Help with possible chain tensioner failure in a 3.0SC

[ARCSinAK]

Hi Gentleman-
Any thoughts on my situation would be great.
The Engine History: 120K
Top end rebuild 4 K back, Rebuit valves, rings, all seals.
After about a thousand miles noticed a knocking/tapping noise, which seems to match the revs but is less dramatic the higher the revs. I listened with all of the usually diagnostic tools, hardwood Dowel, Metal Bar ect.
Sounds deep, worse at 950 Idle than a 1100 idle. Hard to tell where it's coming from. I have listened to all the available spots, under the case on the timing chain covers ect. My original thought was that the PO may have re-used the rod bolts and the new top end created more compression and thus leading to a possible rod bearing failure. However, the sounds has remained unchanged after another 3K of spirited driving. The engine runs strong and pulls to 6K. The general opinion I have gathered is that if was a rod bearing it would get dramatically worse in a hurry.

Yesterday, I decided to change the oil and has a look at the magnetic sump and tank plugs. Took a drive got up to 180 degrees, drained the oil, inspected the plugs for pieces of metal and metallic residue. Found no shrapnel and minimal residue.

Here where things get interesting, I added ten quarts of 20/50 and started the engine. The flat six was chattering like mad, scarred me, I thought it was done. Shut her down added another quart and started again, the chattering, gradually, over the course of a minute or so backed off to the sound that has been frustrating me. The same underlining old sowing machine style knock that I have been so frustrated by.

Has anyone else experienced a radical chattering sound after a oil change which then subsides? This 80 SC has had the hydraulic tensioner update. Could a tensioner be loosing part of its tension thus creating the noise and then have lost all or most of its tension after the oil was drained? Only to have re-tensioned itself to a partial state again? Strange how after the oil change the sound was so radical and then returned to the same some what tolerable noise.

I would much appreciate your feedback. I plan to order gaskets for the covers and inspect in the near future but it would be nice to have some opinions first.

Thanks and have a fun weekend.

[VFR750]

Ok, just finished a rebuild. I had a tapping sound at low power before the rebuild. During teardown we found the cam gear on the crankshaft was loose. Was weld repaired and ground. Now, after the rebuild the tapping is gone.

Also reused the tensioners. And of course one decided to crap out during the break in cycle. Rattle on start and then stopped. Next day, after the drain and refill, rattle and then ok.

Pulled the engine and fixed a few things. Found the RHS tensioner was notchy when compressed to it's running height. Installed a new tensioner, problem solved.

I also noted the brand new RHS idler arm was starting to gall on the housing shaft. Took 1500 grit sandpaper with oil lube and polished out the marks on the shaft. The old idler arm was heavily worn and had transferred copper to the shaft. Guess i did not clean the shaft enough during the rebuild. I think the galling contributed to the tensioner hanging up.

As I said, all good for now.

[Dpmulvan]

I would probably stop driving/starting until you have a look inside could It be a rocker??

[ARCSinAK]

I most curious aout how the oil change so dramatically effected the sound and then it returned to the previous noise. If it was a cam gear sound would be effected by oil change? There was about a hour between the time I drained the oil to re-start. Could the pressure in the tensioner have dropped, then return to a partially functioning state?

Would a oil change effect the sound a rocker would make.

[Trackrash]

To answer your original question. When I rebuilt my motor, I also rebuilt the tensioners. Do you have a record of any service done on the tensioners? If they were just re-used as is, yes they could fail.

That said, from your description, it doesn't really sound like a tensioner. Except, when a tensioner is weak it very well MAY make more noise on startup, depending on how the cam was positioned when shutdown.

Have you listened to the bottom of the motor when running? That could show a rod going.

I would pull the valve covers and timing covers and do a through examination.

[ARCSinAK]

Im were I am now, no record of chain tensioner services. obviously hind site is 20/20

The sound has never been louder on start up until after the oil change. Just thought someone may have a theory of why this happened.

I have listened to the bottom end while running. Thing is I have driven aggressively for 3K and the sound has not changed in terms of its quality. Could a rod bearing really handle that?

The valve covers have been off, no visible issues.

Ordering gaskets for the timing covers now.

Still curious about possible clauses of the post oil change sound increase which then returned back.

[porsche930dude]

its not too hard to check for rod knock. just put a dowl down the plug hole and slightly turn the engine back and forth. if the piston doesnt move and the crank does then you found your problem. I dont know if it could survive 3k miles like that but I suppose stranger things have happend

[mnez]

Reviving the thread,
Did you ever determine the source of the tapping?
I now have a very similar tapping that matches your original description.
1986 3.2

[proporsche]

make a video..we will tell you what is up..
Ivan

[mnez]

I have an audio recording from my phone, as soon as I figure out how to add it.

[mnez]

Started a new thread,
Diagnosing a new engine noise