Rebuild problems

[danielt]

Well, I'm about half way through the teardown of my 1981 SC. So far 2 broken head studs, two broken ring, and a stuck camshaft. I cannot completely remove the camshaft from the passenger side. It will slide out until the journals are resting in the next set of 'housings'(lack of a better word) and then sticks. Is this common?
Also, because of the broken rings, two cylinders are scratched. Can this be honed out? What is the recommended repair?
I appreciate any advice. So far the board has been a great help getting me this far.
Thanks,
Daniel

[Jim Sims]

Have you removed the rocker arms and rocker arm shafts from the cam towers? This should be done before removing the camshafts. When the rockers and shaft are out the camshaft should slip out axially. The camshaft journals will pass through the bores (bearings) in the camtowers. If they won't I suspect something is cocking the camshaft. If you haven't removed the rocker arm shafts before doing so throughly clean out the outside of their bores in the camtowers so you don't score the bores when you push them (shafts) out. Remove the shafts with the rocker arms on the heel or backside of the cam profile. Keep everything in order so you can put them back in the same place if they pass the wear inspection. Jim

[john walker's workshop]

make sure no wavy washers are still in there. put the tower in a vise,(padded jaws), and rotate the cam with a 17mm wrench as you pull outwards. they are hard to get out occasionally. built up crud in the unused part of the bores, or scored bores from running out of oil.

[danielt]

Jim, Yes the rockers are off. Still no budge.
John,
I tried pulling on the cam while rotating it to no avail. I have not done it with the tower mounted in a vice though, so I may not of had as much leverage as I thought. I will try.
Thanks,
Daniel
Update later tonight...

[stormcrow]

Daniel,

When removing the cams, make sure you are pulling them straight out otherwise they can bind. As you know when you first start to pull it out, the bearing journal drops out of its housing, so you have to make sure it stays aligned as it is going through to the next one, otherwise it will bind.

If it still binds, you may have damage on the housing or the bearing journal which may have to be removed.

Steve

[Doug Zielke]

Originally posted by john walker's workshop:
..... scored bores from running out of oil.

Hi John!
Just curious...do these cams run directly in the cam tower metal?


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'81 SC Coupe (aka: "Blue Bomber")
Member: SCWDP
Canada West Region PCA
The Blue Bomber's Website
"If it ain't broke...we'll help you fix it 'til it is!"

[Jim Sims]

Since John didn't reply, I will. Yes, the camshaft journals run in the aluminum alloy camtower bores. There is no bearing or babbit like material in the bores. Technically though, like any other journal bearing the camshaft journals really run on a film of oil. This oil is pressurized and supplied by the engine oil pump through spray bars in most 911 engines. Early 911's used a center lubed (an oil passageway drilled down the center of the cam and supplied from the end) camshafts and some engines (935) used both center lubed and spray bar systems. Jim

[magistro]

the cams are binding. loosen the towers from the heads, if still too tight to remove, put cam all the way in. spray w/penetrant heat to 250 degrees and pull cams out.

[Doug Zielke]

Thanks Jim. I was wondering about that as it reminded me of a certain Honda m/c I used to have. The cams ran directly in the head metal and it wore out quickly. Mr. Honda didn't design proper oiling up there. I assume Doktor Porsche did a better engineering job than did his counterpart from Japan.

------------------
'81 SC Coupe (aka: "Blue Bomber")
Member: SCWDP
Canada West Region PCA
The Blue Bomber's Website
"If it ain't broke...we'll help you fix it 'til it is!"

[danielt]

Steve,
Pulling the cam out straight was my first concern, so I went ahead and removed the tower from the engine. Even standing it up vertically, I cannot get the cam to slide out.
Magistro,
The camtower is off of the engine and the cam is not binding per se, as it will still rotate when slid out as far as it will go. It is more like it is catching on something than binding. I would like to try the heating though. Will simply placing the whole thing in the oven work?

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Daniel Tisserand
1981 SC

[magistro]

yes the oven is the perfered way, remember 250deg f. max.