Cam Sprocket Issues

leadrsa729 · 10-11-2018, 01:24 PM

Hello -

I am rebuilding my 1972 2.4L 911T engine. I had some head work done to open intake and exhaut ports, and I bought a DC30 cam to go along with it. The cams are the later post 1982 style cams that use a bolt, not the big nut. Now that I am in the stage of the rebuild where I am putting things back together I am finding that the inner cam sprocket, the woodruf key, and the main sprocket will not fit over the end of the cam. I could force them on I think, but then I am certain there would be absolutely no wiggle room.

I thought these were all interchangeable parts, but are the sprockets and woodruf keys different sizes for the later style cams? Thanks for the help in advance.

Trackrash · Trackrash's Garage

The sprockets and keys should be the same. I did that "upgrade" on my recent rebuild and had no problems with the sprockets fitting the bolt style cams.

blue911rsr · 10-11-2018, 03:53 PM

I always clean that end of the cam with some scotchbrite to make sure
Everything goes together real easy

Walt Fricke · 10-14-2018, 01:13 PM

When I built my SS2.8 with the 3.0 large journal cam carriers and cams with the bolt system, I had no issues with using some existing old keys, inner sprocket pieces, and outers. The cams were new, though, so no deposits or whatnot to need cleaning off.

I certainly see your desire not to have the outer sprocket forced on. I was frustrated enough as it was by how much of a PITA getting the setting just where I wanted, especially being equal side to side. It was pretty easy with the big nut style, since you could hold the cam as you tightened, not just the sprocket, and you could wiggle the cam before tightening to position it where you wanted it between the amount of clearance the pin system has.

But not this issue. Maybe you could measure the OD and ID involved, though I doubt I could do that accurately enough myself considering the small clearances involved and my inexpensive (these days) measuring tools. At least that would give you a starting point.

I take it this issue arises on both cams, so some random imperfection is less likely?

Maybe some very mild clearancing (scotchbrite, or 2000 grit wet/dry sand paper, especially on the chain wheel, would resolve this?

The most I have ever done was take a fine file to the key, but that has been to deal with small distortions of the curved part due to the little screw driver tapped in to get it loose. It is nice not to need to use pullers on the chain gear parts, and I've never seen the outer wheel so tight fingers weren't just fine, but as long as you can adjust pullers wouldn't be the end of the world.

There are methods involving skipping chain wheel teeth that allow you to adjust so that the slop in the pin system can be discounted because you adjust so the chain pulls things tight against the pin right where you want them. Doing that would obviate difficulties in changes happening while the bolt is tightened. I've been too lazy to memorize or use such systems.

Henry Schmidt · Henry Schmidt's Garage

We find this issue is pretty common with new billet cams. We use a crank polisher to size the cams for proper fit. you can use emery cloth to polish the cam ends.