Another 944 Turbo Engine Rebuild Thread

[dlknight]

More stuff!

Whilst I was waiting for other parts I got on with some other jobs on the car. Replaced the aircon O-rings at the bulkhead (again, this time with proper Porsche ones as I was worried the others might leak). I also fitted some rivnuts to attach the brake booster heat shield back securely. I followed this up by reinstalling the front bumper reinforcement with the powder coated brackets and new towing eye mount.







Interesting fact the threaded studs for the timing belt tensioner are identical to the exhaust manifold studs - part number 99906204402

Next interesting fact, make sure you remove the cylinder head oil check valve before sending your head for machining! My fault entirely, I wasn't sure how to remove it as the workshop manual is a bit vague and includes some instructions for updating older cylinder heads with the updated check valve from later models. It was easy to remove, the small M6 bolt in the side of the head is all that holds it in. Then a small knock with a punch and it dropped out. Unfortunately, these check valves are sealed and there is no way of servicing them. The one that came out of my replacement cylinder head appeared to be full of vapour blasting material, I cleaned it out with lots of brake cleaner but wasn't happy about reusing it (and didn't want to pay the Porsche premium tax of £470!!!). I removed the check valve from my original cylinder head which was in great condition (just a little oily). You can test them by blowing compressed air into the bottom and it should push the ball bearing inside the valve up. Replaced the o-ring on the outside and reinstalled into the head after cleaning out the oil channel. I believe this check-valve is to stop the head and valve train draining of oil when the engine isn't running (an attempt to keep the hydraulic tappets full of oil?).





Parts arrived from Porsche and I finally installed the lower compensating shaft bearing cover! I also had a helper in the garage, but she just wanted to sleep in the sun!



Finally I washed the cam tower housing and then reinstalled the camshaft, need to get the rear cover cerakoted to match the finish! (completely forgot about that). Not much more I can do at the moment until the head gasket arrives!

 

[scam75]

Fantastic work as ever! I admire your attention to detail.

 

[dlknight]

Looks like I may have made an error with the piston orientation, luckily a good samaritan on the rennlist forum noticed and let me know. There was nothing in the instructions they supplied with the pistons, so I assumed they arrow pointed towards the front of the engine (this is how they show the piston ring orientation). However, I searched their website and found a Porsche instruction PDF (for air-cooled Porsche) that says if there is a laser etched arrow on the piston it should point towards the flywheel.



So now I have to remove the oil sump / pan and re-orientate the pistons correctly. Gives me something to do I suppose whilst I wait for the head gasket!

 

[scam75]

Well it could have been much worse the further on you got with the build, so a stitch in time and all that! Out of curiosity, what implications would it have caused?

 

[dlknight]

Well it could have been much worse the further on you got with the build, so a stitch in time and all that! Out of curiosity, what implications would it have caused?

The pin bore in the piston is offset very slightly to reduce piston slap in the cylinder. Should hopefully hear back from Mahle Motorsport tomorrow, so can begin removing all the oil sump / pan bolts if they confirm.

 

[blade7]

The arrows point to the front, on a 944 engine.

 

[TTM]

I cannot see the pictures.
Arrows on the pistons should definitely point towards the front of the engine.

 

[dlknight]

The arrows point to the front, on a 944 engine.

Thanks blade - waiting for the Mahle Motorsports engineer to confirm, as if you read the PDF below, it says that it points to the flywheel. The instructions that came with my pistons didn't include that section.

Piston Orientation In Engine
For pistons that have an arrow laser etched on the crown, the pistons are installed so that the arrow points toward the flywheel.
For pistons with slanted dome and symmetric valve pockets, the pistons are installed so that the short end of the dome is located under the spark plug.
Page 6 - https://www.us.mahle.com/media/usa/motorsports/2024-mahle-motorsport-porsche-application-guide-2.pdf

Also in the other document here on Page 3 - https://www.us.mahle.com/media/usa/...d-and-cylinder-assembly-instructions-2020.pdf

The other way to find out is to measure the offset I believe so you can work out the orientation in relation to the rotation of the crankshaft.

 

[TTM]

Looking at the squish area it is not too difficult to tell the orientation anyway but the pictures do not show up.

 

[dlknight]

Mahle have come back and quoted the section from the catalog -

Piston Orientation In Engine
For pistons that have an arrow laser etched on the crown, the pistons are installed so that the arrow points toward the flywheel.
For pistons with slanted dome and symmetric valve pockets, the pistons are installed so that the short end of the dome is located under the spark plug.

2024-mahle-motorsport-porsche-application-guide-2.pdf

Looks like I will be removing the oil pan / sump later and getting started

I will measure the pin offset with my calipers to confirm when reinstalling.

 

[blade7]

A few years back, I was going to buy some of those Mahle powerpak 968 turbo pistons, for a 3.0 turbo Alusil build. Then I read accounts of the coating falling off the pistons, and ruining the alusil cylinders. It seemed that the pistons made in the US weren't the same as the older versions made in Europe.

 

[dlknight]

A few years back, I was going to buy some of those Mahle powerpak 968 turbo pistons, for a 3.0 turbo Alusil build. Then I read accounts of the coating falling off the pistons, and ruining the alusil cylinders. It seemed that the pistons made in the US weren't the same as the older versions made in Europe.

You've already mentioned this a couple of times earlier in the thread, thanks for the heads up but when I searched, I found 2 or 3 references to coating failures. Do you have a detailed list of what was done on each build? you can also find references on the same forum about DIYing your own alusil bores. My point is there could have been multiple reasons for the failures mentioned in those posts.

Another 944 Turbo Engine Rebuild Thread

With the engine on the ground, could you secure the engine crane and use that to lift the front of the shell? Hi John - yes I had seen that mentioned on other forums. In the end I removed the front bumper (the condensor and radiator were already removed) and this provided just enough room...

www.porscheclubgb.com

The person who pointed out my pistons might be orientated incorrectly is running a set with no issue. MAR Motorsport in the Midlands supply several sets a year to 944 owners and have had no problems reported to them.

Am I worried about it, of course, the first start-up is going to be nail biting and terrifying.

 

[blade7]

Wossner were the go to manufacturer when builders had issues with the plastic coating Mahle were using. And then issues started with Wossner too. Maybe Arias are still ok. Or perhaps Mahle/Wossner have secretly sorted out the Alusil issues. I'd use liners if I was building a 944 engine now, you're obviously braver than me.

 

[scam75]

The first start up is definitely a moment of trepidation! When we were trying to build oil pressure, boost pipes were still off and coil lead disconnected, just cranking, and my radiator and turbo water pump both simultaneously erupted with water leaks despite being fine pre-rebuild! A bit of sussing out then an ali rad was ordered and a new turbo water pump (detailed in my thread). This caused a couple of weeks delay waiting on parts and fitting. Intercooler had to come back out and we noticed water coming out of it, rain had somehow got inside it despite the bonnet being closed outside the garage. That would have caused a very large clusterfuck if gone unnoticed!

Then when that was all sorted a puzzling non-start was eventually traced to a rogue connection in the MAF, and just like that, she fired into life! I was in the car on the ramp up in the air while my mate was checking all was good from underneath. That feeling hearing it roar whilst watching the temp gauge slowly rise and heat coming through the blowers, amazing, and makes it all worthwhile. Worth noting the exhaust was not connected past the downpipe at this point, so there was much noise!

Anyway, 10k miles later and all is good. You will be there soon too!

Stuart

 

[blade7]

I'd spin it over without the plugs in a few times to get the oil pressure up. I remember deglazing the bores on a RS2000 replacement engine, and when it started there was a horrible racket for a couple of minutes. Ran sweet after that .

 

[dlknight]

I've been pretty busy but spurred on by pictures of David's quick turnaround I've managed to make some more progress.

Pistons came out and went back in the correct orientation.







Oh, the fun running through the 22 fasteners on the oil pan / sump and the torque procedure

Then I noticed I'd ordered a new water pump stud to replace one that was not as good a state as the others. Unfortunately I'd installed them with Loctite 270 and even though I used heat when removing it I snapped the stud. Lesson learned don't mess with things that aren't broken! After managing to drill out the remains of the stud, I was able to install a helicoil along with the replacement stud!





Cometic head gasket arrived in 2 weeks even though it was a custom size! Excellent service from Performance Unlimited in the UK.



Also another batch of parts from Porsche, including a brand-new oil pressure sender and a Porsche 944 Turbo specifications booklet.



I had a stash of water pump gaskets that I'd come by (I think I was sent a full packet instead of just one, last time I ordered). So decided to use the genuine Porsche instead of Victor Reinz. I took a photo of them side-by-side to compare. The Porsche gasket is made of a much thicker and stout card, but the Victor Reinz gasket is thin and flimsy and possibly synthetic (with a rubbery texture). Porsche gasket on the left, Victor Reinz on the right (of each photo).





I filled some small areas of pitting on the crank case and water pump with a light skim of JB Weld and smoothed it off before installing. I used some Permatex No. 3 gasket maker on both side of the gasket, I had a small weep of coolant previously from this area and hopefully this will ensure it doesn't.



Test fitted the Cometic gasket and head studs so I could make sure the stud height was correct.



Then installed the studs with Loctite 270 and torque the head following the procedure for late cars (20nm, followed by 90 degrees, and then a further 90 degress). I wasn't happy with the initial torque, so checked with a torque wrench set at intervales from 60 - 85Nm and found several nuts were looser than the others. The next morning, I loosened the head using the reverse procedure and then retorqued again with the factory procedure.





Whilst installing the head I found a hole.... hadn't noticed it before but the previous owner had it setup for the steam vent kit, so I've used the list Stuart and David provided to order the required bits.



Bit more progress this week, majority of the belt pulleys and gears are installed, oil filter, and sensors.

 

[scam75]

Great progress, thank goodness you noticed the hole!

 

[dlknight]

More progress over the weekend!

Cam tower got installed along with the steel gasket courtesy of a generous forum member

Used some Permatex no. 3 gasket sealant on the head side as the surface had a few cuts and scrapes.

New oil filter and all the pulleys and gears installed.









Went to install the exhaust manifold studs and found the threads needed some attention, I tried my bolt with a slit cut in to start with, but it needed a tap running through most of them until they would accept a stud.



I've dropped the manifolds off with Matt at MB Engineering for a coat of cerakote, along with the rear camshaft cover.

 

[Eldavo]

Excellent stuff - hopefully the cam gasket gets me some good karma when I start mine.

 

[scam75]

Awesome super shiny stuff! Almost getting to the tickly bit now.......