Identifying Tapping Noise???
 

I went for a brief (maybe 15-20 minutes) but somewhat hard ride (motor was warmed up to 180 and I hit 7000 RPM once - redline is 7300) today. Went back to a friend's house and parked it for about 2 hours. Everything seemed fine. Came out and started it and a fairly loud tapping noise developed. It seemed to be coming out of the left chain housing (I have hyd. tensioners). Frequency of tapping increased with RPM. As the motor warmed up, the noise <u>very</u> slowly faded away (maybe after 5 minutes). Drove it home and everything now seems normal. I was 1 quart down on oil. I'm waiting now for it to cool down so I can do another cold start. Any ideas? Thanks. -- Curt

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1971 911T - 2.5L Big Bore

OK, just did a cold start and no more tapping noise????

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1971 911T - 2.5L Big Bore

Cegerer, hope you were only experiencing an intermittent sticking valve or some such.

In the coming week I will be pulling the engine on my 67 911S 2.2, because of the very same situation you have described, mine has the sound like a failed hydraulic lifter in a V-8. Ive pulled all the valve covers, checked the valve clearances for excess, nothing. Noticed a slight coppery sheen to the oil residue in the cam housing which leads me to believe I have a bearing failure in progress, funny though, I have not been able to identify the exact location, even when using the old hose/rod to the ear trick.

Before pulling the engine, I think I will perform one more test by pulling successive plug wires with motor running, to see if there is a diminished tapping at any particular cylinder.

Don in Redondo

Don,

Unless you happen to know for certain that the valve guides in your engine are NOT OEM, i.e., have been replaced with US-made phosphorus bronze or brass guides, I suspect you will find a slightly-bent valve and a case of an extremely-worn guide for that specific bent valve! The early OEM guides are an extremely-high copper content alloy, and to look at new old-stock heads, you would think they were pure copper! I think your best course of action is to proceed with the tear-down. You don't want to drop a valve because of the worn guides!

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Warren Hall
1973 911S Targa

My tapping noise also sounded like a loose lifter in a big V8. A sticking valve was one of the things we suspected. The "problem" now is that the noise has disappeared! So what do I do? Just forget about it and drive as usual or what?

I just had the valves adjusted about 3 weeks ago. Assuming a sticking valve, would it be reasonable to assume that a) the valve in question may have not been adjusted properly and this lead to the problem, or b) the sticking valve now needs to be re-adjusted, or c) the sticking valve may have damaged the valve guide?

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1971 911T - 2.5L Big Bore

[This message has been edited by cegerer (edited 07-01-2001).]

I have a similar sound in my 78SC, it goes away after the engine warms up and seems to be louder on colder days. But then sometimes...reguardless of weather conditions, it doesnt tap at all. Any one else ever have this problem?

Kemo 78SC

I just did a totally cold start this morning and everything sounds fine (wiping sweat from forehead http://www.pelicanparts.com/ultimate/smile.gif). For me, this was the first time the tapping noise ever happened. I'm really curious as to why. What causes sticking valves??????????????

My biggest fear when hearing this ominous tapping sound is that my engine is beginnig to lose a valve seat, whereby the valve seat insert starts to drop out of its aluminum pocket. Ive had this occur several times in 914's but never with the 911's, and of course it really thrashes the piston, head, cylinder, and valves.

Thought this was occuring with my spare 911 engine, which exhibited some terrible noises after a brief 2 minute turn-off and restart at a local fast food drive-thru.......sounded like I lost 3 out of 6 cylinders. Much to my amazement, now that I have it torn down, there appears to be nothing wrong with the engine except some heavy carbon/oil sludge build up at the bottom 6 oclock position of all the exhaust valves (downside of the design of a flat 6 cylinder engine), which would not allow them to completely seal, virtually leaving me with very little compression on all six cylinders. My theory is that I may have been on the high side of oil capacity for the engine, and after a brief 40 mile highway jaunt and subsequent stop at the restaraunt, this extra oil getting into the cylinders combined with too much carbon build up possibly from runnig too cold spark plugs or too rich a fuel mixture and/or excessively leaky valve guides, caused enough of a build up at the lower side of the exhaust valve surfaces so that they would not seal. What a horrible sounding racket it made, enough so, that limped home and decided to swap the engine out with an existing rebuilt. Funny, in retrospect, I probably could have jumped right back on the freeway and burnt this carbon build up in no time, got another 20,000 miles out of this engine as was, but better safe than sorry.

Don in Redondo

Well I guess I'll attempt to answer my own question after doing some 'sticky valve' research:

1) it's almost always an exhaust valve.
2) it sticks because of carbon, varnish or other fuel combustion contaminants on the valve guide/stem that causes the valve stem to bind slightly.
3) it sticks when the engine is cold because the metals of the cylinder and valve guide 'shrink' more than the steel of the stem, thus reducing the stem-to-guide clearance. Also, carbon buildup 'insulates' the metal and causes it to become hotter than if it were clean.
4a) fuel system additives may make deposits on valve stems worse (oh boy, this is <u>not</u> good - see my Techron post a few weeks ago http://www.pelicanparts.com/ultimate/frown.gif )
4b) fuel system additives may reduce deposits on valve stems and solve a sticking valve problem (oh boy, this <u>IS</u> good - see my Techron post a few weeks ago http://www.pelicanparts.com/ultimate/smile.gif ).
take your pick, 4a or 4b, both opinions are out there!
5) improper or incomplete fuel burning may cause varnish buildup on the valves. High octane fuels with lower volatility when cold may cause more problems.
6) excessive lead in the fuel may cause problems (I use a lead additive, but so did the PO with no problems)

This is what I've been able to find so far. I do have constant carbon deposits on the inside of my tailpipe. Maybe I need a different sparkplug? I also get some black smoke from the exhaust if I really step on it after a day or 2 of 'normal' driving. Comments????

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1971 911T - 2.5L Big Bore