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Lap new 3.3 cylinders to machined heads?

Is it a good idea to put some valve grinding compound on the sealing surface where a machined head and new cylinder come together and then rotate the head back and forth on the cylinder by hand?
Or is it better to install these in the motor the way they are?

The cylinders and pistons are new Mahle 97mm 3.3 turbo from a sealed box and the 1976 930 heads were machined some years ago.
Recently I had the small bevel around the combustion chambers that were originally on 95mm cylinders machined by xtreme heads so they would fit the 3.3 liter 97mm cylinders and pistons.

If it's good to hand lap the heads to the cylinders which of these compounds I have be best to use? Or is something else better?
The tube of permatex valve grinding compund is water based and old but it still squeezes out and the can is 150 grit grease based compound.

Here's pics of the grinding compounds I have and the sealing surface of a machined head and new cylinder.

Thanks in advance for opinions on installing them the way they are or should I hand lap the sealing surface to a uniform grey and wash them off first?



Old 02-03-2014, 12:04 PM
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I have had good luck with the water based permatex
you can use machinist blue to track progress or a sharpie
always by hand
the oil based stuff makes re-applying and cleaning between grinding sessions a pain
I always lap the heads and jugs even if freshly machined , it does not take long and you will always be insured of a tight leak free fit
Old 02-03-2014, 01:33 PM
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Either one is good Clover has always been the standard for lapping compounds. Which ever is in better condition. If it's drying out toss it and get another tube. 150 grit though is pretty coarse I think regular valve lapping compund is about 300 grit. When i was lapping valves on submariens we would start with 150 then finish around 400.But those were Steam valves not the ones in your car and certainly not soft aluminum. Every one i have talked to has just used the stuff in the tube from the parts store.
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88 turbo Guards red Targa slant nose, and yes I am a horsepower junkie, 3.4liter,7.5 to 1 JE pistons, Adjustable WUR, Imagine fuel head, 1 bar waste gate headers,allthe cis toys. Now apart to become the next EFI monster. fabbing my own intake, headers Individual throttle bodies, MS-3, pauter rods, Xtreme twin plugged heads, gt-2 evo cams cop's.
05 Cayenne S lapis blue

Last edited by Ken911; 02-03-2014 at 06:08 PM..
Old 02-03-2014, 06:01 PM
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Although I'm all for lapping (great method for valve to seat faces), don't remrmber anyone (big engine builders) doing that. I just used scotchbrite on the surfaces.
Old 02-03-2014, 06:39 PM
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Ken911,

Good to know I am not the only one on here who used to lap vlvs on Submarines!
Long time since I have been on a 688 ....

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Old 02-03-2014, 06:48 PM
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When I was assembling my engine, I asked Chris from Turbokraft if I should lap the heads and cylinders. I recall he advised that it wasn't strictly necessary if the parts were are freshly (and properly) machined.

The only reason I even thought of doing it is because I was advised by a pro to lap the head and cylinder when I reassembled my Ducati engine. That engine doesn't have a head gasket, just like the 930. In that particular instance I didn't have any machine work done, was just replacing a broken head stud
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Old 02-03-2014, 06:48 PM
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I bought the tube of permatex in '82 and the can of clover in '96, lol.
The greasy clover stuff is in better condition but maybe the permatex is better for this if it's finer grit.
I'll sqeeze out the rest of the permatex into something and mix in a few drops of water and see how it does. Doesn't need much and water clean up is easier doing this at home in the driveway and kitchen.
Old 02-03-2014, 06:58 PM
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Maybe it's to late or I've had a few too many tonight... but if you are at the point of having the head/cylinder apart, why would you not lap them in? After all, you are simply talking about two mating surfaces which will work better if the seal is tighter. I can understand the you don't NEED to argument, but it just seems silly not to as it only takes like 5 minutes~
Not trying to start an argument, just sayin'~
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Old 02-03-2014, 07:31 PM
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Jim a new tube from this century is $3.99 at autozone. Cmon live a little.
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88 turbo Guards red Targa slant nose, and yes I am a horsepower junkie, 3.4liter,7.5 to 1 JE pistons, Adjustable WUR, Imagine fuel head, 1 bar waste gate headers,allthe cis toys. Now apart to become the next EFI monster. fabbing my own intake, headers Individual throttle bodies, MS-3, pauter rods, Xtreme twin plugged heads, gt-2 evo cams cop's.
05 Cayenne S lapis blue
Old 02-04-2014, 03:52 AM
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The head sealing surface is supposed to be machined at a 6 degree angle, per the workshop manual. It is not flat. It is not supposed to be flat, and maximum sealing is not achieved if it is flat.
Old 02-04-2014, 09:08 AM
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If both surfaces are fresh, it isn't necessary, but there's no harm in doing so, either.

We'd use the fine grit lapping compound, look for a smooth dull finish around both sealing surfaces, and keep a lapped cylinder with its corresponding head.
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Old 02-04-2014, 09:34 AM
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Good point might want to blue check it first then lap if it neads it. Just because it has been machined doesnt mean it will match correctly. Especially if the shop that machined the cylinders was not the same one that did the heads. I know there is a 6 degree taper on the cylinders but also remember on a turbo they lift off easily. Mine did so even with the race ware studs which is why porsche went with flame rings later on and which is also why i went to the same trouble with mine this time.
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88 turbo Guards red Targa slant nose, and yes I am a horsepower junkie, 3.4liter,7.5 to 1 JE pistons, Adjustable WUR, Imagine fuel head, 1 bar waste gate headers,allthe cis toys. Now apart to become the next EFI monster. fabbing my own intake, headers Individual throttle bodies, MS-3, pauter rods, Xtreme twin plugged heads, gt-2 evo cams cop's.
05 Cayenne S lapis blue

Last edited by Ken911; 02-04-2014 at 11:14 AM..
Old 02-04-2014, 10:49 AM
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Again, it is not supposed to be flat to flat. There is a 6 degree taper from the ID to OD to promote sealing pressure on the ID. These surfaces are not lapped because of this taper. Check the 911 engine rebuilding forum for more details.
Old 02-04-2014, 11:54 AM
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