Garth S

would appear that you have an odd ball belt - or as Jim said, "funky". Any ( conical) wear on the crank gear, deflected pump shaft, or a bent pivot bolt would cause a full time deflection/mis- tracking in one direction - not a once per belt pass deflection. Similarly, a bent cam gear would cause an oscillation, not a one way deflection,
The Belt has 222 teeth IIRC, and the crank/cam gears 24 & 48 teeth respectively - so that's ~ 4.6 rotations of the cam gear per belt pass. The odd number says check the belt - hand rotation, tooth by tooth.
Strange case - will be interested in your findings.

Jim_H

deliriousga

Have you found out anything?

deliriousga

Not yet. I had to do the 60K mile service on the Boxster (that's an interesting engine) without the manuals Saturday. Finding the spark plugs took me over an hour, but hey, it saved me $650 for a day's work and I got to see how that thing works. I had a soccer game for one kiddo a and birthday party for the other Sunday so I wasn't allowed to tinker.

I'll be pulling the covers off some time this week, but I'm going ahead and ordering another belt, this time Porsche, and cam gears just in case. Everything else was changed before, and I already have an extra oil pump gear. I've had a few comments that others have seen this deflection with the Continental belt so we'll see if that's the problem. I thought Continental was OEM so it would just be the same belt without the name. Hopefully with no waiting for parts after I look I'll be able to have her back on the road by this weekend.

geekapalooza

I have a tad bit of history from my TB job last Summer that may or may not help.... The first Water Pump that was installed induced a wobble on the brand new Contitech TB. You could see the belt move fore and aft on the cam gears through the breather holes. As soon as another (good) Water Pump was installed, the belt wobble completely disappeared. No telling how long the first water pump would have lasted before a dreaded TB failure could have been induced by the obviously defective pump.

If this just happens to be the case with your WP, don't waste any time replacing that puppy ASAP.

deliriousga

I edited my first post so the problem and results are together.

Thanks for the help!

heinrich

Replace the belt.

heinrich

1/2mm is insignificant but what is significant is that it tracks perfectly except for a short stretch.

Glen McCartney

Reading this and time to check my belt tension, when I did I found belt tracking OK, but within 1/8" or less from front of cam sprockets. It wasn't that way when I changed the belt 38K miles ago. TIme to replace all the sprockets and and replace the shoulder bolt and bushings. Was hoping to at least get through the summer, but this is probably better to get cleared up now. Probably alot cheaper too if it gets worse.

Bill Ball

Glen:

One thing that determines belt tracking position is the water pump pulley. If the impeller happens to back off the shaft a bit, the shaft and pulley will be allowed to moved forward, changing where the belt tracks on the gears. Bad bushings in the tensioner arm can also allow the tensioner roller to cant forward too. I think you are right to be concerned now.

deliriousga

I'll be replacing the belt again and since it's open, I'll go ahead and replace the crank and cam gears even though they look ok. I figure at 100K miles it's not a bad thing to go ahead and do the gears since I already have it open and maybe I can get the old ones re-coated for future use. I'll definitely be going over the new belt inch-by-inch before I put it on and while turning the crank several belt rotations before the covers go back on. I wish I had known about the belt possibility before I put everything on, but at least it was caught before anything horrible happened.

Thanks for all of the great info!

geekapalooza

So you're not going to evaluate doing the WP while back in there??

deliriousga

I'll be checking the WP, rollers, idler arm & shoulder bolt closely while it's open, but I replaced them with the belt and it's only been 200 miles so I figure they'll be ok (fingers crossed). I'm checking a new belt out at the local dealer this weekend to see if it has any deflection like mine that's a normal tolerance. The guys I bought it from said I can return it for a swap, but I want to make sure it's actually the belt before I do that.

geekapalooza

For reference, my WP was a Genuine Porsche Certified Rebuilt that was bad and induced the T-Belt wobble (with zero miles since rebuild / installation). Bill Ball's explanation on the WP was excellent, and spot-on. Since I have personal experience with this, I cannot emphasize enough how you should really go over the WP while in there - FWIW.

I could be totally wrong, but better safe than............

Just out of curiosity, what brand of WP was installed? Rebuilt or new?

GregBBRD

Been following this thread with a bit of interest. Got a few questions and a couple of ideas. First, in your original description of the problem, you did not state if the problem occurred at both timing gears or if it occurred on only one side. If it occurs on both, that would indicate that the problem was not related to a cam gear problem, but was probably a belt issue. If it occurs only on one timing gear, then the problem is most likely at that gear.

There is a huge difference between the factory belt and the aftermarket belt. The aftermarket belts are very streatchy and have trouble achieving and holding factory tension.....especially after they have been run for a few miles. We call them "giant rubber bands with teeth".

If you are going to replace any gears, do yourself a favor and replace all of them. The oil pump gear has been superceeded is is no longer aluminum. The crank gears, although steel, wear quite a bit and develop high and low spots. These transfer to the belt and wear the belt. The belt them wears on the new timing gears.

In the beginning of these cars, it was not uncommon to see original belts and gears in very good condition with 60,000 miles on them. As the gears deteriorate, the belt life goes down accordingly. Second belts seldom look good at 45,000 miles (on cars with original gears). On cars with badly worn gears, we've seen belts with 1,000 miles on them that are junk. Rubber on metal always is pretty much the same story......the metal machines the rubber.

Finally, if the problem is indeed at one cam sprocket, make sure that you check the "spider" that drives the cam gear carefully. We have been seeing a few of these with crack and even several that completely break. This immediately shears off the end of the cam and well.......you all know the end of that story.

greg brown

deliriousga

I'll be checking everything out thoroughly, especially with Bill's and your comments on previous WPs. My is the same as you talked about, certified rebuilt.
It occurs on both gears. Jumps over 1/2-1mm at one certain point on the belt every rotation. After this, all of the gears will have been changed between the original job I finished a few weeks ago and this one. I'll post pics of the old ones so I can see if I was missing something another set of eyes picks up.

Hope you all have a wonderful Easter!