Motorcycle Crankshaft Rebuilds & Cylinder Re-bores

irri_tant

How do I stand?

Bear with me as this is a bit of a long winded explanation.

I sent the crankshafts to a reputable UK company to have them refreshed with new parts. This is their bread & butter work and they have done many of these over the years. 

The barrels went to a local two-stroke motorcycle tuner who has done many re-bores over the years and has a good reputation for doing so.

I bought the new piston kits from a UK company who specialise in the supply of Yamaha parts and supplied them to the person doing the rebores.

I'm not a trained mechanic but a practical DIY mechanic and have helped my Father repair cars and my own on the driveway. I raced two stroke motorcycles from 1978 to 1984 and had road bikes before and after those dates.

So the crankshafts were placed in one half of the crankcases to check they spun free by hand. All was good. So I built the motor following a workshop manual just to make sure everything went as it should. Every new moving part was lubricated with two stroke oil that I used when the motor was working fine, so that was the new crankshaft bearings, big ends, little ends, pistons & rings. All went together well.

On the first start-up I ran it for circa 40 seconds and the motor had a noise that could be described as a four stroke valve hitting a piston because the timing was out a tooth. NOTE: mine is a two stroke and has no valves.

So I stripped the motor to inspect and could see no obvious signs of what was making the noise. So I took the barrels and pistons to the chap that did the rebores to check his work just in case. The clearances were checked whilst I was there and they were as advised by the Yamaha workshop manuals. The chap that did the rebores suggested leaving out a helper expansion ring from below the second ring which gum up anyway. The piston still had two rings for the rebuild.

Second build went well and no issue was found but on startup the same noise was still there. This time I ran it just until the temperature started to rise to see if the noise would bed in but it didn't so I stopped the engine. 

Stripped the motor again and found scuff marks and score marks on the gudgeon pins on all four pistons. I didn't look at them the first time around. 

So now the motor is apart for the third time of asking and I'm at a loss as to what is causing the noise. 

The crankshafts and pistons are going back to be checked over by the suppliers / builders but I'm expecting the worst as they don't seem to believe the issues I've been experiencing for what is essentially a plug and play rebuild.

https://www.youtube.com/shorts/tW7JJgv_43I

TIA

IrrI Tant 

Okell

So a specialist did the re-bores for you and he used new piston kits supplied by you that you had bought yourself.

Then you rebuilt the engine yourself?

You don't know what is causing the noise, but are you suggesting that the specialist who did the re-bores did not exercise reasonable care and skill in doing the work?  Are you certain you didn't do anything yourself when rebuilding the engine to cause the noise?

If you are asking what legal remedies you have as a consumer, you first need to identify the cause of the noise and ascertain who - if anybody - is responsible for it.  You might need a report from an independent expert if you don't trust the one who did the work for you.

You haven't given any background to your story.  I assume this Yamaha two-stroke is a classic 'bike?  What did it sound like before the re-build or have you bought it as a restoration project and never heard it running before?

Ditzy_Mitzy

I'm not an expert, but am under the impression that one is supposed to 'size' pistons and rings when reconditioning an engine - normal practice in the car world, I think.  Reboring will remove x number 0.000" from the cylinder block, which then has to be made up in the form of oversized pistons or rings.  If, as has happened here, pistons have been bought from stock, they may be standard sized.  That may have caused poor fit in the bore and the noise.  Maybe it hasn't, but might be worth finding out.  Not sure what else could be going on as two-strokes are simple machines.  Have the bearings been matched to the crankshaft and connecting rods?  Anything that has been ground will no longer match factory sizes.  That could be the source of the rattle too.

Consumer rights?  Probably very few, on the basis that none of the third parties have contracted to give you a working engine.  Any of them could blame the other, or you, for what has happened.  Government guidance suggests that refunds need not be given where the customer has damaged an item by attempting to repair it himself.  The DIY job on the engine would seem to fall into that category.  

irri_tant

Okell said:

1. Then you rebuilt the engine yourself?

2. You don't know what is causing the noise, but are you suggesting that the specialist who did the re-bores did not exercise reasonable care and skill in doing the work?  Are you certain you didn't do anything yourself when rebuilding the engine to cause the noise?

3. If you are asking what legal remedies you have as a consumer, you first need to identify the cause of the noise and ascertain who - if anybody - is responsible for it.  You might need a report from an independent expert if you don't trust the one who did the work for you.

4. You haven't given any background to your story.  I assume this Yamaha two-stroke is a classic 'bike?  What did it sound like before the re-build or have you bought it as a restoration project and never heard it running before?

1. Yes as I'm well capable of doing it
2..I'm not suggesting the specialist got the rebores wrong. I just had him check the work in case it was wrong and all was correct with his work.
3. Yes. I've paid for parts that are 99.5% just like 'plug & play' and put together and they work. 
4. Yes it's a classic. The motor was fine before taking it apart as a precaution to restore the cranks, barrels & piston as the true mileage was unknown from new which I can see on the MOT data. 

This video was from the time I had it apart before the rebores to change a gearbox oil seal which entailed stripping the complete motor. It is still on OEM cranks and bores but as I'd been in the motor I thought I'd have rebuilt cranks and rebuilds done due to mileage. 
https://www.youtube.com/watch?v=_iocsUlET-0

irri_tant

Ditzy_Mitzy said:

I'm not an expert, but am under the impression that one is supposed to 'size' pistons and rings when reconditioning an engine - normal practice in the car world, I think.  Reboring will remove x number 0.000" from the cylinder block, which then has to be made up in the form of oversized pistons or rings.  If, as has happened here, pistons have been bought from stock, they may be standard sized.  

Pistons are new 0.5mm oversize. You buy the new pistons and take them to a specialist to do the work. The specialist who did the rebores has checked his work in case he got it wrong and the possibility his tooling had failed but all is correct. I have checked the clearance also with my feeler gauges and the gaps are within the specified limits

Okell

Well when you ask "How do I stand?", what sort of answer* are you looking for?

If you are happy with the work done by the re-bore specialist (and you seem to be saying that you are happy with it) are you suggesting that the new piston kits must be faulty and asking what sort legal rights you might have as a consumer against whoever you bought the kits from?

In order to have any sort of consumer remedy I think you'd have to establish that the "problem" was being caused by the new piston kits.  but the difficulty you have - as I understand it - is that you don't know what the "problem" is except that it's causing unexpected noises and scuffing/scoring the gudgeon pins.

I can't see that you necessarily have any statutory remedy under the Consumer Rights Act 2015 (legislation.gov.uk) unless you can get an independent expert to diagnose the "problem" and then say that either the specialist or the kit manufacturer is at fault in some way.  And I think that would be easier said then done.

[Edit:  And as Ditzy_Mitzy has pointed out, anybody you try to enforce consumer rights against is just going to point the finger at your DIY engine rebuild - whether or not you think you were easily capabale of doing it]


*Usually when people come here asking for advice about their consumer rights they already know who the guilty party is.  But in your case you don't seem to have any idea who you should be enforcing any rights you might have against.  Or that you have a consumer rights problem at all...?