to bore or not?

customtec · 07-02-2003, 02:51 PM

Ok, got the engine out and tore down this weekend. As I posted before this teardown is the result of PO having #2 bearing spin issue.
1st pic is #1 cylinder... not too bad. Second pic is #2 cylinder... it does NOT hang up a finger nail when scratch across it.

No one in my area can do work on these aluminium blocks. Can I put new rings on pistons a let it go as is? Will the cylinder clean up over time?

FLA944 · 07-02-2003, 03:03 PM

Pick up a cylinder hone and with a reversible drill you can hone it out and remove the scratches and then just re-ring.

measure the distance then between the cylinder wall and piston using a feeler guage. if the gap exceeds the mechanical limit, new pistons are the rule. You will then have to bore and purchase oversized pistons according to the bore.

I apologize for my ignorance as i do not know the posche limits. My rule of thumb has always been if the gap exceeds 0.0015" then bore time.

Rick

ae1969 · 07-02-2003, 04:44 PM

Quote:

Originally posted by FLA944
Pick up a cylinder hone and with a reversible drill you can hone it out and remove the scratches and then just re-ring.

NO!

The block is a special material. A hone will destroy it and the rings will never seat properly. You do not need a crosshatch here like a typical engine bore. You would ideally want to get the last stage done on a sunnen hone...........

If the scratches are a thousand..... you could probably get away with it. You may have a little more oil consumption. It depends what you are really trying to do here. If its slap it together and drive it till she breaks. Go ahead and slap in new rings and hope for the best.

carsontc · 07-02-2003, 05:33 PM

from another thread..

Quote:

Originally posted by porschepatron
cylinder walls were silica impregnated (aka alusil [aluminum+silicone]) which can only be serviced by the Sunnen ck/10 or cv/616 machines. Honing these cyliders will without a doubt ruin the silicone barrier. Sleeving the cylinders is another option and yet another is to just sleeve and not restore the silicone.

drew1 · 07-02-2003, 08:42 PM

customtec,

With the "tec", I assume that you are a technical guy. Even though the shops in your area don't have the automatic Sunnen Hones, they probaly have an AN 112 or something similar. The last step involves honing with brass stones & felt wipers, used with lapping compound. A general machine shop may be able to fab you something out of a regular AN 112 stone set that do the same thing.

drew1

customtec · 07-03-2003, 05:28 AM

I guess really the first thing to go is to have the cylinder bore measured and see if it must be bored out anyway due to overall wear, huh.

I did put one of the piston rings in the cylinder and the ring end gad is alomst 1mm. According to the Haynes book it should be .45mm max. It may be the block is not salvageable!

I call around and ask about a AN 112 or something similar.