toolman0114

What would cause the distributor drive gear on a cam to get destroyed?
They are wiped right out.

gerry72

The usual suspects are; 1)Inadequate lubrication, or; 2)incorrect mesh of the gears.

As to what actually caused it depends upon what you might have thrown into the mix. Is this a dead stock as the day it was cast engine or have you done stuff to it?

toolman0114

It was a built engine, eagle racing crank, skat rods, .030 over, 10 1/2:1 compression pistons, 1.6 ratio full roller rocker, high volume oil pump, 2.05 65cc iron eagle dart heads. The lift with cam & 1.6 ratio is about .745, it's a Comp Cam # 12-212-2 with .480 lift x 1.6

Super6

Sorry to see that. Got to get all the debris out of the engine. Rebuild time?

Above the gear, there are 2 rings on the distributor housing. When the distributor is installed and the engine is running, the volume between the rings is pressurized with oil. A small groove in the bottom ring at the right location will direct a spray of oil on the cam and distributor gears.

Good luck with your repairs.

toolman0114

The funny thing is that the gear on the distributor look like new.

bashcraft

Roller cam? If so you used the wrong gear on the distributor. It should've been a melonized gear.

Super6

I had the same thing happen, except it was the distributor gear that went. You could have shaved with the teeth on it. The cam gear looked fine. I went with a "good quality" cast iron gear from Comp Cams and shortly it had signs of wear on it. I then went with the CC polycarbonate gear and 8 years later, it looks like I put it on yesterday. I put the small groove in the lower distributor housing ring for the oiling effect at the same time I changed to the plastic gear. I don't know if they generally have a good reputation, because Chris Straub said something to me about putting a "real gear on, instead of that plastic thing". I've had it on all kinds of cams in those 8 years. Looks brand new.

bashcraft

How is that the same thing?

Super6

The commonality is that one gear is destroyed and the other looks fine. The harder one eats the softer one or whatever the mechanism is. So I wrote, same thing, but the other gear.

Something else common to the 2 situations is where is all the missing material. In the filter, I hope. Mine gradually lost oil pressure over a period of time and I ended up rebuilding the engine.

bashcraft

OK, I'll give you that one.

BTW, that plastic gear you're running was originally designed for use by NASCAR. NASCAR engines don't drive the oil pump through the distributor gear. That's why it works for them. So far, you've been very lucky.

toolman0114

I'm wondering if it was a bad cam from the factory, where the gear didn't get hardened

REELAV8R

That being a flat tappet cam the gear would not be hardened i believe.
If your distributor is using a melonized gear then it is hardened.
Softer gear looses.
High volume oil pumps also abuse the gears due to increased HP required to turn them.

Super6

Thanks for that input. Chris didn't elaborate. I have run 20W50 with Melling HV pumps such that I had 70 plus psig oil pressure before 2000 rpm. On both solid roller and hydraulic roller cams. This time around I'm running 10W30, so a little less severe duty. Maybe that all adds up to 20,000 miles on the composite gear. The gear still looks brand new. I guess I've been lucky. I did a search and I'd say it was about 50/50. Those that had a failure said that the reason was generally something else, not the gear and that they would rather have plastic parts getting into the pan than metal. I'll talk to Mr. Straub about it, it's his cam that's in the car now.

toolman0114

I have heard about filing a groove in the bottom ring of the distributor to allow oil to drop on the cam gear, but where do I put the groove?

Super6

You might do a search on this subject for more precise instructions, particularly on the depth of the groove. I too had heard about it and went ahead on my own.

The first thing is that you want to make a very shallow groove, you want to get some direct oiling on these gears, but don't want to significantly lower the overall system pressure to the point that you hurt the oil flow to other parts of the engine. The shallow groove is made only in the lower ring of the 2 housing rings.

The location of the groove on the distributor housing is important to deliver the oil where you want it, so the first thing is to make sure you have your engine timed how you want it and have the distributor in the location where you want it to be permanently, while still considering that you may add or subtract some timing at times. You don't want to put the groove on the housing and then later re-clock the distributor to clear your newly-added ignition shielding or to straighten out your tach cable. You want to do that type of thing first and get the distributor location established before you cut the groove.

With the distributor orientation set and in the car, looking down on the top of the distributor, consider the point on the distributor housing at the back to be the 12 o'clock position. The cam is to the right of the distributor when viewed from the front and the distributor gear/cam gear interface is at 3 o'clock position in the top view. Mark the 3 o'clock position on the housing down near the clamp ring/collar and give yourself a reference on the distributor location with respect to the engine, mark it and pull the distributor.

Put tape and a sandwich bag on the housing and gear below the bottom housing ring. Cover the housing above the lower ring too and tape it all up to keep all filings from the groove-making process off the housing and gear. I used a thread file (narrow "V" profile) to make a straight, shallow groove, about 0.025" deep, on the lower ring using the 3 o'clock mark to locate it. The groove is actually a few degrees ahead of 3, since the distributor gear is turning clockwise.

Clean up any filings thoroughly, remove the tape and bag, blow it off with air, oil the gear and re-install the distributor. Re-time the engine, if necessary.

Hope that helps. If I left something out, I'm sure others will jump in.

toolman0114

Thanx for the info!

7T1vette

I'm leaning toward an improperly heat treated gear on the cam. It likely missed the treatment process. I'm not sure how present-day cams are treated. Perhaps all lobes and gear are hardened using induction coil process. If so, that gear may have missed its cycle (for whatever reason). I would discuss with the engine builder and have that shop contact the cam vendor. The cam vendor may want that cam returned for lab analysis.

P.S. By design intent, the distributor gear SHOULD be softer than the cam gear. If one of them wears out, you want it to be the dizzy gear...for obvious reasons. Also, because the dizzy gear is fine, it is clear that there is adequate lube into that area. Either that cam gear was machined wrong (very unlikely) or it was soft.

toolman0114

I have already contacted Comp Cams and got a generic answer.
Either way a composite gear will be going on the dizzy, and the oil groove will be added to it as well