Compression test

[BlueDog]

Does cranking speed affect compression test? Seems like mine is rolling over kind of slowly.

[82vdub]

Cranking speed does effect compression ratios (think leakdown past valves and rings etc here). I would crank it over 4-5 revolutions or until the needle stops rising. Or, you can pull the injectors or glow plugs for faster cranking. Even with a slower cranking speed (within reason), it should get you in the ballpark.

[BlueDog]

I'm getting bad compression numbers on my 1.6na in the '89 Jetta. I think it's time for a re-ring. About 9 years ago I did a re-ring on a 1.6na. It went well and the engine ran great. I've never replaced bearings though. Is it conceivable that someone like me can install new bearings in a 1.6na? I like to think I'm fairly competent, for a guy with a pole barn and a cherry picker.

[82vdub]

I think anyone that has some mechanical abilities can install bearings. You re-ringed it before, so you already had the pistons and rods out. You already had everything apart that you needed, just that you could have put new bearings back on the rod and cap before you installed it. At a minimum, I would make sure you keep the bearings oriented to the correct rod, correct cap (you must put the same cap back on the same rod in the same orientation!) and correct orientation and plastigage the old one's before just replacing them. If you find the crank is worn, you may have to have the crank machined to use an oversize bearing. The Bentley will give you good info on what to measure etc.

[BlueDog]

Okay, Plastigage first. I take it I may find that I only need to do the rod bearings. That would be closer to my comfort zone.

I have a pretty nice VDO 0 to 150 psi oil pressure gauge installed in my Jetta. I'm considering to do the bearings because years ago it would show 115 psi when cold at idle and about 85 psi warm at idle. Now it shows 80 psi cold at idle and only 15 psi at warm idle. The engine has over 400,000 on it. Don't know if this is all original or if someone rebuilt before I bought. I'll get the Bentley out and start reading up on it.

[BlueDog]

BTW, the compression numbers are 50, 440, 280 and 500. I squirted some oil into the one that was at 50 and re-checked the compression. Moved it up to 260 psi.

I flipped the head over and applied some thin oil onto the valves. Shot 60 psi of air pressure into head through the exhaust manifold with each valve closed. No air bubbles. Did same procedure to the intake valves, the intake manifold has been removed, also no air bubbles. I think the valves are just fine but is there a better way to test the valves?

[Fatmobile]

Also remember the I-shaft bearings wear too.