Honing a 944 engine block

Stanton Horne · 05-18-2004, 10:10 AM

Since honing of 944 block has to be done by Porsche Dealer - Does anybody know how I can be sure that it is done correctly and about how much cost?

ae1969 · 05-18-2004, 10:51 AM

It doesnt have to be done by the dealer (they ship them out).

You need to find a machine shop that has the right equipment.

As long as the machine shop has the right specs all should be fine.... are you going with an oversized pistons ? or what are you planning?

It can cost anywhere from 100-300 a hole. I have found some BIG discrepancies in prices. They should be able to inspect the complete block for you as well...

Stanton Horne · 05-18-2004, 01:36 PM

Thanks, for the response. I plan to install new rings after honing, but I am concerned that the machine shops in this area may think that they have the proper equipment which to them, may be just a typical hone that is used everyday on Fords and Chevys. Does the 944 have cylinder sleeves?

ae1969 · 05-18-2004, 04:52 PM

Back up a little.

What happened to this engine? Is it scored? If all looks fine in the holes and the block checks out ok..... you can get away with just swapping in some new rings and all will be fine.

If the walls are scored and you need to fit oversized pistons.... CHUCK the engine and pick up a used one. The oversize pistons are too expensive to make it cost effective.

You are right these blocks are not like a chev/ford. A traditional hone will destroy the block.

I guess in theory it did use a sleeve when it was made. They did use an alusil liner..........

The honing/bore process normally etches the aluminum off the walls and exposes the silicon crystals. The rings ride on the crystals. WHen you look at one of these used engines your first thoughts are that the surfaces are glazed and should be honed. Oddly enough thats the way its supposed to look.

If you were to get a freshly bored out engine you would see that the holes would look almost dull. No cross hatches or nothing. So if you are used to working with an iron block.......Take that image out of your head. hehehehe

Keo_no_ka_oi · 05-18-2004, 06:07 PM

Wait, so assuming the machine shop was pretty compitant (not a bunch of half wit Mickey Mousers) they can hone it? How could someone tell whether or not the shop had the right stuff?

pearldrum · 05-18-2004, 06:21 PM

Wow, I can't believe I didn't see this post earlier. I PMed SoCal Driver earlier today asking him about honing the cylinders. I have an engine I'm looking to rebuild and the cylinder walls look really good, I may just put in new rings.

jjgrow · 05-18-2004, 08:06 PM

I have had bad experiences with honing on two different blocks. Not because the honing and subsequent lapping (the paste that exposes the silicon) was bad, just that the resultant cylinders will be just a tiny fraction too large for the existing pistons. Doesn't matter what rings you put on it.

It'll look and run just fine, but create a ton of crankcase pressure as rpm's increase. It'll also probably blow a gap in your oil pan gasket to release pressure. In my case, on one block it blew the oil filler cap off and on another it would blow the dipstick out. On a street car, you might go about your business and not necessarily notice for a while - especially if you were "taking it easy" on a new rebuild. Eventually after some spirited driving, you would open the hood and find oil spray on the hood and your dipstick out about 2 inches. It can get so bad that the oil in the crankcase air returning to the air intake can cause the engine to run lean and blow a head gasket (yeah, ask me how I know).

You can find a machine shop to do the honing work on the 944 alusil block for not a lot of money, but as was previously mentioned, you'll have to come up with oversize pistons. Forget about it.

If I was down to the short block and wanted to do a kick-ass complete rebuild, and the cylinder walls are not scored, I would maybe get it hot-dipped and cleaned. Wouldn't touch the cylinder walls with anything. As mentioned, new rings will seat just fine on an "old" cylinder wall.

If you have a scored cylinder wall, I would pursue the following course of action in this order:
1) pitch old block and buy a new one from junkyard - $
2) install steel sleeves and brand new aluminum pistons and rods (e.g. JE/Carillo) - $$$$$
- can't use old pistons in steel sleeves because the metals will react against each other (forget what this is called). OEM pistons apparently have a non-aluminum coating.

SoCal Driver · SoCal Driver's Garage

Check Wilks site out. He has a page on this.

www.frwilk.com

The stock pistons have an iron coating.