Re-ringing a 944 8V engine

My friend, "carbon" and I are auto shop teachers at a local trade school and one of our class projects is the resurrection of an 87 Porsche 944. It came in with a broken rod, so we sourced a junkyard engine. That engine, however, was both as-is and seized. We soaked the cylinders in ATF and gently worked the engine free. It now rotates freely. If it were in my home garage, I'd scotchbrite the cylinder walls, re-ring it, replace the rod bearings, put the head back on it it with a new gasket, cross my fingers and plug it in to the car. Because the Alusil cylinders cannot be bored or honed traditionally, the by-the-book "correct" thing to do would be to sleeve the block, but that's not in the budget, so I ask you, the GRM Braintrust, is there a middle ground that will do the bare minimum to prevent it from smoking (i.e.: create a good ring seat) while not setting a bad example for the students? we are trying to train them to be technicians, not junkyard hacks. Ideas?

I have honed a kawasaki cylinder with electrofusion coating with good success. You are not supposed to do that but it developed a nice crosshatch and lasted me several years.

When I was building AMA race motors I used to reuse everything I could (nicasil cylinders). But they weren't rusty. I'd guess that the cylinder is not significantly affected (more than a stain). I don't recall what kind of rings they use in those motors, but they probably took the brunt of the water damage. So a new set of rings (do not set gaps tight) and brake them in hard, short to medium length bursts of full power. Pause for cooling between bursts. You want to make full power but not get things too hot.

I assume this is a low miles motor, Pistons might be junky too. If things don't look too bad I might be tempted to scotchbrite everything and reassemble. If rod bearings are not marked up I'd reuse them.

bentwrench wrote: If rod bearings are not marked up I'd reuse them.

Really!? II do like the sound of saving the $88!

Chrome bores shouldn't rust, although if it was fully wet, I'm not entirely sure which way the electrolytic reaction was going. My guess is the rings rusted and just stained the chrome bore. I'd probably make a crude expanding mandrel (hint: a foam pool float noodle with a length of rod hot-glued in and slits on the sides to hold the cut rectangles of Scotchbrite works really well) and run grey Scotchbrite through w/ WD40 for a lubricant. Try for about a 60 degree crosshatch. Or use a Flex hone if you have one.

New rings, as said above, set gaps toward the wider side of the suggested number. Look at the bearings to make sure the journals haven't rusted. If it's been sitting forever and it's dry, slather some assembly lube on to take the load 'til it's got oil pressure.

Break in is 50% throttle to 50% of red line 10 times, then 75% throttle to 50% of red line, 75 to 75 then drive gently for a bit then let it cool. Next time after it's fully up to temp and heat soaked, do a few hard pulls through the gears and it's ready to race.

We used to break in new road race motorcycle engines after a rebuild on the dyno immediately prior to 100% load dyno runs.

Bores aren't chromed. It's a Reynolds process block that runs tin/iron plated pistons right on the etched aluminum bores. There is a company which restores the bores on these engines, for a very Porsche like sum. http://www.928motorsports.com/services/uschrome.php

Brian

Call me I have a local guy that can hone/bore the block and re etch the alu to expose the silica particle's. In short he can make it like new.

This thread is somewhat useless without seeing the bores. Have you checked compression/leakdown? Bore scope? Checked that the valves are all moving? A lightly rust seized motor is not necessarily a bad one. You might get away with putting a timing belt on it, priming the oil system and running it.

Although I'm not familiar with Porsche blocks, I've run a dingle ball type hone through many plated motorcycle cylinders without issue to freshen them up for a new piston & rings. Just enough to reestablish the cross hatch.

These are not plated. The alu block material has a high concentration if silica in it. Once the cylinders are bored and honed the final step is to etch the bores with acid. This eats away a little of the alu exposing the silica particles. The piston and rings actually ride against the silica. honing with out the etching afterwards is not a good thing. You don't want the pistons or the rings in direct contact with the aluminum of the block.