inactiveuser92616

The car is a california delivered US 1987 944NA
Burning oil and compression is: (Fully warmed engine)
1: 130PSI
2: 130PSI
3: 145PSI
4: 135PSI

I have been noticing a fairly increased oil consumption over the past several months, engine seems laggy, and recently my new roommate (a fellow car enthusiast) said I was puffing some dark smoke out the tailpipe. I know the mixture is near perfect (had it dyno tuned to this altitude last year) so I got worried. Went to harbor freight and bought their best (so decent) compression tester kit, and ran the numbers. Used my roommate's Craftsmen tester for a sanity check, same numbers. I added some oil to the cylinders and compression shot through the roof (200+ psi).

At idle my oil pressure readings have been very erratic; with the needle jumping past 6 bar on the gauge and then dropping back to the 2-3 bar range it should be at. Goes away with throttle/ engine speed. Related?

Is it time for new rings? Does this neccesarily involve removing the engine?

inactiveuser92616

bump!

Fishey

Sounds like time for new rings but I bet the pistons will need replaced.

500

Your compression does look low. Factory manual says 145 psi min. for the NA motor. As all four cylinders are pretty similar, it would make sense that your compression loss is a wear issue (as opposed to having one really low value, which may be a scored cylinder etc.) Adding the oil and re-checking was a good move, shows that there is no serious compression loss around the valve seats.

I would say you are right that it is rings. I have read of many people doing this without completely removing the engine. I had considered doing the same, but in the end, I have just taken everything apart as there is much more I wanted to to anyway.

To do it in the car, you remove the top end of the engine, build a engine support that spans across the engine bay and keeps the engine from falling when you remove the steering rack, cross member etc. from below. (I'm skipping lots of detail here, but if you search this forum, others have posted pictures etc.) After everything is cleared away from under the engine, you remove the pan and then can access the con-rod bolts. Push the piston up through the top of the block, making sure that you've first put rubber hose pieces over the connection rod studs. Ring replacement is pretty straightforward, but care must be taken to:

1) Buy OEM rings.
2) Follow the instructions VERY carefully to mount them the right way up (should mean that the markings are facing up).
3) Check end gaps using a feeler guage.
4) Stagger the rings as per FSM, directions etc.
5) You will need a ring compressor to get the pistons back in.
6) Take the opportunity to replace the rod bearings with new OEM (this is a nice PM thing to do).
7) You must use new connecting rod stud nuts.
8) Get the pistons and cylinders carefully measured to make sure they are within the wear limits. The good news is that these blocks wear really well.

Pat, I'm sure you probably already know this stuff, I'm just throwing it out there in case.

Also, you will probably end up doing a lot of cleaning etc, which is a good opportunity but be careful with the pistons, as the alloy is quite soft.

The hardest part may be getting the new pan gasket on properly. This is hard enough with engine out apparently but with the engine in, it will be even harder. However, it can be done. Search Danno's "Elephant Snot" method, and "K-Swiss retainers") for some good food for thought.

Take a bit to consider if you want to do it in car or remove the engine. There are plusses and minuses to both. For myself, I think I would prefer to remove the motor (you will be most of the way there anyway).

Good luck!

Mongo

Hey Patrat, even though rings are priority here, dunno if you have ever done your rod bearings or not, but it's a good 'while you're at it' thing there. Though I've been around for top end overhauls with the motor still in the car, I'd say you'd get more room to work with by removing the engine. However, it can definitely be done. but putting the motor on an engine stand will allow you to rotate the engine for easier angles to insert the pistons without them falling out....or you could have someone just help you by holding them so you can do the rings.

Good luck to you man, sorry to hear about the motor. How many miles on her?

Mongo

Hey Allen if the motor wears fine he wouldn't need an overbore ring right? He can just replace with the factory size rings?

500

If the cylinder is out of spec, then one option is to have it bored out to the first oversize, which I think is 101.5 mm (100.0 is standard), in which case you need to get the matching oversize pistons/rings, which is a lot of $$$ from what I understand (and the cylinders must be lapped with the sunnen machine). Many suggest looking for a good condition short block as an an economical alternative.

If everything is in spec, than just as you suggest, the original factory size rings are right. I have my fingers crossed for you Pat. Just as a point of reference, when I took my 147K engine apart, the amount of wear on everything was very little. If these engines have had a good diet of oil changes, and not have run with low oil levels, than the chances are pretty good rings are all you need. The silicon on the cylinder walls is harder than the rings, so normally the rings do most of the wearing in these motors.

Andy, I do like your avatar (I mean I like an F-16 as much as the next guy...) but somehow your "other" avatars had even more punch...

inactiveuser92616

roughly 175k on her, mostly highway. Since she still runs (and reliably) I will probably just buy a couple jugs of good dino oil and throw oil and the problem until winter break; when I can go home and pull the engine out for some R&R. I also considered throwing in Joel's S2 motor, but without any experience with megasquirt I think that is a pipe dream.

Mighty Shilling

Pat, if ya want help with the rebuild, call me up. i may be able to help sometime. pm me for the phone number.

but you don't necessarily have to remove the engine to get to the rings... just the head... and the oil pan... and cross member.... so it'll be MOSTLY removed...f*ck it, just pull the engine... but rings are a cake job...

Mongo

If I remember correctly, the engine on the 944 REALLY isn't that hard to drop. There are 2 ways to do it:

1) You can remove your hood and use a cherry picker to pull the engine out after separating the bell housing from the rear of the engine.

2) You can put a jack under the motor and lower it out of the car. This also involves removal of bell housing.

I'm not gonna lie to you but the bolts on the bell housing are an absolute PITA to get to and you'll wish you had a pet monkey that could connect and bolt up the flywheel reference sensor for you too.

But I know you can do it man

Rob

Your engine won't produce the same compression numbers at higher altitudes as it will at sea-level.

For instance, my turbo's numbers where ~130 (IIRC) at 7200 ft with engine warm and throttle fully open. I just checked the other day and at sea-level with the same conditions, 150 psi across the board.

Did you perform the test with the throttle held open?

Jfrahm

There was a guy who put an S2 motor in an NA and ran it with an NA DME. He got it running quite well. He had gotten custom chips for the setup but they never worked, eventually tried the NA stock chip and it ran great, as I recall. Might have been the Denver car with the 968 bottom end, S2 head, etc. Maybe do a search?

I think it would work OK with a little tweaking, maybe a MAF/Mafterburner kit like the supercharger guy is using to finish it off. If you still have an S trans that would be a good match too.

Generally I am not a fan of swaps but if you had a sturdy trans and since you are close by it might make some sense.

-Joel.

Bri Bro

At 5,000 feet you are at 0.83 Atm vs 1.0 Atm at sea level. So take your reading 130 and multiply by 1.17= 152 psi. You need to be burning a lot of oil to see it at the exhaust, might want to check your AFM again.

Peckster

130 is not low for an older engine, but the uneven numbers are cause for some concern. Dark smoke is not burnt oil, so don't believe that your mixture is OK. I'd take it to someone who really knows these cars to have it diagnosed.

Mighty Shilling

Ya know, upon re-reading, this doesn't sound odd, except for the black smoke... Here's the deal... at this altitude, I get the same compression. Like someone said, oil smoke is white/blue... it's very light colored.

Now, as per the smoke, is it at startup, or throughout driving? When I startup from cold, my car sets out a puff of soot, then spits out black condensation (which stains the concrete). After it's warm, there is no problem.

For my oil pressure gauge, I have the same symptoms, which I've been told is the sender or a ground. I'm currently awaiting my Ice Shark Negative cable, we'll see if that fixes it. if not, I'll buy a new sending unit.

What I want you to do Pat, is to start the car, leave it in neutral with the parking brake on, and go out and see what happens from the exhaust. then go take it for a drive, and see what happens when you park it... as in, same thing, neutral with the parking brake, go back and see what's coming out the tail pipe.

Also, check your spark plugs. if they have a chunky black stuff all over the electrode, consider that it is in fact dumping oil into the cylinders, or you're running mega-rich. What is your fuel mileage? does the car leak oil anywhere? what sort of consumption are you talking about? I go through a quart every month and a half due to a leak at the top of the oil pump.

as a baseline, I'm getting 24-30 MPG for city-highway.

Check your AFM, maybe even re-track the thing. good luck.