Reuse my cam housings?

[Brett San diego]

I'm in the process of tearing down the 3.0 L engine of my 1978 911SC, a project started by a broken head stud. I'd like opinions on whether these cam housings are reusable or if they are scrap.

The bearing surfaces have a lot of circumferential lines around them from mild scratching. Nothing too deep, not really felt with the point of a pick tool. I don't think they are a concern. But, my question revolves around the numerous small pits that are present around the whole area of pretty much all the cam bearing surfaces. They are mostly small but palpable with the pointed tip of a pick, and there are a lot of them.

Here are a few pics.







Opinions?

Thanks,
Brett

[bullethole]

Bret.. I don't think that you should reuse the cam towers as they are.. there has to be a way to refurbish them.. if the cam bearing surfaces are all like that it may be expensive, but I would think that a decent machine ship with a line bore machine could bore them out and pressfit some custom brass bushings in (my thinking is that if brass is sufficient for the small end of a con rod and the wristpin on a piston that it would be sufficient for this location. Press fitting them on might be tough.. but its got to be cheaper than replacing the cam tower itself

[VitoV]

Brett, good photos of the consequences of running with dirty oil! These engines do get abused sometimes, don't they?

Good used cam towers are cheap and easy to find-- they rarely need replacement, so they're not in high demand. That might be one way to go for peace of mind. Having yours machined and bushed would be another route, though it sounds like expensive work to me.

The third path is to use the towers you have as-is. Cam bearings don't take that much load, and they operate at half engine speed, so there is more tolerance there. (Putting on the asbestos suit now.) You can probably get more mileage out of those cam towers if the budget pushes you that direction, in my humble opinion.

Vito

[MBruns]

Clean and detail them and see what you have, I buy good used towers for 3.0 and later for around 200.00 pr. so It makes no sense to spend good money to fix major issues, they are not hard to find just post up here.
Mike Bruns JBRacing.com

[Brett San diego]

Originally Posted by VitoV

Brett, good photos of the consequences of running with dirty oil! These engines do get abused sometimes, don't they?

Yeah, it looks like this one got some abuse. I know the first owner did track the car with harness eyebolts installed. And there are signs of a major engine failure and subsequent repair. There is one cylinder head that is different from the others (proper part number, but different casting date). You can see the gouges pointed out in my above picture of the cam housing. I found a broken off "elephant foot" tappet up against the oil sump screen a few years ago. I have found some slipshod use of fasteners during disassembly.

I wasn't intending to split the case, just do a top end and replace head studs, but the cam wear got me worried about the bottom end. The cams also have some pitting on 3 lobes and will need a regrind. So the case will be split and the crank and main bearings gone over. So far, I'm very happy with that decision. When I removed the case through bolts, the sulfurous stench from old oil was overwhelming. Smelled like used gear oil. I've never experienced motor oil having that gear oil odor. The lower bolts had some viscous sludgy residue on them. I'm glad to be getting that out of the engine.

Thanks for the comments. I did not realize used towers can be that inexpensive. I'll have to start shopping.

Brett

[JFairman]

There's a pair of them with rocker covers, likely from the same motor over on the for sale page... FS: 930 Valve Covers/SC Cam Towers

[Brett San diego]

Originally Posted by JFairman

There's a pair of them with rocker covers, likely from the same motor over on the for sale page... FS: 930 Valve Covers/SC Cam Towers

Thanks for the heads up.

Brett

[Walt Fricke]

Were these mine, and I was rebuilding for street use, I think I'd carefully measure the journals to see if they are in spec. I don't have the specs memorized, but Wayne's book must have them - it has about everything else.

And I'd carefully examine the cam journals. They are iron, not aluminum, and might look pretty much OK, with the pitting and scoring being a result of some abrasive particles in the oil working on the aluminum. If the journals are in spec (I think you'd want to use a bore gauge), and you've cleaned them out, I don't see why they wouldn't work. The grooves and pits will just be oil reservoirs.

The main and rod bearings, when you get to them, are likely to look worse. One of the characteristics of the soft surface of bearings like those is embedibility - the ability of the bearing to let hard particles sink into the bearing surface metal, and thus not score the crank or impede the proper flow of oil. We replace bearings because some amount of the surface coating has litterally worn away, which not only opens up clearances and reduces any reserve, but also reduces embedibility.

But the cam bearings have a huge surface area compared with other bearings.

However, if $200 or so resolves worries, why not.

But the aluminum

[Walt Fricke]

Were these mine, and I was rebuilding for street use, I think I'd carefully measure the journals to see if they are in spec. I don't have the specs memorized, but Wayne's book must have them - it has about everything else.

And I'd carefully examine the cam journals. They are iron, not aluminum, and might look pretty much OK, with the pitting and scoring being a result of some abrasive particles in the oil working on the aluminum. If the journals are in spec (I think you'd want to use a bore gauge), and you've cleaned them out, I don't see why they wouldn't work. The grooves and pits will just be oil reservoirs.

The main and rod bearings, when you get to them, are likely to look worse. One of the characteristics of the soft surface of bearings like those is embedibility - the ability of the bearing to let hard particles sink into the bearing surface metal, and thus not score the crank or impede the proper flow of oil. We replace bearings because some amount of the surface coating has litterally worn away, which not only opens up clearances and reduces any reserve, but also reduces embedibility.

But the cam bearings have a huge surface area compared with other bearings.

However, if $200 or so resolves worries, why not.

But the aluminum

[euro911sc]

Mine didn't look like yours, but I used some AL polish and a long die grinder w/ polishing head (not a grinding head) to polish the surfaces up. You might try that and then measure it to see if it meets your needs. Otherwise, as others stated, these are easy to find.

-Michael

[Brett San diego]

Thanks for the further comments.

Walt, I didn't spend a lot of time looking at the cams, but I think the journals on the cams were OK. No really glaring issues to an untrained eye. After seeing the pitting on the lobes, I knew they were due for major work anyway.

Plan is to eventually have a machine shop clean the housings up and help with evaluation/measurements. Meanwhile, I'm keeping my eyes open for good/used housings.

Brett

[KTL]

If you're just planning to regrind to original specs, used stock cams are very plentiful on account of people upgrading their cams. They're "a dime a dozen" and usually go unclaimed on the classifieds. Also note that SC and Carrera use the same cam profile. Only difference is different fastening hardware for the timing chain sprockets- large nut & male cam snout threads for early cams, 19mm wrench size bolt into female cam end bore for later. I believe the change was made in 1980?

[Brett San diego]

Originally Posted by KTL

If you're just planning to regrind to original specs, used stock cams are very plentiful on account of people upgrading their cams. They're "a dime a dozen" and usually go unclaimed on the classifieds. Also note that SC and Carrera use the same cam profile. Only difference is different fastening hardware for the timing chain sprockets- large nut & male cam snout threads for early cams, 19mm wrench size bolt into female cam end bore for later. I believe the change was made in 1980?

That's brilliant advice. I am planning a stock rebuild. Many thanks. I'll keep my eyes open for good used cams as well as housings.

Is there any kind of recommended treatment for used but not yet visibly worn cams before putting them back in? Or just put 'em in and hope they last?

Brett

[KTL]

Nothing special needed to install old cams. Just assemble like you would normally- use assembly lube since the engine will be "dry" of oil.

One thing to keep in mind is the rocker arm faces will not be perfectly matched to the cam lobes. As the rockers and lobes are run together over time, they develop a matching wear pattern. Different cams with your old rockers obviously won't have the same wear pattern. That said, the condition is not going to cause catastrophic failure. Over time they will wear-in again.