1975S 2.7 engine noise when turning over by hand

[Myazel]

I bought this car a while back from a longtime friend who was a vw/Porsche mechanic that had rebuilt the engine back in the 90’s with the normal upgrades of hydraulic tensioner and turbo valve covers. Car was lightly damaged in a parking lot, got parked in a building and had sat for 24 years when I got it last year. Motor was free and I moved on to fixing some small rust issues on the body. Last week I pulled the engine and transmission to give me access to replace fuel lines in the tunnel and clean up the motor and repaint the sheet metal, check clutch and all of that good stuff. Let me be up front I have tinkered on sports cars all my adult life but this is my first air cooled 911. I have a 2003 Targa I did an IMS solution on and some other minor work/upgrades and have been in a lot of engines over the years. This engine was leaking oil like most from sitting as I assumed the oil tank had drained back through the engine which I think is what kept it free. I pulled the plugs and soaked the cylinders with ATF. I pulled all induction and exhaust which surprised be as every exhaust nut came right off. Now here is the question, when I turn the engine over with a ratchet on the crank approximately every 1 and 2/3 revolutions there is a slight catch and noise. This catch and noise retards about 1/3 of a revolution every two revolutions of the crank. To make it more of a mystery if I rotate the engine on the stand to a vertical position with 456 down it will come to the catch and stop turning. I have pulled the chain covers and everything looks good tensioner are up and even looked deep in that area with my borescope. I have borescoped all the cylinders and they look fine. I could understand this if it was in the same place every revolution or two of the crank but a moving catch makes no sense to me. Last night I did a leak down test and all cylinders cam in 3-5% range just as added information. Ed said the car had been driven about 2000 miles after the rebuild before being parked. Rebuild was due to losing a chain from the old style tensioner. Thoughts?

[lvporschepilot]

Could be the chain and sprocket parallelism not quite lined up, and at one particular part in the chain combined with certain forces from the camshaft the noise/catching could be articulating itself.

[Myazel]

This morning I went down and cycled the engine over several times marking the catch on the crank pulley, the catch/noise repeats about 50 degrees short of two full revolutions and will repeat on the first mark on the seventh cycle. Turn the engine on its side or upside down and it will stop the crank when it hits it. I cant see anything in either chain or pulley with my borescope looking inside the chain boxes. Any thoughts would really be appreciated.

[targa72e]

In thinking about things in the engine that are not synced 1 to 1 or 1/2 to 1 the only thing that comes to mind is the timing chain. Someone might know the number of links in the chain so you could compare with teeth in sprocket and see if it works with your math.

john

[Myazel]

So I couldn’t let it set today and kept poking at it and found a couple of small fragments of metal no doubt from when it lost the previous chain wedged in the bottom of gear teeth on the intermediate shaft. Picked it up with the borescope shiver in through the 4,5,6 chain box. So made a little tool up to reach in and pop them loose. Now it is smooth as silk. I turned the engine up with the 4,5,6 bank down, pulled the distributor and am going to flush it real good with mineral spirits through the distributor hole to get any thing else that might be in there out. Still dont know why it was worse when the engine was up on edge but it is smooth in any position now. Thanks for the replies guys.

[fanaudical]

Yikes - Not sure I would fire up an engine that has had known metal bits flying about inside. It may be worth taking apart just to have piece of mind following a rebuild...

[Myazel]

I have spent the last two days cleaning and flushing the case out, the amazing thing is it was driven for a couple of thousand miles before a sideswipe in a parking lot started its decline into just being parked for 23 years. Everything I have found so far has been in the chain cases. I went in there with a pressure fed wand with mineral spirits and washed things out real well and then went through the case with my borescope camera and looked everywhere I could. I think I am clean at this point.

[Walt Fricke]

Good luck. Losing chains, even 23 years ago, wasn't all that common. Stuff which can get into the chain gear teeth on the IS could get into the mesh between the crank gear and the large aluminum IS gear. I'd look closely at that with your scope, as aluminum is, relatively, quite soft. I had the teeth strip off of one in a race motor (probably higher RPMs than you ever expect to run) once. Actually less damage than might have been, as all the rocker arms which ware at the time holding valves open broke promptly, but you don't want to chance that.

Do you know what broke when a chain broke back when? Just one chain?

[Myazel]

Walt the chain broke back in the mid 90’s, it was the 456 bank that broke. I know the mechanic that did the repair work on the car then as he ended up with it as the owner didn’t want to pay for a rebuild so mechanic just brought it. He was very thorough and went through the engine but did not split the case. Did the normal upgrades and put it all back together, car then received minor damage by an ambulance in a parking lot which led to another deal where it went in for paintwork and the body shop owners dies with the car there all tore apart. Owner finally got it back in pieces and just put it in a building. I can see the tracks on the crank/intermediate gears where a small piece of chain debri when through the gears but just chipped a couple of teeth. He drove the car a couple of years after the rebuild with no issues before the other incident. I have been as thorough as possible cleaning things out and thing I have it all out now. Getting ready to close things back up. Thoughts?

[gsxrken]

It’s amazing what some engines will tolerate, and conversely, how small a thing can send one sideways. Which one applies to you is anyone’s guess.
What I would warn you about is that it will probably be a leaker. #8 nose bearing o-ring, rear main seal, cam seals, etc... after 23 years it’s going to complain about being returned to service. You have it on the engine stand already... a deep reseal might be in order anyway, and assure you all the harmful bits are really gone. Your roll of the dice, obviously.