924Board.org

jl924t · Joined: 03 Nov 2002 Posts: 214 Location: Surrey, BC Canada

CMXXXI Does your block you have a standard bore? 86.45mm
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1980 924 turbo

Lizard · Posted: Tue Oct 21, 2003 10:22 am Post subject:

dont forget he has a 79 euro which has higher cr than the 1980 you have
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3 928s,

jl924t · Joined: 03 Nov 2002 Posts: 214 Location: Surrey, BC Canada

had.
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1980 924 turbo

Lizard · Posted: Tue Oct 21, 2003 12:59 pm Post subject:

what happened if you "had" it
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3 928s,

jl924t · Joined: 03 Nov 2002 Posts: 214 Location: Surrey, BC Canada

I am waiting for the arrival of a replacement for my detonated motor. The block is bored out to 87.5 mm and is coming with flat top forged pistons. Should be here next week sometime. From my origional engine I have 3 good std pistons with 200 km on them I thought CMXXXI could use them. I have 3 almost new and 3 in good condition. I detonated my engine twice within a couple of weeks. Once when I ripped a wastegate diaphram and once when I attempted a poor repair of a stripped thread on my wastegate control line and it did not hold ( my fault). Unfortunately the line seperated from the charge tube and the engine "blowed up real good". I have 2 pistons from #1 cylinder both destroyed in the same location (6:00 oclok). Any body want a $400.00 ash tray. Now if I want to save the origional block I either have to resleeve or bore. I will just stash it under my work bench and maybe do it in the spring to have as a spare.
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1980 924 turbo

924 turbo · Posted: Tue Oct 21, 2003 10:25 pm Post subject:

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

I didn't put a micrometer on it, but the owners manual says the bore is 86.5mm with a stroke of 84.4mm, and as 924 Turbo points out, a 7.5:1 CR. There is a code stamped on the engine block corner/edge on the exhaust side by the #1 cylinder that tells what the factory bore is, I think my code is 601 and I don't recall off-hand where the code is explained, whether in the base model manual or the turbo supplement. I'll dig it up in the next couple of days and post if no one beats me to it.

In the interest of "general knowledge", I thought that I would do as best I could to accurately measure the cylinder by using modeling clay to figure out the volume of the piston dish, and the volume of the cylinder head recess. Using those values and a measured stroke, we should be able to figure out with certainty what the actual motor volume and CR is. There has been some discussion recently about compression ratios, and how the piston shape and head combustion chamber affect the CR. Once repaired, I hope to not have to take off the head for a long time to come.

With that said, I think I will forego rebuilding the block for now. The cylinder walls still show good "cross hatching" and the car only has in the neighborhood of 85K miles on it. I'm toying with the idea of porting/polishing the head (will start another thread on this shortly) when I make repairs, and if/when I replace the replacement head with the repaired original, maybe at that time... There is a lot that can be screwed up when rebuilding an engine, and right now I'm of the mind-set of "if it ain't broke, don't fix it". I'm sure many of you can understand.

I'll be ordering parts today or tomorrow and I'll keep posting updates as work progresses.

Edit -
Here's a link to the engine block honing codes:

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'79 Eurospec 931

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

And the saga continues...

After Performance Products kept changing the delivery date on new piston rings, I called the Deves company to see if I could buy directly from them. They followed up, and lo-and-behold, PerProducts ships them the next day, 2nd day air no less. I wonder how long I would have waited had I not called the company?

This weekend I pulled the remaining three pistons (one badly damaged and removed earlier - related thread here: http://www.924board.org/viewtopic.php?t=9484 ) and to my dismay, discovered that all of them had broken compression rings. Thank goodness that Board Member jl924t sold me two pistons last month instead of just one, because one of the broken rings wore the piston's groove to almost double it's original height. I initially didn't want to rebuild the motor, just replace the head when the timing belt let go, but now I'm glad that one thing led to another and I've torn it down to bare block. The broken rings may have worn the cylinders slightly out-of-round, but I don't want to get into overboring it to correct whatever imperfection may now exist. I'll live with new rings in what might be slightly out-of round cylinders, after all, it's got to be better than continuing to run things with the broken rings in there.

.._..

So, to this point I've got new main & rod bearings, front & rear main seals, two replacement pistons, new rings all around, a new water pump and gasket sets. After I get the head back together (waiting on one last valve) I'll start reassebmling everything again and top things off with new clutch components. Looks like I'll miss my New Years target date, but...maybe Valentines Day she'll be back on the road.

(edit - moved photos on server, corrected the post so they'd show)
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'79 Eurospec 931

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Lookin' good!

FWIW- All the compression rings on my pistons were broken also. The machine shop said the cylinder walls were still fine, but the piston skirts were all tapered. The scoring on the skirts was noticeable though, from your pics it looks like those pistons are in perfect shape. I'll bet you'll be just fine without any machine work. Mine had maybe 110k on the clock (broken odo!).

I just dropped the motor in mine the other night. To think, I was planning on finishing it up for my birthday, in June!

-nick

John Brown · Joined: 07 Nov 2002 Posts: 903 Location: Leesburg VA

I'm a johnny-come-lately to this thread. Wanted to add a thought about the original failure. May, or may not be related to this failure, but can't hurt to share.

A detail fine print part of the factory procedure is to tighten the tensioner counter-clockwise. If it is tightened clockwise then the edge of the pulley can become clamped and so the pulley drags badly.

I am guilty myself of trying to stretch the life of the pulleys. Going out right this instant to thow away all the 'servicable spares' I've been saving.

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John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

I've been making some progress with this project, and started reassembling the engine this past weekend.

My "C clamp" type spring compressor didn't cut it because the "stroke" on it wasn't great enough. I had to pre-compress the spring and then put the compressor on things in order to get things to work (and even then the tool bent and distorted). I decided that a hydraulic shop press would do a better job, so I used that to finish putting the head back together. Note the cardboard tubes I used to protect the valve tappet bores.

..-..

I took my time on the engine and ran out of daylight before I got around to the manifolds or the turbocharger. I should have it ready to drop back in next weekend if all goes well.

Click this photo to go to my photo gallery of 30 or so photos of the reassembly in progress.

(edit- moved photos on server, changed post so they are visible again)
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'79 Eurospec 931

Smoothie · Posted: Wed Feb 25, 2004 12:53 pm Post subject:

Aha! This must be the elusive rev limiting rotor - http://209.205.173.209/~camaro/gallery/album47/EngineReassembly37
That thing's way wackier looking than I'd imagined.

Real nice looking engine work CMXXXI.

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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Lizard · Posted: Wed Feb 25, 2004 2:06 pm Post subject:

who that is MESSED up, that rotor is wacky
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3 928s,

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Shame on you for not replacing the timing belt cover

Lookin' good though. That parts blaster is nice, eh? We might be cranking our new motors over simultaneously this weekend- my new injector$ just came in yesterday.

-nick

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS