Timing chain tensioner failure?

LCOX · 08-12-2019, 09:23 AM

My 911 engine is running really rough and has a rattle coming from the left side of the engine near the distributor.
-I've checked the valve adjustment and all is ok
-Could this noise and rough running be from a collapsed chain tensioner? The engine is a 3.0 with pressure fed chain tensioners but is very high mileage 240k on the odometer.
-Can this be checked and repaired with the engine in the car? Thanx L

dannobee · 08-12-2019, 09:48 AM

Could be a collapsed tensioner. Even the oil pressure fed ones would occasionally fail. Yes, it can be repaired in the car without dropping the engine. I wouldn't even start it if you suspect it's failed.

SCadaddle · 09:59 AM

IF you decide to start the engine again, while it is running take your hand and grab the distributor body. If the crunchy noise matches up to the crunchy feeling you have in your hand, shut it down, then remove the distributor cap. Lift up on the distributor rotor and see how much it moves upwards. Should only be slightly detectable, but if it is like an 8th of an inch or more, I would investigate the status of the bushings in the distributor and on the distributors lower shaft. Try to wiggle the rotor side to side. See any scrape marks on the rotor or the contacts in the cap? That's a lot easier fix than a tensioner. For that matter, you can check it without starting the engine again.

lvporschepilot · 08-12-2019, 10:20 AM

If it sounds like a chain grinding over a steel garbage can during engine deceleration and light reving then that tensioner is indeed toast. Easy swap.

As a side note, for those reading this who have the early non pressure fed tensioners, rebuilding those things is a pain. Once air is bleed be sure to not depress the plunger too much in a vice as it will introduce air to the tensioner and you will have to take it apart again to bleed by inserting a wire to depress the tiny check ball. Only depress in a vice as much as is absolutely necessary. It’s a very fine balance.

Trackrash · Trackrash's Garage

I like the idea that it is the distributor, as mentioned. It is unlikely that poor running would be caused by the collapsed tensioner, but possible.

You can use a stethoscope, or a hose held to your ear to isolate the noise.

When one of my pressure fed tensioners failed, it sounded like a bad alternator bearing when I was driving. When I listened with the engine lid up I could tell where the noise was coming from.

LCOX · 08-16-2019, 12:58 PM

I checked the distributor shaft play both up and down and side to side and it appears to be ok.
-Didn't see any scoring inside the distributor cap either
-I also temporarily took off the fan belt and ran the car a few seconds thinking the knocking noise may be coming from the alternator bearings but the alternator checked out ok
-I listened through a long rubber hose behind the distributor in the area of the chain housing cover and could hear the knocking/rattle sound coming from this area.
-Would a compression test be another option before tearing into this area?

Trackrash · Trackrash's Garage

Sounds to me like it is time to pull the chain cover off the left side.

yelcab1 · 08-16-2019, 08:17 PM

Compression test will not tell you anything about the chain tensioner.

Coastr · 08-16-2019, 08:25 PM

It's probably the chain tensioner. Get to pulling off the chain covers - you can do it without jacking the car or dropping the engine. It's a known failure point and if you suspect it you should check it.

911obgyn · 911obgyn's Garage

You should plan on a tensioner and ramps while you are there, there is also a leak area behind the post you can address,