Fitting Cams

[gregguillaume]

All: I am fitting newly reground cams and have a few questions:

The engine is a 3.0L from a 1981 911 SC. The cam had one lobe that was pitted from oil starvation, and need to be pulled and fixed. I took off the cam towers and timing chain boxes, but nothing more.

Both cams were sent to webcam for a weld and regrind (to 964 spec). Journals and shiny, lobes are black (parkerized). Both towers were professionally cleaned at Ollie's and have new squirter tubes, which were the cause of the problem in the first place.

After meticulously cleaning and reinstalling the towers, both cams are back in with assembly lube, and the gears and shims and thrust washers are in and torqued.

Now the question: the effort to spin the left one is like turning a stiff doorknob, and the right is almost the effort to free a stuck pickle jar lid. The left has axial play (slight in and out, and I will measure that to see if it is in spec) and the right has no axial play whatsoever.

I have not retorqued the towers in a different order, but that may be a next step. I used the procedure in wayne's engine rebuild book, and as I said, the heads were not removed, so I thought the chance of binding because of out-of-level head to cam tower join would be pretty low.

So about the resistance spinning the cams--how tight is too tight? Recommended next steps?

Thanks all, for your advice.

Greg

[Catorce]

Loosen the head studs slightly. Then, place the cam towers on and torque those to spec. Finally, torque the head studs in a 2 step torque process.

That is the correct way to install cam towers - it's in Wayne's book but it is easy to miss.

Report back if there is any binding after that.

[trond]

something is not right. On my previous top end job in 2011 I was fresh out of hospital and fogged up from painkillers I managed to leave a thin washer under the cam housing. Everything was torqued up but the cam was reluctant to turn. Thankfully I was able to step one back and I found the mistake early. If your cam is binding there must be something not right. If you used locktite 274 it may set up early (worst case before you have torqued up all the cam housing). Just do that side again. Cost nothing

[mikedsilva]

After assembling a 964 motor, I had a similar situation. One cam was quite free, the other had a very slight tight spot.
With the 964, the recommendation was to change the sequence of tightening the nuts that secure the cam tower.
This gave me a nice free turning cam.

[trond]

Again, if you used Locktite 274 you will need to take that side apart and scrape off all the sealant that will have hardened and try again

[gregguillaume]

I started the disassembly and found 2 things: a bit too much curil T on the cam retaining plate gummed up the works. After cleaning and reassembling it spins easily.

Also, I found the right cam was binding between the plug at the rear of the cam carrier and the cam retaining plate. A few taps and the from of the cam sat flush. I also had and a bit of curil T excess there too.

No cam tower removal required--at least that is the plan.

Thanks for the input.

[Catorce]

I would still retorque everything correctly; it is not done the right way. Cam towers are installed and torqued with head studs loose.

Do it right, small things make a big difference with these motors.

[Walt Fricke]

Well, isn't the proof in the pudding? If his cams spin freely after just torqueing the cam tower nuts, without loosening the head studs nuts, torqueing the cam tower nuts, and then torqueing the heads again, what is lost here?

My rebuilding mentor told me that new 575 acts as a sort of solvent for old 575 on mating surfaces (where the old stuff is very thin), so all I have done is knock off the big chunks which are outside the mating surfaces just to be safe and because it is easy. With sealant which has been squeezed out, wiping that off should be easy with a motor which has not been run, as it never got anaerobic or heated. Just put a little back on and reset. Others have questioned this approach, noting that the data sheet for 575 says nothing about this self-solvent property, but it has worked for me (and my mentor) and I've never had an oil leak there, or from the case halves. Saves a heck of a lot of work, even if you use a solvent like Chisel.