Hi Paul Had that exact problem many years ago, it turned out that the clips were a faulty item! They deformed when hot due to a faulty batch of clips made from incorrect grade steel but when cool seemed perfectly serviceable..
Hi Paul, absolutely no doubt, in the image of the bore you can see the shape of the score at BDC matches the shape of the clip between the two ears of the clip. In the 2 strokes we always used the clips with no ears. the Piston has a small notch to enable a small screwdriver to be used to lift the clip out when needed, this type of clip tends to be pushed into the grove by the bevel on the edge of the pin with no ears for the pin to push against.
Looks like you sorted it Paul, I must say looking at the ears of the circlip how they have worn, looks to me that they are quite softer than they should be, definately a new set needed, earless if poss, also check the groove in the piston. cheers Dave
Your theory seems to make sense Paul. I've only replaced a few circlips over the years and never had one of those "eared" ones. Never had a problem with the other type. Fingers crossed.
I always have the open end up or down, someone told me a long time ago that at high speeds the clip would work itself out of the channel with inertia if the ends were level.
Hi Paul, it is obvious to me that the circlip wore the groove in the bore and also wore and polished the clip as well also it can only possibly have dropped into crankcase when you lifted the barrel. Probably an incorrectly heat treated circlip ??
Is it all possible that the owner has tampered with engine after it was returned to them? I noted the wear pattern in the cylinder seemed to indicate the ears of the circlip was at the 6 o’clock position whereas the image of the piston assembly on the bench shows it in a totally different position. A little over 50 years ago when apprenticed as a motor mechanic my employer insisted on putting witness marks on all major assemblies. This was a dab of paint. He was burnt badly on an engine build where it was obvious the owner had tampered with the engine after it left the workshop. He vowed that it would not happen again hence the witness marks. The owner was made aware of these witness marks so as to remove any temptation.
Harder to fit and remove, but the 'earless' circlips seem better to me: side pressure from the gudgeon pin, with chamfered ends, will push them deaper into the groove. (And less mass, if the comments below about distortion under acceleration is really a concern.)
paul i had this happen on sunday ,i fitted a piston on my b40,iput in the circlips ,made a cuppa and ping out one shot,the circlip did not fit the grooves fortunately i found some that did fit
That’s why it’s always good practise to stuff a bit of rag into the crankcase opening before you pull a barrel off the piston. That way, anything, such as your circlip or perhaps a broken ring doesn’t drop down into the crankcase.
Bizarre, but feasible. The barrel/piston is a sodding guarantee job whatever. but the big end bush possibly not. As Steve Edwards suggested circlip possibly from a dud batch.
Is it just me? The photo seems to show the bottom part is NOT located in the groove. Could it be that it's in on a squif? The ears could still be apart the right amount. I would examine the pic DCSF3869 with a magnifying glass. In all respect i hope im wrong!
I think there would be wear on the piston if there was that much side force to displace the circlip. I have no experience with circlips like that. Are they "handed" ? when the circlip is laid flat is it equally flat or do the ears angle up where they could be rotated by the pin? Is the circlip groove properly made? Could the ear of the circlip get caught in the circlip removal relief notch ( or whatever it's called) and the circlip become unwound out of it's groove? And lastly is that the correct circlip for that piston?
The worrying thing is will it happen again. Hope you find out what caused the clip to dislodge. If not you will be always be expecting a phone call from the owner.
That circlip isn't correct, it should be the other way up and in line with the bore to stop it from being compressed by the reciprocal mass (on piston direction change) would be able to compress it if over revved which you wouldn't think possible with an old pushrod single. I had this once with a racing triple which revved to 10 k, I think I fitted it sideways but I can't remember exactly. The only other way I can think that it would come out is if the radius on the clip wire isn't the same as the groove appearing to be seated and then vibrated free. I think you are right about it falling out on disassembly, no damage at the bottom of the bore or piston suggest this.
It really shouldn't matter which way up they are fitted, but if what you say carries any weight, seeing as the piston moves upwards as quickly as downwards, what you say would only address a possible problem in one direction of piston travel or the other. I think somehow, the gudgeon pin has managed to push it out, but it shouldn't have happened, and this is the first time it has happened after I have reassembled anything. Still a bit of a mystery.
@@paulhenshaw4514 I know it's a bit strange, the orientation of the circlip is important,if it isn't directly inline with the piston the reciprocal force has the ability to "compress" the circlip thus removing it from its seating in the groove if it is inline then the forces push it into the groove, the circlip you have there with the divider loops has more weight on the looped ends and if not inline with thrust has more mass so a bigger propensity to compress under load, I'm not saying this is the cause only that it is possible if this engine was over revved which is unlikely with a pushrod single. You have a mystery which may never be answered given that it was correctly assembled it could only be mechanical failure ..was it a genuine piston? Look, on an engine like that I wouldn't even consider the orientation of the circlip I would have done exactly what you did but there are no side loadings on a gudgeon pin only vibration and for vibration to work that loose it has first to be relaxed.....a mystery wrapped up in an enigma.
for the circlip to become unseated like that ..and be held captive by the gudgeon pin for any length of time ,has to have some lateral force but that just never happens `normally` so its a million to one chance ?? 🤔 gudgeon pin creep under load ? i dunno paul
I think he may have been getting a bit mixed up, it looks like I was the last to reassemble it, but not very long after he had it rebored and an oversized piston fitted. Whether the new piston assembly is at fault in any way or not is difficult to say at present, but it appears to look ok.
@@paulhenshaw4514 Oh dear. If the groove in the piston for the circlip shows no damage, then I presume the circlip may be the issue, as suggested in the comments?
find out if the piston turns around the piston pen , or piston pen turns in the smallend . And I dont like the look of that circlip . Might indeed be wrong material.
