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More P38 problems.

Les Henson

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Well more problems with this vehicle.

The unknown history of this engine, work that's been done on it previously, and standard of that work is continuing to make it very difficult to repair and have running at even close to what is acceptable.

So far:-

Heads were inspected by Zebedee Engineering, and their opinion was that the previous skim was so bad that compression gases were getting into the cooling system because of it. I was doubtful, but they were right. The heads were fitted and the engine ran pretty-much as sweet as a nut. There was a slight lumpy feel to it, and I did a cold engine compression test with the following results:-

No 1 - 190 psi

No 2 - 190 psi

No 3 - 190 psi

No 4 - 145 psi

No 5 - 180 psi

No 6 - 190 psi

No 7 - 190 psi

No 8 - 180 psi

I removed and checked all 8 spark plugs and replaced No4 with a new item (NGK R BPR6ES)

No4 was very dark, but the rest were ok.

As the engine when delivered to me had the O/S head off and No4 cylinder bore was rusty - I assumed that the rings may be stuck in the grooves on that particular piston. I put an additive in the fuel that's supposed to help release the piston rings, and left the engine running for a few hours.

However, once the engine is at full running temperature it feels lumpy as if the timing is out or it's not firing on all cylinders. Brief revs of the engine produce clouds of grey oil smoke, and when I removed the plugs - all 8 are heavily oiled.

As the compression is generally good, and I re-seated the valves/replaced seals - I can only assume that at operating temperature the inlet valves are not fully closing and oil is being sucked into the cylinders on the piston down stroke.

The amount of material removed from the head is unknown, but as the tappets are hydraulic - I would have thought that they would compensate for this.

Although evidence now suggests that the valves are not completely closing - what to be done now to make sure they close.

Would it be sufficient to reduce the length of the pushrods rather than remove half the top of the engine again to get at the lifters?

I would have thought that it would achieve the same thing.

As there isn't a measureable gap with hydraulic lifters, how would I know how much needs to be removed?

As the engine runs fine when cold, but not when hot - the amount the relevant metal expands is the problem I would think that a minimal amount needs to be removed to cure this, but I don't know how much.

Les :)

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I think you should redo the compression test with the engine hot, under the conditions you speculate the valves are not closing.

Low figures will support your idea, the same or higher figures won't.

I'm staying neutral at the moment.

Another possible test, with the engine hot, and maintained hot by running the engine after testing each cylinder, is to do a leakdown test. Not so much to see what leakage you get, but to listen where the air exits the engine; the exhaust pipe, air filter intake, or rocker box oil filler.

My only thoughts on grinding pushrods centre around going through the hardened surface. Either case hardened or work hardened.

I have no experience with the V8, and I don't want any where it's my sweat and my money being used.

However, I'd be asking your questions of people who do work on V8s. I'll pass by the 'obvious suspects' and follow a link from Gordon Finlay, as I believe his work is of good quality.

http://www.gordonfinlay-lpgconversions.co.uk/links.html to read the recommendation.

http://www.v8developments.co.uk/ for the people themselves.

Good Luck.


Someone else you may like to contact is 'allyv8' on the www.RangeRovers.net 4.0/4.6 Forum (thats the 38A to us).

From his comments he is in the UK, and appears to be 'trade'. Whether that makes him competitor or colleague I'll leave you to find out.

This recent contribution from him makes me think he might have something to offer, it's not everyone who monitors sensors with an oscilloscope.


You will, of course, have to register on the site in order to PM him.


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Les - I'm fairly certain you adjust the rockers by placing shims under the rocker assemblies, and measuring the gap between the rocker and pushrod. I can't remember the exact conditions to measure the gap under, though.

I'll see if I can dig something out - I've read about this somewhere but never done it (hence not being able to remember exactly how). It will probably have been the earlier V8s I was reading about, but so far as I'm aware there were no significant changes in this area with the P38a versions.

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Les - I'm fairly certain you adjust the rockers by placing shims under the rocker assemblies, and measuring the gap between the rocker and pushrod. I can't remember the exact conditions to measure the gap under, though.

I'll see if I can dig something out - I've read about this somewhere but never done it (hence not being able to remember exactly how). It will probably have been the earlier V8s I was reading about, but so far as I'm aware there were no significant changes in this area with the P38a versions.

Here's what you need Les, on RPI's website. 'Fraid I wasn't quite on the money - it's an intake manifold off job as you're actually measuring the pre-load on the tappets. :(

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Looks like putting shim steel under the posts is a cure if the problem is the valves not closing. It certainly seems an easy fix (relative to anything else anyway).

Les. :)

Sounds like it'll need measuring up and calculating properly though, else you'll just put other valves out of tolerance :(

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I did post this on your other post at the start of the month....


As you skimmed a load off the heads, did you check that the hydraulic tappets are still within their working range? I found when mine were skimmed, the tappets were going to bottom out therefore had to fit the shims (as sold by RPi).

Its an RPi recommendation, described on their website but basically, turn the engine until the tappet has no load and check under the retaining spring on the top of the tappet. There should be 0.020" to 0.060" clearance. If there isn't you need to put shims under the rocker posts until within spec.

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Sorry Donald, yes you did.

I didn't at that time think there would be this problem, and then thought that the hydraulic tappets could handle the thinner head. I'm going to try the hot engine compression test and then possibly the rocker post cure today, but at present it seems there are no suppliers of shim steel in Swindon.

Les. :)

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The RPi shims are quite cheap and I'm sure they would mail order them.

You need to build yourself a funky feeler guage too. I made mine by belting a welding rod with a hammer to get a flat bit, then filed it to 20 thou, then bent the last few mm over at the end and checked it / adjusted it. Then did the same on the other end for 60 thou.

When I did mine, I noticed that if you think you need to change the dimension at the tappet by xmm, you need a shim that is much thinner than x. Its obvious when you think about it because the rocker amplifies the thickness of the shim... :huh:

I have to confess its surprising that it makes that much of a difference that the inlet valves are maybe not closing... With a bit of thought, you could probably work out the best shims to use without taking the inlet manifold off.

For example, put the thickest shims in, rotate engine until valve is closed, check to see if pushrod is slack in rocker (or at least not tight or valve open). If it is slack, put thinner shims in. A more engineering approach would be to measure the arm lengths on the rocker and multiply the tappet clearance figures to allow the measurement between rocker and valve to be representative.

RPi suggest checking every valve but to be honest, if the heads were skimmer properly, the relative parts should still be on the same planes, therefore I only check front and back, then fit the same shims along the pedastals. Something would have to be really screwed up to result in different thickness shims being required and as this would bend the rocker shaft, it would be the wrong thing to do...

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I'm confident that Zebedee engineering did a 1st class job on the heads.

In an ideal situation (like in a workshop), testing the gap on each would be preferable, but RPI say use the same thickness shim under each post (for obvious reasons), so I'll do as you suggest and average it all out.

Looks like I'm going to get a some advice/ shim steel/ look around this place today :D


Anyone want any trick bits for their engine? I could take a big lunch box/wear a very baggy coat etc! :P

Les. :)

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To be honest, its a bit much hassle working with shim steel is it not? If you are going to make your own, I'd go for something softer (like mild steel).

1. Its not a rotating or loaded component. Its static and bolted.

2. The pedastals and heads are alloy so soft in comparison.

3. Flat and constant thickness is more important than hard in this application IMHO.

Now the Grandmother / Eggs bit - Don't forget to drill holes in the ones which send oil to the rocker shaft :D:D

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Well that didn't work.

I removed the rocker assembly last night, took an imprint of the shim profile and then made 8 of them.


Unfortunately this has made absolutely no difference at all.

On tickover there is a steady flow of smoke - cold or hot engine.

If maintained at slightly higher revs it appears to go, but 'blip' the throttle or increase revs to near 2000rpm and it's awful.

I know the sensible thing to do at this point would be to totally dismantle the engine (it would make a fine article for the tech archive at least :( , but does anyone have any other suggestions of what route to take - even if it's just a diagnostic one?

I've never given-up on a job on any vehicle, but the unknown history of the engine, the obvious idiots that took it apart and 'fixed' it in the first place, are making this very hard work :angry:

Les. :(

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At this point I feel like 'Jonah'

I also have been up and down on this problem, although as all I do is 'talk' about it, my downs don't bear comparison with yours.

I was nervous when you posted on the Rangerovers.net forum, but pleased when I saw allyv8 respond so quickly.

When I saw the suggestions about shims I kicked myself for not remembering that, as it was a 'standard' modification on the BMC B series engine. I built mine with shims, and yes, I knew to have an oil feed hole. I was beaten to the reminder though.

I mentioned the leakdown test earlier, to diagnose the leakage point from the cylinders.

Another 'diagnostic' test would be to disconnect the crankcase breathing system, which 'might' prove if the problem is piston blowby. Of course, if the crankcase breathing system is blocked, making it vent to a catch tank may not change anything, as the crankcase pressurisation on the compression stroke is being vented into another cylinder on the induction stroke.

If the crankcase breathing system is working, and blowby is occuring, it will be very noticable.

You will have the knowledge and experience I don't have, as to how the crankcase breathing system works on these engines, and what is a 'normal' amount of smoke for it to vent.

Just revisiting old ground, do you think the smoke is oil or petrol?

Do you still have a clean Colourtune plug you could use?


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I removed the oil filler cap to check for any excessive crank case pressure (yesterday actually, before I tried the shims), and it made no difference to the smoke, nor was there any really noticeable pressure from the rocker cover. I also removed the small breather pipe from the top of the other rocker cover that goes directly to the plenum chamber. The hole was originally clogged with mud, and I cleaned it out, so I know it's ok. The smoke is dark grey, and smells strongly of oil. The spark plugs are very oily once the engine is up to temperature, whereas they were slightly dark, but dry previously.

At revs a small amount above tickover I would say the smoke syptoms are that of worn rings, as the smoke is steady and constant, but then the puff of smoke when the engine is briefly revved is indicative of stem seal/guide wear.

I would say however that there might have been an occasional backfire, but the roughness of the engine trying to run properly could cause this perhaps.

Considering the oil/fuel mixture that is being burnt I would say that the engine runs quite well considering.

I don't have a colourtune plug, but could get one if you think it would help David.

I would think I would just see a red flash, though are you thinking it might be different from one cylinder to the next?


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I only thought of the colourtune as giving an insight into what was burning in the combustion chamber.

They easily show orange for rich mixture, and blue going on white for a weak mixture.

I can't recall what they show for an oil rich mixture. Given your other comments, I don't think a colourtune would now help. No, I wasn't thinking one cylinder would be different to another. If all the plugs are coming out the same, then whatever is affecting one is affecting them all.

"The spark plugs are very oily once the engine is up to temperature, whereas they were slightly dark, but dry previously."

If I read this correctly, putting the shims in has promoted oil burning? 'Slightly dark, but dry' suggests there was a bit of oil, but it was being burnt. Now the oil has increased to the point that it isn't all burnt.

As a matter of interest, how thick were the shims?

It appears their effect on the valve timing has been significant. Lifting the pivot point away from the cam and the valve has meant all the valves open later, and close earlier. It seems stating the obvious, but I could be wrong, that this has significantly reduced the air flow. One assumes the fuel intake is also reduced, as the O2 sensors keep the mixture stable. If the oil intake has remained the same, this would explain why all the oil is not now being burned. The surplus oil could give your "puff of smoke when the engine is briefly revved ".

It might depend on your tester, but you may well see lower combustion pressures on all cylinders if you were to repeat the tests on the shimmed engine. "Depend on your tester": some testers seem to hit the maximum reading after one compression stroke, others need the piston to hit compression several times before the reading stops rising. Mine is like this, and yes, I do test with the throttle fully open!

I'm not sure what the difference is between how the testers work, just saying that under this 'fault' condition one may pick it up better than the other.

Whatever, I think the shims are going to have to come out. Sorry.

I'll post this for now, but I think we have to re-read the symptoms from the beginning, and re-analyze them on the basis that the valves are closing properly. If doing that still shows one cylinder (spark plug) is different to the rest, then the Colourtune might help, swapped between two cylinders.

I've mentioned O2 sensors. Reading the voltages from those might be useful, just to ensure they are still working, and that the engine isn't running a default fuelling strategy. I ought to know what the voltages should be, but not running a petrol engine myself, I forget. I do assume this system starts in an open loop mode, where the O2 sensors don't control the mixture, then as the engine warms it switches to closed loop, where they do.

I don't know, without looking at a diagram + set of words, if these sensors are electrically heated or not.

Do you know all these items without me looking them up?

That's all I've got for now.

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It seems I'm guilty of not being accurate David.

On re-fitting the heads I checked all plugs and they were dark, but dry. Engine ran fine until it got up to operating temperature when it began to smoke excessively and tickover/revving was lumpy (I assumed since that this was due to oil in the cylinders affecting efficient combustion) I removed all 8 spark plugs and they were wet and oily. Yesterday I removed the rocker shafts and took an imprint of the pillar bases onto 12-thou shim steel, which I fitted to all 8-pillars. The subsequent performance of the engine you are aware of.

Cold compression test was done, and a hot compression test today - both tests were similar in results.

I spin the engine continually with each test until the needle no longer rises (6-7 compressions at a guess).

I didn't have the throttle open, and didn't think it would make a difference?

I get no warning codes apart from windows/sunroof not working.

ABS light takes a while to go out as well, but that's all the dashboard information I'm getting.


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It may be a daft response but seriously Check the oil

1. Is there too much ?..I'm guessing it will be ok, in which Case :

2. WHAT grade and make of oil is in there, they are fussy engines, best bet if it is high mielge is 20/50 Duckhams Classic

This thin modern **** really is awful in an engine that was oginially designed in the 60s

Before doing a Oil & Filter change get a can of FORTE engine cleaner shove a thin in, drive in around for 20 mins, drain oil while hot, then change oil and filter !


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Oil level was a little low, so I topped it up.

Mileage is 127k

The oil that was originally in the engine when I got it is unknown make/type as I didn't put it in there, but it was relatively clear still, so I supposed it was changed not many miles ago.

I would say that the amount of smoke is in excess of what an incorrect grade would cause.


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"I didn't have the throttle open, and didn't think it would make a difference?"

I was taught the throttle should always be fully open. This was taught when I was at an impressionable age, and I've never queried it, or tried a back to back comparison to see what difference it makes. As air has to be drawn past the closed throttle plate it may be that it simply takes longer to reach the maximum reading, and or the maximum reading is slightly lower, as the cylinder fill is clearly affected if most of the inlet throat is blocked.

I just tried a relevant Google, and the most authorative page I found comes from Puma Racing.

" ... Open the throttle fully either by pressing the accelerator or wedging the linkage open under the bonnet. If the throttle isn't open then air can't get into the cylinder and the readings will be far too low. Crank the engine until the gauge stops rising and count the revolutions while you do so. It should normally take no more than 10 engine revolutions (5 compression cycles) to get a full reading. You can count the cycles by watching the gauge too - each jump of the needle is one compression stroke. Write down the final reading and also make a mental note of how quickly the gauge rose on the first few cycles. Then just repeat for the other cylinders. Make sure that each cylinder reaches its highest reading after the same number of engine revolutions. If all readings are good then the test can end there. If any cylinders are low then a "wet" test can be done. This involves squirting a few ccs of oil into the cylinder and repeating the test. The oil will help seal bad rings and increase the reading but won't affect it if the problem lies in the valves or head gasket. Copyright David Baker and Puma Race Engines"

There's more on interpreting the results, and on using a leakdown test, at http://www.pumaracing.co.uk/comp.htm

Really, I think this is a side issue, as the figures you got seemed reasonable to me.

"Engine ran fine until it got up to operating temperature ..."

This comment seems 'interesting'. To me it ties in with the change from open loop to closed loop fuelling control. However, I do need to read up on this, as it is no longer my area of interest / detailed knowledge.

'Up to operating temperature' is just while the car is static, yes? So we aren't talking about a very hot engine, having been thrashed down the local dual carriageway, with very thin oil floating around.

In fact, it's very likely it's only the coolant that is up to temperature. My experience of monitoring oil temperature (alright, in a Mini, with the gearbox using the same oil) is that oil takes a long time to get hot.

So, I'd rule out superthin oil being a contributory factor.

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OK, I've had a quick read of the workshop manual. Section 19, Fuel System, Land Rover V8, Description and Operation, Componant Descriptions, Pre 99MY.

As well as describing what each componant does, it also describes what happens if it fails.

Re the O2 sensors it relates an interesting situation on NAS vehicles; these have additional sensors after the cats. If the wiring to the before cat and after cat sensors are reversed, the system works OK at Idle (open loop working), but as soon as the engine warms, one bank is sent rich, and the other lean, causing black smoke and rough running. Pity yours isn't a NAS vehicle :-)

The sensors on all cars are heated, not just during engine warm up, but during normal running, to ensure the sensor is always warm enough. The 12 volt supply is Pulse Width Modulated, so if you were to try and read it with a multimeter you would get apparently inconsistant readings.

This bit might help:

"In the event of sensor failure, the system will default to ’open loop’ operation. Fuelling will be calculated using signals from the remaining ECM inputs."

We could use this feature to prove, possibly definatively, that the rough running when warm is due to poor fuelling control (strictly O2 sensor feedback. Other factors may affect fuelling, such as the coolant sensor). Either disconnect the O2 sensors, then start and warm the engine, as before, and see if the transistion from 'OK to Rough' occurs as before. Or delay disconnection of the sensors until the engine has warmed, and is running rough. In this strategy the engine should revert to smooth running.

I hope and assume all the other sensors are connected, coolant temperature and air temperature, being the most critical.

For completeness, the O2 voltage output varies from 0 volts Rich, 5 volts Lean.

I can see nothing else which would account for the change in running as the engine warms.

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Not being funny, but are you sure there is no oil in the exhaust? in particular the middle silencer?

Had this on my RRC. Fixed the engine ( new cam etc etc ) put it all back together, ran it and after a while clouds of blue white smoke out the back . . . could have put a tank's smoke screen to shame.

Turned out that the enge problems caused the fuel mix and possibly oil to flow into the exhaust stream. It seemed to collect the middle silncer. When the system got up to temperature, the exhaust gas started burning off the gunk in the silencer causing plumes of smoke.

In the end I ditched the exhaust system from the middle back and replaced it with something else. Smoke immediately went.

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Did consider that at first that Donboy, but the oily plugs wouldn't be oily, and the engine has run long enough from the re-build (5-6 hrs) to at least have made a noticeable difference. The smoke is definitely oil, or at least it smells really strongly of it. The smoke is a grey colour, which sometimes is identified with water, but there is no water loss/cylinder leak for certain. I've done a leak test and it passed that.


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I've come to this late, so it may have already been asked, but are all the cam lobes lifting properly - esp the exhaust valves?

From what i've read so far, concentration has been on the inlet valves, but are the exhaust valves opening properly too?

It was actually a worn exhaust cam lobe that was my problem and made all the mess of the exhaust system and oil in the block. Cause it wouldn't open properly, not all the gas was escaping, and so the next cycle of fuel mix couldn't burn.

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