underdog928

Hi all:

I'm in the middle of a T-Belt/WP project and I'm wondering if I should replace the Cam gears. Here are some pics.

This is the passenger side gear. It has about four teeth where the coating has worn off in the middle of the gear. These two teeth are the worst.


Another two teeth with less wear: (Still passenger side)


Another view of the passenger side gear where there is just a little wear. It looks like this except for the 4 teeth shown above.


This is the driver's side cam gear. It looks like this all the way around.


This is the oil pump gear. It looks the same all the way around.


Thanks in advance to your thoughts.

Mrmerlin

for a weekend fun car you can leave the cam gears in place they still have some life to them.
The oil pump gear should be checked as the originals are aluminum and the new part is steel , should you decide to replace the oil pump gear then you would also remove the 1mm spacer from behind it and then install the steel gear without the spacer.
If on inspection of the oil pump you find its leaking then now is the time to replace the O ring and radial seal on the pump, use STP on the gears when you put it back together make sure the outer bevel of the ring gear is facing to the front of the car and the dimple dots on the center gear and outer gear face the engine, also get the 3 O rings for the oil pump bolts

blown 87

Replace them.

blown 87

I take it you are talking about the gears for the oil pump, not for the gear for the oil pump drive.

Stromius

How about sending them to finishlinecoatings.com and ask Lorna to refinish them. I had good success for about $15-20/each plus shipping with about a week turnaround.

underdog928

Hi Merlin: I do have the oil pump o-rings for the radial seal and the bolts. I'm also replacing the shaft seal on both the oil pump and the crank. Trying the close up all the oil leaks.

Understand the "fun car" thought, but with the A/C fixed, and the T-Belt and other engine things on the list (like fuel lines and intake refresh) i might just make the 928 the daily-driver.

And as Greg said - "replace them", is probably good advice.

So what about the shaft gear. It is already steel and all the teeth are very shiney. Should I replace that one also or is that normal for a steel gear?

GlenL

Those are fine. The edges are still crisp.

Gear wear is another area where people get too excited.

I'd like to see pics of the gears where wear has led to an engine failure.

Mrmerlin

As far as the oil pump gears go they should both be fine (inner and outer).
The oil pump drive pulley might be aluminum if so then you might consider replacing it with the updated steel pulley, a magnet will tell you what you have, usually the steel pulley gear is black

the shaft gear ( this is the crank drive gear for the timing belt) as you state should have a straight edge placed on the tooth edge ( the flat portion and see if the center of the tooth is worn front to back)
The teeth usually wear in the center so if wear is detected then this should be replaced.
As I previously stated the cam gears have life left to them , if more than 40% of the tooth coatings were worn off and the tooth edges were getting sharp then yes replace them but this isnt the case.
If you remove the cam gears then the cam pulley timing will also have to be reset

Mrmerlin

Note it is recommended to turn the cams with the nut type washer thats behind the 17mm securing bolt, this way you dont risk loosening the bolt.
IIRC this washer takes a 30mm wrench.
also its a good idea to put 3 bolts into the cam pulleys after removing the rotors so the pulleys dont have a chance of moving on the spiders per the WSM
Make sure they dont go past and into the cam seal and create more damage

GlenL

Is it going to move with the cam bolt correctly tight?

It looks to me like the rotor isn't strong enough to be used to clamp down the sprocket. It attaches to the cam because then the rotor tip is aligned with the lobes.

Mrmerlin

yes Glen it should move with the pulley bolt tight, However in the WSM is is directed to install three screws so the spider (behind the cam pulley gear ) and the pulley dont move during repairs.

GlenL

Should or shouldn't?

Mrmerlin

the spider should move with the cam pulley as its sandwiched tween the gear and cam however if lets say turning the cam with the 17mm bolt it somehow was loosened then the gear could move,
and then the timing of the gear to cam would be lost.
The 3 screws simply hold the spider into position on the cam gear so that if the cam pulley bolt was loosened then the spider would stay in time with the gear as it is held in position with a woodruf key

Lizard928

I would run them for one more service and the next time you need to go in there plan to replace them. These have tons of life left.

Alternatively have them recoated while they are still in top condition.

underdog928

Thanks for all the great advice guys. Really appreciated.

I have a Porken 32V'r, to set the cam timing. Another WYAIT moment.

And the oil pump gear is aluminum.

Re-coating sounds like a good option. I'm trying to get this car back together for SITM. Still have the Intake refresh to do.

One added comment, although this will be the 3th timing belt put on this car, 1st one done at a dealer prior to my buying the car, 2nd one by my "previous" mechanic, and now this one by me, from the looks of the tensioner (or un-tensioner as it were) I think I am only the second person to see the insides of this thing since the Porsche mechanic assembled it in 1985. OMG, it was completely dry and whatever oil that was in it, had turned to the consistency of peanut butter caked in the back channels.

Just goes to show you, if you want something done right - do it yourself!

I'll measure the "flatness" of the crank shaft gear tomorrow and let you know.

Thanks again.