Engine noise

[david b allen]

I have a newly rebuilt engine that is noisey at idle. I need a method to isolate it without tearing it apart?
thanks DAVE

[700rpm]

Use a motor stethoscope, or, the poor boys' way, a short dowel or a long screwdriver. Put one end on the engine and one end up to your ear, at various places on the engine.

If it is a really new engine, give it about 200 miles to settle in, then see if the noise doesn't subside. If it's still noisy, contact your rebuilder before your tear it apart, or you may void any warranty.

[david b allen]

The engine has 700+ miles, and a 5.5 speed head,unable to isolate it with a long screwdriver
DAVE

[Mitch//pa]

eliminate the accys from turning by removing the fan belt, worth a shot

[1930artdeco]

Depending on the noise you can short out each plug one at a time. Does it increase with RPM increase? I think a bit more info is needed before we can give a good suggestion. Maybe a youtube video?

Mike

[david b allen]

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The motor has new everything Snyder pistons Brattons tin base rods new main babbitt timing gear timing gear plunger spring, valves, valve guides, spring, flywheel lighten and clutch balanced. I am running a B distributor set at 10 degrees it had less noise with A distributor at 0 degrees. The noise does go away with rpm

[700rpm]

Anything else we need to know?

[david b allen]

I have shorted out the plugs, didn't isolate the noise.
DAVE

[david b allen]

I am running a non slip belt and alternator, 12volts.
DAVE

[1930artdeco]

Do you have a 'B' timing cover on it? I have heard that if you change dist. then you need to change timing covers.

Mike

[Patrick L.]

What does the noise sound like ?

[david b allen]

I disconnected the fan belt that got rid of belt noise, next I shorted one plug at a time stayed the same which I previously had done, than I shorted 2 and 3 stayed the same next I shorted 1 and 4 the noise went away. It seems like I have a issue in cylinder 1 and 4. What should be my next step? May be I should PRAY AND SEE WHAT GOD does!!
DAVE

[david b allen]

The noise sounds like a thud not a rattle if that helps.
DAVE

[1wonton]

Make sure the spring is in the little thrust plunger in front of the camshaft, otherwise the cam can float back and forth and cause this noise.

[Tom Wesenberg]

Is the engine still under warranty?
What did the builder have to say?

[david b allen]

I rebuilt the motor and had professionals do the boring and main bearing work.
I am quite sure the cam plunger spring is in but where would that noise on the engine be most prominent?
DAVE

[newshirt]

Check the front motor mount and pulley clearance. If it is cinched down too tightly, the pulley could knock.

[PC/SR]

A thud sound that cannot be isolated is not a good sign. Does it change when you vary the spark advance? I have had center mains act that way shortly after a rebuild. Going quiet when both 1 & 4 are shorted is puzzling. Put your stethescope, screwdriver, whatever on the center main bolt under the water inlet on the drivers side and test again, but that may not tell you much because block sounds go everywhere. Center main can be reset from the bottom.

[Growley bear]

Crankshaft endplay?

[tbirdtbird]

Hmmm.
1. was the sound there right from the very start?
2. Was the builder's break-in procedure followed (did you get such a procedure)
3. What piston-to-cyl wall clearance was used?? This is VERY important to know this.
4. i suspect the noise is there at higher revs just drowned out
5. Dizzy shaft too tight? if so even with good plunger spring the cam will jackhammer back and forth; James Rogers has written a lot about this

Despite the method of shorting out plugs, it can still be hard to get an exact localization of a periodic sound problem.....

(he said it has a new plunger spring)

[Chuck Sea/Tac]

I use a cheap harbor freight stethoscope which has the.metal end removed and a heater hose taped to the end. This really helps isolate the noise well. I had a knocking cam from a weak plunger spring and I couldn't isolate it until I modified the stethoscope, then it was easy.

[david b allen]

One of my model a engine professional says it probably has wrong clearance piston to cyl, he says run it. That is what I am going to do.
DAVE

[tbirdtbird]

I am sorry to say I can almost guarantee the piston to wall clearance is too tight which is why I asked the questions I did. There has been a lot posted about this as of late. That number needs to be between .0035 and .004

You cannot set this clearance to modern specs and succeed.

You are headed for scored pistons and walls, if not already, and very possibly a shrunk piston(s) as a result, which is prolly what you are hearing now. Your engine life I am afraid will be shortened unless this is fixed. And you will have way more metal grit getting into the bearings, shortening their life as well.

I have posted extensively on this because I have fixed several ppls cars who had the misfortune of paying someone to do it wrong. I have posted extensive info on how to fix it. I have been very verbose in order to try to keep ppl out of trouble and reduce expense and aggravation

See if any of your model a engine professionals would be willing to put a good quality bore scope down each cyl. and check for scoring on the cyl walls. If you find it, do NOT run that motor. If you see scoring on the cyl walls it will be much worse on the pistons, which obv. cannot be seen while still in the engine.

[david b allen]

I called a model a engine rebuilder that did my main bearings he said piston to cyl clearance is the problem, noise does sound like piston slap but why it goes away with 1 and 4 cylinder shorted together does not make sense to me.I think I can check piston cly by dropping the pan with a feeler gauge.

[tbirdtbird]

It is very hard to accurately localize slap by shorting. I have tried many times and always get conflicting info. I do not know why, you would expect that methodology to work better!
The bottom of the cyl. is not the area of the cyl where the ignition action is and runs colder than the top of the cyl. You may not get an accurate reading by doing it on the bottom; I myself would not do it there. See what you think about my bore scope idea before you unbolt anything.

See my thread today on pix of a scored piston

[david b allen]

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I live in western mass and am a fair/god mechanic
DAVE

[Quigley1930]

Read Larry Brumfields take on piston slap on todays Ahooga board. Good imfo.

Sewall Tyler

[rocket1]

Try a compression check might tell something.

[hardtimes]

Originally Posted by david b allen

One of my model a engine professional says it probably has wrong clearance piston to cyl, he says run it. That is what I am going to do.
DAVE

Hey david,
Let us know how things work out , after running this engine situation for awhile ! I have had and seen situations like you describe with your engine. I'm posting a picture of a 'home made' device that works for isolating / diagnosing engine problems. Pair of shooter muffs , some surgical tubing ,etc..works great, as the muffs keep out extraneous stuff, so you can consentrate. Good luck.

[david b allen]

Sunday I had two of my mechanic friends over to listen to my noise.
They both agreed it is subtle and goes away above idle I am going to run it and enjoy my 29 warmed up coupe.

[david b allen]

I found where the noise was came from, sloppy fit on wrist pin bushings.
thanks for all your help DAVE

[James Rogers]

If it has an aluminum timing gear, it may have a noise till the gears get worn in.

[BILL WILLIAMSON]

Loose flywheel bolts, or flywheel dowels missing???
Bill W.

[Gary Gregory]

The thud in my engine turned out being cracked babbit thrust on rear main....not good.