When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Here’s some cylinder wall measurements I took from the blocks I have you all my find interesting.
89 2.7L 104mm block 8.50mm
87 turbo block 8.75mm
86 NA block 8.50mm
88 NA block 8.75mm
85.5 NA block 8.50mm
87S block 8.75mm
No. But I would think they are 8.50mm thick. I was surprised that the 2.7L 104mm block measured at 8.50mm. Maybe the 968 blocks have a thicker 8.75mm cylinder wall? Can anyone confirm the 968 cylinder wall thicknesses?
I have heard rumors that the early na blocks have 1mm thinner cylinder walls and that the water jacket is deeper and that makes poorer cylinder stability.
I have heard rumors that the early na blocks have 1mm thinner cylinder walls and that the water jacket is deeper and that makes poorer cylinder stability.
Yes, I think the block that I measured is from an early '85 NA car. I don't remember the exact thickness, but it was 1MM thinner than the 951 block I have sitting around the shop. I can check it again soon.
I'm sure Lart has something for the original poster that will work well.
double check your wall thickness" measurements at multiple spots around the circumference - 928 blocks have a real problem with "core shift" where the barrels aren't exactly centered over the crank journals (but the machined bore is)...this is limiting for those wanting to overbore.
you might have 8.75mm on one side but on the other side 7.5...
The cylinder wall thickness seemed pretty consistent. Maybe +-.05mm. But the later 2.5L blocks have the thicker cylinder walls. And as far as I know all the 2.5L blocks have the same coolant depth around the cylinder bores. It’s the 104mm blocks that have a shorter coolant jacket around the cylinder bores, they also have connecting cylinder barrels for stability and windage ports between cylinder 1/2 and 3/4.
Thought I'd post a quick update and get some thoughts on my options. I was able to buy a complete long block from a 1987 turbo from another rennlister and finally got around to tearing it down last week. Overall, it's in much better condition that mine but I found some scoring in the #2 and #3 cylinder bores. It's not deep, but one of the lines does catch a fingernail. I've been researching and weighing my options which, from lowest cost to highest, appear to be:
1. Disregard the scoring on the new block, slap on new rings and go.
2. Have the pitting on the #3 cylinder repaired/welded and use my original block which has perfect bores and only mild corrosion on the other cylinders.
3. Find another block
4. Find a shop that can hone the bores on the new block to 100.5mm and throw in a set of Wossner pistons.
5. Sleeve the new block and find new pistons.
#1 scares me, but other rennlisters say they have done it without problems.
#2 I'm leaning towards this option as the cost should be low and I wouldn't worry about compression loss like in #1, but will the repair hold?
#3 Sigh.
#4 After calling and visiting several machine shops and Porsche mechanics, I can't find a shop near me (Ventura County, CA) who will hone alusil and have no idea of the cost which seems like it shouldn't be much for that type of work. I'm guessing $500 for the machine work and $700 for the pistons.
#5 TBH, the cost of this one makes this not an option. Maybe if it was a track only car.
No way I'd run that block as is. If it was super rare, maybe you could sleeve it or otherwise have it repaired (welded and re-bored?), but good serviceable blocks are plentiful and cheap, so I'd just find a new one. Same with the head most likely. Those parts are relatively cheap compared to the overall cost of building up an entire motor.
Thought I'd post a quick update and get some thoughts on my options. I was able to buy a complete long block from a 1987 turbo from another rennlister and finally got around to tearing it down last week. Overall, it's in much better condition that mine but I found some scoring in the #2 and #3 cylinder bores. It's not deep, but one of the lines does catch a fingernail. I've been researching and weighing my options which, from lowest cost to highest, appear to be:
1. Disregard the scoring on the new block, slap on new rings and go.
2. Have the pitting on the #3 cylinder repaired/welded and use my original block which has perfect bores and only mild corrosion on the other cylinders.
3. Find another block
4. Find a shop that can hone the bores on the new block to 100.5mm and throw in a set of Wossner pistons.
5. Sleeve the new block and find new pistons.
#1 scares me, but other rennlisters say they have done it without problems.
#2 I'm leaning towards this option as the cost should be low and I wouldn't worry about compression loss like in #1, but will the repair hold?
#3 Sigh.
#4 After calling and visiting several machine shops and Porsche mechanics, I can't find a shop near me (Ventura County, CA) who will hone alusil and have no idea of the cost which seems like it shouldn't be much for that type of work. I'm guessing $500 for the machine work and $700 for the pistons.
#5 TBH, the cost of this one makes this not an option. Maybe if it was a track only car.
If it were me, I'd either (a) rebuild the new block by having the cylinders machined for new pistons/rings, polishing the crank, all new bearings and seals, valve job, etc. or (b) find a decent lower mile motor that is running and run it without removing the pistons/rings, etc. You can get away with some scoring, but once you disassemble an old motor like that you introduce new risks, and --to me-- it feels like false economy not to bring it back to spec given all the time, money and effort needed to get it running in a car again anyway.
Thanks Tom. Ya. I'm trying to find a shop to perform the machine work and haven't had much luck. A lot of the shops mentioned on RL no longer machine 944s. Presumably because the value of the air cooled 911s have gone up so much that that's where the money is at right now.
I took my original block to a welder to see about repairing the pitting on #3 and he said the heat would cause the cylinder to distort. So, I reached out to Santa Ana Engine (thanks V2) and they can do the bore/hone to 100.5mm. They need the the matching pistons so I ordered a set of Wossners. As soon as they come in I'll make the trek down to drop it off. Looks my original block is only good for sleeves at this point.
09-25-2018, 11:56 AM
