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Carrera cylinders - machine tops or no?

Hello all,

Continuing the saga of my 3.2SS MFI build, I the machining of my heads finished yesterday and my attention has now turned to the top surface of the cylinders.

There appears to be some slight pitting in a few areas of some. Not as bad as on the heads, but still perceptible.

The engine, as disassembled, leaked from just about every place it could, and had dilivar studs in the exhaust side. The heads were not completely flat (potato chip shape of about .0012-.0015") although they cleaned up completely with a .003" cut. 1 or two seemed to be a bit taller than the rest but only by .001" or so. Not anymore.

Given the great pains I went to to assure the heads are all exactly the same height, I figured I'd just chuck the cylinders in the lathe, take a few 'thou off the top at the same slight taper and live happliy ever after, knowing all cylinders were also the same height.

I have read on here about how the plating may wrap around the tops of the cylinders and will chip if I try to machine them?

If that's the case and the nikasil does in fact wrap around the top then I know I can rely on that portion to seal against my fresh head surface and I'm best to leave well enough alone. Any pitting that is presenting itself is a good 2 or 3mm inboard from the cylinder bore.

Thoughts? My intention was to have two nice sealing surfaces freshly machined but I don't want to wreck my cylinders. Plus I'd like to put all this together some day!!!

Just because I can, a pic of the "fresh" heads.

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85 Coupe - The Rot Rod! AX beater
Old 03-29-2019, 03:48 AM
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KTL KTL is offline
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I have a set of Carrera cylinders that are low mileage. Seller claimed they had only 16,000 on them and after I cleaned them up, they did appear low mileage. 85 911 Porsche Carrera parts Point being is that even with that very low mileage, even the tops of those cylinders showed some roughness. I suspect this happens due to very very slight movement between the heads and the cylinders?

So I put them on some wet sand paper on a flat surface to remove the ridges and they cleaned up nicely without a lot of "machining." They're still looking good because i've yet to put them in an engine..... So having handled a few of these cylinders, I never got the impression they're plated on the tops because the coloration isn't the same as the cylinder bores. It was very easy to clean up the top surface and the resulting sanding liquid was the same grey color i've seen when surfacing the cam carriers. Not saying i'm absolutely right here. Just sharing my observations.


Also, i've seen a number of guys say it's a good idea to lap the cylinders to the head with lapping compound. Seems like good practice to get the heads and cylinders mating nicely.

Lastly, I recall faapgar here on the forum recommending the use of a 930 head gasket to benefit the mating surfaces between the head and cylinder. It's a 0.50mm gasket so of course your deck height/base gasket/head or cylinder machining should take that into account if you decide to use it.

88 3.2 Cylinder Head Gasket

Cylinder Head Gaskets, what happened ???

3.2SS top end rebuild - compulsory newbie questions

So I think a really good approach here is to clean up the cylinder tops, lap them to the heads and use the "Fred head gasket"
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Old 03-29-2019, 12:48 PM
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I lapped my heads to cylinders using valve grinding compound. Doesn't take much.
Old 03-29-2019, 12:55 PM
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Great suggestions thanks! - I had a closer look at them today (with my reading glasses on )

What I thought was erosion or wormholing or whatever you would call it, that matched the heads, is actually aluminum deposited on the tops or the cylinders. It catches on a fingernail when you feel for it, and cleaned off in a few seconds with a jewelers file.

After doing that I put some bluing compound on the top of the cylinders, and test fit them in the heads. They really do touch only at the inner edges - at first I thought the cylinders were bottoming on the outer edge before they hit the inner surface!!

Just like Kevin I tried to flatten a bit on a surface plate with some 800 grit and proved the flatness right away so I'm happy not to have to machine them.

I'll look into the 930 gaskets..... might be just the ticket and somehow I hadn't seen mention of them before.

Thanks again, Jon
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Old 03-29-2019, 01:54 PM
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Some VW type 1 builders apply Permatex copper coat or 3H to the jug sealing surface after lapping to the head. Supposedly it carbonizes and the carbon helps seal any imperfection. I tried it on a Type 1 I built, I don't think it can hurt anything.
Old 03-30-2019, 04:33 AM
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As to your question about the Nikasil, it only lives in the bore. I have had a ton of cylinders replated and it's just inside. It is very brittle along the top and bottom edges, though.
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Old 03-30-2019, 06:45 AM
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Actually, the cylinder sealing surface on the 3.2 Carrera is tapered from Mahle to improve sealing when clamping force is applied.
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Old 03-30-2019, 02:41 PM
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Quote:
Originally Posted by Henry Schmidt View Post
Actually, the cylinder sealing surface on the 3.2 Carrera is tapered from Mahle to improve sealing when clamping force is applied.
I should probably clarify some of my previous writing - Yes, I am aware of the taper, it's pretty obvious when you put a straightedge on the surface, even more obvious when you are looking for it.

When I "surfaced" the top of one cylinder as a test, indeed, only the very inner edge of the barrel top touched the abrasive, but did leave a very small amount of residue on the paper.

Given the difficulty with machining (or even just getting near) the nikasil, even if I was only going to take off a couple 'thou, I'm going to leave well enough alone, especially since they've cleaned up better than I thought they might.

Thanks to all of you for chiming in!
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85 Coupe - The Rot Rod! AX beater
Old 04-05-2019, 03:57 PM
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Quote:
Originally Posted by KTL View Post
I have a set of Carrera cylinders that are low mileage. Seller claimed they had only 16,000 on them and after I cleaned them up, they did appear low mileage. 85 911 Porsche Carrera parts Point being is that even with that very low mileage, even the tops of those cylinders showed some roughness. I suspect this happens due to very very slight movement between the heads and the cylinders?

So I put them on some wet sand paper on a flat surface to remove the ridges and they cleaned up nicely without a lot of "machining." They're still looking good because i've yet to put them in an engine..... So having handled a few of these cylinders, I never got the impression they're plated on the tops because the coloration isn't the same as the cylinder bores. It was very easy to clean up the top surface and the resulting sanding liquid was the same grey color i've seen when surfacing the cam carriers. Not saying i'm absolutely right here. Just sharing my observations.


Also, i've seen a number of guys say it's a good idea to lap the cylinders to the head with lapping compound. Seems like good practice to get the heads and cylinders mating nicely.

Lastly, I recall faapgar here on the forum recommending the use of a 930 head gasket to benefit the mating surfaces between the head and cylinder. It's a 0.50mm gasket so of course your deck height/base gasket/head or cylinder machining should take that into account if you decide to use it.

88 3.2 Cylinder Head Gasket

Cylinder Head Gaskets, what happened ???

3.2SS top end rebuild - compulsory newbie questions

So I think a really good approach here is to clean up the cylinder tops, lap them to the heads and use the "Fred head gasket"
I don't think I'll have room to add that gasket although it certainly is appealing, the idea of having no gasket has taken some getting used to.

Given that I will have good clamping force (no more dilvar!) and nice fresh, flat, heads, I think I will continue the present path.

I purchased ARP head studs, I'll have to review and confirm the tightening procedure/value to make sure I've got that correct and will double check it after a few heat cycles.
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78 Backdate - The Project http://forums.pelicanparts.com/porsche-911-technical-forum/979976-project-heavy-metal-all-steel-classic-remastered.html
85 Coupe - The Rot Rod! AX beater
Old 04-05-2019, 04:02 PM
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