944tger

Okay so this is going to be a bit long. Please excuse me but I feel like a bit of backstory might help and quite frankly I need to vent a bit. If you don't care about the story just read on a bit further down.

TLDR: After a cylinder head rebuild our 944 Turbo does not start. While diagnosing the no start condition the engine locks up and we now have pretty bad damage in cylinder three. Looking for insights on the cause.

-- Backstory start --

We bought our 944 Turbo early 2022. The car was a bit neglected for some time but nothing major, everything seemed fixable with a bit of time and love. The car didn't run perfectly but good enough to drive the few hundred kilometres back home. It's a 1985 944 Turbo, Zermatt-Silver with burgundy interior. First things we did to the car was change the fluids, fix the rough idle by cleaning the MAF, fix the constantly running heater and a few other small things. Next we replaced the cracked dash that had a horrible aftermarket cover on top with a good used black one. We also changed the steering wheel and shifter to black which goes quite well with the burgundy interior. Next step was to reglue the hatch window which was delaminating. At the same time we replaced all the locking hardware for the hatch to make it lock properly again, not leak exhaust into the car and not open randomly white driving. All in all we didn't get to drive it much in 2022 before the season was over but we were looking forward to driving it in 2023.





Early this year we took it to a Porsche mechanic to get the torsion bars in the back adjusted since the car was sitting strangely high in the back. We also got our drive shafts and the links to the differential replaced to fix a clonking noise in the rear. Since the weather was still ****ty here in Germany I decided to do some TLC to the car. Ever since we got it we felt like it was running rich. Symptoms were mostly very smelly exhaust fumes that would leak in to the car making it a pain to drive, black exhaust tip and black marks on the ground after starting. I hooked up my smoke machine and found a few vacuum leaks. I decided to refresh a few vacuum lines in the car together with a few sketchy looking coolant hoses. In the end I replaced all but one vacuum hose (the one from the belt housing to the air box) and all but one coolant hose plus a few miscellaneous things that seemed broken or that broke while trying to remove them.
I was pretty pleased with my self thinking I had done something good for the car and hopefully fixed the rich running. Sadly I made a stupid mistake. Because I could not get the small coolant hose behind the oil filter off the coolant pipe above the exhaust manifold I had loosened the pipe not realising that the screw holding it in place was a screw holding down the camshaft housing. Of course this broke the gasket and we now had oil leaking on the manifold causing smoke in the engine bay. So I bought a gasket kit, took off the camshaft housing, replaced all the gaskets in it and put everything together again. I took it for its first real drive in 2023 which was fun but also showed that the rich running was definitely not fixed yet. Back into the garage I did all the tests I could find online (mostly Clark's Garage and a few other sites) to find any kind of fault that might cause rich running. By now the car had also started to puff pretty black some from the exhaust after starting from time to time. After a few days trying to find something that might be wrong and not finding anything I was inspecting the spark plugs once again and I realised, maybe the engine wasn't running rich after all and actually it was burning oil... I also realised that the spark plug threads had oil on them. Some research showed that this might most likely be caused by worn valve stem seals. I was a bit bummed out but ordered a head gasket kit and once again began dismantling everything I had just put back together... The inside of the engine looked quite good in my opinion, no oil sludge. Everything seemed well taken care of over its life. The head gasket looked like it might have been at the end of its life soon so I was happy to change it out. The head looked a bit sad and crusty so I had it taken care of since I needed to change the stem seals anyways. Here are a few pictures of what the engine looked like:







The pistons showed obvious signs of prior contact with the valves but no valves were bent so I believe it was taken care of at some point in the cars life. The pictures of the pistons were taken after I very very carefully cleaned them. The dark line in the last picture could not be felt at all with the finger so I determined it to be no issue. The machine shop also replaced valve guides on the exhaust valves since they were worn out.

Here is the head after machining:



After getting the head back from the machine shop I reassembled everything. I double and tripple checked everything and made sure the timing marks lined up properly. I turned the engine by hand a few times, always making sure the timing is still where it is supposed to be. Everything seemed fine so far, I was pretty pleased with the work I had done and I was looking forward to driving the car. I had removed the starter to attach a flywheel lock and in the process broke the soldered connector to the starter solenoid. Ordered a new solenoid but for some reason the starter did not seem to work with the new solenoid attached so I also bought a new starter motor which again postponed the finish of this project. This week after coming back from vacation I was eager to finally start the car and get it out of the garage to use the last few nice days to drive the car. Double checked everything and tried to start the car. Car wouldn't start though... Okay again a bit bummed out but I wasn't giving up. I checked everything to find out why there was no spark. DME relay fine, reference and speed sensor fine, distributor cap and rotor fine and brand new, cables fine and brand new, spark plugs fine and brand new... I could not figure it out. I opened a thread here on the forum (https://rennlist.com/forums/924-931-...-no-start.html) and I have yet to find the definitive cause of the problem. I am suspecting the ignition coil which passed resistance tests but doesn't seem to produce any spark when tested directly... To make sure it's the coil and I am not once again spending money on parts I made sure to rule out any other cause. I used Clark's guides in diagnosing a no start condition and ruling out caused one by one. This brings me to the big mess we are in now...

-- Backstory end --

I trying to find the reason for a no start condition after a head gasket replacement which is mostly caused by no spark. At this point I had tried to start the car around I would guess round about 15 times while trying to find the cause for the no start. I never cranked for more than 2-3 seconds at a time in order not to over stress anything. While I was measuring some voltage at the DME connector while cranking the car the cranking suddenly stopped. Sounded like an almost dead battery and weak starter motor. I had just charged the battery so it was a bit strange but I checked the battery anyways... 12.5V... at this moment a bad feeling started in my gut. I don't know why but I felt something was wrong. I didn't try cracking again and instead went under the car and tried to turn it over by hand. Nothing. Hard as a rock. At this moment the bad feeling turns into panic. Maybe the starter got stuck? Removed the starter... seemed fine... turn it by had again... nothing. Still hard as a rock. By now I am panicking big time. Did I f*** something up? Was the timing wrong after all? Did the belt slip? I drove to the hardware store to pick up a endoscope camera. Back at the garage I removed the plugs to look in the cylinders and check the valves. I couldn't see any valves touching a piston. But then I looked down at the piston in cylinder three. Something seemed wrong. Very very wrong. I was in complete shock and disbelief at this point. Had to take a moment to calm down and decide that there is no way other than disabling everything that I had just put together again(!) and see what was really going on in cylinder three. By now it took me maybe 1/4 of the time it took me the first time to disable everything. I took off the head and man it looked bad... here are some pictures:





So here we are now. Having spend a few thousand € in parts, many many hours of work, never really enjoyed the car since owning the car and having a very broken engine. I am trying not to be too bummed out despite looking at a probably a few more thousand € to fix this mess. At the moment I most interested in understanding what happened and what caused this engine failure? Did I mess up somehow? What do I need to check and rule out as a cause so this won't happen again when we fix the engine and put everything back together again?

Here are a few more observations I made while disassembling. The pistons were all pretty wet from fuel. There was a decent amount of fuel on top of the valves. This pictures shows the fuel on top of the three closed valves at the moment of head removal. Does this seem like too much fuel? Injector leaking maybe?




I am really lacking the knowledge to understand what has happened here. I would say a broken piston might be the most likely cause? But why in this moment? Just bad luck again? Oil was changed after reassembling the head. Cylinders looked fine before reassembly. Timing was double and tripple checked and engine turned over fine by hand.

The second question I have is, can this be repaired? The scratching of the cylinder wall looks very deep. I looked into over size pistons already but I know there is a maximum size you can go. At this point a refurbished block seems to be the most sensible option but I would like some input on this.


Working on cars has really become a passion of mine in the last two years. I learned a ton working on the 944. But this was a really humbling experience. I am trying to stay positive and see it as a learning opportunity but I really have to fight the frustration this is causing.
I am really hoping on some input from you guys to find out what happed to my car and how to progress from here on. Thanks in advance!

harveyf

Wow! I'm sure you are gutted. Just keep in mind almost everything can be resolved.
Based on your excellent writeup, I assume that you never had the pistons out?
It would appear that either a ring got twisted up (but I don't see that happening out of the blue) or you got a piece of debris in there that caused the damage. Just a big guess but the turbos have a ceramic coating on the exhuast manifold ports in the cylinder heads. It tends to break up on older engines. Being ceramic, if it broke up and if it fell back to the top of the valve and then if it fell into the cylinder, then it could be a mighty chisel so to speak. That is a lot of ifs. I think you are almost certainly looking at getting at least that one cylinder sleeved. That will be a big research project for you but frankly any machine shop that has worked on Japanese high performance engines can probably get you going.
You never mentioned replacing the timing belt but I assume you did? And it is intact? Now is a good time to replace the rod and main bearings.
The car is worth saving!!!

BTW, from an oiling standpoint, multiple cranking attempts on the starter is IMHO not abusive or what might have caused this damage. As soon as your oil pressure light goes out and the gauge shows pressure, you are oiling the engine. About the only thing missing is splash oil on the bottom of the pistons. But thousands of us have spent time cranking 944 engines that don't want to start and it does not seem to result in mechanical damage like this.

This will get you started. Article 1 of 5.
https://newhillgarage.com/2018/04/27...ebuild-part-1/

944tger

Thanks for your reply. Yes you are right, we did not take the pistons out. I was thinking about it since the burning of oil might have been caused by bad rings but in the end the wet spark plugs let be to believe that it comes from the valve stem seals and not the rings. Also it just seemed to be too much work at the time. Looking back that might have been a mistake, who knows...

Interesting statement about the ceramic coating. Where exactly can I find it to check if there are signs of breaking down?

944tger

We did not change the belt. It was done by the previous owner in 2020 and driven less then 1000km since then. All writing still visible, seems to be in perfect shape so we saw no need to do it again.

harveyf

See this thread.

https://rennlist.com/forums/944-turb...orts-help.html

944tger

interesting. I will check mine next time I am in the garage.

harveyf

The ceramic was added to push heat down the exhaust at startup and "fire" the cats sooner, as required to meet emissions requirements. It is my opinion that turbo heads should be swapped for N/A heads, moving the turbo valves over the to the N/A heads. This eleminates the possability of the ceramic flaking off and destroying your turbo.

944tger

Do all turbos have it, even ones without kat?

harveyf

I guess I don't know.

walfreyydo

Unfortunately its hard to say what the cause of the issue was, since you only had the head off and didnt do any bottom end work, to me it seems like a piece of debris made it into the combustion chamber - whether thats a piece of ceramic from the head or something else we cannot be sure. Anytime you tear into an engine, cleanliness is extremely extremely important.

Your only course of action at this point is either sleeve (iron or steel) with compatible new pistons, or bore it (by a reputable shop that knows how to bore and hone alusil) and fit oversize coated pistons. These blocks being alusil cant just be bored and honed in the traditional manner by any machine shop - it requires special equipment and knowledge. If you are in the UK I would contact Hartech Porsche

944tger

Hi! Thanks for your reply! I am also thinking about debris that might have made its way in there. I was thinking if maybe the machine shop didn't clean the head properly after machining and some kind of shavings were left in the head somewhere? I blew it out and vacuumed as best as I could before the reinstall... I don't know what else I could have done. I was also thinking about if me cleaning the tops of the pistons might have caused something to get in there. But on the other hand I made sure to be extremely careful. I read and watched a few videos on what to do and in the end I put the piston all the way to the top, put some grease of over the gap between piston and cylinder wall and very carefully cleaned it with some scotch bright making sure not to go all the way to the edge. Finished everything with a clean cloth to wipe away the dirt and grease...

Concerning the repair, does anyone have recent experiences with the cost? I also heard from a few people that the scratches might be to deep and sleeves are the only way to go...

Braymond

Hello 944tger. Sorry to hear about your engine damage. I recently had my 944 block reconditioned by Millennium in Wisconsin, USA. I think it cost about $1200US. They bore and correct oval, then Nicasil the block, then re-bore/hone to spec. The Nicasil process can also repair some light scoring damage. I think there was a bit of an upcharge too for over-size. This is a good alternative to sleeves and allows for more piston/ring options than staying with Alusil. I had someone remove all the steel studs before shipping to Millennium.

I second walfreyddo's recommendation to consult with a reputable shop first. Preferably a shop that has some experience with rebuilding these engines. Seems like you should be able to find someone in your area that is familiar with the Porsche brand

Good luck!

-Bill

944tger

Hi Bill,

Thanks for your reply. Nicasil instead of Alusil sounds interesting I'll look into it. I am trying to find a shop at the moment. It's true that I live in the right country but still sometimes it's not easy to find a shop you feel like you can trust and that offers reasonable prices at the same time. Especially in the Porsche world.

I have found someone who has an already rebored and honed (Alusil) block with the matching oversized pistons. This shop could also install the rest of the engine parts like the crankshaft (which I would prefer as I have no done this and might be lacking the equipment and skill). The refurbished block + pistons is around 2500$ The pistons alone are around 850$ so I have to check how much the machine work would be to compare the prices (if the block is saveable, 1mm is the maximum over size if I understand correctly).

walfreyydo

Yes oversize pistons usually go in 0.5mm increments

T&T Racing

This is my take about blocks and cylinder wall scoring.
You have a block that you know has issues but purchasing another used block has unknowns and could present more issues.

There are several matching items that a block must meet, the girdle matches the block, the lower and upper balance shaft coverings must be matched. You know that your block has these items matched.

Your block can be Nickasil or sleeved with iron or steel inserts. Each requires the proper piston material, in the case of Nickasil, the piston skirts are coated to be compatible with Nikasil. It the sleeves are steel or cast iron, then the piston has to be compatible for that medium.

The 944/951 engine is an interference engine meaning the valves can contact the piston top surface. The photos confirm that interference. The cylinder head can be shaved several times to where the normal gasket thickness is not not sufficient to prevent valve interference.

The engine with the cylinder head is blue printed by a engine shop to determine if one orders special pistons with the pin set to eliminate the interference or install a thicker head gasket, Cometic multiple steel layers has many optional and there is a over thick standard cylinder head gasket. What CR is your goal

​​​​​The bottom line the current engine has two issues, a scored #3 cylinder and a valve to piston head interference in all cylinders.

​​​​If there is oil coating on the spark plugs, besides the valve guide leakage, leaking AOS seals will cause oil entrained vapor to enter the engine at the J Boot. Examine the J Boot for internal oil coating.

Good luck on your decisions.