Cam tower resurface

[pcardude]

Anyone ever have their cam towers resurfaced? is it common to do during a rebuild to help eliminate oil leaks?

Thanks

[pcardude]

I mean the cam tower to head surface

[john walker's workshop]

No.

[pcardude]

Originally Posted by john walker's workshop

No.

Dang. .040 off both sides. Looking back at stuff I did in my 20s is difficult sometimes.

[Walt Fricke]

0.040" seems like a lot. Did someone gouge them with a chisel when separating or the like? They are not wear surfaces.

I would expect that you might have to shave the chainbox ends by this amount so that the cam seal will fit properly. Maybe you could just dispense with the gasket between chain box and case? There is some room for misalignment there, but not a lot.

In addition, your chain will seem to be too long, although you can get idler gears which are a larger diameter than stock to help with the slack there - because the chain tensioner system can only deal with so much slack in the chain before you start to run out of travel.

Plus your rocker arms will be at a different angle, though I suppose you won't run out of adjustment of the elephant feet, and maybe these angle changes won't cause problems like excess side loading on the valve stems leading to accelerated valve guide wear. The rocker surfaces which bear on the cam might wear over a slightly different section of the rocker, but if they are new or reconditioned maybe that won't matter, although I suspect there would be a small change in the effective rocker ratio.

Are good used ones expensive these days?

[Walt Fricke]

Oh - you could use thicker cylinder base shims to get the geometry back to normal, but you'd reduce your compression. Unless you use aftermarket pistons cut to have a bit more than stock.

[pcardude]

The motor was rebuilt 12 years ago. I put a couple hundred miles on it, lost my job, big changes happened in my life and the car sat in storage for the next 10 years. Things finally settled down, I bought a house and I've been tinkering with the car this summer. It's not running very good so I'm thinking about all the mistakes I probably made during the rebuild. I was in my early 20s when I finished the motor.

It's a 2.2 rebuilt in a 7R case, JE 10.5:1 pistons and 1966 L cams. Hydraulic tensioners all that new stuff... I think I was overly paranoid about oil leaks back then which is why I had the cam towers milled down flat. Though I will say it doesn't leak any oil at all.

It runs ok as long as your foot is on the floor. It won't idle for squat.

[Walt Fricke]

Twin plug? 10.5 is too much for street gas without it, even with a really hot cam. Is the L like the 906 cam?

[pcardude]

My plan now is to put 5 gallons of avgas 100 low lead in it every fill up. I seem to remember there being 94 at the pump years ago.

I recall the 1966 L cam being between an E and S but I can't remember now.

[KTL]

Ask Henry Schmidt at Supertec if he can set you up with some cam housing shims. I've seen him post pictures of them here in the past.

[KTL]

Also, I think these housings are not all that stable dimensionally. I've put a few junk ones on a flat piece of glass or a large hunk of quartz (taken from a rehabbed kitchen) and they take a bit of sanding to get the surfaces level. John @ Costa Mesa R&D seems to think they need a resurface. But I think he's also doing that along with some other fixes to later 993 type housings.

https://www.youtube.com/watch?v=PTxkj1QkCYY

https://www.youtube.com/watch?v=aWLsKUJCy0A

All that said, I think their dimensional instability allows them to twist into shape when mounted on the heads? I don't know about that. but I do know it's not unheard of for a cam to bind inside the housing

[Henry Schmidt]

We recondition the cam towers on every rebuild we do. That includes surfacing them.
Generally .005" will bring them around. "040" seems excessive.
Used or reconditioned cam towers are fairly reasonable (in the overall scheme of thing) so when in doubt, replace it.

Ken @ 911 Vintage Parts sells used and reconditioned cam tower for all air-cooled Porsche engines. info@911vintageparts.com

760-731-4911

[x98boardwell]

Henry, do you find with .005 or less (.002 in my case) that you would need to do anything to chain boxes? I would think that is such a small change that it wouldn't affect anything in the grand scheme of things... O-rings for cams, etc..?

Thanks!

[911pcars]

Not an engine builder, but it doesn't take much to restore the concentricity of the cam inside the cam housing oil seal. Just trim a like amount from the chain box as was removed from the cylinder head sealing, cylinder height and/or cam housing sealing surfaces. Excessive machining will affect/change opening/closing valve geometry as well as devices that manage chain tension.

Sherwood

[faapgar]

Ok,you are all DIY guys.The problem is not the flat surface but the cam bores.I mentioned this to Grady Clay years ago and he started throwing out cam towers just like me.When the studs break or pull the cam bearings suffer the most.The books do not tell you that because they did not know.Nightmares for you guys.I throw out 60 -70 % of the cam towers because they they are worn and lower oil pressure.Ciao

[911pcars]

Originally Posted by faapgar

Ok,you are all DIY guys.The problem is not the flat surface but the cam bores.I mentioned this to Grady Clay years ago and he started throwing out cam towers just like me.When the studs break or pull the cam bearings suffer the most.The books do not tell you that because they did not know.Nightmares for you guys.I throw out 60 -70 % of the cam towers because they they are worn and lower oil pressure.Ciao

If the camshaft housing bearing journals (3 or 4) are worn oversize, I would think they could be line bored, rebushed, honed to size and brought back up to spec. However, I haven't read about it being performed on this forum; either that or the supply of good used ones present a more cost effective alternative.

Sherwood

[Jeff Alton]

Interesting info being thrown about here on this thread..

I would love to see empirical data to back up some of the suppositions....

Oh, and I guess Henry is a DIY guy?? LOL....

[KTL]

I agree with Sherwood's thinking that the housings could be bored oversize and sleeved. Just need to be sure all the machining plugs and oil delivery tubes are removed so the oiling holes for the cam bearing bores can be appropriately aligned with the holes in the housing.

These housings are arguably the most abused part of the engine. There's the cam bores (often heavily scored), the rocker shaft bores (often corroded and scratched and gouged), the oil return tube bores (caked with crud and sometimes gouged), the four gasketing surfaces and the oiling tubes. People love to media blast these and usually that does more harm than good, simply in the spirit of getting them clean. I bought a cheap ultrasonic cleaner and it paid for itself in no time when you consider how much time it saved me cleaning the housings by hand, scrubbing them in a slop sink

I know it's not commonly done but my OCD has led me to clean up the gasketing surfaces of these housings a number of times. The valve cover surfaces are usually pretty cruddy and could use a new, fresh surface since it's often not all that flat. The head contact surfaces are usually pretty crappy because someone previously mistreated them in removing the old 574 orange sherbet sealant remnants and it also is not as flat as you'd like it to be. Lastly, the "snout" of the housing, where the paper gasket seals to the camshaft thrust plate, is not all that flat and surfacing it goes a long way toward helping the gasket seal better. That gasket is a notorious leaker and any help you can give it is a big win in my opinion.

Here's some pics of my "machining" done with wet sand paper taped to a piece of quartz countertop. I color the surface with a sharpie marker and when most of the market is rubbed off, I call it good.

[Iciclehead]

KTL, you did what I was thinking of doing to mine.....in theory, this ought to be plenty as it is really just a sealing surface, given that the cams are in the right spot dimensionally.

How long did it take you....like an afternoon of hard sanding or a few dozen swipes? Any insight as to grit of paper you used.....and did you lube with water or WD40 or light oil?

Dennis

[KTL]

Dennis,

I was first way too conservative in doing this and used 1500 grit paper. It took way too long. I opened my eyes and realized the original machine-finished surface on the head contact surface is pretty rough. So now I use 400 grit paper.

Definitely use water and wipe off the paper as you go with a rag by spritzing it with water. It gets quite a bit of aluminum chum buildup on it. Don't be stingy with the paper either. Change it after a while of sanding to keep the cutting effective. I use HVAC foil tape to tape down the paper. It resists water contamination MUCH better than plain masking tape.

I'd say it probably takes me about 10 minutes per surface on the large surfaces for housings that are in decent shape. Much crappier/neglected/molested housings take longer. Lots of shuffling the housing on the paper. Good shoulder workout. Hahahaha........ The cam bore side goes quick but sometimes the casting along the sides of the valve cover area is "fat" and gets in the way of setting your cam bore on the paper. So mill that fat area away because it does no harm in clearing it away.

So if you've got housings that are pretty sketchy, either take them to a machinist to have them put on the grinder table or just replace them. Challenge is, good used housings are becoming harder to find.