Tapping on startup, any ideas?

[Ralph S3]

Slightly concerned by noises from my 2.9 at start up. If the car has been standing for a few days I get a loudish tapping for a few seconds. After a few seconds it disappears. This doesn't happen if the car was started earlier in the day or the day before. Given that it only happens when its been standing I'm guessing its oil pressure related. I'm not sure if I have hydraulic tappets which I'm guessing will behave like this if the oil drains out while the car is standing. Would it do this if the oil pump was on its way out?

What's really bothering me though is that I'm sure it hasn't always done this. I think this is a relative new phenomena which started earlier this year. Car has done about 78000 miles, regularly serviced, solid oil pressure and running well.

Anyone got any ideas?

Ralph

[tvrgit]

Mine does have hydraulic tappets, and is a tiny bit noisy when first started after lying for a while, but goes away after just a second or two - as you say, I think it's the tappets pressurising.

I did have it once, much worse - it was much louder and lasted until the engine was quite hot. That was immediately after an oil change, when my motor factor had stopped stocking the oil I normally used, and gave me another "exactly the same". Well it wasn't - I drained that oil back out, put better oil in, and the noise stopped.

So if you've recently had the oil changed, I'd look there.

If your car doesn't have hydraulic tappets, then maybe they just need adjusted - not sure if that would be part of your car's normal service or not.

[ketvrin]

I agree with Andrew... the oil would drain away from the top of the engine after a few days sufficient to give you this tapping (tappets tap... the clue is in the name ). The other possibilty regarding the oil change is that if you have moved from semi to fully synthetic the tappets will be noisier and it will drain away more quickly. The noise will stop when the oil circulates again and unless you over-rev a cold engine, there will be no real detrimental effect. Worth checking the gaps if you dont know for sure that they are OK.

Good luck

K

[Barkychoc]

The hydraulic lifters are actually down in the heart of the engine sitting straight on top of the cam, although any clattering you'll hear will be at the top end the slack is actually produced down in the 'V'.
They can bleed down a little when you haven't used it for a bit - when you start it up they have to fill with oil again.

Low oil pressure (knackered engine!) and too thin grade / dirty oil can make it worse.

Its dead simple how they work - they pump up with engine oil which takes up all the slack in the valve gear - but there's not enough pressure to open a valve. The oil inlet to the lifter has a one way valve inside the lifter - when the cam starts to lift the hydraulic lifter the oil tries to escape from the lifter but can't due to the one way valve, so it has to push the pushrod up & move the valve etc.
Once it drops back down onto the heel of the cam only oil pressure is taking up the slack again.

If the one way valve fails on one of the tappets you'll get a quite severe tap tap tap from the top end.
Sometimes the valve can get a bit of crap stuck in it, its perfectly feasible to take the lifters to bits and clean them out, but you must make sure the right ones go back into the right holes as they wear to their respective cam lobe.

If you want to read up take a look at this - its Rover V8 but similar.

Ignore references to knackered cams at 60 to 80k - thats a Rover V8 feature!
Also the Rover V8 tappets are not adjustable hence all the pain in the arse stuff regarding shims & tappet pre load.

http://www.v8engines.com/engine-4.htm

[Ralph S3]

Thanks lads.

First thing I'll do is change the oil again just in case its too thin (although I'm pretty sure its the same stuff I always use). Then I'll have a bash at identifying once and for all whether I have hydraulic lifters. If it is hydraulic then that will be it I suspect.

Then I just need to knock out a few end of season jobs to be ready for the sunny days. This is the first year I haven't sorn'ed the car and its being snowing ever since I made the decision to keep it taxed to take advantage of those lovely crisp winter days...!!

[jimed]

From what I can see the only ref to hydraulic tappets in the 2.9 V6 is to some of the S3C's. This is from Steve Heath's updates for the S series book - www.shpub.co.uk/tvrbooks/update_s.html - which is worth a look as it gives details incl how to set them. Maybe your S3 does have them (stranger things have happened at TVR) or maybe the engine was swapped for one from an S3C. Not sure how to tell though without some dismantling; my S3C used to rattle for a few seconds when it'd been sat for a while but it soon cleared itself and the tappets never needed adjusting once they'd been set.
Jim

[TurboTony]

I have problems in the past with hydraulic tappets on Rover V8 engines. I occasionally had a noisy tappet after the vehicle had been standing for some weeks. They sometimes built up sludge from the oil which affected their performance. I was advised to use an engine flush before changing the oil and this cured the problem. It also is good to clear sticking piston rings if the car has been standing for a time and pumping out blue smoke.
Cheers
Tony