Piston broken in half(top-bottom) 5

[dirk489]

I reconditioned a friend's engine which broke later on during running in.The piston broke just on the pin line,conrod bolts snapped clean off, smashed the whole block.
My question is: is this always due to overreving or is there another possibility?
Dirk/Antwerp

 

[Tmoose]

Are the other 3 pistons intact?
I'd be inclined to Zyglo or dye penetrant check them.

Could you post close up pictures of all the ring end gaps?

 

[GregLocock]

The reason we look at the bolts is you claimed they were "Bolts are 55 Ton tensile", torque specs for which are readily available. If they aren't 55 ton material, then sure there could well be other explanations.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[dirk489]

I assumed they were 55 t/sq in. as I said the OLD ones were marked 55T65.This being old English markings I am going to send the remaining ones to be tested further to make sure.
Dirk

 

[dirk489]

Alas cannot get close enough for the rings but no signs of touching neither top or second one.I chequed the gaps which were all within.009-.011"
which is right for 3" bore.I included foto's of the top and side of piston and of the block inside.
Bottom of side opposite of thrust is gone,nearly no marks on cylinder upwards.
Dirk

 

[Pud]

Looks like it is not an uncommon problem with these engines (I assume the correct octane rated fuel was used as it is no longer easily available in the country of the engine's birth?)

http://content.time.com/time/specials/2007/article/0,28804,1658545_1657867_1657786,00.html

I have seen failed con-rod bolts due to one not being clamped the same as the other one - it's the correctly loaded one that fails in fatigue due to the "flexing" of the joint. Fatigue evidence was always very evident though.

H

www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[EHudson]

The rod appears to be an asymmetric design. I have seen one example where a similar rod was installed in the wrong direction and put into service! (an Allis-Chalmers WC)

 

[golfpin]

Dirk, sorry to see the damage...have had a lot of experience with these engines ..I am that old .........from new, they were susceptable to breaking. question time ....
Those pistons do not look new
There appear to be scuff marks that might indicate partial seizure
The con rod bolts were they new, is the source of the bolts known and reliable.. they do not look new.
At first glance at pics I said " over tightened" how ever when some of those very bright contributors started and then I looked at the rest of the excellent photos....how old are the con rods.
What was the compression ratio?
I ask these questions based on my own experience when these engines were new ... did they give trouble, and all the symptoms you indicate we had then [1960]. C/R for the fuel available at the time a problem. Detonation, holes in the piston. I was very surprised to see what appeared to be an original lock tab for the big end bolts!! This was a big no no in our books from a long time back. The theory being that the lock tabs were made from mild steel and would compress when the bolts were torqued and would then relax a little releasing the preload on the bolt. Don,t know if any of this helps hope you get to the bottom of it. If money is not a problem Carrillo type rods, modern day pistons, steel main caps, that would be the way for me.
All the best Golfpin

 

[Panther140]

Look at the wrist pin journal/hole on the left side of the piston. Why are there score marks worn in on the outer side of the left wrist pin circlip groove?

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[Panther140]

Lets say you made a mistake that lots of people make and either didnt seat the wrist pin circlip 100% properly, or you reused an old circlip, or just completely forgot it.

The wrist pin would float to the left side = flex a lot more because the other side isn't constraining flex like it should = leave scoring. Not only that, but it would fatigue the side that cant distribute the load throughout itself evenly because the pin is not riding completely in it. Once it has stress fractures, it will break on the part of the hole that has the least amount of material strengthening it. After that, the pin is going to violently destroy the other side and then smash a bunch of stuff.

Plausible?

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[gruntguru]

It is usually pretty obvious when a circlip is pushed out of its groove by the pin.

je suis charlie

 

[Panther140]

gruntguru - What does it look like if no circlip is put in at all? I have never personally seen that mistake happen. But I have also never seen brand new factory spec bolts sheared off that bad, or a brand new piston completely grenade from an over rev. If this had happened because of such an extreme over rev, how do the other cylinders in the engine look? The wear marks on the wrist pin holes seem worthy of investigation, especially the one outboard of the circlip groove! Id be more apt to ignore those wear marks if they didn't happen on the most dramatic failure point. Those wear marks were caused by something

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[Panther140]

Did you find both circlips or at least evidence of both circlips in the wreckage?

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[gruntguru]

If a circlip was omitted, there would be telltale marks on the relevant face of the bore where the pin would have done some rubbing - long before the failure. Possibly difficult to identify amongst all the other bore damage.

je suis charlie

 

[Panther140]

By the time the wrist pin shifted that far, it would not take much to rip it out of the piston

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[missinglink]

Looking at the piston rings,although they could have moved after the unfortunate event,as you may know already Dirk,piston ring gaps are positoned 120 degrees from each other

 

[EHudson]

The position of the ring gaps means nothing. Rings rotate during engine operation at different rates.

 

[dirk489]

Hi all,
Back from a trip. Thks for the follow up.
to Panther 140:No marks from wrist pin on side of cyl.Other cylinders are perfect.
I can only repeat that a had this sort of breakage before with a Powermax piston.Rod bolts were ARP,so did not break,but the piston was broken in two at exactly the same place.Such shear breakage will occur in the exhaust phase(no compression to hold back the piston)
It was also the exhaust cam that was blocked!
Further small damages occurred when the driver tried to restart the engine before realising what happened.
Looking at the piston underside I'd think this is also showing clear shear!I am not a specialist but the grainy structure shows it.
Dirk

 

[tbuelna]

dirk489-

I looked over all of the (very nice) photos you provided of the failed piston, and I saw no indication of a shear-type failure. The only thing I could see in the photos seemed to indicate tensile type fractures that originated at the wrist pin bore edges.

 

[dirk489]

Tbuelna,You are right:being a bloody foreigner,I meant tensile instead of shear...I still think the piston broke first as there is not so much damage to the fracture. The bottom half of the piston was smashed into smitheriens.It must have got blocked in the bottom part of the cylinder somehow to cause the rod to bend. Why the rod bolts broke then is still a question to me.
Dirk

 

[gruntguru]

I don't think it would be easy to bend a rod 90 deg like that without breaking the bolts.

je suis charlie