3.0 cylinder height groups

Walt Fricke · 03-04-2017, 09:29 AM

I'm going to have to replace a 95mm cylinder. It is a Kolbenschmidt (if I interpret a casting mark correctly)Alusil (redone in Nikasil). Looking in Waynes 911 rebuilding book, it appears that after maybe 1978 or so Porsche stopped having cylinder height groups?

This has cast into it $B (this is what I think is supposed to be KS) 885/4B X, and stamped below that 1703 and an M in a circle. But if they were all the same height, I won't need to find a matching one, just a Nikasil with the right bore and condition.

So id Porsche give up on having different height groups?

Flat6pac · 03-04-2017, 11:06 AM

Walt, the use of height groups through the air cooled years is a true. When cylinders are sent into to be opened and nikisiled the machinist shop doing the job will match heights of the cylinders, so they don't have to be the same group.
I checked this out with EBS when I needed to cover a defective cyl that they couldn't plate.
Bruce

lite75 · lite75's Garage

I would recommend measuring the height of each cylinder before you send them out,
many used cylinders have already been cut down. Without this information you will have no idea of the base shim thickness to have on hand or if you even want to use that replacement cylinder.

KTL · 03-08-2017, 07:01 AM

I don't have the SC spec book scanned but I do have the '84-'87 book. It shows the height groups

prschmn · 03-09-2017, 04:22 AM

I have to wonder how many spigots are within the tolerance deviation of
.025 that is spec'd for the cylinders-there is going to be a cumulative effect
hence one would really want to know there relative heights installed.

pampadori · pampadori's Garage

I'm dealing with something similar now. I just put my cylinders on to measure deck height and got some odd variance from cylinder to cylinder. 1 measured pretty close to 1.75mm while cylinder 3 for some reason is coming up .85mm. Cylinders don't look like they have ever been machined (no shiny surfaces) and the rods were all rebuilt and measured the same.
I plan to check cyl 1,2, and 3 with a straight edge to make sure they are all flat when in the spigots. If they aren't I guess I might play with installing different thickness base gaskets under them to get a comfortable middle ground for flatness for all 3 cyl and appropriate deck height too.

pampadori · pampadori's Garage

Figured out my issue I posted about above.
EBS had informed me that one cyl I had sent in was too pitted to reuse so they sold me a new core and nikasil coated it. Turned out to be a group 5 cylinder and my other 5 were group 6. Besides that, it measured .25mm shorter sealing surface to sealing surface with my calipers than the other 5, which is way shorter than specs in the book says it should be so maybe it was modified at some point in the last 34 years. Who knows....
Just thought I'd mention it here in case someone else finds the post from a search.
I'm going to either send it back and exchange for one that is simile to my other 5 cyl or just add another base gasket under the one shorter cyl. The net will be the same.

Walt Fricke · 03-14-2017, 02:48 PM

Well, I drew the wrong conclusion from seeing that Wayne's book didn't get beyond the 2.7s. I got my 78-81 white spec book out of the tool box, and the cylinder size specs are identical for the 3.0s as those for the 3.2s. Makes sense.

However, from reading the spec you would expect t see the A, B, and C specs stamped on the cylinder down at the base. If they exist on my five cylinders (all from the same engine, all Nikasiled by US Chrome together with the busted one)they are indecipherable. But I have a caliper which goes up to 90mm, so I can just measure. If a replacement cylinder is different, I can deal with that with base shims - I have to add 0.010" with shims to account for flycutting the head to true the damaged mating surface anyway, and my base shims are 1mm to start with, so I think I can handle shorter or longer.