The V8 Owners Forum -

I have been talking with the owner of an LPG workshops here in Herentals and he doubts my verdict of knackered camshaft on my 3.9.

I have 90psi on all cylinders and there is a funny cam type rumble from the engine on little above tickover, I have 102,000 miles on the clock and only a part service history upto 55,000 miles, and knowing how people like to own these cars at that age but cant really afford the servicing costs of them then run them into the ground but you cant do that with a V8 as easily as with a diesel, they need the extra tlc to keep em strong, he told me that 100,000 miles is not really that much and he regularly services a 4.6 with inexcess of 400,000kms on the clock, although I have found for myself and have been told by others that cams are shot by 80,000.

What other factors could see a ridiculously low 90psi on all 8 cylinders?

Please be merciful and I will stay seated and have the valium to hand as read the answers

I'm no expert, but logic dictates that if the cylinders are all equal to within a few % then the problem is almost certainly NOT the cam. It is virtually impossible for all the lobes to wear exactly the same to that tolerance and produce those results.

I would look to a severely gummed up engine that has the rings "glued into place" by gunk and that is giving you the readings as a possibility. Depending on the car it's in you won't need to pull the engine to get the pistons out, either and you can do a refresh job on it with new bearings, a hone, and rings while you're at it. The rumble that you refer to could be the pistons rattling down the bores with their increased slack.
Pull the intake off and the valley pan gasket and have a look-see at the cam first by all means, but I don't think that is your problem.

Anyone else got an idea, I'm happy yo be proven wrong, teaches me more things I never knew.

Not opening the throttle?

I've never come across an engine with uniform but low compressions. Wear doesn't happen that uniformly. Nor does a worn cam show up by a cranking pressure check, in my experience.

I'd first suspect the gauge or method.

DaveEFI wrote:I've never come across an engine with uniform but low compressions. Wear doesn't happen that uniformly. Nor does a worn cam show up by a cranking pressure check, in my experience.

I'd first suspect the gauge or method.

Day off today and re-tested the cylinders as per the method stated in the haynes manual and they read:-

No.1= 90psi
No.2= 115psi
No.3= 120psi
No.4= 120psi
No.5= 100psi
No.6= 135psi
No.7= 120psi
No.8= 130psi

These are a little rough and ish on the figures and did not really improve with a little clean engine oil into the bores only by maybe 5ish psi.

What should I look to do?

Dont want to waste money doing things that wont help or by the old trial and error method either, looked up some re-build kits and they're looking to cost me more than I paid for the whole car!!!!

Oh and for the poster that wanted to know what car, its a Land Rover Discovery 3.9 1998 vintage

dieseldog69 wrote:I have been talking with the owner of an LPG workshops here in Herentals and he doubts my verdict of knackered camshaft on my 3.9.

I have 90psi on all cylinders and there is a funny cam type rumble from the engine on little above tickover, I have 102,000 miles on the clock and only a part service history upto 55,000 miles, and knowing how people like to own these cars at that age but cant really afford the servicing costs of them then run them into the ground but you cant do that with a V8 as easily as with a diesel, they need the extra tlc to keep em strong, he told me that 100,000 miles is not really that much and he regularly services a 4.6 with inexcess of 400,000kms on the clock, although I have found for myself and have been told by others that cams are shot by 80,000.

What other factors could see a ridiculously low 90psi on all 8 cylinders?

Please be merciful and I will stay seated and have the valium to hand as read the answers

90psi on all 8 seems low
But it could be correct if the engine is worn out and you are getting blow by past the rings
Make sure the test is being done correctly
1) Remove All plugs
2) Ensure battery fully charges before starting
3) Fit pressure test gauge
4) Hold throttle fully open and ensure you get at leats 4 compression strokes to get the correct reading.

If the readings are still low
Try adding 5cc of oil through a spark plug hole and retesting
If the compression goes up a lot it indicates a problem towards the rings being worn - if it remains about the same it could be valves leaking - but this is very unusual to happen on all cylinders.

Ian

Sorry you posted when I was writing

Ian

I recon from those numbers you're looking at a new camshaft and followers. New Timing chain and sprockets, and the relevant gaskets.


Something along these lines
http://cgi.ebay.co.uk/Piper-Cam-kit-Lan ... 27b92e1ccf

But please be aware I am not recomending this cam for a heavy 4 wheel drive. but a similar "kit"
Likewise shopping around - perhaps at some of the forum sponsors may get you a better deal

I've also heard that some people can do the job in about 4 hours!

Ian

How about measuring the cam lifts by removing the rocker covers? These cams don't wear evenly.

FWIW, I've never found the usual compression check to be of much use - unless there is a dramatic difference between cylinders. Which confirm the suspicion of a burnt valve or piston or gasket failure. But that might just be me.

Hi
Has it been run on lpg? if so suspect burnt out exhaust valves, probably due a head overhaul also, though at that age I would also suspect worn cam shaft aswell.
Best regards
Mike

Yeah the engine has been run on LPG and for quite a while, she has a Landi Renzo sequential injection and its registered as gas in its log book too, the system is probably 7 or 8 yrs old now and I would suspect that it was heavilly used as she was a london based car for the best part of her life and it would have made the sitting in traffic cheaper!!!

Eawart also suspects burnt out exhaust valves and has suggested a "GAS" camshaft, he tells me that it is best fitted along with an upgraded ignition system ie, Megajolt or an equivalent to ensure fully correct timing, thats only if I am planning on running gas for at least 95% of my engine running time.

Think its strip it down and have a looksee at it and go from there, was hoping that I could buy a list of parts to fit and do her over a weekend but its looking like she'll have to come off the road for a few weeks to sort her out unless I wanna pay through the nose for someone else to do it?

Oh and I have eyed up the piper cam kit from RPI engineering in Norwich, very good price for me!! am worried its worse now though!!!

Perhaps cam kit, stainless valves, skimmed heads, piston rings and hone out the bores.

my plan so far!!!

One thing you could try is a leak down test. I gather from the results you have posted you have done compression test.

With a leak down test you would be able to identify if it is rings or valves which are leaking.

Bryan

Leak down test???

How does that work?

I have done quite a bit of spannering but the tech stuff has never really entered my domain as have always known the problem and had a source of transpo that didnt rely on me fixing it by the next journey.