Bottom end engine failure - at gudgeon pin

[BenMcCarthy]

Hi

I'm looking for any comments/ wisdom on the recent demise of my engine.

Facts known:

1. Engine rebored - full top/bottom rebuild 18 months before.
2. Loud clunk from engine while on the motorway.
3. Pull to halt on hard shoulder steam pouring out of bonnet.
4. Having now had the sump removed at the local garage to do a visual inspection the damage is as follows:
i) con rod to one cylinder only is separated from piston at the gudgeon pin
ii) con rod (now in an 'S' shape) has smashed waterways in the block.
iii) jack shaft/'balance shaft' is snapped in half
iv) cylinder head appears to be fine

Before the engine failure the oil pressure was as usual, water and oil levels as usual before journey started.

Does anyone want to speculate on what might have caused it/ how to avoid this?

Does anyone have advice re my best course of action re bottom end?

Many thanks

Ben

[steveww]

Ouch

Looks like you will need a new block. The original 701 blocks are hard to find but still about if you phone round some of the usual suspects and engine builders. Burton are making new blocks but they are rather expensive. The other option is to go for the tall 711 block which are much easier to get hold of and cheaper, though not original.

Sounds like the gudgeon pin failed or fell out.

[john.p.clegg]

Cylinder head appears fine?-have you taken it off?
Have the valves survived?
Is the short conrod free on the crankpin?
Separated from the piston at the gudgeon pin?Is the rod snapped,the gudgeon pin snapped or the piston broke? (no jokes about my friday night drinking habits thanks)

John
P.S. whereabouts are you?

[BenMcCarthy]

Thanks

Looks like the pin is broken. Possibly the piston connection too.

Not sure if head has been taken off. No obvious problems apparently

I am in South London.

[gwnorth68]

The big question is whether the little end of the conrod is still happily located by the wrist pin of the piston. If so you've just had a simple fatigue failure of the conrod. Were they 125EC rods or (shudder) the dreaded 116E rods (or something else entirely)? (Surely there aren't any 116E rods left around?)
With luck the piston and small piece of conrod may have just "floated" up to the top of the bore and gently bounced off the head/valves without damaging too much.
Tom Moore

[alaric]

Ouch!

During the rebuild one of the con rods in my engine had to be replaced because it was bent. No idea how this could have happened. It looked fine to the eye, but apparently it could have caused a failure and uneven wear of the bore if put back into the engine. Maybe you had something similar - fatigue related as suggested above - and it caused the gudgeon pin to fail. Maybe in my case engine was worn, and the tolerance of the worn parts caused the bend.

Good luck.

Sean.

[BenMcCarthy]

Thanks for your replies - to confirm:

the piston is broken just above the gudgeon pin
this caused the pin to separate - the pin itself is still intact
big end of con rod is in place.
small end failure as described above -

faulty/ fatigued piston?

[types26/36]

Ben,
I've seen something like this before when non Twin Cam pistons were fitted, the T.C. pistons should have holes in the oil ring groove for oil drainage, some pistons have slots in the oil ring groove (example: 1500 Ford pistons which can be used in T.C. with some work)
The slotted pistons are "weak!" at this point and should not be used in a T.C.
Just as a matter of interest what type of pistons are in your engine?
Brian.

[M100]

faulty/ fatigued piston?

Quite likely, not missed a downchange and over revved it have you?

Is the piston pin still a good fit in the con rod?

I've seen a case before where a rattling small end was allowed to persist and the piston eventually failed in a similar way to yours.

[BenMcCarthy]

Apologies for time to reply -
the pistons were QED pistons (new with the rebuild)

car was cruising along nicely in fourth gear when it happened (no down change or over-revving

not aware of a rattling sound

Thanks

Ben