911 SC engine noise
 

hi,
I have just rebuilt the CIS on my SC (cracked airbox) and since I started the engine it is now making this awful knocking noise.

https://youtu.be/63hwGK-h4Ls

The engine was running fine and smooth before I did the CIS.
I also changed the belt, and try running without but noise is the same.
I have checked the spark plugs and all ok, too pic down the plug holes and all piston tops seems black with no debris.
it seems louder than rocker noise.
anyone has experienced this?

Chain tensioner..........
 

JYT,

The noise seems very similar when I had a collapsed chain tensioner/s. Remove the chain housing cover/s and test the tensioners using a long screw driver.

Tony

can I do this in situ?

I really thought it was the bottom end but after draining the sump the oil is absolutely fine.

Chain housing covers removal........
 

Yes. But you have to remove the engine tin at the front of the chain housing covers. An engine partial drop will give you more room to work.

Tony

I agree with the aforementioned diagnosis of a collapsed tensioner, but since the noise started occurring right after you refreshed the CIS unit, I wonder if an object dropped into one of the intakes.

You meant before the airbox cracked ?

The damage could have been done at that time and not caused by your rebuild.

The chain was slack on LH but after turning the engine CW the tensioner did its job...I think :|
It seems now that I cannot turn the engine past TDC either way. so the theory of the dropped object may be the one to pursuit. Although I can account for every nuts and bolts and there is no damage to the spark plugs...
I slacken the valve adjustment of the inlet valves ope at that particular TDC but didn't help tuning the engine.
the noise has changed slightly a few time also.

I mean before I rebuilt the airbox.
now that I've checked the rockers, and chains I have to come to the conclusion that something dropped inside...
I'll get a borescope and have a look...

Yeah, the backfire is a pretty violent event, so it could have sucked in some hidden screw. Hopefully you can fish them out.

Good luck with this.

You need to rebuild your tensioners. You are lucky it is not fully collapsed and you discovered it before it did.

After you get the tensioners in order, I guess you should use a scope in the spark plug holes to see if anything is in there.

Screws from the airbox cold start diffuser have been known to fall into the intake.

If checking the tensioners, no need to do a partial engine drop to gain access to remover the chain covers. Just remove the rear engine tin and the muffler. Plus whatever small items that are in the way like air pump if you have one.

thank you all for your help. there a small screw impeded in*cylinder No5!
looks like the screw from a jubilee clip

Ouch !

Would the embedded screw in #5 cause all that noise ? From your video clip, it sounds like the driver side bank is louder. Sorry about the troubles but interested in your future findings.

yes it was, it's all good now until I have the time and money to rebuild the engine.