Range Rover Classic V8 3.5l Carbs - Loss of Power

[Rui]

Hello there,

I'm writing to request some help from this huge knowledge database that is this forum.

I'm facing quite an intriguing technical challenge with my 1981 3.5l Carbs V8. Symptoms are lack of power and torque and a (difficult to describe) change of engine noise.

So far I've checked and replaced fuel filter, spark plugs, ignition test (making sure ignition gets to every spark plug) and done a compressions test with the following results:

Values are for dry/wet (PSI) test respectively:
Left bank
Cyl 1 110 / 120
Cyl 3 112 / 124
Cyl 5 108 / 126
Cyl 7 106 / 125
Right bank
Cyl 2 102 / 122
Cyl 4 118 / 120
Cyl 6 100 / 117
Cyl 8 101 / 116

The manufacturer's reference gives a pre ignition cylinder pressure of 135 PSI. The missing pressure I attribute it to the high k's (280k) but overall it doesn't seem to have a serious ring, valve or head gasket failure from what I reckon.

The spark plugs that were replaced had no apparent issue apart from a dry sooty aspect (too rich mixture?) on four of them, not from the same cylinder bank.

Additionally there are no coolant leaks, no traces of water in the engine oil and the engine has never overheated (if I believe the temperature gauge). Also, I've done nearly 3000 k's since the first symptoms appeared so I've excluded things such as a bad fuel batch, etc.

I'm no expert in analysing this data but it all seems reasonable on the inside.

Any experts out there have faced similar issue?
Any other tips on what I should start to investigate next.

Cheers in advance,

[nigelpugh7]

For 300k miles I would suspect a new cam, followers and chain are needed at least.

Look here for more info.

http://www.v8engines.com/engine-6b.htm

[bsw]

Well you seem to have checked to obvious things except the carburettor. If it's the original it must be well worn. I'd try to find a s/h replacement and see if it makes any difference.

[plushuit]

Rui said:

Values are for dry/wet (PSI) test respectively:
Left bank
Cyl 1 110 / 120
Cyl 3 112 / 124
Cyl 5 108 / 126
Cyl 7 106 / 125
Right bank
Cyl 2 102 / 122
Cyl 4 118 / 120
Cyl 6 100 / 117
Cyl 8 101 / 116

I am not sure where you have the compression figure from..but originally, the compression was 165 psi. I am not sure how low one can keep running these blocks, but I pulled mine when it got to a dry test figure in the 120s...when it started to become hard to start when hot.

You have a few options. A ring job will bring back some of the compression for 30-50k miles. A rebore for oversize pistons will make the engine better than new..but is timing consuming and expensive. A fresher lower end (newer second hand) is smarter and a rebuilt lower block is the smartest.

[paintman]

Sounds like complete overhaul time. That's a lot of miles if genuine on the original engine.
General concensus is that the standard V8 camshaft life is around the 80k miles figure, so if yours is on its original it, together with its followers and drive chain are going to be VERY worn. That on its own will cause a significant power loss. If you have a look through the link posted earlier you will see what is all too common a sight:
http://www.v8engines.com/faq-gen.htm

Edited by paintman on Monday 9th January 10:40

[nigelpugh7]

paintman said:

Sounds like complete overhaul time. That's a lot of miles if genuine on the original engine.
General concensus is that the standard V8 camshaft life is around the 80k miles figure, so if yours is on its original it, together with its followers and drive chain are going to be VERY worn. That on its own will cause a significant power loss. If you have a look through the link posted earlier you will see what is all too common a sight:
http://www.v8engines.com/faq-gen.htm

Edited by paintman on Monday 9th January 10:40

Agreed, it's what I have found on all the v8 rover engines I have rebuilt.

The 3.5 does not have compression problems generally, nor the porous block of later rover v8's.

My v8 land rover defender had the 3.5 engine with over 100k miles on it.

I stripped the top end as it had all the caked on oil of such a old engine.

I also replaced the cam, followers and timing gear, it made a great difference.

It can be done for a few hundred pounds, I always used piper camshafts and timing chains and gears, and used genuine rover hydraulic lifters too.

Rpi have a eBay shop where all the parts can be bought from.

Good luck.

Nige

[paintman]

Very valid point - DON'T use other than genuine cam followers. 'A quality replacement part' or similar guff means walk away quickly.