So, cylinder no.1 got flooded by a bad injector which got stuck open and washed away the oil, leading to the bore scoring/extreme piston wear.
Could I have caught it quickly and stopped it before it got this bad? Maybe I could have, if I had checked my plugs and done a bore scope right after the first start up. That was one bit of advice from Tom Barker that I didn't follow the first time. He suggested that buying a decent bore scope and checking right away was more than worth it.
My engine did start and run well right away, and I was concentrated on my AFR gauge and tuning tables at first, so I neglected that bit of due diligence. By the time I did my first oil change, it was too late. That first change was already a bright aluminium glitter bomb.
If I had pulled my plugs after the first start I would have found one extremely fouled out of the four, which is what I found subsequently...
Following Tom's advice, I dropped the idea of going to more "modern" injectors as his experience was that EV6/EV14 injectors work great on turbos, but on NA 944's, the original needle/pintle EV1's work best.
I got a set of reconditioned original injectors, but looking at the build sheet, one of the injectors started and finished the rebuild/cleaning process with only a "Fair" spray pattern (Good/Fair/Poor possibilities on the build sheet). That doesn't necessarily mean that was the injector that got stuck. Anything could have happened, some dirt could have gotten in during the installation etc. so i'm not going to blame anyone besides bad luck and my own possible screw-ups, but on the second build I went with new EV6 type 4-hole plate high impedence injectors that I got from 928-944parts.com which need different settings but are working very well so far.
Rebuilding my 924S
Absolutely! Well seen! That was gonna be the subject of my next post about the amazing engine shop I found that bored my block all wrong! Since you spotted that and lunch isn't on the table, yet, I'll explain quickly.barnwerks wrote: Sat Aug 15, 2026 3:50 am Were the cylinder bores reconditioned during the first rebuild? In the photo of the damaged bore, there is, what appears to be, a crosshatch pattern in the un-damaged portions of the bore.
First of all, this was my first attempt at rebuilding an alusil block, and although i'd read the factory manual, I'd never seen how a properly finished re-bore should look like. When I measured my disassembled block, I found it was quite oval and tapered, but a 0.5mm overbore should do the trick. I thought I could find a shop easily, especially in the area where I've been working on the car, which is filled with old industrial zones, but to my surprise, nothing, nada, zilch!
Consulting different experts and fora, I found the consensus was forget about getting it bored, get it sleeved! Here in France, everyone seems to send their alusil/lokasil blocks to a place in Lyon to get sleeved, and over in England, Tom Barker was telling me a re-bore is just a recipe for failure.
Then I stumbled on a shop in the outskirts of Paris that blew my mind. They do everything from Bugatti straight 8's to Jaguar 6's to GM big blocks...I got to know the owner and he won my full confidence. He reassured me that they had done dozens of 944 blocks through the years, and had no problems.
When I picked up the block, I saw the bores had a nice rough cross-hatch, like what I'd expect to find on an iron block...since I had never personally seen what a properly treated alusil re-bore looked like, I thought this must be normal...this is why I didn't immediately pull out the motor and tear it down right after the first glitter bomb oil change...
I've since done a deep dive into hypereutectic aluminium technology, and I know now that my re-bore was doomed to failure. here's a look at all four pistons:
You can see that the other 3 cylinders were wearing way too fast.
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So my first re-build attempt fell victim to a number of "moose moves" on my part that I hope by sharing them I might help someone avoid if he's crazy enough to take on a project like this.
No.1: I didn't fully study the re-bore technique for an alusil block and I trusted my machinist blindly. For the 2nd build I started with a new block which in the end didn't cost much more than having my old block sleeved. The new block made it abundantly clear what a fresh bore is supposed to look like, a smooth matte grey, NOT a rough cross-hatch!
No.2: I didn't pull my plugs and do a bore-scope right after the first start.
No.3: For the 1st build I decided to use Evans waterless coolant from the first start-up, and I didn't pressure test my old oil cooler element before installing it. I got a coolant/oil mix right away, but it took me a little while to figure out what was going on since the Evans is quite oily by nature. I'm using distilled water in my 2nd build, and a new oil cooler element. I think I'll stick to normal anti-freeze when I change it in a few weeks.
No.4: I was having trouble installing the 2nd circlip on my Wössner pistons. Every time I thought I'd gotten the 2nd one in correctly, I'd still be able to push the wrist pin out by hand, so I tapped on them with a socket to get them to seat. One of my pistons actually failed at the circlip land! On the 2nd build I popped the wrist pins in the freezer the night before and assembly went easily.
No.1: I didn't fully study the re-bore technique for an alusil block and I trusted my machinist blindly. For the 2nd build I started with a new block which in the end didn't cost much more than having my old block sleeved. The new block made it abundantly clear what a fresh bore is supposed to look like, a smooth matte grey, NOT a rough cross-hatch!
No.2: I didn't pull my plugs and do a bore-scope right after the first start.
No.3: For the 1st build I decided to use Evans waterless coolant from the first start-up, and I didn't pressure test my old oil cooler element before installing it. I got a coolant/oil mix right away, but it took me a little while to figure out what was going on since the Evans is quite oily by nature. I'm using distilled water in my 2nd build, and a new oil cooler element. I think I'll stick to normal anti-freeze when I change it in a few weeks.
No.4: I was having trouble installing the 2nd circlip on my Wössner pistons. Every time I thought I'd gotten the 2nd one in correctly, I'd still be able to push the wrist pin out by hand, so I tapped on them with a socket to get them to seat. One of my pistons actually failed at the circlip land! On the 2nd build I popped the wrist pins in the freezer the night before and assembly went easily.
Two other things I did differently the 2nd time:
I used a tapered one piece ring compressor. The first time I used a ratchet strap type, like I used when I was a kid and Installation was a bear. I managed to break an oil ring and had to re-order rings from Wössner. The second time piston installation was a breeze.
I did a deep dive into assembly lubes and used three different types the second time. First time I just used the usual Permatex red stuff everywhere. Second time, I used that for bearings, but I used a thicker Liqui-Moly MoS2 paste for the valve followers and oil pump, and Driven assembly oil for the piston rings and skirts. No idea if that was really necessary, but since I became paranoid about failure this time around, I figured it couldn't hurt...
I used a tapered one piece ring compressor. The first time I used a ratchet strap type, like I used when I was a kid and Installation was a bear. I managed to break an oil ring and had to re-order rings from Wössner. The second time piston installation was a breeze.
I did a deep dive into assembly lubes and used three different types the second time. First time I just used the usual Permatex red stuff everywhere. Second time, I used that for bearings, but I used a thicker Liqui-Moly MoS2 paste for the valve followers and oil pump, and Driven assembly oil for the piston rings and skirts. No idea if that was really necessary, but since I became paranoid about failure this time around, I figured it couldn't hurt...
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Tom provides his own software to control the ECU, make modifications and record logs. He also provides his own autotune software that takes a log, an ECU map, and will analyze it vs. the target AFR map and generate a new ECU map. The software connects to the ECU via bluetooth and It's all been easy to learn and use for a newbie like myself.
A few weeks ago, I did run into a hot idle issue, as the car was cutting out both while being stuck in traffic jams and after a long highway run, but after finding my super cheap new after market crank/position sensors had failed, a pair of new OEM Bosch sensors have been working perfectly, and have kept the car running fine while I keep on trying to get the idle adjusted "just right."
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