Dwayne

I've been hearing a clunking or slapping noise that my DD (California) has been making more and more lately. I noticed the noise was coming from the front driver's side cam cover by listening closely and placing my hand on the cam cover, I could feel the vibration when I heard the noise. After I removed the front cam cover, this is what I saw:


As you can see from the picture, the gear was worn down significantly. In fact, the timing belt was very loose as seen in the picture below.


I figure this was the source of the noise - loose timing belt. I decided to proceed with removing the front of the engine and timing belt since I was going to have to replace the cam gear. The passenger side is showing signs of wear as well but loss of metal has not occured yet - just loosing the coating as you can see from the pic below.


Also looking at the oil pump gear, the coating is wearing off too....


Here's another pic of the worn out gear:


So how did this happen? As I recall, when I put the engine back together back in the summer of 2007, the cam gears and oil pump gear all still had their coating. That was at 105K miles. California now has 144K miles. I remember checking the belt tension at about 106K miles since I put a new belt on when I put the engine back together. But bad on me for not checking the cam gears for wear sooner. I figure I drove California about 38K miles without checking the grears. In hindsight, I think I should have checked the belt and gears about every 10K-15K miles and I would have caught the wear sooner.

I'm amazed at how the metal wears so fast. Anyway, I learned a very valuable lesson and just thought I'd share so other newbies like myself can learn from my mistake.

GregBBRD

Once the belt wears through the hard anodizing on the gears, the soft aluminum wears very quickly. Wear also occurs faster if the belt is loose.

atb

Never seen the wear go into the valleys between the teeth, there you go again Dwayne, once again proving that you are an over-achiever.
Nice catch BTW.

Shark_Week

Nice find Dwayne. I thought my gears were worn down, nothing like that cam gear. It looks like your water pump is leaking?

Tails

Dwayne,
Lucky! Just in time,

I check my belt tension every 12 months at the yearly service and more regularly through the holes on the top of the two cambelt covers.

Additionally I check the operation of the warning light via the Technical Bulletin fault tree analysis issued by Porsche, that is contained in Jim's technical CDs, to ensure its correct operation of the tensioner.

Condition monitoring is essential on the 928s.

I don't do as many miles as you have done in you DD California, only 3,700 kilometers in the last 2 years, unfortunatley, but I do enjoy motorhoming.

As usual an excellent photographic representation of what can happen when things start to degenerate.

Keep up the good work and I sure Bill will post the pictures in 'Dwayne's Garage'.

Tails 1990 928S4 Auto

IcemanG17

WOW...I've never seen gears worn that much.....damm

It appears an annual check of TB tension-cam gears is a great idea.... on the lemons racer we don't even run cam belt covers at all......makes checking things EASY

GregBBRD

???

And the first chunk of rubber that gets flipped up off the track that gets tossed into the belt area does what? I'd seal those things up.

danglerb

Small changes in the tooth height (gear diameter) make a 3.14 times reduction in the circumference, and as that reduction approaches the slop in a tooth fitting into the gear, bad things happen.

danglerb

We need clear timing belt covers ....

IcemanG17

the lower pan is there and we put a screen to protect the radiator and keep junk out...I don't think anything can get in there....

karl ruiter

Did you use a Continental or Gates belt? My understanding is that new Continental belts stretch over the course of the first few 100 or 1000 miles, and that is what seemed to happen to me. You were luckier than I, though as mine skipped and bent a few valves. I believe that a Porkensioner is the answer to this problem. I see you retained the stock tensioner, here. I think it is just designed to compensate for temperature changes and not so much changes in belt length. I would recommend going either with the Gates (hopefully Roger's new super strong one) or a Porkensioner.

marton

Lucky, those worn teeth can be very sharp & chew up the belt.

Jadz928

WOW! Great catch, Dwayne.

I've seen this happen on a loose belt before. LINK

SeanR

Yup, perfect example of why I change them if the coating is starting to go.

On the wifes '90, the cam gears were great but I kept getting a TB warning. Took it all apart to find the oil gear had been wearing down. It doesn't take much for the tension light to go off.

davek9

Dwayne I can not tell from the photos, are you at zero TDC when you show that T belt play?

Thanks !