Rapping engine sound

T

troverman

New Member
Hi everyone,

Looking for some help - I don't own a Rover car but rather a 2002 Range Rover P38 with the 4.6L Rover V8. Obviously there are some differences but the core block and valvetrain I believe are very similar to the original 3.5L V8. Anyway, I have an exhaust lifter (tappet) which has stuck down on cylinder #4. I believed that was the source of my rapping / tapping sound and replaced the lifter and pushrod. Upon startup, the engine ran smoothly and quietly but after about 20 minutes, particularly with some light revs, the engine is right back to where it was before - rapping! Additionally, since this vehicle is new enough, there is a misfire on this same cylinder, which I believe was due to the stuck lifter no opening the exhaust valve enough. Spark plug was very dirty black on this cylinder. Final thoughts are that when I removed the original stuck-down lifter, it was very difficult to remove from the bore. I used locking pliers and wriggled it out. There is some light scoring in the lifter bore. The new lifter dropped right in. I did take the new lifter apart and put some oil in it and squeeze it before install.

Any idea what could cause a second almost immediate lifter failure? Could the light scoring on the lifter bore create the problem? Could the problem be in the valves themselves or similar? I also changed the oil - I have tried very light oil (0w40 all the way to thick oil (20w50) and no difference.

Thanks for any help,
Tyler in USA
 
Hi, The difficulty removing the lifter from its bore is one of two things, the burnt oil on the end of the lifter is making it a tighter fit and you were scraping it off. The other cause is the end of the filter has got a compromised case hardening and the end has slightly mushroomed over and scratched up the lifter bore, it's not the end of the world so don't worry about it. The next step is take off the rocker cover and turn the engine over and check the both valves are opening fully, which if not would indicate the cam lobe has worn down. Check all the valves for operation to see if they all operate fully, to assess whether you can live with one noisy one or it needs a new camshaft and lifters.

Colin
 
Hi Colin,

Thanks for the suggestion. You are suggesting that the cam has become so worn that even with the hydraulic lifter fully extended, it still isn't making full contact and thereby causing the rapping noise. That would also explain the misfire code on this cylinder. However, it would not explain the lifter becoming "stuck down" correct? Glad to hear the scratching on the lifter bore is not an issue. I will be pulling the cylinder head on this bank next week. Before the head comes off, I'll remove fuses for fuel injector and ignition and crank the engine to see if I notice anything, then I will manually turn the engine over. Hope its not the cam - that's more work!

Thanks
Tyler
 
Hi Tyler,

Over a period of time, the diameter of the lifter at the base is increased through use. This usually means that withdrawal from the top is not possible, so they have to come out from underneath. That is why you needed to do what you did to remove it. I don't believe that your second lifter failed almost immediately. I am inclined to think that the lifter was not the original problem. I am not saying that your original lifter wasn't stuck in its bore preventing the valve opening, rather there is another problem afoot.

Have you noticed any coolant loss during the time the noise has been evident? How many miles is on your engine? Have the heads ever been removed?

Ron.
 
Hi Ron, coolant loss yes…but due to the common heater core oring leak. The coolant is ending up on the footwell. One more project I need to complete. No signs of head gasket failure. No pressure in coolant bottle when cold, coolant does not smell like exhaust.

What were you suspecting?
 
I doubt the lifter was stuck 'down' as that requires the cam lobe to be completely worn away. Stuck 'up' is a possibility. P38s heat up Very Fast which makes the lifter bore even larger and you started with a loose one; that will lower the oil pressure and flow into the lifter and they naturally leak down so there may be more leak down than the oil system can replace. check what the exhaust valve is doing. if its doing near the same as the rest in movement i'd be cleaning out the oil system around the lifter (and dismantle and clean the lifter) to ensure full flow and that it hasn't picked up some gunk from the previous work.

Coolant loss on a P38 can create a cracked bore which can tick in a similar way to a lifter. There should be some pressure in the overflow tank to prevent the coolant boiling in the heads. Unfortunately removing the heater core is one of the cars worst jobs...I'd bypass it till you have lots of time and two mates to help...
 
troverman said:
Hi Ron, coolant loss yes…but due to the common heater core oring leak. The coolant is ending up on the footwell. One more project I need to complete. No signs of head gasket failure. No pressure in coolant bottle when cold, coolant does not smell like exhaust.

What were you suspecting?
Click to expand...

Nothing specific at this stage Tyler, merely seeking further information. Is your engine still running the factory fitted Bosch Motronic ML.2.1 fuel injection system? If there has been a misfire on this cylinder since it was reasonably new, had it been looked at in the past in terms of fueling? Have you changed the coil pack?

Ron.
 
I have owned many Land Rovers in the past…Range Rover Classics, a Doscovery II, and three P38s counting this one. I had been away from Land Rovers for quite a few years but found this one last year. Zero rust, one owner since new, all black paint still on chassis. Amazingly all electronics worked. Many new OEM parts. The vehicle had 150,000 miles on it and the engine was blown which is why the owners were getting rid of it. The head gasket had failed and coolant / oil mixed and they kept driving it. So I purchased a used 4.6L from a salvage yard with 165k and removed and replaced the engine myself. I installed new Bosch coil packs and new plugs and wires at the time. It ran well with an occasional misfire on this same cylinder no. 4 but the engine was quiet. After about 5000 miles the engine began the clacking / rapping sound and I tried an oil change, thicker / thinner oil, and replaced that lifter. Cam lobes don’t look great but they aren’t worn completely out by any means. Engine and everything is stock.
 
Are the rockers and shafts the original items Tyler? The aluminum alloy rockers have a steel insert, but I understand if the insert comes loose, they will squeak, but that is not a clack. :hmm: A spark plug that is very dirty black sounds like a fuelling problem.

Ron.
 
Another possibility worth checking is that apparently the valve guide tolerance was slightly on the tight side for the P38-era V8's.
A build up of carbon would be enough to cause a valve to stick in the guide and cause a miss-fire and/or noise similar to what you describe.
 
Hi Ron, rockers and shafts are original. As I mentioned, when I pulled the original lifter out, the lifter had collapsed and clearly couldn't be opening the exhaust valve fully on that cylinder, so I assumed that's why it was so black. The work on this engine begins this week, so I'll more updates soon. Thanks
 
PeterB76 said:
Another possibility worth checking is that apparently the valve guide tolerance was slightly on the tight side for the P38-era V8's.
A build up of carbon would be enough to cause a valve to stick in the guide and cause a miss-fire and/or noise similar to what you describe.
Click to expand...

This is one theory myself and another mechanic had discussed as a possibility. The head will be coming off, so we will see.
 
Finally working on this. My original engine has been sitting in the shop. I decided to rebuild that cylinder head since it appeared to be in better shape. Removed all valves. Thoroughly cleaned head and it looks great. Valves are in great shape and reasonably tight in the guides. Replaced the valve seals. Lapped the valves back in. Cleaned the springs, assembly lube on the springs and reinstall. I have one cylinder (#4) which has had a misfire for some time. It seems clear with the head removed the problem is ignition as the piston head was “cleaner” than the rest from being washed with gas. Valves and spark plug very oil covered and wet. I did perform a compression test prior to removing the head and found good compression on all cylinders except #6 had 130psi instead of the 150-155 on the others. Upon removing the head it became clear the head gasket was failing on that cylinder. The fire ring was still intact but the material was crumbling just behind it and out towards the exhaust side. Some oil and carbon buildup was evidence of a leak. I’m sure this was likely causing the lower compression in that cylinder.
 
Slight tappet sound? Slight misfire? Sounds like my 3500S when I bought it. Rover dealer diagnosed it as 'lazy tappet'
More knowledgeable engine tuner identified it as worn camshaft. Performed a number of tests;- compression test with throttle open and shut. I can't remember the details, but he convinced me that he knew the problem. Cam shaft was a revelation, with several lobes worn virtually round. The result, so he said of neglect; using cheap oil and not changing regularly. Expensive engine rebuild with new cam and followers, and engine has been quiet ever since..
When I bought the car it had only about 70,000K on the clock. Now past 100,000K and still quiet. I always use the recommended oil with high ZDP content. Much cheaper than another new cam.
 
I'm hoping it's not the cam. I have a brand new set of 16 lifters (followers) to install. I was told to soak them in oil, which I have been doing for almost 24 hours now. I laid them down on their side, with the oil hole upwards, in a container with enough oil to cover all of them. Is this the proper way?
 
troverman said:
I'm hoping it's not the cam. I have a brand new set of 16 lifters (followers) to install. I was told to soak them in oil, which I have been doing for almost 24 hours now. I laid them down on their side, with the oil hole upwards, in a container with enough oil to cover all of them. Is this the proper way?
Click to expand...


Been thinking of doing the same. I too have the followers to fit as I think I have the same symptoms. I have been advised not to fit them. I'm guessing the cam wears to fit the followers.
 
If you are using new lifters you need to also regrind or replace the camshaft. The lifters and cams wear together and the camshaft cam profile slopes across it to promote lifter rotation. to allow that to happen the lifter bases are also ground to a curve. As the cam wears the slope changes to flat hence a new lifter on old cam won't line up and will wear very quickly.
M
 
How much of your engine's history do you know? My engine, referred o above, had had a very bad history, with the car having been through numerous owners during the car's 'Banger' period. Undoubtedly, oil changes had been ignored or only cheap oil used, so the cam had suffered irreparably. I have learned my lesson and now only use oil with ZDP, as we are advised to do with the V8.
If you do not know how your car/engine has been cared for, it is possible that the cam is worn. My experience shows how much wear the lifters can compensate for.
Find a tuning company who knows about and understands the compression tests with throttle open and shut, or someone on his Forum explain it, and you can get a guide as to how much your cam is worn.
From what it cost me to have a new cam fitted, it is not a trivial job. I am sure that this Form knows how to do it.
 
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