markscott

Upon inspection of my cam timing gears prior to belt change I am noticing a bit of a wear pattern on the teeth. The gear teeth seem to be worn with a bright concave pattern on the outside surfaces. These patterns are on both cam gears but not the others. Is there a known cause for this and should I be alarmed? The belt was a round tooth type and the car is an 89' S-4.
Other info...I purchased this car with a known problem. The cam timing gear 5-8 had come loose and destroyed that sides cap/rotor along with snapping off the cam at it's attachment point resulting in 6 bent intake valves etc. Needless to say I have the engine is out to do the heads/valves and replace the broken cam. The cam tensioner was also empty of any fluid do to a broken boot. As the motor is out I will be going over everything else that I can prior to the reinstall.
Many thanks,
Mark
89 black S-4
86' 944 NA

Chris

Replace the cam gears, a timing belt that is too tight can accelerate the wear of the gears but over time they will all wear eventually.

Now they are bright and shiny you have worn through the annodization.

Chris

Tom. M

definitely replace your tensionerl..seems if it is dry...the tension when hot..will be higher than normal..accelerating wear on the cam gears...

Later,
Tom
midlman@rennlist.net
89GT

bd0nalds0n

Mark:

Are you in SoCal? I had a similar problem (except I bought the car immediately before the cam gear sheared), and when I was picking up my car at Precision Motorwerks in Anaheim, there was another car in there (and I think it was a black '89) with the same problem. Didn't know if you ended up with the car if the owner decided to punt.

Bill Ball

Spots of wear through the anodization can be monitored, but concave teeth means it has gone too far and the gears should be replaced. As Chris said, the only known cause for accelerated gear wear is over-tensioning. Tom mentioned one cause of over-tensioning despite a proper setting when cold - an empty tenioner, which you report. I am going through the process of trying to figure out why my new gears wore through in 20K miles despite a tensioner setting of low-normal. My tensioner indicated it was full (oil came out of the overflow port) when I checked it recently but it took so little oil to fill it, I'm suspicious and I am going to disassemble it soon.

I remember that car being discussed here. Congrats of taking a risk, and I hope the rebuild is successful.

markscott

Thanks all for replying. You are truly princes! I am getting quite an education and will be purchasing another gearfor 1-4! After reading your posts it seems this problem is not totally uncommon. No, I didn't get the car from so-cal. I bought it from a guy in Denver who had just purchased it from a party in Indiana. The cam broke just one mile after his wife received a "good bill of health" from what used to be his mechanic. Bummer. I bought it as a project as I have allways liked the 928 and this one is in great shape otherwise. What a "project" this has turned out to be.
Mark

Jim R.

I just replaced all the gears-cams, oil pump, and crank due to wear. The cam gears were worn in the center of the teeth, but the oil and crank gears looked good while on the car. On closer inspection with the gears removed, there was wear on all the gears. My tensioner was bone dry, and the belt was about 4.5 years old. If the cam gears are worn, take a good look at the others off the car for wear.

Good Luck, Jim R.

Bill Ball

Jim R's comment reminded me that the stock oil pump gear is aluminum. If it is worn, the replacement from Porsche is steel - more durable. The crank gear is steel - less likely to wear than the aluminum gears, but needs checking topo, as Jim noted. I need to give all of these close look soon too.