Assessing an unknown engine

[Bruce M]

Perhaps you’ll need to drill or cut the piston to get access to the rod bolts, ideally without damaging the rod?

[RobFrost]

Perhaps you’ll need to drill or cut the piston to get access to the rod bolts, ideally without damaging the rod?

I contemplated that but I'd have to do both, and one is a good piston (one broken). A new oil pump driveshaft is £60. A new piston, more. Although in truth, I'm probably replacing all the pistons. But I think drilling the piston is a harder job too.

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[Lightweight_911]

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If it's of any help I have a used oil pump connecting shaft you're welcome to ...

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[RobFrost]

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If it's of any help I have a used oil pump connecting shaft you're welcome to ...

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Thanks, that's most kind of you, (if it comes to that).

I might drop Mike Bainbridge a line as I'm sure he has dealt with this eventuality on multiple occasions.

[911hillclimber]

I thought Mike had retired?
That lump of alloy jamming the piston should tap back into the case where it dropped in from?

Gary is right, free one side of the engine of pistons and you will make progress after that with the crank exposed.

If the pump is tight it may be with metal parts from what has failed maybe.
When my 3.2 exploded the damage was absolutely everywhere, I though I'd lost the whole engine. The skirt of #6 piston had been munched by the timing chains and metal was in everything, inc the pump.

[RobFrost]

I thought Mike had retired?

Hopefully he still wants to share his experience.

Don't the pistons pass through the cylinder holes in the block halves?
That lump of alloy jamming the piston should tap back into the case where it dropped in from?

Do the rods move on their big ends or tight?

When my 3.2 exploded on #6 cylinder with very extensive damage everywhere the rod was bent and twisted but free on the crank.
It was 'wrapped' around the cylinder cross web and the cases would not part but did open enough for a 1/4" drive socket to reach the rod bolts and undo the cap.
Took ages to do mind.

The lump of alloy easily tapped back in with a screwdriver. Sorry, I should have mentioned that. Yes, all is moving freely now apart from the crank not turning. I'm pretty sure the oil pump is preventing it. Pistons 3 and 6 are in the fully-in position, which allows the case to part about one or two cm or so before they're both hard against the webs beneath. I can part the back of the engine more because pistons 1 and 4 are near top dead centre, but I think it unwise to pull it apart at an angle. Even if I open the back of the engine more, the crank can't separate from the IMS drive gear because it would need to move in the other dimension, i.e. at right angles to the separation of the case, which it cannot do.

I don't know enough about the IMS construction to know what would be freed up if I remove the circlip from the end. And the circlip's too fine for my pliers - I would need to get some fine ones or rip the circlip out with a pair of picks in order to find out. I need to turn the crank independently of the oil pump - or free up the oil pump. In the absence of other ideas, next step I think is to put a hose or jetwash into the oil pump whilst rocking the crank backwards and forwards - see if there's some piece or pieces of metal in there I can tease free with a bit of lubrication.

[Lightweight_911]

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The clearance between the oil pump gear & the housing is very small - so I doubt you'd be able to shift any debris that way ...

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[RobFrost]

Ok so I gave the Internet a few days to critique my proposed solution, or come up with a better one. I wasn't that keen on putting a grinder inside the engine as I know how they can grab and shoot across and instantly take a chunk out of something.

Here goes nothing...



I have a little air powered cut off disk, which is inconceivably puny - with the advantage that it can't do too much damage too quickly. Sadly it also comes with the disadvantage that it can't do too much damage too quickly. It seemed stable in the hole, if it jammed it instantly stopped and it was controllable. There was barely enough room to get the angle to cut the shaft and it was slow going.

As soon as the shaft began to flex, it was totally obvious this was going to free the crankshaft.

It soon became clear I would not have enough room to cut right through.



But I did thin it enough to weaken it so I did some of the case bolts back up and forced the crank round, twisting the driveshaft. Where I had weakened it. This gave me enough turn to get wrist pins accessible.



It was clear this one had ended its days without oil and very hot.


Piston 6 appears to be a bran new piston, and this is where the story starts to become clear.





Sitting on its con rod is a lightweight chunk of metal - not magnesium but aluminium alloy.





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[RobFrost]

That little piece of alloy has stamped on it the numbers 84V5, which is a fragment of the stamping 84V55 which are the dimensions of the pistons, and features in the casting inside them. I checked all the pistons for missing chunks and there were none, so it would seem that this engine has failed immediately after being rebuilt with a new piston. Sadly, whoever built it left pieces of the old piston inside the case.

In fact there were more chunks to be found.



Now for certain we will find chunks of piston within the oil pump.

Apparently alloy grounds in the oil pipe.



Pump teeth look ok from here.



And all mint in the first chamber.



This tab didn't look quite right but I'm sure it is. Nothing for it to bolt to if it were a complete hoop.



More evidence of sealant which could block the oil passages.






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[RobFrost]

Sorry I didn't get a photo, but when I got into the 2nd chamber of the oil pump, I found no aluminium chunks. But it was starved of oil, and the oil pump case was corroded, causing it to be jammed. It turns out I could probably have forced the crank round without doing too much damage to anything. The gears are in great shape but it's hard to say whether this will pump well given the pitting on the inside of the case once it's cleaned up.



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[RobFrost]

Good and bad sides of oil pump.

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[Gary71]

Wow! Big day

Time for a new oil pump. They are expensive for sure, but so is doing all this again.

Best of luck

[RobFrost]

I'm no expert but the crank journals and shells look to be in good shape to my eye.


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[RobFrost]

I've yet to take apart the cam assemblies and the rest of the engine, but tentatively I'd say the engine was run for a short while after a piston replacement, possibly recently rebuilt, and failed due to chunks of piston left in the engine.

The heat, fatigued piston rings and broken valves cutouts in the pistons, suggest the back of the engine ran dry of oil, overheated to the point a piston jammed, slipped a cam, which broke two pistons.

There was some metal paste in one of the oil passages near the pump, suggesting the steel pump simply pasted the aluminium without damage to steel, but the paste blocked the flow of oil.

The corrosion in the otherwise good oil pump suggests the seized oil pump was a later development while the engine sat.

It would have been nice to have a working engine, but on the plus side, the fact it was aluminium circulating the engine is a blessing, since it seems to have been too soft to damage the steel parts.

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[RobFrost]

Current plan I think is to put it back together with JE 10.5:1 86mm pistons in Biral cylinders. Twin plug the heads, but run it single plug unless needed.

Possibly have some case work done. Being 1970 I think it has no piston squirters which might be helpful on a 10.5:1 engine.

Not sure about shuffle pinning, cams or carburation. Maybe a mod-solex grind. Keeping the MFI would be nice, but I know it'd need adapting to the engine.

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