Oil Pan Gasket - While I'm in there...

[dr bob]

My experience --

The leak-down test demands more air pressure than a Motive bleeder can generate, and more volume than you are willing to supply with the hand pump.

The leak-down tester uses a couple pressure gauges with a calibrated orifice between them. The air on one end, hose to spark plug at the other end. Since you are 'calculating' leak-down as a percentage, using 100 PSI on the upstream supply side lets you read downstream pressure directly as the percentage (actually 100 - minus the gauge reading). So your compressor with a decent pressure regulator will be essential. For the connection to the spark plug, I use the hose from my compression gauge kit, one with a quick-disconnect fitting on the gauge end.

You'll want to lock the motor at TDC compression on each cylinder as you test. Air in the cylinder will cause the crank to spin if it isn't right at the top of stroke. The flywheel lock you use while loosening the crank bolt will be perfect.

All that said, a set of good compression readings will usually tell you more about the actual condition than a leak-down test. I depend on a leak-down test for engines I can't warm up and test for compression, like a used engine on a pallet. I can listen for where air is leaking out too, something that would help with that used-engine assessment.



For injector cleaning, assuming I don't need to replace filters or pintle caps, I can clean them myself on or off the car. Off the car, I use a cannister with cleaning fluid in it, and add compressed air at a fitting on top. The bottom has a hose that happens to fit over the top of the injector with a small clamp. I put the injector in a large glass cylinder (I use a cheap flower vase...) and throw a towel over the top to contain the spray. As Tom suggests, a 9V battery is plenty to open the injector. An actual 12V is probably safe for pulsing with low duty cycle. The 9V battery is cheap and easy, and safe to just keep it open for cleaning.

I've found that Berryman's B12 from Wal-Mart is a good cleaner for my casual needs. It was $5 a can yesterday on the local shelf. The car will run OK on the same chemical, so I use it for on-car cleaning too. Same rig, but I connect it to the front end of the fuel rail with a modified rail cap. It's drilled and tapped 1/4" for a fitting common on GM cars, and the ball behind the fitting is replaced with a 1/4" brass tubing ferrule inside. Return hose to the tank gets pinched, and air pressure equals fuel pressure in the cannister. fuel pump fuse comes out. My car gets good fuel, but doesn't see enough driving to reliably keep injectors spotless. The on-car method is easy and inexpensive, and it works for my car and my needs.

The B12 has a hefty dose of toluene, methanol, and a couple other solvents including isopropanol. Causes cancer and brain damage on skin contact, faster via eye or nasal/oral contact. Very flammable, and the mist is explosive. Keep the battery and switch well clear of the injector itself. And everything is done outside, away from friends, toys and structures that don't need to burn. They sell an even more intense cleaning product called IIRC B60 for barn-find cars and seriously neglected fuel systems. I have never needed it, but after reading some descriptions I'd be way tempted to try it in a longer-stored CIS/K-jet car before even turning the key the first time. Best to get varnish and deposits out as much as possible before clogging the rest of the system pieces.

[RedMeanzGo]

I would add the oil pickup tube and dipstick seals/o rings, they're pretty easy to do and will give you some peace of mind later.

For the dipstick o ring, there's information around on the use of (I think I'm remembering this correctly) a slightly thicker o ring, and/or 2 of them to really seal things up.

Cheers

I've did a deep dive on the dipstick tube seal a while back. The TLDR version is to use McMaster's o-ring # 9263K221. The factory o-ring is very slightly smaller than the tube it goes into, so while it might block oil from coming out when under no pressure, as soon as you add a little boost-induced crankcase pressure, it will leak. Pushing down on the tube does not help because the flange (or spacer on later tubes) prevents the tube from going down far enough to squish the o-ring. Lindsey tried to solve that by adding a second o-ring under the flange, but that relies on constant, perfectly plumb, downward pressure, which the little mounting tab at the top of the tube was never designed to do. A second o-ring also makes the tube stick up a little higher, which throws off the oil level reading by that same amount. The McMaster o-ring solves the issue once and for all, with no downsides. See drawings below.



DS1900.gif



Ds2.gif



DS3900.gif



ds5900.gif

This is awesome information ! Thanks Tom ! I live about a 45 minute drive from McMaster Carr, so next time I'm in that area I'll be sure and pick some up. (They only come in bags of a hundred, so if anyone needs one... LMK !)

[Tom]

I would add the oil pickup tube and dipstick seals/o rings, they're pretty easy to do and will give you some peace of mind later.

For the dipstick o ring, there's information around on the use of (I think I'm remembering this correctly) a slightly thicker o ring, and/or 2 of them to really seal things up.

Cheers

I've did a deep dive on the dipstick tube seal a while back. The TLDR version is to use McMaster's o-ring # 9263K221. The factory o-ring is very slightly smaller than the tube it goes into, so while it might block oil from coming out when under no pressure, as soon as you add a little boost-induced crankcase pressure, it will leak. Pushing down on the tube does not help because the flange (or spacer on later tubes) prevents the tube from going down far enough to squish the o-ring. Lindsey tried to solve that by adding a second o-ring under the flange, but that relies on constant, perfectly plumb, downward pressure, which the little mounting tab at the top of the tube was never designed to do. A second o-ring also makes the tube stick up a little higher, which throws off the oil level reading by that same amount. The McMaster o-ring solves the issue once and for all, with no downsides. See drawings below.



DS1900.gif



Ds2.gif



DS3900.gif



ds5900.gif

This is awesome information ! Thanks Tom ! I live about a 45 minute drive from McMaster Carr, so next time I'm in that area I'll be sure and pick some up. (They only come in bags of a hundred, so if anyone needs one... LMK !)

I had a bag at one point, but I'll never be able to find it now. I'm guessing it's just a matter of time before some of the 944 shops start selling these individually. Maybe @944online ? buy a bag of 100 for $8, sell them for $2 a piece -- think of the profit margin!

[whalenlg]

I would add the oil pickup tube and dipstick seals/o rings, they're pretty easy to do and will give you some peace of mind later.

For the dipstick o ring, there's information around on the use of (I think I'm remembering this correctly) a slightly thicker o ring, and/or 2 of them to really seal things up.

Cheers

I've did a deep dive on the dipstick tube seal a while back. The TLDR version is to use McMaster's o-ring # 9263K221. The factory o-ring is very slightly smaller than the tube it goes into, so while it might block oil from coming out when under no pressure, as soon as you add a little boost-induced crankcase pressure, it will leak. Pushing down on the tube does not help because the flange (or spacer on later tubes) prevents the tube from going down far enough to squish the o-ring. Lindsey tried to solve that by adding a second o-ring under the flange, but that relies on constant, perfectly plumb, downward pressure, which the little mounting tab at the top of the tube was never designed to do. A second o-ring also makes the tube stick up a little higher, which throws off the oil level reading by that same amount. The McMaster o-ring solves the issue once and for all, with no downsides. See drawings below.



DS1900.gif



Ds2.gif



DS3900.gif



ds5900.gif

This is awesome information ! Thanks Tom ! I live about a 45 minute drive from McMaster Carr, so next time I'm in that area I'll be sure and pick some up. (They only come in bags of a hundred, so if anyone needs one... LMK !)

I’ll sign up for a couple of your surplus!

[whalenlg]

I got a back of 25 from mcmaster, so if anyone needs a couple PM me

[whalenlg]

Kicked off the project this weekend. Due to consensus, I decided to pull the whole engine and go after every seal that I haven't done to date.
Posting pics of my spark plugs (~4k miles over 4 years. Note that I did a cam tower reseal in late 2021, so not sure if that might have affected the plugs). Also the injectors before I rebuild/clean.
Compression test came out 135-140psi, so I think we are good there.
Progress so far - pulled injectors, intake, radiator fans, plugs, distr., starter & airbox. Drained oil & coolant.

[Tom]

That last spark plug looks pretty oily. Are you planning to pull the head? That oil could be a bad oil seal and/or valve guides. Either way, definitely worth investigating the source of the oil on that plug. With the engine out, I'd probably send the head out for resurfacing and a valve job unless it's been done recently.

[whalenlg]

Hi Tom - I'm pulling the engine so easy to pull the head.

Any good machine shops around that would know their way around a 944 head?

Is a leakdown worth it give the compression test results?

Thanks!

Mike

[Tom]

Ted Robinson at German Precision in Santa Clara, assuming he's still in business. I also had Jerry Woods (JWE Enterprises) rebuild a head for me with good results. Both have who's-who p-car resumes. As for the leak down, given the oil on the plug, I'd vote yes. Would be useful to rule out excessive ring blow-by (although most likely you would have seen smoking and/or oil consumption issues if that were the case).

[whalenlg]

Leak down results - 1 and 3 look too perfect...I scoped the cylinders while trying to find TDC for cyl 2 & three. Tops of the pistons looked like they had a coating of oil. Pics not that great but posted.
1=0, 2 =5% 3=0% , 4=9%
Pics attached