gbgastowers

I just purchased a 1980 Euro S motor(M28/12 4.7L) that had low compression and would not start. I have a M28/11 with a badly scored cylinder from a piece of valve spring caught in the piston ring and cylinder. After removing the heads on the new motor I was surprised at how good everything looked. What should I do? Just have the heads rebuilt and check the rod and main bearings and put it back together or should I also replace the rings? I am a pretty experienced newbi. I took the other motor down to the bare short block in preparation to send it to 928 Motorsports for repair and nikasil coating so I know enough to be dangerous. Any advice on what I should do would be helpful.I have turned the motor after oiling the cylinders and it is very smooth.

gbgastowers

222

danglerb

I'm not sure how at this point you go about checking the condition of the rings, but I can't see putting it together without knowing the source of the low compression. What sort of numbers did it have and how was the testing done?

Measuring the bearing wear etc is pretty straight forward, check and replace as needed

I don't see a reason not to have the heads serviced from one of the motors while you sort out the bottom end. Maybe have the shop look over the two sets of heads and pick the best pair and rebuild them.

The way I look at it is that I want to try and manage costs when I can, but once the overall cost of a motor passes some point it becomes prudent to spend even more to assure no issues and lower the risk.

tailpipe

if you went this far you might as well do it right and replace the rings also do it right the first time and you wont be back to do it again later

danglerb

Is this one of the motors the cheaper 944 rings work well on?

karl ruiter

I put a used Euro S motor in mine and had huge quantiies of white smoke. Never totally found the cause, but when I pulled it apart the oil rings just shattered. My guess is that something happened to them (heat, time?) to make them very brittle and some were broken in place. My suggestion would be to not touch the main bearings, but pull off the rod caps, and push out the pistons. If your rings shatter when you remove them, you need new ones anyway. If not measure the end gap and re-use them if they are good. Plastigauge and inspect your rod bearings (they have some history of being an issue), and reuse them if they are good, or just replace them if the cost is not a problem for you. From where you are it will cost you little $$ to at least inspect the rings and rod bearings and it could save you huge time. Imagine that you get this thing in the car and you find a problem that means you will have to pull it back out and tear is all the way back down. How long will it sit before you want to come back to it. For me it was a couple of years. If you just bite the bullit for rings, mains, and rods, you are looking at something like $1000 for parts, so I would not take that path if money is an issue. But inspecting them will just cost you a set of rod nuts and a pan gasket.
Not sure what your plan is on the heads, but they often need valve guides, and if I do that I will generally do a grind at the same time. Valves should be fine.

gbgastowers

I think rings are only about $35 which isn't the issue. I guess I was just thinking why disturb them if they might be good but it looks like there is no way to tell at this point. Gunar

Kiln_Red

Interesting situation to be in. I would feel encouraged, in your position, seeing as you have two engines that should both be reusable. Do you have pictures of the head gaskets from the "new" engine? What did they look like? Was there water in the oil?

If I were in your shoes, I would probably favor going the route of getting the replacement engine in now since it's the closest to being complete. Since the other engine needs more work and money, this will allow you all of the time in the world to get it right. That's the way I look at it. It's important to source the compression leak with the replacement first though. If you have some feeler gauges and a good straight edge handy, check the mating surface of the cylinder heads for warping.

Everyone has their own opinion about re-ringing our engines. I wouldn't do it if I were you. Our engines our made of an Alusil casting as I'm sure you're aware through your research of the services the good folks at 928 Motorsports perform. Re-ringing one of these is sort of a controversial subject among 928 owners. I'm sure you'll get a lot of responses on that matter momentarily, so I'll pass on the opportunity to dive into the subject myself.

I would go ahead and do the rod bearings, if I were you, while I had the engine out. Why not? It's a pretty straightforward preventive maintenance practice. And what better time to do it then with the engine already out? I wouldn't split the block and do the mains though. That's a different ball game. Quite a bit of work. Even with the engine out of the car. Do that on the original engine when you get it back with it's nice, new cylinder walls.

Ultimately, focus on repairing the original engine if the funds permit. That would be the approach I would take. Do as little work necessary on the replacement to get it in and get it running. Then, when the other is rebuilt and ready to re-install, pull it out and set it aside. Think of it as a "just in case", or, sell it.

James Bailey

You were TOLD that it had low compression which may or may not be true. However not knowing if it was overheated or if the low compression was due to rings you really need to ring it BUT do not use a hone on the cylinder walls !! Buy the gasket set and do all the seals, get the heads surfaced grind the valves. Then put it together and run it. Be very careful when installing the pistons or you will break rings and score the cylinders in the process.

dcrasta

New Rings, Seals, Bearings, gaskets..

You are saving already by not having to re-nikisil the block (if the bore checks out.).

LIke the others have said, you are in there 90 yards might as well go the last 10 yards and build a motor that will last another 100-200k miles. Besides, once you pull the pistons (to check the rings) you need to check the bore and then you might as well get your machine shop to recondition your heads, clean up your pistons and fit you with rings..

Jim M.

How many miles were on the replacement engine? Which cylinder was low compression? Did you do a compression test before tear down? From the picture of the cylinder head it looks like you may have a bad head gasket on the 2nd cylinder from the left at the 6:00 position. Could that be the source of low compression?

If you didn't do a compression check before hand and don't know which cylinder was low then my recommendation is rings and rod bearings as well as all seals, gaskets and o-rings to go with re-built, resurfaced heads.

mark kibort

why would anyone have you nicasil a old 928 engine??? just curious. thats a monster amount of work and cost. why not just have it honed and put oversized stock 928 pistons back in? Nicasil is tricky and you need to know a LOT about what ring package to use, and even mix and match oil vs compression rings. . That should only be done with a stroker effort in my opinion. But, you are in good shape with the new replacement engine. Just re-ring it, re bearing it, and put it back together. I dont care what anyone says, with the bores in ok looking condition, just put in some mixture of assembly lube and oil to lube the piston skirts and rings for that first start up. re alusiling would not be a bad idea, but it doesnt look too bad from the pics and that would create a ton more work. just pull out the pistons, re-ring and reassemble. be careful!

mk

mark kibort

those pistons are WAY too clean. probably had a bad headgasket leak, which means the rings could have problems too. did someone clean those heads or did they come off that way?

Ad0911

Looking at the studs. some of them (especially top row) appear to have some rust. Bearing in mind the discussion about the studs a couple of months ago on this forum, what is the opinion here? Replace or not?

mark kibort

I would leave them be.