Disco 3.5efi problems since new cam

[robp]

Hi all.

First post on the forum after reading for ages. Hoping someone can help me.

I have a 93 Discovery 3.5 efi. Only use it occasionally for off roading at weekends.

Just after the new year I replaced the cam, tappets, timing chain and gears.
The old cam and tappets were quite worn and once finished I felt like a new engine.

Since then I have only done about 500-700 miles in it. One of the tappets started to periodically become really noisey and would then settle back down again. It seemed to happen once the engine was warm.

Was running Halfords 10w/40 semi synth oil but now realise that was a mistake too

Last weekend had a day at an off road site and the tappet noise was with me most of the day but no drop in performance.
When I left the site for the drive home the noise seemed to be worse and it felt like the engine was missfiring and under load I am getting a poping back through the air intake along with a drop in performance.

Left it for a week and then restarted this weekend, still tapping and as soon as it warms up its missing and popping again.

So.....my initial thoughts were a sticking / blocked tappet? Tried some wynns hydraulic lifter treatment with no success. Is it possible for the tappet to get stuck and keep the valves open causing my symptoms?

My next plan of action is to strip back down again. The original cam kit I got was a Britpart and I am wondering if one of the tappets is dodgy as I have now read numerous threads advising against cheaper tappets.

Would I be safe to replace the Britpart ones with Original LR ones after this milage or is the damage already done, will I need to replace cam too??

I have also seen a number of threads advising removing the rocker covers with the engine running to identifty the troubleome tappet. How do I do this with the plenum chamber in the way? Or do I remove that first and then put it back on once the rocker covers are off?

Anybody got any other thoughts on what I could check before starting to strip it down again?

Sorry for so many newbie questions, I did try a search but didn't find anything that matched. When I replaced the cam it was the first time I had gone that far into the engine and was really pleased but am now worried I have stuffed it up

Cheers Rob

[ChrisJC]

I think I'd pop the plenum, remove the rocker covers, then refit the plenum and restart the engine to see if you can identify the noisy tappet.

At least that way you can confirm it is indeed a valvegear problem rather than something else.

But then I would say you need a new cam and followers.

Chris.

[robp]

I think I'd pop the plenum, remove the rocker covers, then refit the plenum and restart the engine to see if you can identify the noisy tappet.

At least that way you can confirm it is indeed a valvegear problem rather than something else.

But then I would say you need a new cam and followers.

Chris.

Cheers for the suggestion Chris. Is there an easy way to identify which tappet is at fault?

Is there anything else that would give these faults?

[BanditSid]

Rob,

If the tappet is noisy I would imagine it is causing the rocker to valve gap to be too large. If so, the old trick to find the noisy one was to slide in a feeler gauge between the rocker and valves one at a time with the engine running- something like 10 thou would be a good starting point - it should quieten up and the misfire should improve when you find the faulty one.

[robp]

Rob,

If the tappet is noisy I would imagine it is causing the rocker to valve gap to be too large. If so, the old trick to find the noisy one was to slide in a feeler gauge between the rocker and valves one at a time with the engine running- something like 10 thou would be a good starting point - it should quieten up and the misfire should improve when you find the faulty one.

Cheers mate, will try that next weekend and go from there

[unstable load]

It could be a sticky valve, too.
As it sticks open, it causes the lifter to be "loose" and it will account for the popping via the intake.

Just a thought.

[kiwicar]

Hi
These engines need 20/50 in them as the oil pump is designed to run with the stuff and all the bearing clearances are intended for 20/50. If you run thinner oil, firstly the tapets do not operate as designed, they will tend to be partially collapsed as the oil is too thin and flows too easily out the hole in the hydraulic tappet, secondly the oil pump tends to drain back when not running leading to oil starvation on start up. Did you run the cam in properly? or just bung in the 10/40 and warm it up at idle then drive it? If it is the later I suspect your cam and tappets are shot, especially if you ran the new cam on semi synthetic from new as it will have very low Zinc and phosphorous levels.
There are loads of threads on here on this subjectc, worth a read as they cover this topic in alot of detail.
Best regards
Mike

[robp]

Hi
These engines need 20/50 in them as the oil pump is designed to run with the stuff and all the bearing clearances are intended for 20/50. If you run thinner oil, firstly the tapets do not operate as designed, they will tend to be partially collapsed as the oil is too thin and flows too easily out the hole in the hydraulic tappet, secondly the oil pump tends to drain back when not running leading to oil starvation on start up. Did you run the cam in properly? or just bung in the 10/40 and warm it up at idle then drive it? If it is the later I suspect your cam and tappets are shot, especially if you ran the new cam on semi synthetic from new as it will have very low Zinc and phosphorous levels.
There are loads of threads on here on this subjectc, worth a read as they cover this topic in alot of detail.
Best regards
Mike

I did put in the 10/40 from the start but when I first started it up I ran it for about 20mins at 2500-3000 rpm to bed it in and all seemed well. As expected it was noisey as it first started and then quietend right down. Wish I had read up on the oil first I just referred to the Halfords oil guide while i was in there

[robp]

It could be a sticky valve, too.
As it sticks open, it causes the lifter to be "loose" and it will account for the popping via the intake.
Just a thought.

Cheers, all thoughts gratefully appreciated
Sorry for what might be a stupid question but how can I diagnose a sticking valve
Thanks Rob

[ramon alban]

Hello Rob, If your cam is worn or badly worn its possible to diagnose this without having to dismantle anything on your engine,

Check out the following and give it a go!

The Diagnostic Process.

# Warm up the engine and set the idle to a steady and easy to remember speed (say 800 rpm).

# Using suitably insulated grips/pliers, remove one spark plug lead at a time from the distributor (or spark plug) and observe the drop in idle speed for each cylinder.

# Note down the results for each cylinder in turn from No 1 thro 8.

# Removing the plug lead from a normally functioning cylinder will cause a drop in idle speed of approximately 250 rpm (so, from the suggested speed, down to about 550 rpm).

# Removing the plug lead from a cylinder with a badly worn cam will cause a drop in idle speed of approximately 100 rpm (to about 700 rpm).

# Intermediate results between 250 and 100 drop in rpm indicates a degree of partial cam wear.

# It's possible, of course, that a smaller amount of change in idle speed can be caused by a spark plug/lead malfunction which must be eliminated by substitution before blaming the cam.

# Detection of a small (say 100 rpm) drop in idle speed (not due to spark plug/ lead issues ) now really warrants a visual inspection of the cam function. See rationale, below.

# So only if found to be necessary, removal of a rocker cover will confirm any faulty valve lifting issues (on Efi models this is only possible on the L/H bank after removing the plenum chamber).

# Dealing with any intermediate results may warrant dismantling further as explained, but might also be taken together with assessing further symptoms of probable cam wear as follows:

o Idling seems to be OK but raising the engine speed to (say) 2000 rpm induces significant jerking/vibration (as if a plug lead is removed) which then partly diminishes at higher rpm.

o Not easy to detect, but a general loss of all round performance over long periods of time.

o the spark plug on a cam-affected cylinder may be partially fouled with oil/carbon deposits.

# Obviously, not all engines are the same and a degree of judgement is going be called for but if the specified dynamic test process causes the idle speed to fall by the approximate maximum 250 rpm on all eight cylinders, then its very unlikely that the camshaft is worn.

The Rationale.

On a normally functioning engine, each cylinder contributes an equal amount of energy or torque to the overall output of the engine enabling it to idle smoothly at the chosen test rpm. Removing a spark plug lead has a significant effect on the output rpm fo two reasons.

1) One eighth of the total amount of energy has been lost and 2) The other seven functioning cylinders now have to work harder to compress the fuel/air mixture in the non working cylinder as well as keep the engine ticking over at the best speed it can achieve. Usually, a drop of 250 rpm.

When an engine has a badly worn cam, whilst it's still possible to adjust the idle speed to the chosen test rpm, the idle may not be perfectly smooth because the cylinder with the worn cam is making little or no contribution of energy/torque to the overall engine output. Disabling a good cylinder still has an effect similar to that described above, but removing the spark plug lead from a cam affected cylinder detracts very little from the test rpm.

At the same time, the energy required to compress the fuel/air mixture in a non functioning cylinder is less because either the induction and/or the exhaust valves are only opening a small amount. With this double jeopardy, the drop in idle speed is much less than that caused by disabling a good cylinder. Usually falling by typically 100 rpm.

The partial fouling of the spark plug on a cam affected cylinder is expected, especially on an Efi engine, because of a potentially rich mixture due to the inadequate induction of a full volume of air whilst at the same time the normal amount of fuel has been injected into the inlet tract by the ECU.

By performing the dynamic test process it's possible to pre-assess the condition of the camshaft without recourse to removing the plenum chamber or ant other parts of a Rover SD1 Efi V8 engine.

To make the job easy to perform you will need an inexpensive digital multimeter with rpm (tacho) function.



Regarding diagnosing a sticky valve (perhaps a more unusual event than a worn cam), the simple answer would be to perform a compression test on each cylinder (Google "Compression Testing") but because an affected cylinder would also generate zero power output the procedure above would also detect such a condition.

[kiwicar]

Hi
Good to see you ran in the cam (well partially) you stand a better than even chance of having the cam still in good condition.
Firstly I would follow Ramon's procedure to diagnose the situation. If it comes out as the cam is most likley OK then I would do an oil change for 20/50. When you drop the oil out catch it in a clean bucket and when it is all drained out pass it through a coffee filter, wash the filter with petrol and have a look at what is left in the filter from the oil, it should give you a good idea of how much metal has beel lost of any cam lobes (if any at all) to knock 60 thou" off the cam lobe (the amount needed to overcome the preload on the tappet) will require that volume of cam lobe in your sump, some of that should show up in the coffee filter even though you have the oil filter in the system. If you do find alot of metal particles then cut open the oil filter and have a look at that to confirm your findings. You may find having the right oil in there is all that is needed to sort the engine, if not then it is time to start stripping it down and finding out what has happned.
Best regards
Mike[/b]

[DaveEFI]

I'm pretty sceptical that the 'wrong' oil could wear out a cam in a few hundred miles.

Besides - as I keep on pointing out - BL changed the recommended oil from 20-50 to 10-40 during the life of the SD1, and presumably for other RV8s too.

Not, of course, that the viscosity has much bearing on what additives the oil uses.

I changed the cam on my SD1 EFI at about 100,000 miles - all of those on 10-40, usually Duckham's. It had far less wear than I've seen on other engines with less miles. But mine at least had had oil changes at the times specified in the manual.

[Darkspeed]

Always check that its not just blowing exhaust manifold gaskets for the tapping noise and spitting and popping could also be running weak / air leaks / timing issues.

Just other alternative things to consider.

Did you change the rocker shafts and cam bearings as well or just the cam and followers?

Andrew

[robp]

Always check that its not just blowing exhaust manifold gaskets for the tapping noise and spitting and popping could also be running weak / air leaks / timing issues.

Just other alternative things to consider.

Did you change the rocker shafts and cam bearings as well or just the cam and followers

Just changed cam and followers along with timing gear and chain.

I am going to follow Ramons dianosis procedure asap and will report back

Will look for leaks around manifold when I do the rpm test above on each cylinder

Rob

[andy2986]

Hi Rob,

Long time no see!!

Im back from AbuDhabi on the 7th of Dec, I could pop round and have a look if you haven't had a chance by then...

Andy