Ticking noise after rebuild 70's 911T

[Heinz911]

By using a engine stethoscope I found out that the noise is located around the nr. 4 head. I opened the covers again and found the inlet rocker moving with some resistance. Although I doubt this can cause a ticking noise I took the rocker of to have it measured.
An other possibility that crossed my mind is that the valve adjustment screw is hitting the cover, but i found no marks so it seems impossible, maybe I will check the clearance with some clay.

[Flat6pac]

Sometimes you get a bearing nitched when you drive the pin through and that causes a tightness. Sometimes you just have to swap it out.
Bruce

[gianluca 911]

handed over to center corrections for engine components, check all tolerances
aspect of the diagnostic

[Heinz911]

The nr. 4 inlet rocker bearing was out of spec. I bought a new bearing and it is currently being replaced. Hopefully this is the root cause of the valve clearance being of and therefore of the ticking, but I still doubt this causes such a loud tick. Only one way to know....

[Heinz911]

Today I tested the engine by cranking it with the starter. Even with the rocker removed the tick remains. So my doubt was correct. When I removed the spark-plug the tick disappeared. This supports my worst assumption that it is a drive-shaft bearing that makes a noise during the compression stroke. No spark-plug equals no compression and the tick is gone. Is there an other way how to confirm this, or should I just mentally prepare for a total tear-down?

Thanks for all your responses!

[gianluca 911]

could be a piston pin?
* my experience by removing the spark plug noise diminished ..
My own thought opened the engine but the bearings are ok

[Heinz911]

Gianluca, thanks for the suggestion. It could be the pin but I installed brand new Mahle P&C's so I don't think it is likely. The chance of me not having applied the correct torque to the stretch bolts seams more likely.
But first I will travel to your beautiful country tomorrow and do some thinking floating on lake Garda

[gianluca 911]

ok enjoy the lake excellent choice if I were going to let me know Venice
hello

[Rslevin]

Have you discovered the problem yet? At 1.3 of engine RPM it could be the distributor cap is not seated and the rotor is clipping the edge of the distributor cap. I have had this happen on an Alfa, and 6 hours later, after tearing into the cams and several other false directions, I noticed the distributor cap was not locked in correctly.

[Heinz911]

I used a stethoscope to locate the noise and it was mainly around cylinder 4, so not the distributer.
I'm preparing to take the block out of the car next week, hopefully I will find the cause then. I will keep you posted!

[gianluca 911]

problem solved but not identified
only thing done reverse piston cylinders
3> 6
2> 5
1> 4
now it is ok

[TwoSeatsOrLess]

How on earth did you even think to try that? Glad it worked out for you...

[HawgRyder]

Is there a piston pin offset in your type of engine?
If so...perhaps the piston (noisy one) was rocking in the bore slightly.
I would think that with new pistons and correctly sized cylinders...there would be very little side-to-side movement.
Bob

[Heinz911]

My engine is currently out of the car again. And I'm now tearing it down to inspect the drive shaft bearings, both big and small end. I'll keep you posted.

[Heinz911]

Finally opened up cylinder 4 to find scratch markes on top and bottom side of both pistons and cylinders. Less then 50 miles ago these were brand new. Seems that the piston tipped, but how this is possible with new stuff I don't know.
See pictures below and let me know what you think of it.

Thanks!

[piggdekk]

Which pistons/cylinders were You using? What was the tolerance? Did You measure the piston and the cylinder at different heights before installing them?

I've been seizing a few engines in my carrier , but in this case I'm inclined to believe that You had the wrong tolerance to start with. The wear shows a bit of a X pattern that happens normally when the piston overheats and expands due to too tight tolerance.
I'm pretty sure that if You had a lean condition the seizure would have looked different.

Something similar could happen as well if the cylinders were machined without clamping them. They would measure fine when they are not clamped, but they will have the wrong shape when clamped: narrower on the top and bottom, wider in the middle. It is common on Harley engine where the cylinders are also compressed and their walls are pretty thin. Ask me how I know....

Let's hope the experts will chime in, I'd be very interested to know what they think!!
The good news is that the cylinder doesn't look too bad, so You should be fine with a new piston, assuming that the cylinder measures fine. No doubt I'd take all cylinders off and measure them all before restarting this engine.
luca

[Heinz911]

In my rebuild I have used original Mahle forged S pistons in cast iron T cylinders. Can this combination be the source of the failure. Maybe the expansion of the S pistons (that are normally used in Nikasil S cylinders) is greater than the standard T pistons?

Does anyone have experience/knowledge on this?

Thanks!

[piggdekk]

Have You used rings for cast iron cylinders or those for nikasil cylinders? I'm pretty sure you can't use the same rings.
At which tolerance did You set the pistons?

[E Sully]

Did they use Biral cylinders for the S originaly?

[Peterfrans]

Did they use Biral cylinders for the S originaly?

Yes they did