ammonman

When I've got the engine fully up to temp and I get HARD on the accelerator I get some lifter rattle. I am running 15w-50 synthetic year round. I am going to give it the Rislone treatment this weekend and see if that gives some relief. Would really like to get through TT rebuild, rear suspension refresh, and front brakes in the next couple of years before having to deal with new lifters. Anyone have any other suggestions?

Mike

Mike LaBranche

Sounds like you're not driving it enough, for long enough periods of time. Gunk builds up and moves around making lifter clatter a hit or miss deal. The lifters themselves probably aren't the problem, you just need to exercise them at high speed and they'll quiet down considerably.

Alan

What makes you so sure thats what you are hearing?

Detonation, exhaust rattle/gaskets , motor bottoming out due to mounts - you sure...?

Alan

smiffypr

The lifters (tappets in English), rely on oil viscosity to work, and if yours are only ever noisy when the engine is hot, that could imply that your oil is getting too thin due to getting too hot. Have you checked the temperatures of the oil cooler hoses to see if oil is actually flowing through the oil cooler? You might need to replace the oil thermostat.

ammonman

I took a 90-100 mile run last weekend that included a stretch of road called "The Pig Trail" that has plenty of elevation change, twisties, and opportunities to push hard for a minute. At the end of the trail I got back on the interstate highway and had lifter (or tappet for those outside the US playing along) rattle while accelerating hard up the on-ramp. This fits with the oil t-stat being faulty. I'll stick a temp gun on the hoses this weekend The motor mounts are new this past summer and the car had an intake refresh about 4 years ago according to the PO. Based on the condition of the knock sensor plugs they appear to have been replaced then. I am going to check the exhaust manifold bolts this weekend but I am not getting any visual indication of exhaust leakage from the flanges. I will look carefully at each runner with a light and a mirror to see if there are any cracks in the runners. I'll report back what i find.

daveo90s4

If it really is lifter / tappet noise you'll hear it when the engine is good and hot (a few really hard laps on a track, say) and then let it idle. The hot / thinner oil combined with lower idle oil pressure will make any lifter noise clearly audible. If it is making this noise under hard acceleration up the on-ramp, with plenty of oil pressure and after just spirited on road short bursts (but not when hot idling) I'd wonder if it really is lifter / tappet noise. Could it be pinging? How's your oil consumption?

blown 87

That sure sounds like detonation instead of a lifter rattle.

ammonman

Detonation sure does make more sense as the idle oil pressure is from 1.5 to 2 bar hot depending on ambient and is very smooth with no abnormal noise. It does tick some when cold after initial start until it is good and warm. Guess I need to see about borrowing a Hammer and checking the knock sensors. I'm 99.9% positive cam timing is right as I just did the annual timing belt inspection and verified cam timing with Ken's spiffy tool. If the knock sensors check out what else could it be? Base timing somehow not right? Bad plug wire(s)? Hall sensor is new. Coolant temp is right at +180F to +190F and varies little with ambient. Plugs are 6 months old Bosch coppers.

Mike

blown 87

Several things can cause detonation, but if it is bad enough you can hear it, then that is pretty severe case of it.
What grade and kind of fuel are you running?
How is your oil consumption?
Have you ever had the carbon cleaned off of the pistons?

worf928

Yup.

I agree with Blown87's questions. Basically: Is your fuel crappy? Are you ingesting oil through the breather system? Carbon build-up is common (IMO) on auto 928s and can easily lead to detonation.

Since you have a '90 you have the diagnostic port and if you can buy/beg/borrow a Bosch Hammer or Theo's Software you can rule-in or rule-out, objectively, detonation/knocking.

ammonman

I always run premium 92 or 93 octane. When I'm around home I buy Shell at a local station that claims no ethanol in their premium fuel. I will use about 1/2 quart of oil in 6 months, but I don't put that many miles on as I travel 50% for work. The car had 172k on it 2-1/2 years ago when I bought it and it just turned 185k. Never had any carbon cleaning done so that is a possibility. Do I just need to find a long stretch of empty road and do an Italian tune-up?

Mike

blown 87

find a shop that has a motor vac or better yet one that does the BG intake cleaning.

FredR

If you hear this noise when cold starting at tickover that is a sure sign that the check valve holding oil in the feed to the tappets is leaking.

If you hear a rattling noise when the engine is hottish and accelerating hard I doubt that is tappet noise. One of the things I noted when sharktuning was that my engine seemed more sensitive to knock when at or around 3.5 to 4k rpm [the zone where the flappy transitions]. Can you link the noise you hear to that rpm interval by any chance? Do you have any reason to suspect the octane rating of the gasoline- perhaps wait until you use the current tank inventory and then try a different brand to see if hte problem attenuates.

I also noted your use of the word "rattle"- best way to describe the sensation of pinking I know of [but tappet noise also rattles!]. I would say the tappet rattle is more prominent than pinking- others may perceive it differently.

Regards

Fred

ammonman

Both check valves had seats and plungers cleaned and new o-rings installed when I did the cam cover gaskets, galley block-off pins, and chain tensioner pads.

smiffypr

I agree that if you don't hear the noise at idle, its probably not the tappets. When I have heard it due to heat, it has always gone away when the revs are raised just a little.