Jonny-Jimbo Posted Friday at 17:28 Share Posted Friday at 17:28 Hi, I've just been stripping a Herald 12/50 engine I bought to put in my 1200 Estate. I was told it had a tick, maybe a lifter. Sadly, it seems it was actually piston slap. On removal, the piston is beyond use. The bore however has only very minor scoring, that is visible, but can't be felt with a finger nail. I think it will dingleball up okay. However, the piston and conrod connection is very stiff, I can move it by hand, but it's not as free as I expected. However, is this normal on a 1200 as I've never stripped one before. I'm wondering if the engine got hot, seized the gudgeon pin, causing the bore wear from the piston running at the wrong angle? Photo of piston wear for the sake of a photo. Quote Link to comment Share on other sites More sharing options...
glang Posted Friday at 17:39 Share Posted Friday at 17:39 Is the wear like that all the way round the piston or just what we can see in the photo? Quote Link to comment Share on other sites More sharing options...
JumpingFrog Posted Friday at 17:55 Share Posted Friday at 17:55 (edited) Looks like you have press-fit gudgeon pins (no circlips), they do take more effort to move when cold than the fully floating type. The pin is an interference fit with the rod (no bush), and a close fit with the piston, but the idea is that the fit with the piston will become loose once the engine heats up due to higher thermal expansion of alloy. You could try heating the piston up in a tub of hot water and see if it floats properly. Although, I think it's unlikely the gudgeon pin fit would be to blame for the damage, looks more like oil film breakdown from overheating to my eyes. Edited Friday at 17:57 by JumpingFrog Quote Link to comment Share on other sites More sharing options...
glang Posted Friday at 18:08 Share Posted Friday at 18:08 Good spot. Its strange how the damage doesnt seem to be the same above the rings... Quote Link to comment Share on other sites More sharing options...
Jonny-Jimbo Posted Friday at 20:39 Author Share Posted Friday at 20:39 I did think it odd too that the wear is just below the rings. I have removed the rings, and they felt right - correct sort of tension and no cracks etc. There is scratching on the other side of the piston, but it's only on a few points, not all the way round. I inspected everything carefully as I removed them - I've not found any lumps of metal, the oil didn't have glitter in it, and when cutting the oil filter I didn't find any debris / foreign matter. This was no4 cylinder, which I think if often the most prone to over heating problems. Makes sense with the gudgeon pin, so if I can find a good used piston I may slap it back in with a basic hone. This car will only be used for a few local journeys next spring time - if I was thinking of doing RBRR etc I'd properly rebuild the engine! Quote Link to comment Share on other sites More sharing options...
glang Posted Friday at 20:59 Share Posted Friday at 20:59 Whats to stop it doing it again though? Not a problem with the oil control ring restricting bore lube or something? Quote Link to comment Share on other sites More sharing options...
Nick Jones Posted Saturday at 21:26 Share Posted Saturday at 21:26 (edited) If the gudgeon pin joint is excessively stiff then it will excessively side-load the piston skirt and quite possibly produce the kind of damage shown, though I’d expect to see similar damage on both sides. It should move reasonably freely even when cold. Presumably the other three do? Incidently, the piston diameter above the rings is slightly less than the skirt which is why there are no marks there. Edited Saturday at 21:28 by Nick Jones Quote Link to comment Share on other sites More sharing options...
glang Posted Sunday at 05:29 Share Posted Sunday at 05:29 Might be more wear one side than the other due to direction of crank rotation? Does make me wonder how oval the bore is now☹️ Quote Link to comment Share on other sites More sharing options...
Jonny-Jimbo Posted Sunday at 14:48 Author Share Posted Sunday at 14:48 @Nick Jones there is similar wear to both sides of the piston. As stated though the bore has very minor marking - commensurate with what one may expect for an engine that's doing about 50,000 miles in 50 years and never been rebuilt (mains, big ends and pistons are all std size) The interesting thing was that the car was still driving nicely, no loss of power and was just 'ticking' a bit from the piston slapping about. Quote Link to comment Share on other sites More sharing options...
65redspit Posted Sunday at 15:26 Share Posted Sunday at 15:26 37 minutes ago, Jonny-Jimbo said: @Nick Jones there is similar wear to both sides of the piston. As stated though the bore has very minor marking - commensurate with what one may expect for an engine that's doing about 50,000 miles in 50 years and never been rebuilt (mains, big ends and pistons are all std size) The interesting thing was that the car was still driving nicely, no loss of power and was just 'ticking' a bit from the piston slapping about. At least you caught it before it let go properly and knocked a hole through the block ... Quote Link to comment Share on other sites More sharing options...
glang Posted Sunday at 15:35 Share Posted Sunday at 15:35 Amazing if its been like that all that time! Youd think the piston would have freed off after those miles... Quote Link to comment Share on other sites More sharing options...
Nick Jones Posted Monday at 19:46 Share Posted Monday at 19:46 Probably rust on the gudgeon pin from long periods stood idle. Possibly it was really stiff at some point and has freed off “enough” and it may well be freer when warm. Anyway, if the bore looks good enough to hone, the main challenge is finding a good used piston of the right size letter (will be a letter stamped on the crown indicating the bore grade) to replace it with. These old iron engines are tough and not highly stressed, so will survive things that would quickly demolish a modern engine. Quote Link to comment Share on other sites More sharing options...
Wendy Dawes Posted 19 hours ago Share Posted 19 hours ago (edited) I may have a useable 1200 piston from my recent rebuild I’ll have a look later and post a photo, if any use to you I can post it would £15 be reasonable if it’s any use it is the circlip type Edited 19 hours ago by Wendy Dawes Quote Link to comment Share on other sites More sharing options...
Jonny-Jimbo Posted 15 hours ago Author Share Posted 15 hours ago Thanks Wendy - if you could that would be great. I do have another spare 1200 engine I was going to pull apart for a piston, but it will be a faff to strip it down only to find out that they may not be the right size! Quote Link to comment Share on other sites More sharing options...
Wendy Dawes Posted 10 hours ago Share Posted 10 hours ago The ones out of my rebuild are std I cleaned off the crown on one of them to check. I had a broken ring on No.3 and some strange metal deposits on 4 but 1 & 2 seem reasonably ok I’ll photo the skirt and add to this thread so you can see what you think Quote Link to comment Share on other sites More sharing options...
glang Posted 6 hours ago Share Posted 6 hours ago Just thought JJ a good idea to check the straightness of the conrod? Watching CarSOS and theyve got an engine with bent rod that has suffered similar piston to bore contact as yours... 1 Quote Link to comment Share on other sites More sharing options...
Jonny-Jimbo Posted 5 hours ago Author Share Posted 5 hours ago Thanks Wendy, I'll check what the letter code is stamped into my current piston and go from there. Thats certainly worth it Glang, I wouldn't assume it's okay given the wear. 1 Quote Link to comment Share on other sites More sharing options...
Wendy Dawes Posted 4 hours ago Share Posted 4 hours ago Sorry not got Conrods they went back in the rebuilt engine. Quote Link to comment Share on other sites More sharing options...
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