[lampler]

Hello,

It seems to me that the 4 valve 968(and 944) cams have a built-in fault with a chain wheel life of 120 to 150 000 km. What to do, except to buy new ones from Porsche? Are there any rebuilt/renovated or not OEM around?

Regards

Leif

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[Brian]

i think that pete at rs barn may have something. his web site is linked on the side bar here ===>

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[earossi]

RS Barn has worked out a sprocket repair. I believe that Pete charges about $650 to rework both cams. I also recall that he will do it on an exhange basis; so, he can send you out reworked cams immediately and you return your damaged cams. Suggest you contact him personally.

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[Harvey]

[quote name='earossi' date='Mar 8 2006, 07:47 PM']RS Barn has worked out a sprocket repair.  I believe that Pete charges about $650 to rework both cams.  I also recall that he will do it on an exhange basis; so, he can send you out reworked cams immediately and you return your damaged cams.  Suggest you contact him personally.

[right][post="17112"]<{POST_SNAPBACK}>[/post][/right][/quote]



I'm curious....how do you replace worn teeth on a cam and have them be strong enough? That is, when metal is welded, the tensile strength between the new metal and the old varies. Am I wrong? Or are the teeth and lobes renewed some other way?



Harvey

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[Ryan]

Metals can be re-tempered through a specific heating and cooling process.

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[S_Cal968]

Just speculating, but the only way I would think this could be done is by allowing the welded part to slow cool [annealing]. Once cool, finish machining can be done. After that the cam is heated as a unit and quench hardened. The problem with welding is the grain alignment is not the same as the original cast cam. It would be interesting to see how a repaired cam holds up over time.

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[insite94]

Just my $0.02, but I bit the bullet and bought new cams at $700 each. Just couldn't sleep as well knowing I had 'rebuilt' cams. Real or imagined, I had visions of the sprocket shattering around the shaft. Yes, expensive insurance. Not intending to spark a debate about my knowledge of metallurgy - it's lousy, and minimizing worry was the objective.



In the future, I am preventing cam teeth issues by inspecting the variocam pads for wear. Why? Wear of the pads causes the chain to stretch, which wears down and weakens the teeth, which cause the chain to wear, which causes further...etc. The solution is preventative maintenance - change the pads and the chain, both cheap by comparison. BTDT, and spent a small fortune in the process.

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[Harvey]

[quote name='S_Cal968' date='Mar 10 2006, 02:59 PM']..... The problem with welding is the grain alignment is not the same as the original cast cam. It would be interesting to see how a repaired cam holds up over time.

[right][post="17180"]<{POST_SNAPBACK}>[/post][/right][/quote]



I'm with you S_Cal968. I'm skeptical about the long term...grain lining up, etc. I've seen too many metals break along the weld line. I'd like to know who's used these repaired cams and for how long.



Harvey

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[bob blackwell]

The solution is to remove the old sprocket from the camshaft and weld a new sprocket on in place of the damaged one. Partswerks in chicago do this as well as Pete at RS Barn. Rebuilding the teeth is not an option that I know of. When my exhaust cam sprocket shed several teeth I also went with a new camshaft for the repair. I sent Pete my old exhaust cam for experimenting with replacing the sprocket. Good luck, Bob Blackwell.

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