heinrich

Many questions, few answers. The crank gear was worn at 81k miles of ultra-conservative grandpa-style driving all its life. So ... I do not know why or how, but the gear was worn badly, and I hadn't considered it when replacing the cam gears and pump/belt. That belt, the one that wore the crank gear, was likely a Porsche belt as the services had been done professionally and I know the service people.

The one that walked forward at that point, was a federal mogul belt with the strange indented tooth peaks ...... I think Garth had posted a pic a long time ago. I happened to receive a conti this time around, so I installed it. No peak indents on that one. But I also replaced the crank drive timing gear ... all seems to be well now. Apparently it was the crank gear. And I suppose one could say statistically, I replaced TWO things and the problem is now fixed. Gear and belt.

Big Dave

MY belt that walked forward was the result of (this is the theory so far) a bent tensioner arm bolt. See the "Progress" link in my signature. I have the strong suspicion that something else is bent, too, but I won't know for sure until the engine is out...which will in the next few weeks.

While we're on the subject...how can I specifically determine whether I need new cam gears or a crank gear? Someone mentioned that if they're shiny, they need to be replaced. That doesn't make much sense, so I'm looking to be educated a bit....

heinrich

no teflon, no value. if the teflon (grey-brown stuff) is off or not intact, toss 'em.

mark kibort

wow, hard to believe the crank gear would be worn by the belt. you would think if it was worn, the pulleys would be destroyed!!(aluminum vs steel).
anyway, none of those issues on mine, other than the ones i know about!

Ill know more, once i get in there and replace the existing belt. also, as a side note, we wont know if the tension was off, as mentioned a year ago, i lost the spring "thingie" that sends the signal for tension loss. it broke right at the cam cover connection. figures, id have a belt misfunction when that thing was not working (connected) . that will be replaced too this time around.

MK

heinrich

Get a used thingie from Jim or Mark, it won't be more than a couple of bucks..... you need it.

Big Dave

Too bad used cam gears and crank gears don't cost only "a couple of bucks."

Can you tell from this pic if any of them need replacing? It looks like the oil pump gear is shiny, but I don't think that one was coated in teflon to begin with.

(sorry for the thread high-jack)

mark kibort

what about used GT cams! $2k now plus labor or $4-5k later!

MK

goliver

Mark,

Another thought though not backed by and real science. On my old car (an '87 5sp) the plugs in the caps at the end of the camshaft went bad and allowed the chains to rattle like a mother, especially at idle. Just for the added insurance you might go for the upgrade which are pins that are in the bottom of the cap to effectively block the oil return to keep the tensioners pumped up. Even though they are pressurized by a spring as well they will rattle loud enough to scare the crap out of you. With a couple of missing teeth and the chain way slacked if might skip a few teeth and then who knows how much damage then. Just a thought. Apparently this failure is common on the 16v 944s.


Regards,

Fogey1

Am I nuts or just ignorant?

Mark's picture looks like a cam drivechain sprocket to me. I don't even see the timing belt.

Not that missing teeth off a steel piece is a good thing ...

Will

drnick

mark,

what are the specs from your cams, same as GT? why the additional cost for later replacement, do you need to pull the engine to replace cams?

Vilhuer

Indented tooth peaks on cam belt is just one innovation some belt manufacturer(s) use. It's not sign of bad belt design or anything like that. Might infact be better than smooth teeth.

docmirror

I took off a Federal Mogul belt recently, and put on a Conti. I asked the Gates people about the groove in the peak of the belt tooth, and they said it's for compression flex when going around a small radius gear. The same effect can be seen on some V-belts that have a notched or sawtooth inner form. If the radius is small and the distance between pullies is large, apparently there is a hetrodyning, or Phugoid moment that sets up on the belt. I guess the grooves damp out that effect and reduce vibration.

Garth S

- which all would appear to be important factors when considering the small diameter crank gear, and the 'back-flip' imposed by the tensioner roller. On the toothed side, grip is generated by the valley and side of the tooth - not the tip; however, as the tooth is made of an extremely high modulus 'rubber', it will flex little - the notch must serve to permit a better distribution of flexion forces, and one can speculate how this may better preserve the integrity of the belt material.
I have found this type of belt to have required NO subsequent readjustment of tension: two seasons on the S4 and one on the '80 (with full HDT drive upgrades). So far, it's an innovation that has appeared very positive.
The profiles attached are the pre '83 square tooth, the conventional HDT (center), and the newer dimpled HDT.

IcemanG17

Mark
Heres a unrelated ??? for ya. Looking at your pic, your tires are huge! What size tires do you run front and rear? Did you have to do any fender mods to make them fit?
Thanks

Warren928

I have heard that the slippage of the belt by 2.5 teeth and onward causes bent valves. You bucked the system! Maybe you had some advantageous cam timing that gave you alittle room to slip extra.