The Black Rat

[greenMachine]

Bummer!

Is the sleeve mentioned above still an option?

I had lost count, but FOUR! I hope your engine builder is going to do the right thing, I can't see how this cannot be sheeted home to him?!

Good luck! (again!!)

[ManiacLachy]

So not the halfmoons?

[The American]

No, I went for a look, and clearly weeping from the rear main. The engine builder is now talking with the workshop directly to trouble shoot further before making the call to remove the engine.

[The American]

Compression test shows one cylinder at 80psi, which explains the leaking rear main.

Gutted!

[greenMachine]

That is a bummer.

However, colour me slow, but what is the connection between low compression and a leaking rear main? Crankcase pressurising?

[The American]

That is a bummer.

However, colour me slow, but what is the connection between low compression and a leaking rear main? Crankcase pressurising?

The assessment appears to be that if cylinder pressure is going into the crank case, it maybe overwhelming the seal.

I’ve had a chance to think on it, and I think there are two issues, which might not be related. The compression test numbers didn’t lift when oil was added to the problem cylinder, which suggests the top end has an issue. That’s not necessarily going to pressurise the crank case.

Either way there’s something quite wrong with the compression on number 2.

[greenMachine]

For sure, No2 is demanding attention.

Re crank, or VC pressure, your vents to the catch can, and then to the atmosphere aren't blocked? That is the only connection that I can think of.

[The American]

The more I think on it, I think there are two possibly unrelated issues:

1) rear main leaking due to unknown cause
2) Compression loss on no2

I’m not convinced that 2 is causing 1, but hopefully will find out when it’s torn down.

Wish me luck.

[ManiacLachy]

LUCK!

[greenMachine]

for sure, good luck! And stay away from black cats, ladders and mirrors ...

[The American]

Just to update this thread, The Black Rat is in bits with the engine out and at a machine shop/engine builder for a strip and assessment.

I’m starting to order bits (gasket set, headgasket etc) for reassembly. Will update again when I have an update from the machine shop.

[Okibi]

"Gentlemen, we can rebuild him. We have the technology."

Look forward to hearing the results.

[greenMachine]

Tell me when I can uncross my fingers and toes

[The American]

Not a complete diagnosis yet, but:

- low compression was a valve not sealing on no2. I’ve asked what the failure was (at this stage they just know it’s leaking).
- Speedy sleeve for the rear main was pushed in far enough that it contacted and was grinding against the main cap putting metal through the engine. New bearings required throughout as a result. This wasn’t the cause of any of the symptoms but would have been a real issue if run for long.
- Main caps loose in the register which is not ideal (but not an obvious failure). Recommended billet main caps or rectification work for the OEM main caps (I’ve ordered Mazworks main caps).
- No conclusive result re the main seal, but the machine shop with check the seal surface on the crank, and also whether the crank is correctly located in relation to the seal (because it has previously been line honed for the ARP main studs).
- The engine builder suggested a gapless top ring to reduce blow by induced pressure on the seals (have accepted this recommendation)

So far, all I need is a seal and gasket kit, new bearings, the main caps and top rings. I have a seal and gasket set, the bearings and main caps are ordered, and the engine builder is sourcing the rings to suit my pistons.

Interestingly, before going down this path, I had opinions from the engine builder (original) and the tuner. So far the tuner appears closest to correct. He assessed top end as likely cause of low compression and proposed this as unlikely to be linked to the rear main leak, which seems to be the case.

[greenMachine]

Good to see progress!

Looking forward to more updates ...