Tough Question...

[engineer1776]

Hi! I have a tough question to describe. My 1986 Carrera makes a noise between about 2600 RPM and 3400 RPM. It seem to originate from the upper part of the engine. It could be described as a knock or a sound short, but I think the best way to descibe it is to imagine the sound a little boy makes when playing with toy cars and blows air though his lips. The car has about 115K miles and the engine was rebuilt about 3K miles ago. Could it need a valve adjustment?

Any suggestions?

Thanks,
Mark

[livi]

Welcome to the forum, Mark !

I am just a rookie, but I think a bit more info is needed. Is the sound dependent on which gear ? On accell or decel ? Clutch engaged / disengaged ? When driving in a strait line or only when turning ?

Oil consumption ? Last time for valve adjustment ?

For all I know it could possibly be a normal sound from an old wonderfully screaming boxer six engine..

[yngwie1]

Is there a little boy in your engine compartment? Hehe. I have no idea. Good luck.

[Grady Clay]

Mark,

Markus is right on the money. More diagnosis are necessary.

A good test is to get under the engine and inspect the juncture between the outboard of the cylinder and the inboard side of the head for each cylinder. You are looking for difference among cylinders in oil/carbon at the junction.

The symptoms you describe are typical for a cylinder-to-head compression leak under power. Usually this is caused by a broken cylinder head stud.

The easiest diagnosis is to remove the valve covers and put an Allen wrench on each head nut (24 total). Torque spec is unnecessary; just see if one is free, loose or missing.

Next diagnostic procedures would be cranking compression test and a cylinder leak test.

Post your observations/results here and you will have some very expert advice from many on the Forum.

Best,
Grady

EDIT for my lame syntax

[aircooledsonly]

Suggestion, remove alt belt see if noise goes away.

[bigchillcar]

i think that were it an alternator bearing, you'd notice it change through the entire rpm range. you can't do any better than advice solicited from grady to help diagnose. i know that gets said all the time, but it's correct all the time..so..
ryan

[engineer1776]

Thanks everybody. The noise is made in every gear when accelerating or cruising within the 2500-3400 RPM range. Will it cause more damage to drive the car (like to a mechanic)? Can the valves be adjusted without dropping the engine? (I'm new to the Porsche world).

I'll definitely use your suggestions and post the findings/results.

Thanks again,
Mark

[Huh]

Mark....If you need a good mechanic that won't kill you on work the guy I Jimi@allroad motorsports in bloomington. You can adjust the valves without dropping the engine. Join us newbies....especially another Indy guy.

[bigchillcar]

mark,
checkout the technical articles that are posted on pelican's other pages, closer to the main entry page. should have one on valve adjustments or you can always buy wayne's book..advertised at the upper right of every page.. "101 projects for your 911"
ryan

[Mysterytrain]

I had a noise on my SC that was making me crazy. Kind of a hollow sound same rpms you state..I changed the belt to a factory style with a solid inner surface rather then the cogged type..the noise went away.

[JeremyD]

Originally posted by Grady Clay
Mark,

Post your observations/results here and you will have some very expert advice from many on the Forum.

and not many better than Mr. Grady Clay

You might be an exhaust leak too - get underneath the engine and inspect your exhaust and fittings...

Although a head stud is a real possibility.

[engineer1776]

I had the valve adjustment done on the car. Some adjustment was needed, but there were no broken head studs. Unfortunately, even though the car runs better, the noise wasn't eliminated.

A few other possibilities that have been suggested to me include:

1. It could be that the car has been chipped which is causing the timing to be off enough to cause the detonation.
2. It could be that there is carbon on the piston tops which is causing the issue to appear. (not sure if this is a clearance issue or if the increased carbon causes poor combustion resulting in detonation)
3. It could be that the catalytic converter is coming apart on the inside and that what I am really hearing is a rattle inside the converter. This may be the case as the car has a soft surge in it which is consistent with a bad O2 sensor.
4. One of the mounts on the converter shield has broken which will cause the same rattle.

Any thoughts? If I was to pursue the catalytic converter failure, could I install a new pipe and O2 sensor then re-sell the unit to recoup my losses if it didn't work?

Thanks,
Mark
'86 Carrera

[mede8er]

Are you saying the sound dissipates above 3400.......

[engineer1776]

Yes, the noise goes away at high RPMs. The noise occurs in the 3000 to 3800 range during light load conditions. If you're full on or free wheeling it's not there.

[mede8er]

When your guy checked the head studs did he also check underneath for visuals of an exhaust leak......

Always try the simplest fixes first....throwing money at replacement parts is the last resort.....