The V8 Owners Forum -

Can anyone throw any ideas past me on this one, basically, my rover p6 fitted with a 4.6 has been running quite rough and down on power and feels way off balance - chugging almost. I checked sparks - no problems there (megajolt fitted). So got the compression tester out results as follows:-
no 1 - 120psi
no 2 - 150
no.3 - 150
no 4 - 150
no 6 - 10
no 7 - 150
no 8 - 10
So, no 1 possible rings? but numbers 6 and 8 barely any compression at all which has got me thinking. Being neighbouring cylinders could it be one shared problem such as head gasket. The engine does not overheat or use water, neither does it use lots of oil - or blue smoke.
Could there be any other explanation such as incorrectly set lifter pre-load.
I would like to eliminate anything before taking heads off. Thanks in advance - Andrew

The obvious thing is a blown head gasket between 6 and 8 - you wouldn't loose coolant and gases would not get into the coolant.

Bolts holding rocker pedestal to n place come loose?

Ian

garrycol wrote:The obvious thing is a blown head gasket between 6 and 8 - you wouldn't loose coolant and gases would not get into the coolant.

Definitely.

Chris.

Thanks for all replies, head gasket sounds likely then, I'll be in the garage tonight then

Andrewrv8 wrote:Thanks for all replies, head gasket sounds likely then, I'll be in the garage tonight then

Fingers crossed it's not a failure due to the support for the gasket dropping.

Darkspeed wrote:

Andrewrv8 wrote:Thanks for all replies, head gasket sounds likely then, I'll be in the garage tonight then

Fingers crossed it's not a failure due to the support for the gasket dropping.

I'm not quite with you there, on the deck face ?

I've only once seen a gasket fail on an RV8 between two cylinders. That was on an early P5 high compression run on the cheapest petrol and pretty neglected, service wise. And it had damage to the block face.

I'm hoping you have more luck.

If the liner was not fully seated at the factory its possible for them to drop in service The alloy previously supported by the liner can move inwards due to the pressure of the fire ring - The fire ring support is reduced and can then fail. Its rare.

Andrewrv8 wrote:

Darkspeed wrote:

Andrewrv8 wrote:Thanks for all replies, head gasket sounds likely then, I'll be in the garage tonight then

Fingers crossed it's not a failure due to the support for the gasket dropping.

I'm not quite with you there, on the deck face ?

I dismantled a P38 engine last month that had a failed head gasket between 5 & 7.

Chris.

ok,head is off, and yes head gasket failure. Liners look OK so straightforward job I hope. This engine is definitely not neglected in any shape or form. My next dilemma, do I remove the other head and fit my stage 2 heads (supposedly destined for my tr7 v8!).
Thanks for the interest and replies.

It might be worth checking the ignition timing. Incorrect timing can cause higher than normal cylinder pressures. Also check the head for flatness.

DEVONMAN wrote:It might be worth checking the ignition timing. Incorrect timing can cause higher than normal cylinder pressures. Also check the head for flatness.

I admit that I did have ignition timing issues prior to fitting the megajolt, but I checked true tdc at that time and I'm happy that it is now correct. It could've happened then to be honest.
I've yet to set the carb up properly - she is running quite rich. I have an AEM wideband fitted. This is the next task on the never ending list.
I will however check the head for straightness prior to refitting. Thank you.