924Board.org

Slam

Guys, we need your thoughts, condolences, input, what have you. I've also posted on the Cars/Pats Wanted section.

Gracie's 931 has spun (at least) the #1 rod bearing. Local machine shop guy says the rods and caps can be saved. When I saw the crank I was shocked - the entire bearing had been extruded and the crank is quite scored. Can these parts be saved by a good machinist?

The local machine guy also reckoned the car had run out of oil, but she was fanatical about this. I drained the pan before removing it and there was plenty of oil in it. Of course, very pearlescent. I also noticed that when I turned the crank by hand I could hear considerable hissing as the piston's compressed air bled past the rings - are they shot too?

She says she heard a bump under the car and thinks something came off. There's scrape marks on the outside bottom of the pan, but nothing's missing. The oil pickup was intact. Do the oil pumps on these cars fail? She says she lost oil pressure suddenly - bang, and the car died.

So we're in for a rebuild, at least. I've spoken to Don at EBS and he's got what we need. Great guy, too, especially after she phoned to talk to other major US parts houses and was treated like a dumb chick by all of them. Pelican excepted.

So far I can't diagnose exactly what caused the failure. I do know the rod bearings were going, because oil pressure read low on the gauge, which tended to be quite lively - bounced around a lot.

She's beyond miserable. And to top it off, she lost her job today due to workplace renovations which weren't scheduled till January. And she's got the flu.

I never rains.
_________________
'88 944 Auto - may or may not resurrect

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

Spinning a rod bearing is really not such a big deal. That's why they make oversized bearings. The machinist will turn down the crank journal and it will be just as good as new.

The worry is what exactly happened in the first place. When you say the oil was "pearlescent", was it milky? As in, the headgasket blew and coolant mixed with the oil? That would significantly reduce the lubricating properties of the oil and could easily induce spinning a bearing. Once the bearing goes, the oil pressure will suddenly drop to zero.

The "hissing" sound from compression when you spin the motor by hand is normal. The air is actually hissing out of the opening exhaust valves. Is the head still on the motor? I would suggest a leak-down test from the mechanic. This will tell you how the rings are doing and how the valves are doing. If you have a broken headgasket, it should be apparent also.

If the head has never been off and the headgasket/valve seals/etc. are original, then this is as good a time as any to do it.

Don't give up on the car! It's just wounded, not dead

nick

Slam · Posted: Wed Oct 12, 2005 8:53 am Post subject:

Hey, -nick,

Yeah, concensus is that the crank is okay - but the rod caps are chewed as well. I've never seen one this bad. Still, the wonders of machining...

No, we didn't get coolant in the oil gallery - I know exactly what that looks like because I had a Bronco that punched a hole in its block.

I'll look into the hissing. It seemed to come from the piston bottoms (past the rings), but you're probably right and I'm being paranoid. The head is still on but it looks like the motor will have to come out anyway. There's no way I know of to pull the crank out with the engine in.

What fun! A winter build project...
_________________
'88 944 Auto - may or may not resurrect

numbbers · Posted: Wed Oct 12, 2005 9:26 am Post subject:

I wouldn't mess with the old crank. My advise is to buy a used engine from someone on this board, and rebuild it. That way, you know that whatever caused the problem, will not be reinstalled in the car.
_________________
1980 924 Turbo

924RACR · Posted: Wed Oct 12, 2005 9:28 am Post subject:

The hissing sounds perfectly normal, don't worry so much. OTOH, you should do the full rebuild including new rings anyway (too cheap to not do so), so you'll be able to check for bad rings then. Yes, I 100% recommend EBS, they're great and do really know their 924's. I use them all the time for race parts.

You mentioned the oil pressure gauge bounced around a lot. Unless you had a flaky electrical connection, this was a dead giveaway of impending bearing failure - according to those with 944's I've heard from. Apparently for them tihs is a sign of impending #2 rod bearing failure. The bump she heard was probably the actual spin. Darn.

As mentioned - no problems reconditioning the crank. Just make sure to replace or have reconditioned any rods that experienced that bearing failure. If you don't, the replacement bearings will also fail. Ask me how I know.

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

Paul · Posted: Wed Oct 12, 2005 10:03 am Post subject:

You need to completely strip the block including the oil galley plugs and have it hot tanked so that you can get all the metal out of the oil passages.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

Kenodog · Joined: 25 Jun 2003 Posts: 2669 Location: Vancouver,B.C.

My oil pressure jumps to max.(past 10 bar) then back to 4-5 then back up to 10 again and so forth.It is a used pressure sender from Lizard that,like my old one,once it was taken out of the head got a miniscule piece of dirt in the little hole.At least this is what I thought it was.
May I ask why it will jump around if the bearings are about to go ?
Oh and Slam that sucks man.
I'll sell you my 931 cheap if you're not wanting to rebuild yours.
_________________
1979 Euro 931, Olive
1981 931, Sabine
1991 Ford Ranger XLT 4x4, Ricky
1996 Ford E-350 ex-FedEx Van
2014 Mazda CX-5 (Kinderwagon)
2019 KTM 790 Adventure
2024 KLX300
2024 KLX140

Chrenan · Joined: 15 Jan 2003 Posts: 3903 Location: Canada

Slam, not much input from me, but I'll keep my eyes peeled for a 931 parts car in the city, you never know.

Any chance something blocked the oil pickup tube?
_________________
1987 951 - M193 Version for Japan

924RACR · Posted: Wed Oct 12, 2005 10:07 pm Post subject:

My guess would be that the bearings, when about to go, are worn enough that they're possibly even moving around, causing actual fluctuations.

Definitely fix your oil pressure gauges, make sure they're reading steady! Or rebuild the engine NOW, before it becomes expensive!!! It's a lot cheaper to swap in new bearings (at $60/set for rod bearings, same I think for mains) and a new pan gasket than $400 for a re-ring kit PLUS machining.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

Kenodog · Joined: 25 Jun 2003 Posts: 2669 Location: Vancouver,B.C.

That still makes no sense as to why bearings that are slipping alittle would reflect on the pressure sender gauge which isn't in the engine but screwed to the back of the head.With the crank whipping around and oil slopping about everywhere inside where the bearings are.

_________________
1979 Euro 931, Olive
1981 931, Sabine
1991 Ford Ranger XLT 4x4, Ricky
1996 Ford E-350 ex-FedEx Van
2014 Mazda CX-5 (Kinderwagon)
2019 KTM 790 Adventure
2024 KLX300
2024 KLX140

924RACR · Posted: Thu Oct 13, 2005 3:37 am Post subject:

I'm postulating, not proving anything, here. Bottom line, fix your oil pressure gauge or start saving for a rebuild.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

Slam · Posted: Thu Oct 13, 2005 4:48 am Post subject:

Gents, thanks for the input.

I think it's pull the engine time, frankly. Disassembling it will reveal exactly what failed, but I'm gonna bet on very worn rod bearings being the culprits. As I understand it, pressure gauges are pretty basic - if they read remotely right then they're a good source of info. Plus, at this point there'll be metal everywhere in that motor - in other bearings, too. Best to do it up right. Plus, this'll be our chance to deal with head issues and get rid of the oil leaks. The only downside is that she loves the car and won't be able to drive it for some time. Oh yeah - and money...

Kenodog - (And somebody please correct me if I'm worng) Oil flows through the crank, to each bearing on its way through the motor, and if the rod bearings develop too much clearance, oil leaks past them and you lose pressure further on down the line.

Hey Chrenan - the oil pickup looked clean, but I bet it'll be filled with metal, which certainly wouldn't help things.

Getting another engine to rebuild? Hmmm... First, gotta find one. Then gotta get it here. We may look at this if the machinist figures he can't save the crank after all, but I'd like to - for now - go on the assumption that this one can be rebuilt.

And I just did the head on my 944!!!!!!!!!!!!!! Gimme a break!!!!!!!!!
_________________
'88 944 Auto - may or may not resurrect

numbbers · Posted: Thu Oct 13, 2005 7:51 am Post subject:

Yep, I didn't notice it was a 931, since this is posted in general discussions. Finding a good 931 engine for a resonable price is probably too hard. But, since the crank is the same for an NA, they are readily available. I see them on Ebay frequently. Also, you might find an NA at an auto dismantler, and use the whole block.

So, the question is why did the bearings fail? How many miles were on the block? I have never heard of an oil pump failing on these cars. But, you don't want to go through all of the money and work of rebuilding the engine, just to have it go out again.
_________________
1980 924 Turbo

Slam · Posted: Thu Oct 13, 2005 9:04 am Post subject:

Theoretically, the block had over 120,000 miles on it. Which really isn't that high. Then again, odometers in these cars are notorious for failing, so who knows? If I do pick up another crank, will I need the rods that go with it? If machining's gotta be done anyway, I should be able to use the ones I've got, no?
_________________
'88 944 Auto - may or may not resurrect

numbbers · Posted: Thu Oct 13, 2005 9:56 am Post subject:

Well, your rod(s) on the bad bearing(s) will have to be resized. That involves welding on new metal, and then maching the rod back to original size. That will cost some money. If your machinest is good, it will all work out. But, if you can pick up a block with rods and a crank for cheap, then you will just need a standard rebuild. That might save you money. However, it is questionable if your 931 pistons will work with the bore of a new block. Although the boar of the NA and the 931 are the same, the wear patterns of your 931 pistons and the replacement block may be considerably different. Your machinest can tell you if they will work. Otherwise, you will need oversize pistons and rings, and you can have the block bored to match.

You can also just replace the rods that are damaged, or replace the full set, with either new or used rods. Just have everything balanced as part of the rebuild.

I have had bad luck with turning a crank undersize, and using oversize bearings. It resulted in low oil pressure, and excessive oil consumption. That is why I recommend replacing the crank, rather than resizing it. Since there are a lot of 924s in junk yards, the cost of a used crank and rods, may not be anymore than the work needed to repair yours, and way safer. Then you also have the issue of replacing your oil pump, and getting all of the metal out of the engine. You will definitely need to check your cam and cam jornals to be sure that they didn't get damaged.
_________________
1980 924 Turbo