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Brad01mc's Avatar
 
Join Date: Oct 2005
Location: Redlands, CA
Posts: 225
Timing Chain Replacement Interval...

Hi List!

I'm new to the whole Porsche experience and just bought a 1978 SC. I'm completely in love with this car. I can't believe I've waited so long...

Anyway, my question is simple...

What is the recomended mileage interval (typical) for changing the timing chain(s).

Aside: I also own a 1961 Mercedes and you can check the chain stretch by lining up the cam index marks and look at the crank timing marks to see how many degrees the chain has stretched. Once it gets over ~3-5 degrees, it's time to change.

I've searched the archives and can't find any procedure similar for the 911's.

Can someone please give me the "low down" on 911 timing chains?

Thanks!
Brad

Old 10-13-2005, 10:05 AM
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KobaltBlau's Avatar
 
Join Date: Mar 2004
Location: City of Seattle, WA
Posts: 3,374
SCs can go 200k or even closer to 300k without major engine work with the right circumstances, and this includes the chains. If the bottom head studs get corroded, bets are off, but you get my point.

The normal routine I've seen is when you do a rebuild for another reason (or change cams, say) you check the chains and gears and replace them together if need be. The chains are pretty bulletproof and you don't see them getting replaced at a standard interval.

I'm not sure offhand what the chain pitch is but they make a chain stretch tester for 1/2" pitch bicycle chains, if something similar is available for our chains it might be a good idea to check. Here's what the bike chain checker looks like, it has pins on each end and the one on the "dial" end is eccentric:

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Andy
Old 10-13-2005, 10:17 AM
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Grady Clay's Avatar
 
Join Date: Dec 2003
Location: Arapahoe County, Colorado, USA
Posts: 9,032
Brad,

I agree with Andy, that is usually not an issue with a 911 as the chains outlive most everything else in an allready long life engine. The chains are a standard item to replace at an overhaul. You can replace them with split link chains without splitting the case if the need arises.

On a 911 you can generally tell the condition of the chains by looking at the cam sprockets and idler arm position.

The only exception is an engine that has had solid tensioners. Those can over stress the chains if not kept in proper adjustment.

I have never seen a chain fail, even with all sorts of jumped cam timing carnage from other causes.

The critical issue is keeping proper functioning chain tensioners and replacing the chain ramps when opportune. Any engine older than the late 70s should have confirmed late plastic ramps.

Best,
Grady

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Old 10-13-2005, 10:28 AM
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