924Board.org

[Slam]

Guys and gals,

84 Euro 924 is smoking when I get back on the throttle after engine decel. I believe I need to put in new rings and want to have a go at this with the engine in the car. I know I SHOULD pull it but I just don't want to. So I wanna pull the head, pop the slugs out from underneath, hone myself happy and reassemble.

Pros and cons? And otherwise...

Thanks!
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'88 944 Auto - may or may not resurrect

[Fifty50Plus]

First thing - Check valve stem seals. Some/all could be bad and cause smoke.
Second - Unless you have a proper hone done on the cylinders, sticking new rings in will not do much good. In the block hone with a dingleberry hone is next to useless.

Chuck
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1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA

[Grenadiers]

Check blow-by and compression first. May not be rings.

My Euro 931 engine is down to the block. Was done by PO, however, light to slight rust formed, and am taking it in to have a pro go at the re-hone. Even though I have a set of dingleberries myself! (Insert joke: here)
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'83 944 Track car.
'88 924S Track car.
'89 944 Turbo
2004 Winnebago Vectra monster RV
2012 Jeep Wrangler
2014 Kia Soul
2001 Ford F350 powerstroke

[Slam]

Yes, before I attempt to rotate my dingleberries in those slug-holes I'll check pressures and seepage. Heh.

Engine doesn't smoke on startup, oil pressure is VERY low at hot idle, no loss of power.

Will report back here with my findings.
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'88 944 Auto - may or may not resurrect

[Rich H]

No real problem with pulling the slugs, but if the oil pressure is low won't you want to do the mains while you are in there? That is really a block out job.

The crank/flywheel is a huge lump to try and lower from the block plus the TT needs to move back which means the gearbox out...

Rich
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[daniel]

Chuck is spot on, It is a really bad idea to just R&R rings on an old tired motor. Often the new rings will be WORSE than the orignals. The reason is that over many miles the bore becomes out of round, but the rings in there wear (over an equally long period of time) to the same shape. So when you put in new rings that are springy and perfectly round, they dont match the wear pattern in the bore and dont seal properly. They MAY bed in with a lot of mileage at high revs (we have done this with overnight rebuilds on race motors) but they are just as likley not to.

Rebuild it properly, plently of help here to keep you going. You'll be so much better of in the long run.

Daniel
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Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet

[TJC]

I too would have to agree with what has been said above, but I do have a couple of questions.

What oil are you using...type, brand, weight?

How many miles on this engine?

How long has this been going on?

Is it a puff of smoke or more than that?

What brand of oil filter are you using?

How often do you change oil?

What is the oil pressure at hot idle?

I also suggest you do a cylinder leak down test as well as a dry and wet compression test and report your findings. This will help us give you proper advice.

Good Luck!
_________________
'95 BMW 318i/5 ..."Pearl"
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"
'04 BMW X3..."Xander"
Still on the Prowl!

www.ttrs1.com

[Slam]

Some more of my tale:

http://www.924board.org/viewtopic.php?t=31868&highlight=

As to the questions TJC posed, here's what I know:

I'm running Rotella 15W40, fresh a month ago. Rotella used to be one of the best-kept industry secrets but I'm not so sure nowadays.

The odometer in the car works but I'd bet I've got at least 250,000 km on the engine. I got the car in 2008 and who knows? I don't trust the odo.

The problem only surfaced in the last two weeks. Before that I was only chasing a pressure issue.

The car emits just a puff of smoke.

I use only Bosch or Mahle filters.

Oil pressure at hot idle with the OPRV NOT shimmed is about .5 bar. Shimmed I get 1 bar.

There's no bouncing of the gauge.

Haven't had time to do a compression check but the weekend's a long one.

Daniel, I agree with you in principle but I love to experiment for the sake of the fun of it. Of course, in cases such as this experimentation can get expensive. I'm closer to a decision now, so thanks, folks.
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'88 944 Auto - may or may not resurrect

[Joes924Racer]

You should not try a hone job with car in block you gotta
pull it brother.
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[Slam]

Reading you 5 by 5.
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'88 944 Auto - may or may not resurrect

[TJC]

I'll be interested to see what your test numbers are.
_________________
'95 BMW 318i/5 ..."Pearl"
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"
'04 BMW X3..."Xander"
Still on the Prowl!

www.ttrs1.com

[Slam]

Well, I had time to do a compression test today and here are my results:

First test, engine cold, dry, throttle closed:

1: 160lbs, 2: 150lbs, 3: 150lbs, 4: 151lbs

Second test, engine cold, dry, throttle open:

1: 169lbs, 2: 161lbs, 3: 150lbs, 4: 155lbs

Third test, engine cold, throttle open, oil in cylinder (wet):

1: 169lbs, 2: 161lbs, 3: 150lbs, 4: 155lbs

Third series of tests, average of five readings, wet, throttle open, cold:

1: 163.4, 2: 163, 3: 142.8, 4: 151.2
First run through I got 170, 168, 149, 152.
Last run through I got 159, 160, 140, 150.

Haynes' max permissible variance between cylinders: 43lbs.
Maximum variance according to my tests: 21lbs.
I attribute some of my variances to running the battery down too far while testing, or to basic incompetence.

Spec compression: 114 to 156 lbs (according to Haynes).

I adjusted my valves before the test. Intakes on 3 and 4 were loose, intake on 1 slightly loose. Intake on 3 starting to gall but lifter okay. Looking at the test numbers points to an issue in #3, maybe.

The plugs on 2, 3 and 4 looked pretty good for mixture with a little soot. The plug for 1 was sooted up more than the other three. I put in new plugs and changed the fuel filter while waiting for the battery to recharge. I'm on dialup right now so can't post pics but I'll put them up on Tuesday when I'm back at work (working hard, of course...).

Correct me if I'm wrong, please, but it looks to me like my rings are basically okay and cylinder 1 has high compression because it's full of carbon. 2 as well, but less so. The cam area was pretty dirty.

I couldn't do a leakdown because I didn't have the right fittings but I'll pick some up soon, however, maybe the issue is in the valve guides instead of the rings.

Any input much appreciated. And sorry for the long post!
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'88 944 Auto - may or may not resurrect

[TJC]

I'd have to say that the compression figures look pretty fair actually...although #3 is a bit suspect. I'd still be interested the CLT test results and where your're hearing any air passing through i.e. intake, exhaust, crankcase, cooling system (visual).

Since your smoke is a puff occuring when you accelerate after deceleration your problem could be, as mentioned earlier, valve seals. It could also be worn valve guides as you thought since the vacuum is quite high at that moment.

Of course the oil pressure issue will still need to be addressed.

Let us know the CLT when you can.

One question, does the car idle properly, and is there any "miss" upon acceleration?

One more question... sorry... has the engine had ever any overheating issues?
_________________
'95 BMW 318i/5 ..."Pearl"
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"
'04 BMW X3..."Xander"
Still on the Prowl!

www.ttrs1.com

[Slam]

Thanks for the input, TJC. The idle is fine and there's no miss on accel. In fact, the thing runs very well. I was going to say "for its age" but it just runs well.

As long as I've been driving this car there's never been an overheating issue (head gasket's fine). The gauge stays around the first mark, just out of the white zone. Actually makes for a chilly ride in winter!

Now I've had a night to sleep on this it seems my collection of symptoms point to a worn out head, basically. Excellence Tech Notes II, page 14, compliments of Bruce Anderson: "If you have worn valve guides and coast down a hill under compression, when you get back into the gas, the car will smoke." That's what mine does. Toss in a low oil pressure issue and I think the valve guides are worn (the dirty cam area and noisy valves would seem to support this), the cam caps are worn as well (contributing to the low oil pressure), and it's time to R&R the head. I have a couple of spares.

I think using very low visocity oil in winter was a mistake, and I think I've been running rich for too long as well. And age is taking its toll.
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'88 944 Auto - may or may not resurrect

[RC]

Comp figures all look Ok. Slightly lower readings on 3 - 4 probably weak battery as stated. Initial tests appear good with little variation.

Overheating will decrease ring tension, induce glazing and result in lower comp. #3 & #4 run hottest.

Compression readings indicate sealing between COMPRESSION RINGS & bore, as well as valves, gasket, etc. The oil rings, 2 thin scraper rings with spacer/expander, are responsible for what the name suggests. They are not designed to seal pressure and will NOT influence any comp test. In other words it is possible to have good compression yet still consume & burn oil from worn oil rings.

That said, valve stem seals sound to be at least a substantial contributor, given the decell then accell scenario. Even broken rings will not affect oil pressure. Personally would change stem seals first along with oil pump plunger & spring. Yeah I know ..... And thicker oil too.