Yep, your symptoms actually sound identical to my current situation. Honestly, if it weren't for the cloud on startup after the coolant system pressure test, that also was a slower and rougher start, and then the 2nd cloud a few days later, the car has run fine and I wouldn't even know I had a problem.

Rather than a full motor replacement, how about a just a set of Euro S heads? That would give you bigger valves, but allow you to use most of your setup as is.

Having done it both ways, I really recommend pulling the motor, even to replace a head or a cam carrier gasket. It is just not that hard of a pull, the overall work is less, and the quality of the end job is better.

karl,

That's a great idea and I came to a similar conclusion earlier today. I have a pair of Euro heads from an M28/11 motor on hold that I will purchase if I have to remove mine to replace the head gaskets. I'll have them gone through and refurbished if they're pitted, then have a 3-angle valve-job and head restoration performed, then reinstall those on my motor. As you say, that will improve the breathing, and probably even more so with the supercharger. I'm probably going to add the rest of the Euro intake pieces as well - intake distributor (already have the legs), Flap Nozzle / throttle body to realize the full benefit and may renew the injectors while I'm doing all of that. This should be much easier than the motor swap, considering how packed the front of my engine bay is with the custom intake, radiator, and supercharger setup, and I don't have a lot of other while you're in there stuff to do since motor mounts are pretty new.

We'll see what tonight's spark plug pulls reveal. Ideally, there's not much coolant sitting in the cylinders as I'd like to be able to start the car one more time to put it on the lift and swap it with the 914 while I wait on parts, if that's the direction I go.

Advice I'm getting on whether to pull the motor for this job or to do it with the engine in the car, since it's a 16v seems fairly evenly split, so I've added a poll to the thread so I can see how wide the overall distribution is. At this point I'm leaning toward doing it with the motor in the car, but the poll may sway my decision, and if I'm pulling the motor, that may change what I decide to do about repair or replace.

If the Euro heads you have lined up don't work out I have a spare set somewhere in LA. Bought them many years ago just because and have never even unpacked them.

Pete--

I voted to pull the motor for the headgaskets. Even though you added the unrealistic qualifier that this is the only thing you will do. There's No Such Thing as "just replacing the headgaskets" on a 16V motor. For all the things including the heads and such, engine in the stand is just so much easier than engine in the car. There have been more than a few "engine pull parties" that let the starving masses help out; supply pizza and suds after it's out, and two problems are easily solved at once.

--

Having larger Euro valves or intake runners is almost inconsequential with the supercharger. The limitations on the SC car are related to cylinder pressures & temperatures, and subsequent detonation. If the runners or valves are a little smaller, the boost pressure is raised with a pulley change to make up for it.

+1. Visual in the cylinder is best if the plugs are not already wet.

I voted the way we would do the job, in my shop, if I thought the engine was fine and I just had to remove the heads. (Like the survey said.) No question, leave the engine in the car, in that situation.

This engine, which got really damn hot, would come out of the car.....again, no question.
If the pistons and bores are not scuffed, it's because they are completely worn out.

Very true.

After plug removal, the news looks to be as expected. #6 has coolant in the cylinder, probably #7 too and #2 and #3 are questionable too. Here are the photos so you can see for yourself and advise. Captions are below each photo


https://cimg4.ibsrv.net/gimg/rennlis...ec490ccc7d.jpg
All Plugs



https://cimg7.ibsrv.net/gimg/rennlis...e3e93b27e0.jpg
1-4



https://cimg4.ibsrv.net/gimg/rennlis...b1d38cc2dc.jpg
5-8



https://cimg3.ibsrv.net/gimg/rennlis...c9339afbc7.jpg
1-2



https://cimg9.ibsrv.net/gimg/rennlis...626b483b2f.jpg
3-4



https://cimg1.ibsrv.net/gimg/rennlis...b2b167ab59.jpg
5-6



https://cimg6.ibsrv.net/gimg/rennlis...71d1712f95.jpg
7-8




And here are the boroscope results. Plugs did not actually seem especially tight which is probably why even outside the motor and on the base of some of the plugs, you can see the burned coolant remnants. Photos are captions with the cylinder # and then a letter for each photo in that cylinder

https://cimg1.ibsrv.net/gimg/rennlis...c74d66a546.jpg
1A



https://cimg2.ibsrv.net/gimg/rennlis...7128dd64f8.jpg
1B



https://cimg3.ibsrv.net/gimg/rennlis...52d230ae64.jpg
2A



https://cimg5.ibsrv.net/gimg/rennlis...8b41bfe545.jpg
2B



https://cimg6.ibsrv.net/gimg/rennlis...e18a71db48.jpg
2C



https://cimg7.ibsrv.net/gimg/rennlis...a2aca0b927.jpg
3 - this one was do close to top of the stroke this was the only shot I could get



https://cimg0.ibsrv.net/gimg/rennlis...68a95da2a7.jpg
4A



https://cimg3.ibsrv.net/gimg/rennlis...8c8feab2db.jpg
4B



https://cimg4.ibsrv.net/gimg/rennlis...4403cb40f5.jpg
5A



https://cimg6.ibsrv.net/gimg/rennlis...ba0c1dd50a.jpg
5B



https://cimg8.ibsrv.net/gimg/rennlis...b79610c61e.jpg
5C



https://cimg9.ibsrv.net/gimg/rennlis...5cd2a32ffc.jpg
6A



https://cimg1.ibsrv.net/gimg/rennlis...64e962a5cb.jpg
6B



https://cimg3.ibsrv.net/gimg/rennlis...c872d98f2b.jpg
6C



https://cimg4.ibsrv.net/gimg/rennlis...6cfb21559d.jpg
7A



https://cimg6.ibsrv.net/gimg/rennlis...326b2ef651.jpg
7B



https://cimg7.ibsrv.net/gimg/rennlis...9585567c77.jpg
7C



https://cimg8.ibsrv.net/gimg/rennlis...a3cdc6bc1e.jpg
8A



https://cimg0.ibsrv.net/gimg/rennlis...2fa35e8e79.jpg
8B


Based on these findings are we concerned about the rest of the health of the motor where the safer bet is to replace what was a solid motor that ran well with a rock-steady idle with a complete different engine? I don't want to go to the trouble of doing the heads only to fire it back up and find out the bearings, crank or something else are actually bad. I have driven it twice since the first coolant cloud and it seemed to run fine.

Next question - it's on the floor under my lift with the 914 above it. Looks like it's not going anywhere for a while. If I leave all the plugs out and loosen the coolant reservoir cap so it can't build pressure, can I turn it over to push any coolant out the plug holes, reinstall the plugs and then run it for 5 minutes in order to be able to swap these 2 cars around or am I going to have to do that by pushing it?

All advice welcome and appreciated. Thanks.

Awesome thread and documentation! Sorry I could not participate today (Mom suddenly in hospital).

Again much appreciation to everyone for sharing their thoughts and insight. It will be fun to see what Pete does with this engine given it resides in such a unique and special car. :cheers:

Enjoy!

Sure, why not, it's not like the cylinders are full of water. You're head gaskets are leaking, they haven't failed completely. That's just my opinion, it's a gamble but at this point it's reasonable.

So, the outside of the spark plugs had water/coolant sitting around them....that's the corrosion on the metal. Note that this stain on the spark plugs is not coolant from the inside of the engine!

Is the coolant sitting on the top of the pistons from the inside of the engine, or did that run down the spark plug hole when you took the spark plugs out?

Crank the engine over, with the spark plugs out....several revolutions to "clear" out all the coolant that is currently in the engine.

With your bore scope, confirm all the coolant is gone.

Install the pressure tester and pump it up and let it leak down a few times. Recheck with the bore scope. If the coolant comes back, it's from the inside, not from the outside of the spark plugs.

BTW....those bores look pretty good, from what I can tell from your pictures.

I'm thinking remove the heads, from what I see in those pictures.


And yes, if you crank the engine over with the spark plugs out (blowing out the coolant from inside the cylinders), you can then install the spark plugs and start the engine to move things around. (No pressure on the cooling system, from your tester, but you can leave the tester on the tank.) Just don't shut it off, if it builds pressure in the cooling system....that will push coolant back into the cylinders.

Greg, thanks for your continued input. Yes, I've never personally changed the plugs in this motor - was actually going to do that as part of the prep work for the upcoming 928 events (Mitty, SITM, PEC), but they were all pretty loose, like tensioned, but maybe 5-7 ft. lbs by feel so some of that coolant had made it's way out of the spark plug holes and corroded the metal on the outside of the plug itself. I put towels over both sides of the plug holes and cranked the motor over a few times - nothing came shooting out into the towels and it spun over just fine (sounds funny though with no compression - don't think I've ever done that in any motor before, almost like it's not even spinning).

I'm glad to hear your input on the condition of the bores. This motor seemed very good other than a few oil leaks - nice steady idle, smooth, etc and this project will be much more affordable if I only work it from the head perspective and not the complete motor replacement one if you think my odds are good to salvage what I have without tearing it apart. For a motor oil I run Driven DT50 synthetic which according to Lake Speed at Driven will support temperatures of up to 350 degrees for short periods, so maybe that was a contributor to not having more damage and the car seeming to run fine both during the event and now afterwards.

Sounds like you think I can start it and move it onto the lift once the cylinders are free of coolant while I figure out the best way to go.

Right now, I have a few options:

1. a fully rebuilt M28/10 motor that would be bolt in ready, but is really way beyond my budget (thousands) so not really an option
2. A pair of Euro heads from an M28/11 I could get for reasonable money, hen have renovated and a valve job done to them, install with new gaskets. I keep all my existing intake parts
3. A different pair of Euro heads (don't know specific year yet) I could get for reasonable money, then have renovated and a valve job done to them, install with new gaskets.
4. an 4.7 M28/19 complete built engine. One head mounting hole has been welded at a bolt hole, but tested. I either keep all my existing intake parts or also buy the L-Jet parts that were part of this same motor, but my K-Jet setup seems to be working so well, I'm afraid to go the electronic injection route.
5. an 85/86 M28/43 5.0L block with M28/15 16v heads - a hybrid engine build. Pistons had the extra notching done to work with the 16v head

Which of these options seem good and which are not as good?

Sad news, Pete. I hope you can get it fixed soon.
Good luck,
Dave