Bad compression... what to do ?

[Rob C]

How much timing chain stretch would be required to cause the valve timing to be off so as to affect compression ?

My

[Peter J. Bierman]

Extreme blow by would we an indication off severe ring or cylinder wear.
If you take off the oilfiller cap when warm and its getting real cloudy, you have a problem.
Valve or valves not sealing would be possible but hard to spot on the outside.
Valve timing that far off becaude off timing chain is allmost impossible, couse injection timing would be way off too causing hard starts and loss of power ( a lot )
to rebuild or not to rebuild is depending on whats wrong.

Hope this anwers your question.

Peter

[NH2112]

A leakdown test would tell you in which area the problem lies (valve sealing, rings, leak into water jacket) then you'd just have to decide whether it's worth the time and money to repair or replace. They all CAN be done in-chassis, if you'd rather spend time than money.

[Rob C]

I'll take the cap off and check for a cloud when I get back. Is this best done with the engine hot or cold ? Presumably I would also smell exhaust (or perhaps fuel) if there was excessive blow-by ?

I have heard a little bit about leakdown tests... is this done with the head off to check how well the rings seal ? Is there a recommended on-line description of how to do it ?

Whether I do it with the engine in or out of the truck is not a big deal... doing it myself is, though. Not really any spare cash to blow on other people doing the work that I can do myself.

Any other thoughts ?

[SaintC]

I once did a ring and bearing job on a 4 cylinder Isuzu engine in my Chevy Luv...without removing the engine. I had blown a head gasket, and figured while I was there, why not. It was actually alot easier than I thought it would be. I used a glaze breaker on the cylinders, replaced the rings with standard, and the piston rod bearings. I used to drive hills at that time, and the difference in power was very noticable.

Recently, I had to replace the main set and rod bearings in a chevy 400...without removing the engine. This engine is very close to a 6.2, so my experience will be close to yours. The oil pan CAN come out without lifting the engine, if the engine is in just the right position. I lifted mine about 2 inches, and it came out just fine. While you are there, replace the main set and rod bearings. The main set was a real pita. I used the cotter pin trick that most manuals tell you about, and even that was real tough. Use moly assy lube. I did not do a ring job, so good luck there.

Follow the instructions, and you should be all right. Not to mention, once you get it all back together, I think you will be very pleased with what new rings will feel like.

Don't forget the 500 mile oil change.

Use Clevite "P" bearings. Doc recommended them to me for my scored crank because they have a thicker lining....at least I think that is what he said ;)

[ 12-19-2003, 07:53 PM: Message edited by: SaintC ]

[NH2112]

Basically what you're doing in a leakdown test is filling the cylinder with air then seeing if the pressure bleeds off (and how fast) and where it's bleeding from. It's the same idea as a cooling system pressure test. If the valves are leaking you'll have air hissing in the intake or exhaust manifolds. If there's a crack in the water jacket you'll get bubbling in the radiator or coolant recovery tank, and if the rings are worn you'll be able to hear air escaping into the crankcase by listening at the oil fill tube.

I think you should be able to make a leakdown adapter out of an old glow plug by breaking the tip out and drilling through the threaded portion. Braze a male 1/8" NPT --> male #4 JIC adapter to it, make up a length of hose with a female #4 JIC fitting, a suitable pressure gauge and ball valve in it, and put a male air hose fitting on the free end. Steel tubing could be used in place of the hose as well.

[john8662]

To Check the blow by, when you get the burb back go drive it and get it up to normal operating temperature. Pull over or drive back home, pop hood, leave engine running. Just take off the oil filler cap with the engine running. Judging what your seeing:

If the smoke cloud comes out solid filling the entire tube then coming out in a solid cloud, bad blowby.

If you just see a little smoke, just a fine mist, thats usually normal for some engines with some miles.

If none, that rocks!

You don't want to sniff it for a fuel smell, it will just have a nasty oily smell to it, a "blow-by" smell.

Good luck..

One concern about that low compression reading in #2. Could be a leaky head gasket. Make sure the radiator recovery tank is full, drive to operating temp, leave runing, open recovery tank filler cap (plastic tank) and look down inside for bubbles coming from the radiator. That might be some indication.

[Rob C]

Thanks for the replies, everyone. When I get back, I'll start checking things... I'm sure I'll be back with more questions.

Rob