engine knock

[Alan L]

My SC has developed a slight knock (tock tock noise), when hot, from #1 cylinder. Many people may not hear it above the usual valve clatter etc. But it is there, and with a screw driver against the cylinder it sounds nasty. It only appears after the engine has heated up. I can feel it with my finger on the screw driver.
I rebuilt the engine from the crank up about 3 years ago. The build went very well - fired up pretty well right away after being a box of bits for many months, no oil leaks (even now) and no issues until now. It has done 20-30k kms since rebuild.
It worried me enough that I wanted to get at it early before any damage done.
I have stripped it down as far as removing # 1 piston. I was expecting to have found something by now, but there is no obvious indication of a problem.
It really caused me to suspect bearing or wrist pin end, but the pin seems fine, and tight, and I could only check the rod bolt end by removing the bolts. I did tweek them with a socket to check they are still tight. Rock solid.
Any suggestions where to look/check. The valve gear seems fine - the rocker pins were all tight.
I have noticed the cam has about 5 mm end float. Is this normal? There is no sign of wear on the sprockets.
Regards
Alan

[Gunter]

5 mm is a lot.
With that much play, the cam lobes may have hit something in the cam towers.
Page 207 of Wayne's book gives the cam shaft axial play as max 0.40.

[Alan L]

I take axial play to be circumferential slop. It is tight in the bearing housings. The movement is longitudinal - end float. Someone correct me if I am wrong here. Please.
There are a set of shims that set this in place and the alignment of the crank/cam sprockets are critical. From memory I used the shim settings of previous. There was no sprocket wear when I pulled it down, and none now.
But I do wonder, in the absence of anything else obvious, whether this movement is an issue.
This is with the housing off, and sprocket removed, but thrust plate still bolted in.
Alan

[Gunter]

Axial play is longtitdinal = end float
Radial play is circumferential = slop

I can't remember now what part limits the end float of the cams but, looking at Wayne's book page 157-79, it should be the thrust plate?
I think the end float is non-adjustable and determined by the length of the cam (The shoulder of the first cam bearing against the thrust plate?)
Someone confirm, please.

You could check the other side for axial play and see if it is within the limits.

[911pcars]

Can you remove the con rod cap and remove the piston assembly? Inspect the bearings.

If noise was isolated at no. 1 cylinder:

Rod bearing
Wrist pin
Piston slap (excessive clearance)
Valve noise (excessive valve lash, worn rocker arm)
Loose chain tensioner (outside chance since it's next to no. 1)

Sherwood

[Alan L]

When I was trying to diagnose the noise initially my primary suspicion was a wrist pin clip mis installed, forgotten, fallen out. The noise seemed to be prevalent in the cylinder as opposed to the head or block. But this of course could be misleading. But definitely isolated to locailty of #1. All other cylinders very quiet compared to #1 which had the source of the tock noise.
The wrist pin was quite tight to remove. Because I have #2&3 still intact, I could not drive it out and had to pull it out in direction of cam chain side. It was quite a struggle and I had to make up a tool to slip down the bore of the pin to hook the lip on the other end. Several goes tapping with hammer to free. it. I don't think there is any detectable movement there.
I have not removed the bearing cap at this point - but could do so. Trying to disturb as little of engine as possible. New bearings had been installed. I was concerned as #1 was the first rod I torqued up, and later wondered if I had put to much lube paste on this cap - realising the clearances are 1 thou basically. Wondered if it torqued down properly. I used less paste on others. But looking at Waynes book, there is a fair smear over the surfaces.
I could lift the rod, but am still wondering about the 5 mm play in the cam end float. Both cam sprockets show no wear on edges. The shims sit behind thrust washer. I used the shims that came out originally - which from memory tied in with Waynes book - 3 one side, 4 other. Since there was no sprocket wear when I pulled it down, I put it back same way. No sprocket wear now - but I do have about 5 mm end float. Can't find any sign of wear in this area that might be origin of noise. Definitely not valve clearance - already re did them originally looking for noise, and checked when motor came out.
Regards
Alan

[3.2 CAB]

5mm end-play seems to be quite a bit out of spec. That is about 1/4" that it has in its movement. Maybe someone more up on this could chime in. Good luck!! Tony.

[Alan L]

Yes, I intend to pull the cam out tonight and have a look - see how come I have this much play, and whether it could cause the noise. Odd there is absolutely no wear on the edges of the sprockets. Maybe it has self aligned itself. But also I would have thought the chain ramps would tend to align it too.
Just dont want to put this thing back together and still find the noise.
Alan

[Alan L]

The end float has gone when I tighten the sprockets back on to the shaft. Phew.
At least I dont have to worry about that bit.
I am suspecting the wrist pin rod bushing, altho I don't know how bad it would have to be to make the tocking noise. I did not replace them, and there is no discernable play. But I can rock the pin in the rod end ever so slightly. I can get no movement up/down, but can get a slight rock in the vertical plane - ie straight up/down. It is detectable to feel, and no more.
Would this be enough?
Alan

[911pcars]

Originally Posted by Alan L

The end float has gone when I tighten the sprockets back on to the shaft. Phew.
At least I dont have to worry about that bit.
I am suspecting the wrist pin rod bushing, altho I don't know how bad it would have to be to make the tocking noise. I did not replace them, and there is no discernable play. But I can rock the pin in the rod end ever so slightly. I can get no movement up/down, but can get a slight rock in the vertical plane - ie straight up/down. It is detectable to feel, and no more.
Would this be enough?
Alan

From your description, my guess is excessive wrist pin clearance. Remove it and have it measured just to be sure. The small end of the con rod can be rebushed and resized if that's the wear area.

Sherwood

[Gunter]

From your description of the very slight play for the wrist pin/bushings I don't think that would be the cause of the knock.
A broken valve spring for #1 and/or a broken "Elephant" foot can make a clacking noise.

[Alan L]

Is it possible to remove/refit the rod without splitting the crankcase?
Alan

[911pcars]

Originally Posted by Alan L

Is it possible to remove/refit the rod without splitting the crankcase?
Alan

Yes. Assuming the engine is out of the vehicle, you can remove the con rod nuts from the no. 1 crankcase opening (the nuts install from the piston side). However, to have full access to the big end cap, you might have to remove the opposite cylinder (no. 4).

At this point, you're almost down to the short block and the beginning of a slippery slope. You can either replace the damaged bearing (if confirmed) and call it a day before reassembling or inspect all the con rods and replace them all, then re-ring, reface valves/valve seats, etc., etc., etc. How far you go depends on the overall condition of the engine, miles, type of driving, budget, long or short term ownership, etc.

Sherwood

[Alan L]

I replaced valve guides/valves/rings/crank bearings etc etc about 3 years ago. Trying not to split the engine again.
I did not do the small end bushes. They seemed fine - tight, no noise etc. But 30,000 Km later this may have been a mistake. Will pull the rod and get measured.
Was just hoping I could get it back in without splitting case. If out of spec, will pull them all.
Alan

[Alan L]

Have just had #1 small end bearing measured. It is still in spec. Just. (0.050mm clearnace - waynes book says up to 0.055)
The machinist doubts it would be enough to cause the noise.
About to measure big end clearance. Pulled the piston from the bore - no broken rings etc. No sign of tightness/wear.
Still looking for any suggestions. No broken valve springs (replaced with new ones).
Alan

[911pcars]

Did you also measure the pin clearance in the piston? Should be the same clearance as the con rod small end. If you're sure the noise is from no. 1 cylinder, check everything associated with that cylinder.

In hindsight, I would have suggested running the engine, then shorting out the no. 1 cylinder by disconnecting the plug wire. This temporarily removes the load from the cylinder. Noise from worn parts will reduce slightly when you do this. Helps to isolate the real cause.

Sherwood

[Alan L]

The pin clearance in the piston is -ve - quite tight - tighter than sliding fit.
The big end bearing /rod clearance is 2 thou by plastigauge - well within spec - and that was without torquing it fully down - just cranking the halves together a bit. So, definitely not there.
In spite of the fact the small end clearance is still within spec, I think it is about the only thing worth changing. Just can't find anything else. While I've got engine out, tempted to do them all. Pelican only seem to sell head gaskets by the set. I've only pulled the one head so far, so I have 5 spare gaskets looking for a home. May as well use them and be done with it.
It sounded like a wrist pin noise to me. I thought maybe a clip had come loose, or I had forgotten one. I think that is my best option.
Good suggestion to pull the plug wire. Never thought of that. Even better might be to pull the plug - remove the compression. That would have been a good move.
Regards
Alan

[Alan L]

It seems to have been the rod bush(es).
Just completed first run in car since reassembly ,1000km, and noise gone.
In spite of fact they still measured just within tolerance. This is measured cold of course, maybe they open up a fraction more when hot.
Alan