Chain rattle revisited
 

OK. Here's the scoup...

I put the car on the lift today and removed the chain housing on the right side to have a look see. The good news is that I didn't see anything wrong and the bad news is that it still rattles and I don't know why.

I felt around the housing with my fingers trying to feel any abrasions where the chain might be hitting the housing or any filings or shavings ... I couldn't see or feel anything. The chain ramp looked OK, and from what I could see of the other two, they looked fine as well. If I pushed really hard I could move the chain maybe a little less than a 1/4" between the rail and cam sproket. (seemed pretty tight to me) And I inspected the cam and idler arm gears as well. Although I don't know what a worn gear looks like I didn't notice anything that looked bad. When I looked at the gears both of them were covered in a hard yellowish brown varnish. It was pretty easy to tell where the sprokets were wearing because of the shiny metal contrasting with the varnish. Imagine a tooth of a gear ... The bottom part was shiny from contacting the chain and the sides and top still had the varnish indicating that it was not wearing on that area. Both gears looked like that.
Is that what it is supposed to look like?

I'm freeking out here...anybody got any bright ideas?


P.S Anyone looking to to a rebuild should be pleased to know that I pulled my valve cover and used a standard 10mm allen head socket with a 6 in. extension and could easily reach the head studs.
=$2.50 at Autozone instead of $30 bucks for the special Porsche tool.



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Leland Pate

___79 SC Targa

I don't have much experience, but hopefully this will give you one data point. Before I replaced my tensioners, the chain was taut. There was no way I could significantly deflect the chain by hand. Nonetheless, it was rattling a little. I didn't measure the deflection, but it certainly was not as large as 1/4". With the new tensioners on, the chain seemed at least as tight (probably more, but I didn't check it).

If you can measure the spring rate on your tensioners, I'd be glad to do the same to my old ones (for comparison).

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Graham Archer
83 911SC Cab

Lee,

Yes, that brown varnish is typical on all 911 engines' timing chain gears ... nothing to worry about!

Glad to hear your regular 10 mm drive will work on the head barrel nuts!

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Warren Hall
1973 911S Targa

Yes, your description sounds normal. Some motor oils result in less of that dark varnish stuff.

Sounds like the chain is not trying to climb out of valleys in the sprockets. FYI, wear (here or on your motorcycle) will change the shape of the valleys in the sprckets. They shoudl be round, symetrical. When worn, they will loose that symmetry.

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'83 SC

I know the varnish looking stuff is normal, and I'm glad to hear that my sprokets seems to be ok.
What do you all think about my chain ... should I be able to push on it between the ramp and cam sproket and get it to move any amount?

I really wish I could solve this problem... http://www.pelicanparts.com/ultimate/frown.gif
Thanks,

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Leland Pate

___79 SC Targa

One more thing I forgot to add...
There is a bushing between the tensioner and idler arm. I can freely rotate the bushing...is that ok? I don't know if it is supposed to be tight or not. The bolt that holds the actual tensioner onto the housing was tight but I could rotate that bushing easily.
What do you all think?

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Leland Pate

___79 SC Targa

leeland,
I remember the look on the local porsche wrench when I told him I could squeeze the (old style) tensioners with my hand. The old style should be extremely difficlut to install once they have opened (using screwdriver to wedge back in). Even those death guards are set low on the neck of the tensioner-few 16'ths.
Maybe you have the update, but if not, I would get a screwdriver in btween the tens arm and the idle sprkt and have a look see for some play by moving your screwdriver up and down. Only intense centrifugal force of your chain should be able to force them babies down. I think some instructions on 'loading' the tensioners require a vice!
At lower RPMs a tensioner going south will not be holding the chain tight, and makes a hell of a noise cause the chain is trying to bunch on the sprocket. Jump a tooth and she's gotta get some serious work done.
This is all in reference to the enclosed oil piston type tensioner. Good for conversation peice, but not for having in your engine. good luck

Thanks Tlook,
I do have the updated tensioners...they're about a year old now.
I can't push the tensioner down at all. What I'm talking about is the area of the chain between the top right (clearly visable) black ramp and the top side of the cam sproket.

Do you have any ideas as to why my chain stops rattleing after the engine warms up? So far, nobody has been able to answer that question.
Thanks,

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Leland Pate

___79 SC Targa

Lee,

This will only be a 'SWAG' (Scientific, Wild-A$$ Guess) but considering that the supply line to those tensioners is only about 1 mm ID, and is off the #8 bearing, and tapped off the cam spray-bar line ... my feeling is that the thick oil during warm-up has too small a line to go through to be of much use to the tensioner during the first five minutes of warming up. You know, I think a clear plastic chain tensioner cover would be a fascinating thing to have in place ... anyone have any 'spare' covers from which a pair of molds could be made? I'm thinking clear epoxy resin for fiberglass work might be suitable ... fun experiment, anyway!!! A lot more fun to watch than my old 'Ant Farm' in the '50's!

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Warren Hall
1973 911S Targa

The lattest excellence just had a tech Q/A on something like this. I forget all the details and it's at work. I'll be there Sunday.

I looked at that excellence today. Anderson said pull the left hand side chain box cover, if the idler arm is close to making contact with the box it's time to change the chains.