Hello all -

I got my 1961 3.8 rebuilt and back in my grubby hands a few weeks ago, and there have been a few problems - stalling, hot start issues, and so on. Most of them I've either solved or I am chipping away at. There is however one issue that has defied me, and my limited experience with this engine has me stumped. Hoping you all can help.

Issue: Weird noise. Best description is if you had a bolt rattling around inside a glass jar, or if you had something loose in a cup. Higher pitched, metallic, almost a clinking. It is not a thud, whack, clunk, hard tap or anything like the typical "typewriter" tapping from the valves.

When does it happen: Once the engine is warm, and oil has gotten thinner. The warmer, the easier it is to hear. Eventually you can hear it quite easily even inside the car, with the hood open. The sound is somewhat random, not in time with the engine as far as I can tell. It is most easy to hear when you rev up the motor and then let the throttle drop, but you can hear it, randomly but consistent present, during normal operation. It does tend to either go away or become unnoticeable at higher RPM.

Where does it come from: Its really quite hard to pinpoint, even with a mechanics stethoscope, but it seems to be from the exhaust side cam cover, nearest the front of the engine. If you take the oil filler cap off and put a hose in one end and your ear on the other, its quite easy to hear. Stethoscope seems to confirm its easier to hear around that same area - basically the area forward of the oil fill cap. It does not appear to be the timing chain.

What have I checked already: My first thought was a tappet cup had come loose, but that does not seem to be so. All cups were the same height, none were loose and none showed any damage. The tappets can be freely rotated in their cups, but I detected no specific issues.

My theory: Frankly, I'm scratching my head. My leading theory is that one or more of the tappets is loose in its cup - enough that it rattles around as the cam and valve spring push it back and forth. But I don't know if a tappet can get loose in its cup - can it? Do they make varied tappet sizes? The sound, to me, would make sense if a metal cylinder was clinking around inside a metal cup, but I don't know if that's actually possible, nor am I sure if the tappet could rattle around with the valve spring and cam providing tension.


Does anyone have an idea? Does my loose"rattling tappet" theory have any merit? Its driving me nuts.

Thanks,

Allan

 

A recorded sound may be helpful.
Has it always done this since getting it back from the rebuild ?

 

in the 4.2 engine this noise is always from the exhaust side of the cylinder head

the reason is the tappets.

the solution is the tappet holdown kit.
it's a few brackets with self drilling bolts that keep the tappets from moving upwards and hitting the cam lobes.

 

Noises like this are hard to pin down and do travel from where you think they might be. Might seem strange but have you checked that;
a. A blade on the cooling fan is not hitting something. Worn engine mounts can let the engine move slightly and a close fitting fan might have one blade just tapping away.
b. At the same time look at the small fan on the front of the generator and the fan belt to make sure these is not tapping on something as the noise is coming from the front of the engine where these components are.
C. Lastly as you have had the cam covers off did you check the chain tension. Both the chain tensioners are situated down in the same area. A worn and loose chain tensioner might cause a tapping noise.

 

I would fit a tappet hold down kit to the exhaust side at least but noises like this can be hard to trace. The stethoscope route is probably the best. Certainly what I use. Is the noise approx half crankshaft speed? This would indicate cam & tappet related.

 

Yes, always done this since the rebuild. Hard to say if it also did this prior to, since the valves and piston made so much noise that they would have masked it. Recording the sound is somewhat challenging, but I will give it a shot.

@Jose: This is the 3.8, but I do understand your point. I checked the tappet cups / guides with a micrometer and they all seem to be the exact same height, and I see no damage or marks of any kind. Is the guide issue one where it can make noise and come loose but show no damage or evidence?

@Cass3958 - believe it or not, yes I did check some of those things, because its driving me nuts. I didn't check the chain tensioner, but stethoscope on the front of each cam cover, and by the chain tensioner itself, did not reveal anything of note.

@Glyn M Ruck - Its hard to say if the noise is at or half engine speed - it does not actually seem to be tied to engine speed specifically, except that it is easier to hear as the engine comes down from say, 2000 rpm back to idle. Otherwise the noise is random - its always there, but not at a regular interval, and not at the same pitch and duration - its variable.

I'll try get a sound recording.

 

yes I understand it is a 3.8, what I meant is that this symptom is more prevalent in the 4.2, but also happens in the 3.8. Exhaust side.

there is another thread here about this.

if it sounds like a typewriter typing at 160 words per minute, you'll need the tappet holdown kit.