Yamaha Fresh Update: Good Money After Bad?

[ClareQuilty]

Some of you may remember I had a Yamaha Fresh which had been apparently run without oil prior to my ownership; and I sprang for a partial rebuild (around 2,000 baht). I think they put a new piston and rings and so forth.. but left the crankshaft alone. It didn't work out as the bike then wouldn't run well once the engine was hot (coughing, sputtering, dying), so, after a few months I took the bike back and he replaced (I think) the crankshaft and timing chain, and also the part which generates the electric power along with myriad bits and bobs. Total bill about 3,000 baht. Obviously I'm into the bike for more than its worth, but, such is misfortune.

Alas, I drove it one day after this repair and the lights conked out on the way home at night, and the bike wouldn't start the next day (I suspect the generator or alternator would be the most likely culprit here).

I have a second Fresh which was also rebuilt in the 'first stage' kind of way I mentioned above (that one for just about 1,650), and it seems to be running OK, but the fellow who rents it has described the 'coughing' or 'loss of power' phenomenon that the first one had, though highly intermittent. I suppose it could be a similar symptom but with a different cause, but I'm beginning to become entirely wary of four-stroke engines: I've had tremendously better luck with two-strokes.

[apetley]

Four stroke engines are great. It's the mechanic that's the problem.

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[BSJ]

Four stroke engines are great. It's the mechanic that's the problem.

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CQ prefers Khun Chep-par-dun-anny-wun. Maybe their related?

[Turkleton]

Groundhog Day......

OMG

[thaicbr]

Four stroke engines are great. It's the mechanic that's the problem.

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Op. your mechanic is shxt. simple really.

Find a better mechanic.

[ClareQuilty]

I'm skeptical of blaming the mechanic, as it is in the nature of any 'top end' rebuild that the 'bottom end' may turn out to also have problems, no?

I can't really blame him for a partial rebuild not fixing those parts which are not replaced. And he has rebuilt several two strokes for me and they've been flawless in operation for years after the rebuild.

[thaicbr]

I'm skeptical of blaming the mechanic, as it is in the nature of any 'top end' rebuild that the 'bottom end' may turn out to also have problems, no?

 

I can't really blame him for a partial rebuild not fixing those parts which are not replaced.  And he has rebuilt several two strokes for me and they've been flawless in operation for years after the rebuild.

So he's a 2 stroke mechanic. Cool

Now find a decent 4 stroke mechanic. You say he put a piston and rings in.. but were they actually for the bike in question or just a rough generic size... I have seen it done.. the mechanic grinding down the piston skirt to match the old one...

And as for your question. ... no

Sent from my i-mobile i-STYLE Q6

[ClareQuilty]

I'm skeptical of blaming the mechanic, as it is in the nature of any 'top end' rebuild that the 'bottom end' may turn out to also have problems, no?

I can't really blame him for a partial rebuild not fixing those parts which are not replaced. And he has rebuilt several two strokes for me and they've been flawless in operation for years after the rebuild.

So he's a 2 stroke mechanic. Cool

Now find a decent 4 stroke mechanic. You say he put a piston and rings in.. but were they actually for the bike in question or just a rough generic size... I have seen it done.. the mechanic grinding down the piston skirt to match the old one...

And as for your question. ... no

Sent from my i-mobile i-STYLE Q6

Yeah he just orders the part for the bike new from the supplier - it comes in a box and fits precisely. He's shown me before..

As for my question - how can it be that a partial rebuild can fix all problems? Its precisely that - a partial rebuild, and thus fixes only those problems located in those parts which are replaced. Typically the reason for the need for a rebuild seems to be either running without oil or extremely high kilometers (in my case it has been the former, mostly), and thus both the 'top end' (piston and rings) and the 'bottom end' (crankshaft, timing chain, etc.) could have discrete problems as a result of lack of oil. The attempt to 'do it on the cheap' by only doing the top-end is not unreasonable I think, but it is certainly no guarantee of success.

(I believe I've got the concept right even if I'm admittedly quite unsure as to precisely what parts are the 'top' and 'bottom' 'end' of the engine - perhaps someone can clarify these parts for me.. for example which includes the 'wrist pin'?)

[BSJ]

Everything is subjective so I know bike and cars are a bit different. When I worked in the family garage there was always at least one head job being done on any given day.

The bottom end maybe OK. Any decent mechanic will test to see what the condition of the engine is as a whole before he recommends anything.

A cylinder leak down test will often point the mechanic in the right direction. Blow-by at the rings, at the valves, cracked head allowing cylinder gases to enter the cooling system or exhaust, head gasket blown.

Just guessing isn't the right way to do it.

[VocalNeal]

Claire,

You've got to get a bit more precise.

If I read the OP I decipher that the bike ran OK before the piston/ring job? If this is correct? Replacing the piston has nothing to do with the rough running after. The mechanic has done something else.

As the bike is air cooled the rough hot running subsequent to the work could be wrong valve clearances or bad spark plug or a short in a wire somewhere that is influenced by vibration.. IF all other stuff was untouched?

The lights conk out? Gradually get dimmer until out or suddenly expire? Different cause for each event.

[ClareQuilty]

Claire,

You've got to get a bit more precise.

If I read the OP I decipher that the bike ran OK before the piston/ring job? If this is correct?

No, the bike didn't run well - hence the piston/ring job. It ran and shifted somewhat poorly and had a lot of smoke from the tailpipe, hence the piston/ring job. I'm not the sort of fellow to spend a couple of thousand on a piston/ring/gears job on a bike that's running OK!

But let me update - the bike is back now and running fine. They said it was 'overcharge' and thus blew out the lights (all the lights!). They've apparently adjusted the charger and now everything seems normal, they even replaced the blown-out lights at no charge as they did consider it their error.

I'm driving it a lot to 'break it in' before I pass it on to anyone else. I think I'll also change the oil again in about two weeks at the end of a 'break in period'.

Edited May 22, 2013 by ClareQuilty