Honing Cylinder Barrels

vouvray · 02-10-2003, 10:21 AM

I posted this already in the "Engine Rebuilding" section, but thought I might get more responses here. I am rebuilding a '73 911 Targa, and my cylinders have been off of the engine and stored for several years. Two of them got dirt dobbers' nests (or something) in them. They all cleaned up beautifully, except I can still see and feel where the dirt dobbers were. I've read that these cylinder linings were impregnated with some type of silicone. Is it possible to hone the cylinders without comprimising the silicone? These cylinders are + .10 (from a previous rebuild), and I can still see hone marks at the bottom of the cylinders.

Tim Walsh · Tim Walsh's Garage

are they off a t or an e or s?

vouvray · 02-10-2003, 10:26 AM

When I bought the car 6 years ago, I was told it was an "E". When I looked up the numbers on the injection pump, it is for a "T". Are the cylinders that different between the 2 models?

Superman · 02-10-2003, 10:28 AM

If they had the silicon treatment and have been bored out, then the boring would have removed the silicon, unless they were re-treated. If the treatment is still there, they should not be honed. Wash them within an inch of their lives, but don't hone them. If the ring lands on the pistons are still tight, I have heard of installing new rings with NO lube. This allows the new rings to really bite the old cylinder surface.

vouvray · 02-10-2003, 12:40 PM

The "No Lube" thing kind of scares me. How do you go about seeing whether the silicone is there or not?

rvanderpyl · rvanderpyl's Garage

Nikasil (Silicone impregnated) cylinders where not used until the 2.7 in 1974, up until that time the motors used cast iron cylinders with aluminum fins on the S and E, and a full cast iron cylinder on the T. So the cylinder can be bored out without worrying about replating. In fact I would say that as they are cast iron you could treat them like any cast iron block and have them honed to establish a proper scoring pattern before you reassemble them. However the Porsche factory manuals don't mention anything about whether this is desirable, or neccesary to do.

vouvray · 02-10-2003, 01:43 PM

Thank you for your help.

911pcars · 04:52 PM

If the T cylinders are in pretty good shape (no deep scoring), you can bore them nominally (0.040") and purchase some pistons from JE, Arias or ?? to fit (actually the other way around). A Porsche-specific or motorcycle shop should be able to machine and mate these for you. The type of cam will have a bearing on valve reliefs needed in the piston. With the quality of gas as it is, you probably shouldn't venture too much beyond 9.5:1.

Alusil cylinders are all aluminum cylinders that are etched so the harder silicon particles provide the wear surface for the iron-coated, aluminum pistons. As rvanderpyl states, these were used beginning with the early CIS engines.

Sherwood Lee
http://members.rennlist.org/911pcars