Distributor drive gear - pinned?

[hemigeno]

OK, got a couple question here, but first the background...  When I was getting the Hemi back on the road after winter hibernation a couple months back, I set the total timing at about 34-35 degrees at well over 2,500rpm.  Ran like a champ after that, and had fun with it that day.  Parked the car for two weeks, and then hopped back in it for another spin around town - but when I got it fired up again, the car would hardly stay running and didn't have enough power to get out of it's own way.  After limping back to the shop, I threw the timing light on it, and it was WAY retarded.  Like, off-the-dial retarded, even at higher rpm.

I specifically remember tightening the distributor clamp, and a friend who helped me the time before confirmed I hadn't forgotten.  Just to be sure, I put a wrench on the clamp bolt and it was still really snug, so I'm 100% sure I haven't gone crazy (in that regard anyway).  I reset the timing, and it ran good again even though I didn't have much more freetime to put it through the paces like I had hoped.  It took a fair amount of spinning on the distributor to get the timing back where it needed to be.  I had taken the cap off and cleaned the rotor/cap terminals, but it was seated well both times the car ran and I really don't think there are any issues with the cap/rotor.

While I was at Vance Cummins' shop a few weeks later, I asked him what he thought the problem might be, like jumping a tooth on the cam, etc. etc.  Vance didn't seem to think it was the cam gear or chain, but he DID think it could be the distributor drive gear/oil pump shaft.  He said he's seen pressed-on distributor drive gears that would stay in place on the oil pump shaft when warm, but after the engine cooled down would move some on the shaft the next time the engine started up.

The shop that built the motor 9 years ago used a Comp Cams billet roller camshaft (24-000-9 core number).  I assume they changed out the drive gear & shaft from stock, but I'll try and remember to ask the guy about it sometime.  Vance said that pressed-on gears were notorious for moving like that, and that he normally runs a piece that has been pinned in place to prevent this exact thing from happening.

My questions are...  Are the billet style drive gears normally just pressed on, or also pinned onto the oil pump shaft?  Anyone seen this type of phenomenon and/or have any different ideas about the cause?  Is there a particular supplier of a billet gear pinned onto the shaft, or should I just put a new one in and forget about it for another few thousand miles?

Thanks,

Geno

[firefighter3931]

Geno, the dist drive gear for a roller cam should be pinned. I'm assuming that this drive has a bronze gear, correct ?

The bronze gear is a "wear item" and needs to be changed periodicly.....if yours is a bronze gear it could simply be worn out. I would pull it and inspect closely. 

Mp also makes a pinned gear for flat tappet cam applications with the hardened tip. Allways a good idea to use one on a warmed over performance build. 



Ron

[hemigeno]

I snuck out of the office for a few minutes this afternoon and pulled the distributor & drive gear/shaft out.  Some moderate wear on the drive gear teeth can be seen in the pics I shot.  Didn't realize how much lint the shop towel put on the gear until looking at the pics    The gear was definitely bronze, and was pinned.  Looks like they used the right part and it just wore away some as you (Ron) said it should.

Anyway, I already have a Milodon 21525 shaft on the way from Summit, so I'll see if it'll hold the timing for more than 1 day...



Geno

[firefighter3931]

Yep, that one has been around the block a few times. 

How many miles on the motor since the rebuild Geno ? Hyd or solid roller ?



Ron

[hemigeno]

How many miles on the motor since the rebuild Geno ? Hyd or solid roller ?

I've put probably 8k miles on it since 1999 when this solid roller cam was installed.  I guess bronze and lead (-foot) don't mix, eh?

[firefighter3931]

How many miles on the motor since the rebuild Geno ? Hyd or solid roller ?

I've put probably 8k miles on it since 1999 when this solid roller cam was installed.  I guess bronze and lead (-foot) don't mix, eh?

Naw the leadfoot is fine    that's not what hurts the bronze gear  Mr Billet cam core beats up on the little bronze gear 


If the build has 8k miles you might want to look at the lifters and valvesprings as well. On the lifters, the axle bearings need to be inspected and the VS pressures should be compared to the "as installed" tension to see if anything has changed.   


Roller cams make great power but require a little more maintenance. 




Ron