Jim Clark

Is it a must to utilize a ridge reamer or hone walls before installing new rings?

Working on a 2.5 944 n/a 87 model

Al P.

the alusil cylinder bores in your engine will not take kindly to that kind of treatment.

If you've actually worn the cylinders to the point where there is a ridge you need to bore, hone and then have the cylinders treated. Porsche used a very hard material for these blocks and they virtually almost never "wear" out. The down side is that if you do bore them you need to use the Oversize Porsche pistons as they're iron coated to run in the aluminum bores (say pricey)

These motors also run a very tight piston to wall clearance. You probably would want to check with a local Porsche shop for clarification on all of this.

Bill L Seifert

Do what Al P says, and then if the block is worn out, buy a junkyard motor, those oversize pistons are impossible to get.

Bill Seifert

1983 944 Race car
1987 944 Race car in prog.

Jim Clark

Am I safe to say that if the bores are good, as they are, and I'm replacing the rings and bearings, that I should be good to go with a 180-220 grit Flex-Hone to clear the glaze and prep the cylinders for the new rings.

Geo

No. Just use new factory rings.

JJG

You don't need to lap the cylinder walls to expose the silica? New rings will seat in a "used" cylinder?

Geo

That is what I've been told. It counter to other engines, but I've been told that as long as the bores are OK, just install new rings, but it's important to install FACTORY rings.

The 944 engine (don't know about other Porsche engines) runs counter to conventional engines in this regard.

adrial

I've been told that you need to hone the bores to accept new rings.

Whats wrong with Total Seal rings?

Geo

You absolutely do not hone 944 cylinders. There is a lapping process for fresh bores. But, what I have been told is to use OEM rings in good bores. There are other rings that work OK, but you have to be very careful of the material. I cannot remember which is the correct material. I plan on using OEM.

adrial

Why, why does everybody have a different opinion?

By honing, I was referring to the lapping process.

Why shouldn't they be lapped again to ensure proper ring breakin?

Geo

I'm telling you what I was told virtually unanimously when I got my car.

Here is my guess.

The lapping process does not smooth the silicium. It removes minute amounts of aluminum to leave the silicium at the surface. The silicium is hard and does not wear down. So, no need to remove more aluminum.

I've also been told ring material is critical. OEM or similar material (which is different from rings for iron bore cylinders). I've been told if you have new OEM or similar material rings and a good bore, you're all set. Other than a resize, I've yet to read of anyone having their cylinders lapped before installing new rings.

GlenL

I'm rebuilding my 928 engine, albiet for the first time. This is Alusil like the 944. (No surprise there...)

What everyone says is to do a careful inspection and if things are good, put in new Porsche or OEM rings. Just lightly oil the bores. That's what the manual says too. No honing, ridge work or lapping. None of the special etching soultion. Nothing; just re-ring and go.

If the bores are too scratched, out-of-round or otherwise messed up, then you can have them bored and then etched to bring "out" the silicon. It is almost always cheaper to get a new block (even for a 928!) than to mess with the boring. And the oversize pistons? Forgeddaboutit! The few that have gone that route get bigger pistons like 100mm or 104mm for compatable Porsche engines. Usually racers.

cruise98

I have spoken to my local expert and he says the Sunnen guru recommends against doing anything to the alusil bores if they are not scratched, scuffed or worn oversize. Do use the factory Goetze rings though.

Chris Prack

Well your Sunnen guy would know. Porsche specifically requires a Sunnen machine to hone the cylinders. You need a specific grit set of stones and silicone paste to do the job.

If your cylinders are clean then do yourself a huge favor and do NOTHING to them but clean them, oil them and install the pistons' well oiled with new factory Goetze rings. Nothing more is necessary. Save your money.