Camshaft Housing Fit

leadrsa729 · 05-30-2010, 12:55 PM

Hello -

How loose should the camshafts be in the cam housing once the head nuts and housing nuts are all torqued to spec?

I can turn the right one a little easier than the left - both by hand, but I really have to grip the left in order to turn it.

Thanks,
Sanford

Flat6pac · 05-30-2010, 01:32 PM

If youre worried about running clearances, flip the housing around, knock out the rear plug and place it on the other end. If you still have too much clearance, the 3 bearing housings are very inexpensive.
Bruce

hcoles · 05-30-2010, 05:27 PM

good question, if I remember this is discussed in Wayne's book. I think it explains that you can retorque and see if there are improvements. Did you check that the top of the heads were equal? One of the pro engine builders on here will have better info. I checked this during my top end rebuild but forgot what happened.

cgarr · cgarr's Garage

Did you replace any cylinders or heads?

leadrsa729 · 05-30-2010, 05:35 PM

Hi -

I didn't replace any cylinders, but had the intake ports opened up to 36mm on the heads, and then a basic valve job. That's all the machining done.

leadrsa729 · 05-30-2010, 07:07 PM

I also retorqured in different order twice, but still ended in the same result. Is it OK to continue as is or should I be concerned?

4sd911 · 12:19 AM

Cams should turn freely with your fingers. If you have to grip it to start to turn the cam then something is out of alignment. Were the heads fly cut? I know you probably have loctite between the heads and tower, but if you torque the heads down without the cam tower check with a strait edge to see if they are flat across the tower mating surface. If they are not strait the head will come loose. This would only be a test as you don't install the tower to heads that are torqued.

cstreit · cstreit's Garage

When I use assembly lube on them it's rather difficult to turn them. Did you use a heavy assembly lube?

If so, maybe pull the cams and oil them up good and then try it. SHould be easier.

jpnovak · 06-01-2010, 09:23 AM

I install the cam into the housing and turn without being torqued. This will give you a feel for the rotational drag prior to putting the screws to it. It should not change between free and torqued. If so, you have something amiss.

did you verify cylinder base gasket height? Did you pre-torque the heads to seat the cylinder sealing rings? Did you make sure the cam tower pin receptacle holes were nice and clean?

Did you dry assemble to check clearance and cam drag?

Walt Fricke · 06-01-2010, 07:23 PM

I once had a situation somewhat like this - one cam seemed "tight." Oh well, it will be all right.

Well, it wasn't. The engine started when finished and installed, and promptly (as in seconds) things went to hell. The pin on the right cam sheared off all the "teeth" on the inner cam vernier wheel! The cam had siezed in the far (front) bearing. I had to pull the plate on that end of the carrier in order to knock the cam out. It wasn't budging.

But I had lubed it just fine - there was red Torco assembly lube inside behind that cover plate.

A machinist touched up the cam carrier bearings, which were only a little scored in this one place, and things were back to good to go.

But I never knew what had happened. Maybe somehow a piece of grit found its way in there.

As a sequel, a year or so later that cam broke in half while running on the track. I guess the twisting had weakened or cracked it.

Anyway, you get the moral of this tale.

Walt

leadrsa729 · 06-11-2010, 08:39 PM

Thanks for all the advice. I've disassembled the tight side and reassembled. Torqured everything down, still tight.

I disassembled again. This time I checked that the heads were all flat with a straight edge when torqued by themselves. They are.

This time I joined the camshaft housing to the heads and torqued those nuts. The camshaft spins freely. As soon as I try and torque the heads it immediately gets tight, even at 75% of the full torque value.

I've verified deck height, and the cylinder base gaskets are correct. Could it be that my head gaskets are tweeked? One of them is very tight in any of the three cylinders that I put it in while the other two seem to move a bit.

I'm thoroughly frustrated at this point. Thanks for any help you can give me.

911pcars · 06-11-2010, 09:46 PM

Quote:

Originally Posted by leadrsa729

I also retorqured in different order twice, but still ended in the same result. Is it OK to continue as is or should I be concerned?

if all the fasteners are torqued to spec and the cam rotates freely, I'd go with that. That's a strategy many engine builders perform. Also works with the crankcase and crank.

Sherwood

4sd911 · 06-11-2010, 11:04 PM

Since you have the heads on the tower maybe try installing it back on without the head gaskets as a test, if still tightens up them something must be out of alignment, if not then might be the gaskets.

leadrsa729 · 06-12-2010, 06:14 AM

Hi 4sd911 -

I just put the tower and heads back on without the cylinder head gaskets, and the cam spins freely now! Do you think it's safe to assume that it was the gaskets, and buy 3 new ones to install and continue, or should I be checking something else as well?

Thanks

4sd911 · 08:04 AM

Sounds like its the gaskets. What kind of gaskets / engine is this? Are these the CE rings?

leadrsa729 · 06-12-2010, 08:16 AM

It's a 4R 2.4 Magnesium case from 1972, 911T. I'm not familiar with the term "CE rings". What are those?

4sd911 · 06-12-2010, 09:10 AM

These Pelican Parts - Product Information: 908-104-391-00-M17 they call them GE rings but others call them CE rings. They should compress when the heads are torqued. Make sure that the groove in the clyinder is clean, this could keep the ring from compressing. Are you using a engine stand so you can turn it to have the cylinders pointing up when installing the head/tower, if not be careful they don't slip out.

leadrsa729 · 06-12-2010, 09:22 AM

So are these gaskets/rings a one time use kind of deal? When they compress after torquing down the heads are they no longer any good?

4sd911 · 06-12-2010, 09:55 AM

I'm not sure, some would reuse them so long as the engine hasn't been started.

Walt Fricke · 06-12-2010, 06:53 PM

I got away with reusing a set of CE rings once when I had to pull heads after torquing but before running the engine. A friend claims to have a way of opening them back up for reuse (as you can see, they crush slightly around the garter spring when the heads are torqued), but my attempts to do that have been obvious buggered up failures so I have never reused ones from a running engine. They are supposed to be one time use items.

In your case, I'd be inclined to purchase three new ones no matter what. Even as cheap as I am. Especially if you find that 1) the grooves in the tops of the cylinders are all clean, and all of the same width and depth, and 2) you can't tell that one of these CE rings is obviously larger or otherwise has some feature which caused your problem.

The first CE rings were fairly fat suckers. At some later point (at least by the 2.7s) they became thinner and more delicate. I can't imagine you have one fat one (it would be immediately obvious, as this is not a subtle difference) if the 2.4 takes thin ones (but isn't it a fat ring cylinder?).

Or one cylinder which is grooved for thin rings, and the others for fat ones (again, that would stand out and the fat ring just wouldn't go in). But maybe something like this possible?

A manufacturing defect in one of these rings seems the most likely. If any part of the ring got beyond its groove, that would be like one tall cylinder. Or in some unimaginable way it acted like it was solid, and wouldn't crush as needed.

I don't think the opposite could be true - if you had two normal rings, and one that was not tall enough (like a squashed used one), torquing should not distort the cam carrier, as it is the head to cylinder surfaces which mate and are put under compression by the torque.