924Board.org

OR_Sunset · Joined: 04 Jan 2003 Posts: 312 Location: Veneta, OR

Pulled the engine this weekend. Main and rod bearings look good. For new bearings, I expected the main bearings to be smoother, but they aren't trashed I don't think. The Rod bearings look pristine. As soon as the crank was free of the pistons it turned over very easily, leading me to believe is is a piston/ring problem.

The cylinder walls are not scored, though. The cross-hatching is undisturbed all the way up the walls. I don't know. I found a gummy residue in the upper portion of the cylinders, maybe it is gluing the rings the the walls. I assume acetone is a safe solvent to use to abate this residue. If that solves the problem, I will be happy enough.

What would cause this residue? If I need new rings, what is the best way to go about replacing them? Stock or aftermarket? And what tools will I need?

Thanks again and again everyone.

Joes924Racer · Posted: Tue Sep 16, 2003 7:29 am Post subject:

Aftermarket, deeves or total seal, if you dont have aHaynes look
in the 924 FAQ heres a link http://www.porscheclub.ru/Tech_info/repair/Haines/01_Engine02.htm#_01_026. You will need to remove the old ones and clean the grooves in the piston real good buy a groove cleaner and you need a piston ring installer and a installer for installing the pistons into the block..The Deeves rings are kind of spendy though though you dont have to mess with measuren end gap of the rings and filing if the gap is wrong there all pregapped and ready to install.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

I think I would be making real sure I knew what actually "seized" before I put it back together. I don't remeber the story on how it seized. Was it a fresh rebuild or an engine with a few miles on it? Did it just not start one day or did it actually quit running due to seizing up? Any heating or oil pressure problems? Just trying to keep you from doing this more than once

Todd

OR_Sunset · Joined: 04 Jan 2003 Posts: 312 Location: Veneta, OR

Well, some instructive work today. I put the rod bearings and caps back together and the engine turned fine... the pistons moved very freely in the cyls too. Until I torqued the rod bearing caps to spec. So I think something happened to the rod bearings or the bearing caps?

It was running so well before. I think the engine has a total of around 2 hrs of idleing and 25 miles of actual driving on it (during which time I had 70-90 psi of oil pressure). So it is brand new. I need to get in touch with Alex to see if the bearings were standard or oversized, and get new ones.

I just can't get my head around what could have happened so that the bearings were fine and then within one day are too tight on the crank... I even picked up some heavy duty moly assy lube to protect and free the engine... no dice.

It also seems really tight between the caps and the crank throws. But everything turns freely until the bolts are tightened even just a little. I would hate to buy new bearings and find the same to be true. Is there some other explanation I am missing?

Sleykin · Posted: Tue Sep 16, 2003 3:36 pm Post subject:

Get some plastiguage and lay it on the bearing surfaces to form a "T". That will show clearances and roundness when you torque the caps. Was the crank ground? If not you may have a tapered journal. Is it just one rod bearing or all of them that get tight? You may have had an instance of too much "crush". That happens when the inserts are longer than the rod/cap. The motor can run in for a bit and then the inserts deform and make things tight. If you have the crank out mike the journals and mike the rods with the inserts in and torqued down. Also mike the rods without the inserts to check for round.
I assume the caps are marked for the rod they are associated with and the direction they go??

Good luck with it
_________________
Glenn Neff
Medford, OR
87' 924S

Richard · Joined: 04 Nov 2002 Posts: 617 Location: Pacific N.W.

If the plastigauge test shows ok you may want to test for a bent crank. I really sounds like you have the wrong size inserts though. To see if the crank is bent, snug one main bearing up at a time, starting in the middle and working outwards. If it seems loose untill you tighten a certain bearing, then the crank is bent. Once again, I don't think this is your problem.

If you do get new rings, don't trust the manufacturer. Test each ring for end gap by placing evenly in the cylinder. After all that work, it is silly not to double check.

924RACR · Posted: Tue Sep 16, 2003 9:53 pm Post subject:

Agreed, plastigauge it and make sure you've got the right bearing clearances!!!

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

OR_Sunset · Joined: 04 Jan 2003 Posts: 312 Location: Veneta, OR

Thanks, guys... I will get some plastiguage asap. I did the "bent crank" test, and it doesn't seem to matter which bearing cap gets tightened. As soon as one of them is even FINGER tightened, it seizes up. I think the bearings are the wrong size, so there is zero clearance between the crank journal and the bearing surface. Some measuring to do I guess, so I'll get right to it. Thanks again.

Joes924Racer · Posted: Wed Sep 17, 2003 7:22 am Post subject:

yup I used plastiguage thing before it works if you do it nice and easy
[correct string placement] I had to try used stock bearings once and the results were what I exspected. Its like used silly string from a spray can.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

numbbers · Posted: Wed Sep 17, 2003 9:53 am Post subject:

The bearings should be marked for size on the back side. However, if you had bearings installed that were oversize, the engine shouldn't have cranked in the first place. I had a flat head Ford that my Dad rebuilt for me, that had such tight clearances that it wouldn't restart after it had been run for a while and warmed up. I would have to push it to get it started. After a couple of thousand miles, it wore in, and I never had another problem. But, if you can't go finger tight without binding, something is really out of wack.
_________________
1980 924 Turbo

endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

From re-reading your post I would suspect you either have excessive lube on the back side of the bearing inserts or dirt. Yoou may also have a failure due to the use of moly lube. Do NOT use it again. This should be used only for camshaft breakin not engine assembly. It will embed itself into things like bearings and plug oil filters. You may have blown a chunk of this stuff thru the filter and caused the seizure. I have never seen it happen but I have read about it. Use Lubriplate 105.

Todd

OR_Sunset · Joined: 04 Jan 2003 Posts: 312 Location: Veneta, OR

Wow... I wasn't aware of the lube issue. The kind I bought specifically states that it will break down in motor oil, and SHOULD be used on parts of the rotating assembly. Are there different kinds? This stuff wasn't cheap either.

I plastiguaged all the bearings last night and they all came up with 0.015 clearances. Perfect. So, then I tried a little experiment. #3 rod bearing cap was the one freezing up, but showed no problems. I swapped it with the #2 cap, and the engine turns over very easily now. I don't know if this is good or not, but it seems plausible that whoever rebuilt the engine last got these out of order.

I cleaned all parts with WD-40 and lint-free cloth, assembled everyhting with assy lube and a coating of Marvel oil. All the parts are torqued to spec and VERY smooth, although a little tight, as is to be expected. Force to turn the engine now: 23 ft./lbs to get it started turning, less to keep it moving.

I am going to put everything back together this weekend, hopefully it will start. If it does, I am thinking of going for a LONG drive to help break things in a little.

Joes924Racer · Posted: Thu Sep 18, 2003 9:53 am Post subject:

Hope it all works out for you Im thinken you found the prob. and itll work that will be a relief
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

Lizard · Posted: Thu Sep 18, 2003 12:20 pm Post subject:

I would have to say there might have been something in between the bearing and the rod, however I am not sure how good it is to be swapping the bearings around, I personally would measure EVERYONE of the crank surfaces to see if it has been reground and make sure you get the correct bearings, you dont want to have to take it apart again, also make sure you dont get the connecting rod caps mixed around, they ONLY go on 1 way! and ARE rod specific
_________________
3 928s,

Zuffen · Posted: Thu Sep 18, 2003 12:35 pm Post subject:

the main caps should be numbered
_________________
Bob Dodd - 924turbo@cox.net
931 1982, 944 1982 euro, 924S 1988SE, 93 968 tip 06 Silver Cayenne S, 06 Black Cayenne S

I have Way too many cars, parts for the 931,944 and 951