CCCP

Does anyone have any experience with just replacing the rings during their engine rebuild? My block has minimal scratches and slight discoloration. Oversized pistons are hard to find and extremely expensive. I am considering just putting on new rings and not touching the bores. However I have heard that new rings on a worn block will yield worse results then reusing the old rings. Anyone have any input?

Dan87951

Im not 100% sure but I believe I heard you can't use new rings on our blocks without getting the Alusil re-applied otherwise the rings will stick to your old bores.

StoogeMoe

First off, Alusil is not a coating. The block is an alloy of aluminum and silicon, with heavier concentration of silicon at the bores. They are shiny because the silicon is at the surface through a special lapping process. That's why they last long, because they are basically ceramic. You do not want to touch the bores because of this.

I rebuilt my engine using new rings and had no problems. My machine shop guy said you can have problems with new rings seating, but I followed the normal break in period and had no issues.

The real question is why do you think you need to re-ring?

____________________________________
1986 944 NA - Guards Red - 91k miles - minty
1983 944 NA - Platinum metallic - 3000 mi beginning a new life
1985.1 944 NA - Guards Red - donor car
1984 911 Carrera Coupe - Guards Red (gone, but not forgotten)
"If you're not living on the edge, you're not living"

CCCP

I am building a car that will exclusivley see track use. I want the most robust engine i can build.

500

I have wrestled with the same question. As with you, my bores look blemish-free. The engine-builder at the machine shop I had my parts spec'd out at (Whaletail Canada) emphatically advised me to not have anything done to the bores (I was contemplating having the Sunnen lapping process carried out). This individual has a good track record of excellent re-built 928 and 944 motors.

I also emailed Marc Thomas of Devek about this issue (as he seems to have a fair amount of experience with this) and he too advised me that if the bores look perfect, leave it alone. The crucial elements I was reminded of were:

1) Check ring gap (adjust if necessary

2) install the rings in the correct orientation (note which side is up!).

3) Lightly oil piston sides and cylinder wall.

4) Use a non-detergent, non-synthetic oil for break-in. (Follow a normal break-in procedure).

Based on this, I have decided to leave my bores alone.

Thanks

M758

When I rebuilt my spare 88 motor I put in new rings, but left the bores alone. I can't say how well it has worked since the engine is still sitting my engine stand. It will get installed if needed.

CCCP

Looks like the current game plan will be to have the bores buffed and lapped at the machine shop and have the pistons swain coated to fill how ever much material the buffing takes off. Has anyone done anything like this?

GlenL

Who is advising that approach?

You only need to put in the new rings. No machine work. No coatings. That is what the Porsche factory manuals say.

CCCP

I have a reliable source telling me this is the next best thing to going to a 100.50mm bore. Also I have extensivley read the facotry manual and I do not recall it mentioning anywhere that only the rings should be swapped during a rebuild.

AlpharettaRK

I replaced rod bearings and rings on my race car earlier this year without pulling the block from the car. Having built motors before but never a Porsche I was amazed at the condition of the cylinders. With 75,000 miles on it, problably 20,000 of them on the racetrack there was no measurable wear whatsoever. There was not the slightest hint of a ridge on the top of the cylinder. It is an expensive procedure to have the block bored properly. If the cylinders are round and not scratched the best course is to just put rings in. I went from using a quart of oil per hour to about 1/4 of 1 quart on a 5 hour track weekend. I call that operation a success! Here's my engine building tip. I wipe the cylinder bores out with WD-40 before installing the pistons. It helps to get any crud and dust out, provides lubrication to get the piston in and then burns off immediately after the engine starts so the rings can seat. And yes, use conventional oil for 1000 miles or so. Good Luck!
Cheers
Randy

Calmchaos

Im reringing and just leaving the bores alone as well.
+1 to that!

GlenL

The manuals are often criticized for not be clear enough for all readers.

What it does say is that the bores need to be enlarged and new pistons fitted _if_ the bores and pistons don't meet spec. In other words, don't do anything if the specs are met. Whether the numbers are far enough out of spec to spend the money is another decision point.

Also, the bores are machined to match the pistons. I'm leary of coating the pistons to match the bores. And that's a ceramic coating? I've heard of variaous metal coatings but not that. Ceramic on the top for certain.

I've rebuilt my high-mileage 928 (same materials) with just re-ringing and the results were very good. Many, many others have done the same. In fact, the common wisdom is that if the block needs machining then throw it away and get a good used one.

Then again, it's your $$$. Sounds to me like $1000 that could be spent on suspension upgrades.

CCCP

The pistons are not coated to match the bores. First the pistons are balanced then coated. Then the block is buffed to match the pistons. The machining process is almost identical to what one would do if he were going oversized, only such a small amount of material is taken off the block that the pistons can fill it with a fresh coating.

There must be someone that has done this who can tell me long term effects.

M758

I don't think coating the pistons is a good idea. For that mater i don't think buffing the bores is good either. If you want to cut the bores then go through the entire process for these bores as spelled out in the manual. This requries the proper sunnen machine to do the work. If you don't have access to that process don't touch the bores at all. The reason is these bores are alusil and not regular steel or aluminum. So normal machining process destory the bores.

CCCP

Yep, the machine shop I am using utilizes the sunnen machine. After the buffing they use the same felt pads and everything to bring out the silicon in the block so the end result should be the same as a rebore.

This is the company that does the coating: http://www.calicocoatings.com apparently their process is identicle to the swain coating and they were recommended by the machine shop I'm using.