How Tight are Cam Bearings in Tower

[North Coast Cab]

How tight should the cam bearings be in the cam tower? I had to pull my rockers and cam on one side to fix a leak and the cam is incredibly tight. I had to use a wrench to turn the cam bolt while pulling in order to get it to slowly rotate and pull out. There is a little scoring on the cam bearing. The cam is a new WebCam.

Is there an issue with the cam or the tower/box or does it just need more break-in?

John

[Superman]

I'm no expert, but I believe your cams should rotate smoothly in the cam housing bores.

[Grady Clay]

John,

Is this for your ’76? Do you have 3-bearing or 4-bearing cams & housings? How does the old cam turn?

The cam should turn freely with your fingers with oil on the journals. There are three possibilities; cam bent, housing bent or incorrect journal size.

To check the cam, support it on V-blocks on the end journals and measure the run-out on the center journal(s). Spec max is 0.02 mm.

With a micrometer and bore gauge you can measure the journal clearance. Spec clearance is 0.025 to 0.066 mm with 0.10 mm wear limit for both the 4-bearing (nominal 49 mm) cams and the 3-bearing (47 mm) cams & housings.

There isn’t a good way to measure the cam housing for bend. A good indication is if the cam is properly free when the housing is off the engine and not when torqued to the heads – the heads are bending it. I always torque the cam housing with the cam installed and check it for free rotation during the process. In this case look for improperly machined heads or varying cylinder heights. Another possibility here is a crankcase where the cylinder seating surfaces aren’t in the same plane. A good straight-edge will tell.

Don’t assemble an engine with a “tight” cam. Find the problem.

Best,
Grady

[North Coast Cab]

The cam's are new and the motor is a 3.0 w/4 bearing towers.
I has a big oil leak around the chain box / cam area. The sealing plate and o-ring/gasket had holes in the towers which were oblong w/one of the three studs broken. I was going to flip the tower around until I discovered the same thing on the other end. So, I happen to have another cam tower and when I inserted the cam in there it moved nice and smooth. I guess the whole cam tower was a mess....hoping anyway.
Should have her back togetehr and running this weekend.

John

[Grady Clay]

John,

It would be worthwhile to find out why the issue with the sealing plate/O-ring/gasket/studs. It could be the cylinder height or heads have been cut enough for the sealing plate to no longer be centered in the chain housing opening. Carefully measure that. If not centered, find out why.

A remote possibility is the case has been machined where the cylinders seat.

If the cylinders/heads have been cut, you may have piston-to-head or piston-to-valve clearance issues. If the piston EVER touches the head under some condition (no matter how slight), the rod bearing will fail or worse. (Of course the CR will be pleasantly higher. )

If this is the case, the only way to center the sealing plate is to fly-cut the chain housing where it mates to the case. This in turn causes another issue; the chain is now too long. The “fixes” for that are a “half-link” for the chain and/or an idler sprocket with one more tooth.

Now you have an engine where most important parts are custom machined limiting easy servicing and repair. Of course there may be an issue in a stock class.

Best,
Grady