Thread: 1993 D1 3.9L V8 - buggered sparkplug hole

If its an original engine it may still have steel shim head gaskets. They are prone to leak with age. The spark plug hole thread can easily be fixed on or off the vehicle, either Helicoil or Re-coil do kits for doing this.

Recoil Heliciol Thread Repair Kit | eBay

Thanks bee utey.

I'm not game to try a repair with the head on the car for a number of reasons.

1) I can't get the plug out - it has backed out roughly half way then stripped the thread. I'd need to weld something to it and rig a puller.

2) I'm sure there's now a heap of debris on the top of the piston and it needs to be cleaned before the crank turns even slightly.

3) It doesn't deal with the coolant leak.

If there's a way to do a sound thread repair on the head and no sign of slipped liner(s) then I'll get my heads reconditioned, the thread repaired and put it all back with a new cam, cam chain and lifters. I'm confident that the rest of the bottom end is in good shape. I'm the second owner and the car has been on LPG since the first few hundred KM. Oil changes have been made more often than required and there are no other rumbles or noises.

The objective is to get another 100,000km out of the vehicle if possible.

Sounds like a good plan Macca!

Make sure that you run in the new cam and lifters at 2500 rpm for at least 20 min - I didn't and ended up doing the job again

If it is cylinder liners, you should be getting nasty clack-clack when hot, which sounds like a very loud lifter. Guess who now has this happening, after spending most of last year trying to fix the engine? As I have no money yet for doing a full rebore with top-hat liners, I am going to try a $12 bottle of
Chem-i-weld to see if that stops the liner moving,

cheers Charlie

I'll certainly consult the brains trust on the cam selection and other hints when at that juncture.

One thing that makes me optimistic that it's not a liner is that this motor has always been very quiet when hot and has never been cooked in the time I have had it - and no reason to think the previous owners cooked it either. Overheating is the best way to ensure a liner could go.

Originally Posted by MacMan

Overheating is the best way to ensure a liner could go.

So everyone says but mine has never been overheated either

Hey, you, stop leaving greasy fingerprints on my cloud

Got the heads off yesterday.

Both of the tin head gaskets had failed in multiple places. There was a leak from the water jackets at #1 and #7, with very obvious communication and sharing of coolant and exhaust gasses between #1 and #3. The other bank showed communication between nearly all the cylinders.

Most of the liners have the slightest detectable step downwards off the top of the block but the neither of the gaskets show signs of being battered by the liner(s) or any localised blasting to suggest that there's been a steady supply of coolant up one or more of the liners. Although the liners are supposed to be perfectly flush with the top of the block I'm not convinced that any motor that has run for this long would still have them perfectly flush because of the different coefficients of expansion between the dissimilar metals.

I looked at another Disco locally with 220,000km and a broken transmission as a possible engine donor, but without disassembling it completely I'd never know for sure if it has a block that's any better. It has also spent its life running straight petrol and looked pretty sludgy in the top end. Mine on the other hand has run almost all of the 300,000+km on LPG and I was stunned at how clean it was in under the rocker covers and valley gasket. My thinking is along the lines of "better the devil you know".

The other Disco started well and ran fairly quietly when cold but it would still be a heap of work to wreck another car and the sludge was a real turn off. In terms of cost, a complete of rebuild any motor - my current one or otherwise - is out of the question at the moment, so I think I'll take a punt on getting the heads refurbed, the thread repaired, new cam and lifters, a gasket set and then hope for the best. Even a low mileage engine from TRS or similar wreckers will cost around $2K and have no fewer assumptions on general health than doing this for half the cost.

Any leads on suitable head rebuilders in Melbourne? Also interested in suggestions for camshafts - standard profile versus something different.

When you reassemble it, don't torque up the outer row of 4 bolts. They cause the heads to warp and leak, Later engines dropped them altogether,

From: RPi Engineering - V8 Engines

Use conventional tin (shim steel ) gaskets to retain compression ratio. This is actually better than it may seem, you can (we would) refit the outer 4 offending bolts as Rover, but torque them to only 20-25ft/lb so they fill the hole but have no detrimental effect, this is generally the best option if your head and block faces are new or near perfect order.