My air cooled monoshock trials bike project (pic heavy)

[thaiguzzi]

89 Aprilia Climber 280 Rolling chassis and bodywork.

96 Yamaha RXZ 135 engine, bored 2mm o/s to 142cc, headstock, front downtubes, green book and no. plate.

Built originally by a German bloke i never met in Pattaya and finished off by Chris (Darkside Moto x). Although functional, and engineered correctly, the whole thing had been built, how can i say, to a budget, no disrespect to the original builders.

Gearing is 12/51 (std is 15/38). Weight dry, no fuel, but inc 600ml of oil is 81kgs currently.

Original cost was 17k. I have spent an extra 9,495 baht in total (total price around 26 odd k), of which

# 1,120 baht plus postage (USA) were the Boyesen power reeds

# 2,200 baht plus postage (UK) were the S3 steel wide footpegs

# 2500 baht for the paintwork.

That leaves 3675 baht for all the odds'n'sods locally bought like new chain, 90 degree throttle, flywheel extractor, seat re-cover, stickers, etc, and LOTS of s/steel fasteners. Virtually all the fasteners have been lightened in the lathe inc hex and allen heads. The only non stainless fasteners on the bike left is the front 8mm engine bolt (long), the new c/head sleeve nuts, and the 3 wheel and s/arm spindles.

I have in excess of 80-90 hours work in it.

Long term stuff still to do;

# HCP (hard chrome plate and regrind to size) the front forks next time i'm in the UK.

# Purchase new tires.

# Re-do the ex system, which i'm gonna actually start this week.

Now everything is sorted to ride well, it is a hoot and performs very very well.

BEFORE (as purchased);

[thaiguzzi]

DURING;

move the air filter to a safer and higher area, inc a bunch of rubber filter hoses from various bikes from the local shop, bought and tried about 6, ended up using 3.

Seat recovered, heat shields for the exhaust made.

Had to replace the mish mash of incorrect c/head nuts, so whipped the head off for a peak inside. All good, 2mm o/size bore. Could'nt get genuine RXZ nuts, so replaced with Honda Dash sleeve nuts. Note replacement custom fabricated oil pump cover (dry - everything blanked off behind).

[thaiguzzi]

Note the crummy stick welding around the join on the top tube head steady between Yamaha and Aprilia frame parts. Now all ground out and redone with mig (no photos).

[thaiguzzi]

Wanted seperate covers instead of one piece for the flywheel stator and gearbox sprockets, so had to remove the L/H side cover and cut it about. All good inside, and at the same time check the wiring for ignition to the cdi and coil and bin the rest. Had to buy a correct Yam flywheel extractor (300 baht) for stator removal.

Finished up not too shabby. Easy access to the g/box sprkt and flywheel stator now a nice looking seperate cover.

To modify my R/H cover, accentuate the clutch cover, recess the oil pump cover, get access to the oil pump drive (the pump had already been binned prior to purchase as no room for an oil tank), i had to take the cover off. Binned the gears for the rev drive and oil pump, pulled the clutch for inspection, replaced the shock rubbers, filed the clutch drum tags, and the found a shim and a circlip on the floor of the cover... The k/start quadrant gear floats on the mainshaft gear, absolutely shagged bush, wobbling all over the place (hence lost circlip). Machined a new bronze bush and replaced new circlips.

I loved the prices; top end gasket set 35 baht (inc alloy head gasket!), full gasket set 95 baht. C/case seals were all good.

[thaiguzzi]

Finished R/H cover (nothing behind the fabricated drilled alloy cover).

Boyesen reeds from the States and the std reed cage and IN manifold. Money well spent.

Aprilia Made In Italy name plate (plastic unfortunately), c/w brass 4BA screws.

Nice touch - just make it out.

[thaiguzzi]

Waiting for silver and lacquer top coat paintwork, 8 pieces of plastic for 2.5k inc black pinstriping on the tank;

[papa al]

Please leave bike it to papa in your will.

[thaiguzzi]

Ah yes, the stand in the above photos. S/steel tall stool for 250 baht in the town market, down to the local s/s gate makers, cut it down to 14" in height and tig weld in the 4 horizontal struts... for 100 baht. And polish the welds which i did'nt ask for. Total stand cost = 350 baht.

[thaiguzzi]

AFTER (now);

R/H side;

Stickers were 250 baht for the lot inc spare black ones (Powered By Yamaha and the Climber). The Aprilia one has the 3 colour Italian flag in Racing. Very good quality, 2 day turnaround, very happy with the blokes work.

[thaiguzzi]

L/H side;

just about every motorcycle made always looks better from the timing side (R/H) than the primary side (L/H), inc this one, the weird tank design does'nt help.

Farkels. Bling. S3 steel footpegs. Much wider, much more comfortable.

[thaiguzzi]

Very pretty petrol tank. New paintwork accentuates the lines. Almost (sacrilege i know) Nortonesque in the black on silver...

Very nice form and shape, just like a woman....

red reflector is only on there to cover up an ugly square hole.

[papa al]

A little to the left please.

[thaiguzzi]

Had 1/2 an hour on it this morning, before it got too hot and i got too sweaty. Gonna be not riding it for the next day or two, 'cos i'm now gonna attack the exhaust system after lunch. Not happy with the overrall design with the expansion chamber thingey up there by the tank above the motor. Want to move it further back under the seat area, maybe change it into a mid pipe silencer box and hence the downpipe be longer. I've studied trials bikes on the net, past and present, and most do'nt even use an expansion chamber as we know it. Also still has a couple of pinholes that i've got fed up chasing with the mig welder.

Have a nice day boys and girls...

[papa al]

No expert but aren't expansion chambers usually tuned to optimize power at peak power RPM.?

Like in racing.

Trials not same, right?

Going ring now.

[seedy]

Very Very Nice ! Kudos !

[Ulic]

Impressive

[TheKnave]

Very pretty, which, I suppose, was your goal.

The RXZ 135 engine is not even remotely a trials engine, however. Trials engines have massive flywheels, and fairly extensive tuning to favor low-end torque. The RXZ is a street bike. The combination won't work for trials, except for photographs...

[taninthai]

Wow nice project and looks great you obviously no your stuff when it comes to bikes, do you wanna make me one???

Edited November 13, 2015 by taninthai

[thaiguzzi]

# Thanx for the kind replies and comments.

# Studied trials ex systems all evening yesterday, both air and modern liquid cooled motors. Went to my local car ex. repair/maker this morning. Got some pipe, some 90 degree bends made (could'nt do 180's), and some tube for a mid box silencer. 150 baht for thelot. Pics to follow next week. Let's make a new ex system...

# Re, pretty bike, shame about the engine. I've ridden and worked on motorcycles all my life, yes the majority large road bikes, and yes, i am not that experienced in trials bikes (my last bike i built in the UK was a 247 Montesa Cota in 2003). Yes, my bikes i build are pretty, but then that was my profession in England, inc magazine features and bikes in the Crossbow Calendar, all Triumph twins. But they must also be functional.

I have ridden this bike, TK has not. As stated gearing is 12/51, not the std 15/38. This alone makes a huge difference. The RXZ engine makes 20 bhp, and for a 2 stroke, a nice even, broad spread of power. Not even remotely peaky. If you check my other recent thread out, the Boyesen reed mod also improves throttle response throughout the rev range especially just off idle. I would also say the std flywheel/stator is not a lightweight racey item.

Also, a huge range of today's trials bikes sold have flywheel kits as aftermarket kits available, so heavy flywheels are not just a std trials engine design today. For the heavy flywheel type bikes of yesteryear, you are looking at TY Yam 350's, and the Spanish/Italian 250/350's of the 70/80's. Even the 125/175's of the day did not have a big flywheel effect.
This bike works, and works well.

Built in 2003, sold unfortunately in 05;

[farangmick]

Lovely job. Born and bred not far from Silsden, I could go and watch Dougie, and then Martin Lampkin practice. They made it look so easy, I had to try. Kept falling off and getting hurt, so I stuck to the road.

[Overandout]

I'm not going to get into if the motor is correct for the bike an all that, and the bike isn't really my style, but it's great to see someone actually doing something instead of just talking about it !!

It looks great and you are obviously putting effort into getting it to be what you are happy with, and that it what it is all about.

[ktm jeff]

Those engines are fitted to bike and sidecar outfits that lug water and/or gas bottles around all day. Often with several people on. Plenty of torque for an 88 KG bike.

Skilled engineering at its best. Wonder how many kids today can set up a lathe or miller.

[thaiguzzi]

Because i had'nt owned a 2 stroke in nearly 40 years, my initial plan was to use the bike as a basis to put a 200 Lifan 4 stroke in. They will fit quite comfortably, the problem is carb, manifold, and air filter/hose space. With a twin shock, no problem. With the monoshock, not easy. A bloke in England has done a couple of very nice Aprilia Climbers using Honda 200/250 engines, but again, the carb is not where it should be.

Back to 2 strokes, and the RXZ in particular. After riding it for a few sessions, i actually got to really like the 2 stroke motor. In an ideal world, money and freight no problem, i'd just have a rebuilt Fantic 200-270 motor sent over from the UK. In reality, i've grown to really appreciate this RXZ lump, and as a practical bonus, i can get every part locally by walking in my nearest favourite m/c corner shop.

Gearing is so good, that 1st gear is an excellent crawling/walking pace with no use of the clutch.

Just finishing off a complete new exhaust system today, been at it the last 2 days. Pics to follow.

[thaiguzzi]

The only bad thing about the motor in this chassis, is the gearbox sprocket to s/arm pivot distance. The original Rotax engine had the sprocket as close to the pivot as possible - very good design. This engine is about 3" further fwd. Again, with the monoshock in the way, there is no practical way moving it any further back due to where the carb is.

[thaiguzzi]

Ok, so i was never happy with the original exhaust system. Seemed to be made up of a couple of 2 stroke (motocross?) downpipes, an expansion chamber, and a very long 1" diameter pipe to the original Aprilia silencer. It also stuck out quite a bit, hence the need for heatshield(s) - ouch, that's hot, my knee hurts.

So down to the local car exhaust repair man shop, get some 43mm pipe, get him to knock me up some 90 degree bends (could'nt do 180's), and supply some 3.25" round for a mid section silencer. All for the princely sum of 150 baht. Original system on the right.

I'd googled and researched trials bikes exhaust systems for hours, so had an idea what i wanted to make. Initial mid section was heavily baffled with WE Wassel 4 stroke baffling and a homemade tube. Did'nt like the finished result, more googling/research, and realised it was also over-restrictive. Time for a MK II (on the right), using 3.75" round. Getting the oval shape was just sticking it into a 15 ton press and squashing. Note new packing; a home made perforated tube (i like drilling holes!) and 2 packs of proper exhaust packing from my favourite corner m/c shop, 30 baht per pack.

End plates for the oval mid section sileencer need 43mm holes for the pipe diameter. I don't have a 43mm drill bit, so into a 4 jaw chuck in the lathe and bore it out;

[thaiguzzi]

Back when i had my shop in England, we must of had 50 sets of custom made pipes fabricated (mainly Triumph, some BSA/Norton some Guzzi, some HD), but that was sticking the bike in the back of the van, trucking it down to our local master sheet metal fab shop, telling them what we wanted (always in S/S), waiting a week for God-Pipe-Bender-Man to do his magic, and picking it up again. This time was the first i've ever done myself, using a cut'n'shut method and pre-formed bends. Not too shabby for a first attempt.

All tacked up with no place to go... Sounds like a familiar song coming on...

First coat of aerosol Ex Hi Temp paint in the proffessional ThaiGuzzi spray booth...

[thaiguzzi]

Before;

After;

Before;

After;

Before;

After;

[thaiguzzi]

I'm really pleased with the end result. A lot less sticky-outy. I had considered running the downpipe along the bottom of the cylinder barrel, but that would have meant a shorter head to mid section silencer length, and all trials bikes want this piece as long as possible, so up and over it went. The Aprilia original alloy silencer i would have liked to keep, but it was in a poor state, previously welded up (poorly) and bashed about. A new Aprilia or universal alloy trials silencer is over $200 plus P&P, and eventually it would need replacing either with me crashing and bending it, or just eventually rotting out. So a new genuine Tsugiki silencer was procured locally for 300 baht. Cheap, and easily replaced. Very eighties...

The thing runs better than ever before, throttle response was always pretty good, especially after the Boyesen reeds were fitted, but now it truly is outstanding, albeit louder than before, and as testified by a recent couple of "offs" i experienced.

The first was a 1st gear wheelie that got out of control, no damage to me or the bike, but with me paddling/running after an out of control riderless motorcycle. Yeah, i know, cover the back brake at all times... The 2nd was again a 1st gear steep ascent, and losing the front end on sandy loose soil at the top (rider fault). That one hurt. Again, no damage to the bike except paintwork on the mudguards now have battle scars. Or scratches. Or character as i call it.

[canthai55]

Nice Bike. Did you use GTAW to weld the pipe ?

[thaiguzzi]

Nice Bike. Did you use GTAW to weld the pipe ?

Thanx. Re; GTAW - que? No unnerstan. Is Tig or gas in those abreviations? If so - no. I have a 33 year old Danish made 180a Mig welder, bought new in 1982. I am self taught, over the years have got a bit better at "sticking bits of metal together" with said Mig to the point where i am half decent, but no way would i call myself a qualified welder/fabricator. Can stick weld (even worse) but have never tried Tig or gas (brazing). My fabricating skills are not great either ie rolling, folding etc. When i had my shop in the UK, all fabricating (ie sheet metal work, pipe and tube bending) was farmed out to one of two shops locally dependent on what the customer wanted to pay and what he wanted, ie the best, or that'll do nicely. Crank grinds, valve seat work and cylinder boring/honing was also farmed out. Everything else was done in-house. Main bearing housings, c/case mods, head work etc, our own yokes (triple trees to American readers), one off spindles, machined parts etc etc.

My forte is mechanical and machine shop. I build engines, complete bikes, and operate lathes, milling machines etc. You could describe my basic job skills as "turner/fitter". Certainly not "welder/fabricator".