C4Russ

Has anyone ever drilled, tapped and inserted a set screw in lieu of the compression pin or roll pin on the distributor gear?

I was thinking that a properly placed set screw with a bit of weak Locktite would be a good alternative. This would allow very easy belt changes and would take out the biggest worry/time consumer when doing a belt change. If I didnt' have to drill that thing, I could put in a new belt at the 15,000 mile mark each service in a matter of minutes.

Does anyone see concern if the set screw would remain in place? Any other gotcha I'm not thinking of?

garrett376

I installed a steel "roll pin" instead of the soft metal "compression pin" out of necessity - didn't have the original part on hand. The roll pin is nice because it's well retained, and sturdy enough to tap it out if needed later on. I would think that a set screw would not be as balanced as an even-shaped pin of some sort (if that even matters...?!). I put so few miles on the car that I doubt I will ever need to replace that belt again.

What kind of drill bit did you use to drill out the old pin? With a series of cobalt burs (very small to large size), it's actually quite simple to remove the original pin. If I knew Pelican carried the correct part way back when, and that it was so cheap, I would have used the original part.

chris walrod

I would only use a roll pin and not a set screw. When you drill out the original pin, please keep in mind you only need to drill out the head of it as the rest of the pin will punch out. I have done is with cheap HSS bits. No worries

C4Russ

Thanks Chris, I do appreciate your opinion.

However my question is there a technical reason to not use a set screw vs. the compression pin or is there any drawbacks to doing so?

As Porsche doesn't sell service parts for doing the belt, they have a logical reason to use the pin, i.e. no service parts are available, use a lesser cost solution.

For routine maintenance a set screw is simple and easily R&R. I could easily R&R the distributor to replace the belts, lube the bearings, replace springs etc. I don't want to beat this death and I may just take the shaft and gear to a machine shop to have them drill & tap and machine a proper length screw.

markc123

p/n for roll pin 930.602.922.00 cost 1.97
engine overhaul after set screw backing out.... cost $$$$$$$

Oddjob

I would use at least the red (strong not weak) loctite. Since you are not bottoming out the set screw into anything solid, it would basically be loose, so you would need the loctite to really stick and hold it in - I would not be comfortable with that at all. A preferred option would be to use two long set screws and come in from both sides and bottom them out into each other.

C4Russ

Mark, Believe me, the thought of anything coming loose is scary. I know full well that if something gives inside, it's going to make a big mess.

Oddjob, I was thinking that I'd machine the hole so that the set screw bottomed out onto a shoulder so that it did apply pressure to stay set.

I'm thinking out loud here and may never do anything like this. I like the option of having a solution that, to my way of thinking,(for what that is worth) lends itself to a simple fix.

Chris M.

I also used a roll pin when reinstalling my dizzy. I had to compress the shaft just to get it in there so I don't think it's coming out and as others have said, should I still own the car in another 80K it ought to be easier to get out.

c

chris walrod

On top of the roll pin (5/32"), I would stake the pin at both ends and put a dab of RTV at both ends, just to ease my paranoia. Who needs drugs when I am that paranoid

Dave R.

Why use a set screw?

Why not just replace the pin with a high-grade, small diameter bolt (and nut)?
Loctite it (red?) to your heart's content...

I don't think drilling the compression pin is that big a deal. In particular, the steel of the pin is much softer than the steel of the helical gear (which appears to be *very* tough).

Anything you do to the set screw (or bolt) to ensure it won't come off, will make it harder to get off when the time comes. I suspect that by the time you finish securing the set screw/bolt to the point where you have peace of mind, it will take about as long to undo it as it would to drill the compression pin.

sullivs

Dear C4Russ,

The distributor shaft and the drive gear are hardened, so you may have some difficulty tapping threads in the gear. Also too, the washers that are in the inside of the assembly provide some spring tension, and reduce the slop. So you have to compress the gear onto the shaft a little to align the hole in both the gear and shaft. The original pin is lower strength steel and deforms slightly when installed.

I think your best bet is go to large hardware store and look in their cotter pin, woodruff key area. I had found some replacement tapered pins at a farming supply store. They were almost an exact match. They are soft steel, and a little longer than needed. You will need to squeeze the gear upwards to compress the spring washers, and align the holes. Tap the pin in, and deform it a little. Then grind off any that is sticking out too much. Then you are done.

I just rebuilt my distributor, and it was much easier than I expected. In my opinion you are complicating things if you try to use a threaded fastener.

Just my two cents worth. Good luck,
Steve

springer3

It is not just the matter of the set screw backing out. If you drill and tap the hardened gear, you could leave behind a burned place from the drill, or you could leave a nick in the metal. Either can initiate metal fatigue that over time will cause the gear or the shaft to break. The high stress from a tight set screw is probably not anticipated in the design of the gear or the shaft.

Metal fatigue is a complicated subject, but the engineers that designed the engine understand it quite well. Stay with the factory design, especially inside the engine. You are 99.9% sure not to cause a problem, but unless you know better than the factory engineering team, why take the risk?

C4Russ

I appreciate the viewpoint from the many smart people on this list.

I'll not take on this task and leave well enough alone. I've got plenty of other tasks to do that can consume my time without possibly destroying the car.