Strange Piston/gudgeon Pin Failure

[bren]

Anyone got any idea what might have cause these failures? The gudeon pins have snapped in two. The same thing happened in two different engines. Both CA18DETs (similar to RB but 4 pot rather than 6), both using Wiseco pistons, both failed in only 100kms.

Its a strange one as I know of lots of people using Wisecos in CAs with no problems and yet this one guy has two identical failures. Any idea what he is doing wrong?

[EfiOz]

Have you got a pic of the top of the piston?

[BezerkR32]

piston is not fauling on crankshaft counterweight is it, or crankshaft have excessive endfloat? unless pin is grabbing little end and piston, lubrication problem. never seen anything like it, thats big.

Anyone got any idea what might have cause these failures? The gudeon pins have snapped in two. The same thing happened in two different engines. Both CA18DETs (similar to RB but 4 pot rather than 6), both using Wiseco pistons, both failed in only 100kms.

Its a strange one as I know of lots of people using Wisecos in CAs with no problems and yet this one guy has two identical failures. Any idea what he is doing wrong?

[bren]

Those are the only pics I have Im afraid. Its a guy in another country thats having probs, I havent been involved with the build myself. The pistons are nothing out of the ordinary, as I say, they have been used with great sucess in a large number of engines to date so I cant see why they would suddenly foul on the crank. I can see maybe one set of pistons being mispacked by Wiseco but two, and both sets going to the same guy? Nah, too much of a coincidence.

Maybe the piston to bore clearance isnt correct and the pistons nipped up when the engines got hot but to snap the gudgeon pics? Ive seen the effects of hydraulic locking and even then it was the rods that bent, not the gudgeon pins snapping.

Very wierd.

Edited July 15, 2006 by bren

[Mik]

Did you check the rod side clearance? It could be caused by too much clearance.

[bren]

Its not my build, I had nothing to do with building it. What do you mean by rod side clearance?

Edited July 15, 2006 by bren

[EfiOz]

I've seen it before in a V10 Viper and it was a detonation issue. It broke 2 gudegeons and had 4 more cracked ones.

That was a brand new engine with Wiseco's. It was rebuilt and retuned (the right way!) and it's never had anothe problem since, even with the same pistons.

[bren]

Hence your request for a picture for the top of the piston. Ill see if the guy can get some

[discopotato03]

I tend to think that the gudgeon pin tried to sieze in the small end bush . You can see how the bush has tried to screw itself out of the rod and no doubt up against the inside of the pistons gudgeon pin boss . Since both pins are sheared in the middle it seems logical that half the pin was trying to stop the piston articulating with the rod and was the weakest link . Luckily the other half must have kept the small end located in the piston otherwise the rods and pistons would now be schrapnell on the road . I would be measuring up the broken and surviving pins to see if the tolerances were adequate .

I would also check to see if the propper lubrication was available to all four rods/pins/pistons .

Cheers .

Edited July 15, 2006 by discopotato03

[bren]

Ill pass on your comments, thanks

[rob82]

Get pics of the bigend bearings too.

[T04GTR]

ok. the only thing that causes a gudion pin failer is either a clerance issue or fauly materials. (dodgy gudion pin)

the fact that it shered could be due to the fact that its been hammering away at its self. elongating the piston pin bore and/or hammering the bush in the conrod.

to a point where it has hammerd it so hard that its fractured the gudion pin.

or.. partaly siezing in the pin boss or little end. ie.. one side getting galled andthe othere side being ok.

so basicly the cause is to little or two much clearance inbetween the piston and the gudion pin or two much clearance between the gudion pin and smallend bushing

ie.. poor engine assembly.

ps... if anyone for a minute thinks that detonation has caused this please slap yoursefl

[Adriano]

Find out how much squish it has, maybe the piston is hitting the head

[rob82]

ok. the only thing that causes a gudion pin failer is either a clerance issue or fauly materials. (dodgy gudion pin)

the fact that it shered could be due to the fact that its been hammering away at its self. elongating the piston pin bore and/or hammering the bush in the conrod.

to a point where it has hammerd it so hard that its fractured the gudion pin.

or.. partaly siezing in the pin boss or little end. ie.. one side getting galled andthe othere side being ok.

so basicly the cause is to little or two much clearance inbetween the piston and the gudion pin or two much clearance between the gudion pin and smallend bushing

ie.. poor engine assembly.

ps... if anyone for a minute thinks that detonation has caused this please slap yoursefl

I'm with you on this one, detonation isn't going to do this. I would still like to see the big ends as they will probably show more of the story. If the little end is hammer the big end certainly is going to be showing signs of abuse as well.

[bren]

Ive asked the guy for big ends pics Hes gone a little quiet though, Im interested to find the cause of failure so hope he replies with the list of info Ive requested.

[Mik]

Its not my build, I had nothing to do with building it. What do you mean by rod side clearance?

I mean the side clearance between the rod and the crank. If this is too large, the little ends get a hammering.