Piston/barrel dramas

[jellywrestler]

just pulled a barrel off and found some lovely marks in it, these are both sides of the barrel and there's similar marks at the bottom.
From the top the piston looks all good but has started to go bad on the sides particularly above the gudgeon pin area, rings are had it.
285 miles on a new sleeve and piston it's a twin cylinder two carbs what went wrong?

[F5 Dave]

Bleeding heck Spyda, that's queer. But how thin is that sleeve? Is there something queer about the gungeon pin-small end arrangement? Or clearance of the piston inner to the rod? Can't quite see the circlip arrangement

[pete376403]

gudgeon pin circlip come out?
I preferred teflon buttons over pin clips for this very reason in my speedway bike motors.

[gammaguy]

what sort of engine is this?

[Grumph]

Just one bore of the twin damaged ? But both sides of the bore ?
The damage areas are too wide to be circlips - plus no "tram tracks" of gudgeon pin ends so I'd guess you haven't lost the circlips.
If they were NOS pistons, my guess is an undetected damaged piston...some time ago I saw a waterbus with a NOS piston which cracked right through in a very short mileage.
Were the oil ring end gaps checked ?

[jellywrestler]

Just one bore of the twin damaged ? But both sides of the bore ?
The damage areas are too wide to be circlips - plus no "tram tracks" of gudgeon pin ends so I'd guess you haven't lost the circlips.
If they were NOS pistons, my guess is an undetected damaged piston...some time ago I saw a waterbus with a NOS piston which cracked right through in a very short mileage.
Were the oil ring end gaps checked ?

one of the clips had come out but that was after most of the damage had occurred as there's only light scuffing. Basically I suspect the faults occurred and started to melt around the clip to release it, also these piccies are of both sides of the top of the bore, the bottom is same or worserer...
I've yet to take the front barrell off to check the piston but the bore looks OK and compression check was cool.
New made piston by OMEGA, good reputation I believe New made liner/sleeve.
Ring gaps checked? Your guess is as good as mine. I didn't rebuild this engine and have already found quite a number of simple faults with it so can't rule it out at all, of course I can't just say that'll be it and rebuild it only to find something else.
F5 Dave liner 3.67 thick, plenty thick enough i reckon

[Spearfish]

I'm not sure if it would be a factor for this type of damage but were the pistons facing the right way?

[jellywrestler]

more piccies, two are from the bottom of the barrell and the other two from the top looking down
the damage is reasonably uniform on both sides

[jellywrestler]

what sort of engine is this?

Vincent Twin

[Paul in NZ]

Combustion gasses escaping past ill fitted piston eroding the cylinder wall?

Something corrosive getting in there???

Material fault in the sleeve???

I'm a dumbarse so with something like that I'd ask the nice guys at headmaster as they do have some experience in forensic engine work.. (mostly warrenty and hire companys I think)

[F5 Dave]

Nah I got no idea. No clues from the underside of the piston? The rod to gungeon? Presumably these pistons are used as common fitment to vinnie engines? That is if I'm allowed to refer to them as Vinnies without some secret society hunting me down like the dog that I am

So at top & bottom centre where they should, if anything, be rocking forward & back they are brinneling out the sides but not trenching. The rod is still secure & not wobbling with crazy side to side movement?

[Grumph]

Drop the sleeve out - I'm betting there's no barrel where the marks are - or at least those spots will be very thin.
I've seen similar damage spots on a speedway JAP where there was a blowhole in the barrel casting - and read of the same hot spot damage on a RD Yam with a faulty barrel casting.
If this is the case I seriously doubt if that barrel is reusable. Bloody hard to get a TIG in there.

[Woodman]

Could be a conrod alignment issue. If the gudgeon and big end are not parallell the piston will be cocked over in the bore. From memory the specs for rod alignent are .001" difference over 6 inches, e.g. if you put a 6 inch bar through the gudgeon and another through the big end the difference between both ends should not exceed .001"

My first thoughts though were the circlips had fallen out, and I'm with Pete345673 and am a big fan of teflon buttons.

[Paul in NZ]

Drop the sleeve out - I'm betting there's no barrel where the marks are - or at least those spots will be very thin.
I've seen similar damage spots on a speedway JAP where there was a blowhole in the barrel casting - and read of the same hot spot damage on a RD Yam with a faulty barrel casting.
If this is the case I seriously doubt if that barrel is reusable. Bloody hard to get a TIG in there.

Ah - now we are onto something. Seen damaged bores on a resleeved hot rod triumph 650 because of this

[Spearfish]

If it was thin with a casting fault wouldn't it be random and look pushed out rather than looking almost like it was knocked?