Hi guys, I'm looking for a bit of help here if you don't mind...
These pics are from a 02 CR125 running on std Unleaded petrol, 8 plug, 32:1 fuel:oil and is jetted reasonably well to the best of my knowledge(It's not actually my bike). It has a Cometic thin base gasket with two head gaskets to compensate. The piston is a Wiseco, about 2 months old with few hours on it, it was correctly run in. One thing though, the small end bearing was a spurious make sent to us by our supplier, I suspect most of you are going to say this is the problem :( and I'm inclined to agree, I just want to be sure(We'll certianly buy Honda or Wiseco from now on)! The filter was spotless and there was no dirt in the engine. I haven't heard the owner complain about detonation but I'm not sure he'd be aware of it if it occured so it can't be ruled out.
Anyway the bike lost compression on the MX track the other day, no big bang or anything, it just bogged down and cut out. After he pushed it back to the pit the compression had returned, it looks now like the ring was stuck in the groove after the engine failure, then just freed up; this probably isn't significant, just thought I'd mention it in case. He didn't restart the bike or anything, just brough it home and stripped it down.
So you can see in the pics what he found, the small end has broken up and some of the bearing case and needles have worked their way into the combustion chamber, destroying the piston and fairly mincing the head. There are light scores down the piston skirt but the cylinder plating is fine besides some chips to the port windows. The bottom end feels fine but we will flush it out fully to be safe.
So I guess I have a few questions... I'll just mention that the guy doesn't have a heap of money at the moment so we can't risk just rebuilding and hoping for the best :)...
1. What happened!?! I have never seen detonation damage but suspect the damage to the piston was not caused by detonation, but just by the bearing fragments?
2. The deepest gouge in the head is about 1mm, can this head be safely repaired(skimmed is it?)? And if so what specs should we ask for, is there a better squish angle/band size or dome shape(For std European unleaded) we should get while it's being done?
3. Is it OK to fix up the small chips in the port windows with a Dremmel or similar, if so any tips for making sure we do this right? BTW. There is nobody in this country that can do this(That we can trust anyway) before you suggest getting a local guy to do it... If necessary we can send it to the UK but this is last resort because of shipping costs, exchange rate etc.
4. The bearing runner in the top of the conrod feels perfect but is there some good way to check it?
Thanks VERY much for any help it's much appreciated!
Philip
These pics are from a 02 CR125 running on std Unleaded petrol, 8 plug, 32:1 fuel:oil and is jetted reasonably well to the best of my knowledge(It's not actually my bike). It has a Cometic thin base gasket with two head gaskets to compensate. The piston is a Wiseco, about 2 months old with few hours on it, it was correctly run in. One thing though, the small end bearing was a spurious make sent to us by our supplier, I suspect most of you are going to say this is the problem :( and I'm inclined to agree, I just want to be sure(We'll certianly buy Honda or Wiseco from now on)! The filter was spotless and there was no dirt in the engine. I haven't heard the owner complain about detonation but I'm not sure he'd be aware of it if it occured so it can't be ruled out.
Anyway the bike lost compression on the MX track the other day, no big bang or anything, it just bogged down and cut out. After he pushed it back to the pit the compression had returned, it looks now like the ring was stuck in the groove after the engine failure, then just freed up; this probably isn't significant, just thought I'd mention it in case. He didn't restart the bike or anything, just brough it home and stripped it down.
So you can see in the pics what he found, the small end has broken up and some of the bearing case and needles have worked their way into the combustion chamber, destroying the piston and fairly mincing the head. There are light scores down the piston skirt but the cylinder plating is fine besides some chips to the port windows. The bottom end feels fine but we will flush it out fully to be safe.
So I guess I have a few questions... I'll just mention that the guy doesn't have a heap of money at the moment so we can't risk just rebuilding and hoping for the best :)...
1. What happened!?! I have never seen detonation damage but suspect the damage to the piston was not caused by detonation, but just by the bearing fragments?
2. The deepest gouge in the head is about 1mm, can this head be safely repaired(skimmed is it?)? And if so what specs should we ask for, is there a better squish angle/band size or dome shape(For std European unleaded) we should get while it's being done?
3. Is it OK to fix up the small chips in the port windows with a Dremmel or similar, if so any tips for making sure we do this right? BTW. There is nobody in this country that can do this(That we can trust anyway) before you suggest getting a local guy to do it... If necessary we can send it to the UK but this is last resort because of shipping costs, exchange rate etc.
4. The bearing runner in the top of the conrod feels perfect but is there some good way to check it?
Thanks VERY much for any help it's much appreciated!
Philip