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Old 10-26-2020, 07:03 AM
v8volvo v8volvo is offline
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Location: Montana, USA
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Quote:
Originally Posted by volvo-express View Post
... car as not been layed up for prolonged period...maybe 1 week without the head on it. When preparing the deck I used quite a bit of penetrating oil so maybe that washed the rings?

Is the best to soak the pistons.. ie drop oild down the bore and hopefully it will lube the rings again?

Later this morning it will be interesting to see if pistons 1 and 2 will return the same compression without putting oild down the bore.
Sounds like you are on the track now. Penetrating oil or solvent used for cleaning the block surface could well have made its way down into the bores and washed them down.

When I have a head off I'm in the habit of wiping a clean cloth soaked with clean engine oil around the cylinder bores just before reinstalling the head to make sure the rings are lubed when the engine starts again. Maybe lacking that let the ring seal suffer. The increase in compression with the wet test is a good sign that it'll come right back. It can be a little deceiving since the volume of the oil also increases compression ratio and can theoretically cause part of the boost in the compression readings with a wet test, but with such a large increase you saw, I think it is a good sign that loss of ring lube and seal was the main issue.

It probably would have come back in due time running the engine, as ngoma said, but that would probably take a while, maybe not until the oil warmed up and thinned out. Meantime the rings and bores might see excess wear. So the best play now, especially while you already have injectors out, is probably to manually add some oil to lube the rings, then retest, reassemble, and be good to go.

The one risk you want to be sure avoid when putting oil down the injector holes is making sure the engine can't end up in hydraulic lock. The preferred safest method is:

- put a several ounces of clean motor oil down each injector hole into all 6 cylinders, plenty of oil, not just a few drops.
- then, using a wrench on the front of the crankshaft, slowly turn the engine by hand through several full rotations. This ensures that the pistons have cycled in the bores a few times and get the oil spread around the perimeter of the cylinder bore.
- now, expel the excess oil from the cylinders (to prevent hydrolock) by cranking the engine on the starter with injectors out. This will blow any excess out of the injector holes. During this step, putting rags across the top of the engine (weighted down by a few pieces of wood if necessary) can help limit the mess, otherwise it'll shoot oil mist everywhere.
- finally, reinstall injectors, etc, and start it up. Or, if you wish for confirmation/recordkeeping purposes, perform a compression test first, then reassemble and run.

A method like this we have seen revive some long sitting engines that had almost been given up on for dead.

One other tip -- make sure the glow plugs are disabled while doing all of this, since the plugs wet with engine oil will make a lot of bad smoke if they become energized and get hot. And definitely make sure they are disabled if you do any compression tests with oil in the cylinders, since the hot plug plus the compression provided by the tester can cause the oil to ignite like fuel (diesel is fuel oil, remember!) and the engine try to start on that cylinder, which will blow up your compression tester!

Best way to disable them is to remove the fuse for injection/glow system, or just unplug the small black ground wire from the bottom of the glow relay under the hood.
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86 745 D24T/ZF 345k lifted 2.5"
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