Assessing an unknown engine

[RobFrost]

There’s no (visible) scoring on the bores from that damage?
Difficult to see from the photos, but is the top of the piston clean or is it some deposit build ups that then look like damage?

To my eye all looks good aside from the break. Here, I cleaned one up. What's surprising is the valves seem intact (so far) and there were no chunks of metal in the chamber... although maybe I washed them out with transmission oil.



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[Gary71]

Fair enough, that’s broken! Slipped timing chain maybe?

Valves may look ok but probably warrant replacement.

[RobFrost]

Fair enough, that’s broken! Slipped timing chain maybe?

Valves may look ok but probably warrant replacement.

I'm trying to think if the two broken pistons were on the tight side. One side cam nut was absurdly tight. Maybe it was so tight they couldn't time it, or maybe as you say, it slipped and tightened by the turning of the engine. Come to think of it, there was actually a fragment of windscreen glass in one of the chambers. I ruled out that it had been in there when running and assumed it washed in as I was soaking and disassembling the engine. But maybe that blocked a valve from opening and the cam slipped?

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[RobFrost]

Not being one to give up easily, I returned to the last stubborn cylinder after 24 hours soaking in transmission fluid and carb cleaner.

In a rare moment of lucidity I realised the seized piston couldn't be restricting the crank's movement, because I could tap the cylinder up and down on the piston with a mallet, while the crank still wouldn't move. So the crank must also be seized within the innerds of the case.

I wondered if taking the sump plate would yield any information, but it didn't, other than an absence of metal flakes, shavings or other debris in general.

So I worked the barrel up and down a few times on the piston (oo-er missis) then began inserting ever more 1mm plastic shims between the barrel and the case as I rocked it backwards and forwards with the mallet. It really stuck at the end, but after about an hour it came free.

It should not be surprising that it was difficult, given that a good proportion of the piston rings is smeared up the side of the piston.



My next quandary arises out of the fact that the crank will not turn, making it impossible to get the wrist pins out. Any suggestions there? The only answer I have, is to skip straight to splitting the case. Is there any reason not to do so?

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[911hillclimber]

I can't think of a reason why you cannot split the cases and free the crank as long as you have no cam chains fitted to the cams.

The tight crank could be a number of things from a seized oil pump to the main bearings.
You need to have that stud/corner welded anyway, so simply tear it all apart.

[Gary71]

In for a penny…

[Gary71]

You’ve come this far. Finish the job

[hot66]

quite looking forward to seeing the condition inside

[neilbardsley]

Can you split a case without removing the pistons? Will the case move pass the stuck piston?

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[RobFrost]

Can you split a case without removing the pistons? Will the case move pass the stuck piston?

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The piston isn't stuck. All barrels now off. Something within the case is stopping the crank from turning.

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[RobFrost]

quite looking forward to seeing the condition inside

My money's on damage within the cam drive system because those pistons have hit valves and the cam nut probably got tightened. Maybe some bent and broken teeth on the IMS drive?

The crank rocks back and forwards a few degrees suggesting to me some secondary system attached to it.

Some major torque must have been sent through the cams. If we say 150Nm torque for the cam nut, and it was turned at the sprocket which is about one twentieth of a metre radius, that requires 3000N or 660lb of force.

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[Gary71]

Can you split a case without removing the pistons? Will the case move pass the stuck piston?

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Yes, but at this point you can pull the circlips out, knock the gudgeon pins through and pull them off.

[RobFrost]

Can you split a case without removing the pistons? Will the case move pass the stuck piston?

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Yes, but at this point you can pull the circlips out, knock the gudgeon pins through and pull them off.

Possibly. The crank's at 90 degrees so some are alongside each other with the end of the case blocking the other side.

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[Gary71]

Can you split a case without removing the pistons? Will the case move pass the stuck piston?

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Yes, but at this point you can pull the circlips out, knock the gudgeon pins through and pull them off.

Possibly. The crank's at 90 degrees so some are alongside each other with the end of the case blocking the other side.

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I’d neglected the seized crank!
Just split the case and worry about them later then

[911hillclimber]

Yes, just tear it apart, every bit of the engine, then check things out as you will have to anyway.