99% certain it has a clone in a dirtbike model, and since modding dirtbikes is a well established practice, I think that you could find and use the parts made for the dirtbikes.

[jackcorbett]

Fast, reliable, cheap. Choose any TWO.

Actually Jack, did you ever check out the Mazdaspeed Miata with the FACTORY turbo? I never did drive one, but was always curious at how that thing would go. I mean the Miata is so light, and I LOVE turbos, especially when they are factory. When you get into aftermarket FI, you will get some 'reliability issues'.

I considered buying the Mazdaspeed Miata when it first came out as it would have possibly been very similar to my supercharged Miata EXCEPT it was standard issue. Later on various add ons were available from firms such as Jackson Racing that supposedly would prevent the Sebring superchargers from causing Miata engines from burning lean. But after three engine burn outs I was no longer interested. But now even the standard Miatas are producing 170 horsepower compared to my 1992's original 116. This is without supercharging or turbocharging. I'd say that was about what my 1992 was most likely producing with the supercharger and other extra market equipment. Considering the light weight of the Miata that should produce some pretty exciting performance. Not like a Corvette or top model Porshes that do zero to sixty in 5 seconds or less but still....around 6.5 seconds-7 seconds. And with near perfect handling with a dead on 50-50 weight distribution, great reliability and low price.

Sorry, but I cannot comment on the 250 engine in a 150 CBR. As for the large thumper you mentioned, I once had a Honda 500 XL on and off road bike that weighed around 290 pounds. It was not bad on the highway but in the woods it was too much. Handling not good for that and too much torque and too much weight. And around the farm I finally went out and bought a 2nd 185 Honda XL (I had traded my previous 185 XL for the 500 XL) but at that time I also had a 650 BMW twin for the street and later a BMW K-100 RS. In the dirt the 185 XL was much better than the 500 XL, it started better and it could still do around 70 miles an hour on the street.

Edited January 26, 2008 by jackcorbett

[dave_boo]

Fast, reliable, cheap. Choose any TWO.

Actually Jack, did you ever check out the Mazdaspeed Miata with the FACTORY turbo? I never did drive one, but was always curious at how that thing would go. I mean the Miata is so light, and I LOVE turbos, especially when they are factory. When you get into aftermarket FI, you will get some 'reliability issues'.

Anyways, back to the original post, it is supposed that the 250 heads will fit on the CBR 150, but I do not know, and do not know anyone that has ever done it. But my thoughts are that it probably would work, and it's not like parts for a CBR 150 are expensive or anything. Also, I wouldn't worry about the bottom end not withstanding the power of a 250cc. 1) Manufacturers generally make the bottom end stronger than it needs to be to avoid having to fix bikes under warranty 2) Honda is known for building super tough engines 3) a 100cc difference is unlikely to put that much additional stress to the bottom end and 4) supposedly the 150cc is the same engine as the 250cc but with a smaller cylinder head.

Actually what I have been thinking for a while is why doesn't any one talk about engine swaps in this country. In the states, it is standard fare with lil' Asian boys swapping an Acura engine into a civic. Everyone is always talking about getting larger displacement bikes in this country, so I don't know why people haven't done it.

The 150 sportbikes, be it Honda, Yamaha, Kawasaki, etc., seem to be based upon the 1 cylinder dirtbike engines. (The proviso is I am NOT a mechanic, but looking at the engines makes me think they are the dirtbike engines.) If you are talking the CBR, it seems to me that the engine from the CRF would work, and I think the idea of a CBR with a 450 cc thumper engine producing 55 hp seems very intriguing: http://www.powersportstv.com/2007/Honda/CR...torcycle/23190/

I also *think* the CBR 150 engine is the same as the CRF 150 engine (once again I am NOT a mechanic, so get more information before spending $$--AND I do not own a Honda so haven't looked into it very much), and there are tons of big bore kits for the CRF 150: http://www.xr100.com/crf150.htm

Does anyone know really what engine is in the CBR 150? Like the engine model? I am 99% certain it has a clone in a dirtbike model, and since modding dirtbikes is a well established practice, I think that you could find and use the parts made for the dirtbikes.

Not quite the same....the CRF is a SOHC versus the DOHC CBR (in that respect it's closer to the CBR 125R). Of course it's also aircooled (I really don't like air cooled engines, but that's just me!)

Here's an image of the CRF cylinder:

And here's one of the CBR cylinder:

Look pretty darn close to me.

Edited January 26, 2008 by dave_boo

[Richard-BKK]

The Honda CBR-150 is using the same engine as the CBR-125R and Honda Sonic 125, the main difference is the cylinder and cylinder head. In basic is a CBR-150 a bore-up for the CBR-125. If we calculate the bore and cylinder wall I would say that paying it safe would be around 175cc (what is also compatible with bore-up kits available on the market.)

Placing a 250cc cylinder of a CBF-250 (bore x stroke 73.0 x 59.5 mm) on a CBR-125/150 is technical a bit more complicated, first "biggest" problem is the mounting screw holes are not the same, second major problem is the length of the stroke which is for a CBR-125/150 only 47.2mm

[PeaceBlondie]

I am no mechanic, but I always understood the CBR125/150 watercooled, twincam family to be its own breed. I cannot think of an example of an engine family being both water and aircooled. Asean motors/goodspeed has a kit that both overbores and strokes the 150, and I suspect the bottom end is not designed for double the output of the 125 model.

[madjbs]

CBR125 has a SOHC air cooled engine while the CBR150 in Thailand has a DOHC water cooled engine so I dont think they are the same.

[Phil Conners]

Actually what I have been thinking for a while is why doesn't any one talk about engine swaps in this country. In the states, it is standard fare with lil' Asian boys swapping an Acura engine into a civic. Everyone is always talking about getting larger displacement bikes in this country, so I don't know why people haven't done it.

Main reason: The Law. It's illegal to make any modifications to bikes in Thailand. You get caught they take your non-standard parts and hit you with a (granted, small) fine.

[dave_boo]

The Honda CBR-150 is using the same engine as the CBR-125R and Honda Sonic 125, the main difference is the cylinder and cylinder head. In basic is a CBR-150 a bore-up for the CBR-125. If we calculate the bore and cylinder wall I would say that paying it safe would be around 175cc (what is also compatible with bore-up kits available on the market.)

Placing a 250cc cylinder of a CBF-250 (bore x stroke 73.0 x 59.5 mm) on a CBR-125/150 is technical a bit more complicated, first "biggest" problem is the mounting screw holes are not the same, second major problem is the length of the stroke which is for a CBR-125/150 only 47.2mm

In just looking at pre '06 model CRF-150, and of course based on the assumption that the mount holes line up, you're looking at a 63.5 x 49.5 cylinder versus the CBR-150's 63.5 x 47.2. So if you were to buy a bore up kit based on that model, you wouldn't have as much increase in displacement as a CRF owner would enjoy. I've sent off an email to Honda asking about the similarities....here's hoping they'll share. I can't contact an American dealer, since CBR 150's aren't sold in the States.

[Richard-BKK]

The Honda CBR-125R is also liquid-cooled single-cylinder four-stroke engine, and as I said before identical to the CBR-150 (with exception of the cylinder and cylinder head)

SOHC stands for Single Overhead Camshaft. That means that there is only one camshaft per header. Inline engines will contain one camshaft. V-type and/or flat will contain 2 camshafts. For a SOHC engine there are usually 2 valves per cylinder but there can be more with the addition of cams for each valve.

DOHC stands for Double Overhead Camshaft. Now there are 2 camshafts per header. So in an inline there are 2 camshafts because there is only one header, but there is 4 in a V-type or flat engine. These DOHC engines usually have 4 valves. One camshaft for the exhaust valves and the other for the intake valves.

Advantages to having a DOHC engine over a SOHC is that the engine has twice as many intake and exhaust valves as a SOHC motor. (Main difference between CBR-125 and CBR-150, 2-valves or 4-valves) This makes the engine run cooler and more smoothly, quietly, and efficiently. But the downfall is that DOHC engines cost more for repairs. To ensure against expensive engine repairs, make sure you change your engine's timing chain about every 60,000 miles. (In both the CBR125 and CBR150 the camshaft is powered by a chain system)

Edited January 26, 2008 by Richard-BKK

[mikethevigoman]

Will a Honda 250 top end fit on a CBR 150 case? Just looking at it would suggest so but I would like to know a bit more before bring in the bits.

If so what is the preferred model, what else is required besides carb, pipe, ignition etc.

Anyone done this?

The bottom end wont take it, better to try and shoehorn a 250 engine in it,. Edited January 26, 2008 by mikethevigoman

[submaniac]

Jack--> You've got me really curious as to how you blew up so many engines. How many pounds of boost was your supercharger pulley set up for? And what did you do for fuel management (which is always the most important thing)? I am making the assumption that you were running stock internals. I also *think* you were running a piggy back ecu instead of a stand alone ECI, which is kind of asking for trouble. The piggy backs also retard timing when they retard the fuel. An engine running lean produces crazy high horsepower. Too lean...and well, you have 'problems'

That is why I like the idea of a FACTORY turbo because they would have factory beefed up internals (sleeves/forged pistons/lower compression pistons) instead of having to tear apart your engine and doing all of that. With the stock turbo, the Mazdaspeed was not that much faster than the non-turbo model. But who would buy that car without putting bigger turbos? I mean it just seemed like you could get crazy horsepower, like what they are doing with the Mitsubishi eclipses making 400+ hp from a little 2.0 liter 4 banger. In a Miata, well you would have a modern Shelby cobra.

Getting back to the CBR issue--> once again I reiterrate that I am NOT A MECHANIC (at least I know little about motorcycles) and I do not own a Honda, and have not really looked into comparable Hondas.

I guess I am wrong on the engine being similar to the CRF, meaning that you could not use the big bore kits or any other parts meant for the CRF. However, I still do not think that necessarily precludes a complete engine swap. A liquid cooled to air cooled swap (CRF engine into CBR) is doable if you throw out the radiator and cooling system.

Even if it is not the CRF, there must be a comparable Honda engine that would fit into the engine compartment of a CBR frame, and I would think it would be from one of the dirtbikes as they are similar sized and also designed to be lightweight and powerful. I have not looked into it because I do not have a Honda, and I do not think that my bike is underpowered. However, enough people have expressed interest into having more powerful bikes that I am surprised that it isn't more well discussed. I think if more research is done into it, it is feasible. After all, people have managed to fit a small block chevy 350 into the engine bay of a Porsche 911. Fitting a larger cc engine into a CBR frame does not seem out of this world.

I mean I think there are some distinct possibilities for having a more powerful bike at a lower cost. When I was looking for my bike, I have found a few non-running NSR's and TZM's that were dirt cheap (as low as 5,000 baht). If you got one of these as an experiment, and found a cheap dirt bike engine, you may just succeed. How about getting a non running NSR/TZM and swapping a two stroke XR/YZ engine in it? And another advantage to the dirt bike engine swap is that there is a huge market for dirtbikes (at least in the U.S.) and they are constantly getting wrecked from being too 'offroaded'.

As for legal issues, I really do not think there is much of a chance of being caught, to be honest. I just got my bike registered last week, and I doubt that Dept. of Transportation even checked the engine numbers. To look at it, they would have to take off the plastic fairing which wasn't done, so I don't think they checked. I think it is even more remote to be caught by a cop, as they too would have to take off the fairing to check the motor number. And if the cop is in the process of taking a screwdriver to your fairing, and you haven't bribed him yet, you deserve to get your bike impounded. If you just keep the old engine whenever you need to do a rubbing, you should be fine.

[dave_boo]

The Honda CBR-125R is also liquid-cooled single-cylinder four-stroke engine, and as I said before identical to the CBR-150 (with exception of the cylinder and cylinder head)

Yes, the throw is similar. But there are more differences, which you alluded to.

SOHC stands for Single Overhead Camshaft. That means that there is only one camshaft per header. Inline engines will contain one camshaft. V-type and/or flat will contain 2 camshafts. For a SOHC engine there are usually 2 valves per cylinder but there can be more with the addition of cams for each valve¹.

For a clarification:

1. Actually more cam lobes (but that's just being pedantic).
   

Advantages to having a DOHC engine over a SOHC is that the engine has twice as many intake and exhaust valves as a SOHC motor. (Main difference between CBR-125 and CBR-150, 2-valves or 4-valves) This makes the engine run cooler and more smoothly, quietly, and efficiently. But the downfall is that DOHC engines cost more for repairs. To ensure against expensive engine repairs, make sure you change your engine's timing chain about every 60,000 miles. (In both the CBR125 and CBR150 the camshaft is powered by a chain system)

As a side note, not only does the DOHC have more valves, it also increases the area that the air can come in. Reason being that if you were to create a valve twice as big as those in a DOHC to get the same movement, it wouldn't work. There would be more turbulence around the valve (since you're trying to force more air in at one point instead of forcing more air in over several points), the mass of the valve would be greater (increasing the chance of valvetrain float), SOHC doesn't allow you to have those fancy variable valve jobbies, etc.

[canuckamuck]

As for legal issues, I really do not think there is much of a chance of being caught, to be honest. I just got my bike registered last week, and I doubt that Dept. of Transportation even checked the engine numbers. To look at it, they would have to take off the plastic fairing which wasn't done, so I don't think they checked. I think it is even more remote to be caught by a cop, as they too would have to take off the fairing to check the motor number. And if the cop is in the process of taking a screwdriver to your fairing, and you haven't bribed him yet, you deserve to get your bike impounded. If you just keep the old engine whenever you need to do a rubbing, you should be fine.

The cops are running CBR's. It wouldn't take a genius to spot a different engine.

However, I wonder how much modify is too much. Would just a non stock exhaust do it?

[Hog Head]

DOHC lessons and blown Mazdas aside, is there a ROW or domestic larger top end that I can swap out, given a fair bit of mechanical experience in doing such things

[dave_boo]

DOHC lessons and blown Mazdas aside, is there a ROW or domestic larger top end that I can swap out, given a fair bit of mechanical experience in doing such things

Rumour has it that the Chinese knock-off bikes use old cast off Honda machining tools to create their engines. Will this equate to parts that will work on a CBR? Don't know, but it'd probably take big brass ones to find out.

[PeaceBlondie]

Rumour has it that the Chinese knock-off bikes use old cast off Honda machining tools to create their engines. Will this equate to parts that will work on a CBR? Don't know, but it'd probably take big brass ones to find out.

Don't machine tools have useful lives of ten or twenty years? The CBR tools may be less than 7 years old.

[Richard-BKK]

Ask any Thai mechanic a CBR-150 cylinder, piston and cylinder head assembly fits on any CBR-125R and Honda Sonic 125 engine. The Honda Sonic is using the same engine as the CBR-125R.

The only difference between the two engines, SOHC and DOHC is in the cylinder head. Anybody who says otherwise has never seen both engines.

[submaniac]

DOHC lessons and blown Mazdas aside, is there a ROW or domestic larger top end that I can swap out, given a fair bit of mechanical experience in doing such things

Yeah, but "off topic" is fun.

Seriously, if we can just find out the engine of the Thailand CBR (model number, family, anything) I think you will have won half the battle there.

It strikes me that Honda is a global company. Any country on the face of this earth, it is pretty much guaranteed that there is some "Honda" in it. Given the $$$$ for R & D, I find it hard to believe that Honda only uses this engine in Thailand, and does not have the same family of engine somewhere else in this planet. Furthermore, it is only Thailand and a few other nations that have the 200cc limit. If you can find out what family/engine the CBR has, and can find a similar family of engine from another country, you would be set. Just find out the engine, another model in another country that uses the same family of engine, but larger cc and you could import either just the head or do the entire engine swap.

I just don't know what that engine family is, or other Honda models that use it, as I don't have a Honda and really don't care about Honda (except for the cars) that much. There are so many CBR owners on this board (given the CBR owner's thread) that somebody has got to know.

[madjbs]

Sorry Richard-BKK, you are right, the CBR125 is in fact liquid cooled as well. For some reason I had it in my head that it was air cooled.

[dave_boo]

Rumour has it that the Chinese knock-off bikes use old cast off Honda machining tools to create their engines. Will this equate to parts that will work on a CBR? Don't know, but it'd probably take big brass ones to find out.

Don't machine tools have useful lives of ten or twenty years? The CBR tools may be less than 7 years old.

I was basing that 'musing' on the fact that I agree with submaniac. I find it difficult to accept the fact that there are enough fundamental differences between the engines used in the CBR line and CRF/CBF to preclude the swap. If a design works, why would Honda go to lenghts to change it? Ergo(blatant rip off of the 'Architect'), it's seems likely that a SOHC aircooled cylinder/head should mount up.

However, it may be best to just buy one of those up bored kits designed for the CBR 150R in the first place. Than you have a gaurantee it will work(i.e. you don't p!ss away some money for nothing) and it mantains a stealthy stock look.

My question is, why can goodspeed have a CBR 125R oversize kit to 176 cc and they only can take the CBR 150 up to 170(and that's with a +2mm crank but only a 66mm bore)? Why does the 125 get a bigger piston (although curiously both strokes stay the same)? And if the bottom end is the same, why isn't the +4 mm crank listed under the CBR 150R? With that crank and the top end(the 66mm one), you'd be looking at 175 cc, which is actually worst than taking a 125 up the way it's available in goodspeed's website. You'll have piston which isn't as overly square, which won't let you rev higher. Of course, the torqure will be better. /me wondering if you can just get the (125) cylinder, reuse your own head, and the oversized crank netting you some 192 cc.

[submaniac]

I was basing that 'musing' on the fact that I agree with submaniac. I find it difficult to accept the fact that there are enough fundamental differences between the engines used in the CBR line and CRF/CBF to preclude the swap. If a design works, why would Honda go to lenghts to change it? Ergo(blatant rip off of the 'Architect'), it's seems likely that a SOHC aircooled cylinder/head should mount up.

Dave, thanks for agreeing with me!!! It is a strange sensation as it so very seldom happens!!!!

NEW INFORMATION ON THE CRF'S

Actually there is a new wrinkle in the entire engine swap/what heads would work. I just checked the Honda website, and the CRF's that are 250cc and above ARE LIQUID COOLED. Specificaly the CRF250x, and CRF450x. Both are 4 stroke, single cylinder. But they are SOHC, not DOHC, like the CBR. See specs: http://powersports.honda.com/motorcycles/o...odelId=CRF250X8

So in terms of tweeking your cbr, since the CRF 250 is WATERCOOLED the heads may just bolt onto the CBR 150 pistons. Or, if (as I would be more inclined to do), you could easily swap out the CBR 150 engine for either the 250cc CRF engine or (muhahahahaha) the 450CRF engine:

http://powersports.honda.com/motorcycles/o...odelId=CRF450X8

As for swapping cylinder heads.

As for the CRF 250cc, the honda specs for bore and stroke are= 78.0mm x 52.2mm

For the 150CBR the specs are 63.5mm x 47.2mm.

Of course I would say that swapping in the ENTIRE ENGINE would probably be easier, and I think either the 250cc or (yay!!!) the 450 cc would fit.

It is nice what you guys are talking about in terms of the big bore kits, but geez, you are only talking an increase of displacement from about 20-25cc's. I really do not think the minor power increase would be worth the headache. But going to nearly double the cc's to the 250, or triple the cc's would be worth the effort. My $0.02.

[submaniac]

This is a CRF250 piston and cylinder Kit I saw on ebay (current bid, $26):

http://cgi.ebay.com/ebaymotors/2004-honda-...tem300193392441

The CRF250 cylinder:

Looks pretty close to the CBR cylinder:

Me thinking out loud "could you not just swap the cylinder and piston" and keep your original heads. I think the length of the cylinder would accomodate the additional 5mm stroke, and if not couldn't you rechamber the heads? (I think keeping the original CBR150 heads would be a good idea as it is DOHC.)

Just a thought

[dave_boo]

I was basing that 'musing' on the fact that I agree with submaniac. I find it difficult to accept the fact that there are enough fundamental differences between the engines used in the CBR line and CRF/CBF to preclude the swap. If a design works, why would Honda go to lenghts to change it? Ergo(blatant rip off of the 'Architect'), it's seems likely that a SOHC aircooled cylinder/head should mount up.

Dave, thanks for agreeing with me!!! It is a strange sensation as it so very seldom happens!!!!

NEW INFORMATION ON THE CRF'S

Actually there is a new wrinkle in the entire engine swap/what heads would work. I just checked the Honda website, and the CRF's that are 250cc and above ARE LIQUID COOLED. Specificaly the CRF250x, and CRF450x. Both are 4 stroke, single cylinder. But they are SOHC, not DOHC, like the CBR. See specs: http://powersports.honda.com/motorcycles/o...odelId=CRF250X8

So in terms of tweeking your cbr, since the CRF 250 is WATERCOOLED the heads may just bolt onto the CBR 150 pistons. Or, if (as I would be more inclined to do), you could easily swap out the CBR 150 engine for either the 250cc CRF engine or (muhahahahaha) the 450CRF engine:

http://powersports.honda.com/motorcycles/o...odelId=CRF450X8

As for swapping cylinder heads.

As for the CRF 250cc, the honda specs for bore and stroke are= 78.0mm x 52.2mm

For the 150CBR the specs are 63.5mm x 47.2mm.

Of course I would say that swapping in the ENTIRE ENGINE would probably be easier, and I think either the 250cc or (yay!!!) the 450 cc would fit.

It is nice what you guys are talking about in terms of the big bore kits, but geez, you are only talking an increase of displacement from about 20-25cc's. I really do not think the minor power increase would be worth the headache. But going to nearly double the cc's to the 250, or triple the cc's would be worth the effort. My $0.02.

It may be easier swapping the entire engine, with the exception of the transmission(?). Another thing that we need to take in consideration when trying to just swap the cylinder and head from the 250 is the throw. If you get too much, you increase the chance that the connecting rod comes into contact with some piece of the engine housing since the angle will be steeper as it goes through its stroke.

So I guess the thing comes down to...where can we find a fairly fresh CRF motor for less money than what it would cost to go big bore kit? And this is keeping in mind the very different 'responses' of the two motors.

**as a side note**

that last question I asked in my previous post WOULD NOT work, due to the dished parts of the CBR 125R's piston. Namely, being a 2 valve, it would cause problems with the CBR 150R's 4 valves.

**edited part**

submaniac just posted this before I posted mine, but I wonder if someone with an ebay account could send that guy an email requesting a measurement of the stud holes. It would be simple to than measure a CBR 150R to find out if at least that part matches out. Some minor machining could be easily taken care of.

Edited January 27, 2008 by dave_boo

[submaniac]

Another, better pic of the CRF cylinder. This is of the 'big bore' kit if you want to go to 263!

[submaniac]

Here's a 450cc engine for $1300, kinda pricey, but...whooo...imagine the fun with your CBR bigger bike HP.

http://cgi.ebay.com/ebaymotors/2003-CRF-45...tem160201699974

Here's a complete 250cc engine for $999.

http://cgi.ebay.com/ebaymotors/HONDA-CRF-2...tem220194949407

Keep in mind, that I have seen them cheaper. You just have to look around on ebay.

For those of you with CBR's (since I don't have one) take a look at the pictures of the complete engines, and compare them to your CBR engine. Based on the design of the cylinder, I think it just might be from the same family.

Also, I did email seller with the measurements between the studs.

Edited January 27, 2008 by submaniac

[submaniac]

Picture of the CBR 176 bore up kit I found off of aseanmoto. The more pics of the CBR cylinder I see, the more I think it is similar to the CRF.

Edited January 27, 2008 by submaniac

[PeaceBlondie]

Maybe you could fit a Suzuki L650 Savage air cooled engine........you could fit a Triumph 2,300 cc triple....or a small block Chevy....you could buy a BMW F650 with full warranty....you could move to a country that sells bigger bikes....