red911 Targa

Hello Fellow Listers:

I have just rebuilt my 2.0 911 motor to 2.7 in a 1966 full restored 911 coupe.

The motor ran perfectly on the engine stand, but had a noise that I would say is a rod knock. This is based upon 13 years of Formula Vee racing, where I had my share of rod knocks.

Here is what happened:

New motor, 275 miles on it.
10.6 compression, twin plugged, Webers, AE Pistons (Aluminum), rebuild 901 gear box, lightened Aluminum flywheel and Tilton Clutch, M&K Stainless muffler with cookie cutters welded on (looks neat),

I heard the knock and checked for bearing material in the oil, NOTHING, absolutely nothing,

Ran the motor with new oil in the sump, still noise. Removed the sump, NOTHING.

Thought it might be a rocker, so checked clearances on each rocker, but all were free (NOTE: I did not check the valve clearances, but the rockers moved nicely), removed top spark plugs and took a compression check, low 165, high 175 across all cylinders.

Took motor out and carefully looked at all the parts, nothing was broken, no foreign objects in the case. The heads and valves did NOT hit any pistons. There is no leak around the heads, perfect sealing. The only thing that I thought was a broken crank, due to my newness to the lighthened flywheel and Tilton Clutch, but is not in two pieces.

What is my issue??

I have heard that if you hit the crank with a steel hammer, it should ring, my crank does not ring. There was very LITTLE bearing wear, but a little piston slapping with the AE Pistons, but that would not sound like a rod knock, or would it??

Wevo solid mounts front and rear too, so the noises are loud, without a engine mat, but with Dynamat.

Any ideas??

Thanks in advance, Tom, who is pretty frustrated now

Steve Weiner-Rennsport Systems

Tom:

Q's:

What are your deck heights?

What are your piston-to-cylinder wall clearances?

What is an "AE" piston? (are they JE's?)


Get that crank magnafluxed,......its cheap and you'll know if its flawed.

red911 Targa

Hi Steve,

Yes, they are JE Pistons, sorry.

The deck heights are not tight enough to cause any hitting of the head, no marks whatso ever.

The distance between the piston and the cylinder are very tight, but without any binding.

The noise became louder, like a rod knock each time that I ran it in my garage.

Thanks for your help.

Tom

Steve Weiner-Rennsport Systems

Hi Tom:

JE's must run looser than Mahle's as you already know and the exact clearances are important to know when diagnosing things like this. Its one of the big variables at work here,....

Measure at the top ring lands and at the skirts.

After that, you should plan on rechecking your rod bearing clearances and how they fit the rods (bearing crush) and crank journals. Factory-sourced Glyco bearings fit FAR better than aftermarket Glyco ones do so Caveat Emptor on those depending on where you sourced them.

I know this is going to be a PITA but better now, than later,............

red911 Targa

Hello Steve,

Fortunately, I have found the issue. The Tilton clutch fingers were worn and that leads me to believe that the throw out bearing was slightly rubbing on the fingers and that the noise would increase based upon RPM's. Additionally, no material was found in the transmission gear oil or the engine oil and filter when I cut it apart using the Longwood filter opener.

Thanks for your help. Once I reassemble the motor, I'll let you know if a $.25 spring will keep the throw out bearing away from the clutch.

Tom