Compression depression

qualityhardware · Post by **qualityhardware** » Sun Jul 30, 2006 7:55 pm

I have a '52 M38 that I have been restoring for my dad for some time.

Got the engine rebuilt about two years ago and am finally getting it on the chassis and fired up.

This M38 was an unloved basket case that we found in one guy's backyard. It had an abortion of a 12v conversion with half the 24v harness sort of attached, rust all over the body and water, water everywhere.

In any case, there were a lot of mix and match parts on it. Forensic sanding of the body revealed the following:

It started as a military jeep.
It became a Civil Defense jeep.
It became a DOT jeep.
It was painted red, white and blue with a brush and driven to near destruction by a crazy person who my dad bought it from.

If there were timing marks on either the original flywheel or the crankshaft pulley, they have been replaced with parts that don't have them.

I have done all the tricks to set the timing sans the mark on the crankshaft pulley. Compression test to TDC. Marking the position of the #1 plug cable on the distributor, etc.

I can crank all day but I am not getting any fire.

I did a compression test and the most I can get out of any cylinder is 90psi. I see in the manual that standard is 135psi and minimum is 100 psi.

This engine was really beat up when it was rebuilt, and I believe it had already been bored out .030 over before we got it rebuilt. The machine shop bored it out .060 over.

Would this level of boring be the cause for the weak compression in the cylinders?

I am stumped and quite frustrated.

Thanks,
QH

Post by **Ryan_Miller** » Sun Jul 30, 2006 8:19 pm

As for the compression, if the shop rebuilt the engine, it should have clean cylinder walls and new piston rings and piston heads, along with new valves seated properly.

That should give you good compression.

You could have some sticking valves?

As for the spark, you may not have the oil pump/distributor indexed properly.

Wes will be along here and give you more info.

Sorry to hear you are having trouble, but I bet it can be worked out. Don't get discouraged.

davem201m38 · Post by **davem201m38** » Mon Jul 31, 2006 1:17 am

Before we go any further, a simple question.
Do you have a spark at the plugs?, have you pulled a plug out to see the spark jump across the gap?
All the best,
Dave.

maeserik · Post by **maeserik** » Mon Jul 31, 2006 3:29 am

read this :

http://www.g503.com/forums/viewtopic.php?t=73941

check the rotor in position when cyl.1 needs firing
in the instructionmanual ther is a picture where you can see the position of the shaft of the oilpump through the install hole for the distributor, maybe someone has these picture digital ?

when you have a spark at a wrongmoment it is normal nothing happens !

good luck !

qualityhardware · Post by **qualityhardware** » Mon Jul 31, 2006 4:04 am

Thanks guys. I do have spark. Checking the ignition switch to the #12 wire to the distributor to the battery returns a reading of 23.8v to 24.2v.

I pulled different plugs and observed spark as I cranked the engine. Same thing with the condenser points in the distributor. Every time they open, there is spark.

Here is a diagram of the firing order of the distributor as well as the position the rotator is in when the #1 cylider is at TDC.

There is plenty of fuel flowing into the system as well. When I crank the engine, you can definitely smell gas. I even sprayed some starting fluid into the carb and that didn't even do anything.

I am completely stumped.

davem201m38 · Post by **davem201m38** » Mon Jul 31, 2006 6:07 am

Odd!! very odd. If the timing is correct then my guess is it has to be spark or fuel. I'd would have expected an odd BANG and a splutter even if the timing was way out with petrol in the cylinders. I would deffinately have expected a BANG!!! with starting fluid even with the timing completely out as the fluid (usually ether vapour this side of the pond) doesn't dissipate straight away and there's often a build up in the intake manifold and the cylinders and often some gets left behind after the exhaust stroke and it will ignite on compression alone if there's enough air.

Do you have enough from your batts to spin the engine and give a good spark. Could it be that all the energy is going into spinning the engine and not enough is going to the plugs. I had this on an M201, the engine would just 'catch' as I took my thumb off the starter button and the engine was still spinning on momentum and suddenly the coil got full current.

I know you say you can smell petrol but have you checked that your actually getting enough from the pump and pump pressure. In the past I've had a worn pump that was great once the engine was running but couldn't manage to start the engine.

As for the compression you could try a shot of oil through the plug hole to help seal the rings and see if the compression improves, if it doesn't you might have a sticking valve or maybe more, but I would still have expected a chug/cough/splut from one of the cylinders.
Good luck,
Dave.

Post by **Ryan_Miller** » Mon Jul 31, 2006 6:15 am

Follow Dave's advice.

I would also put some marvel mystery oil as Dave suggested in the cylinders to help them seal.

The piston rings may not have worn enough yet to "break in or wear in" to form a good seal.

Like Dave said, you should be getting a Bang with all that fuel and some spark.

Bob_C · Post by **Bob_C** » Mon Jul 31, 2006 6:45 am

.060 over shouldn't be a problem. My engine is .060 over and runs great.
I know several people who have even had their engine .080 over with no problems.

Are the valves adjusted correctly?
And did you check to make sure your oil pump wasnt 180 off?

qualityhardware · Post by **qualityhardware** » Mon Jul 31, 2006 11:07 am

I agree with all of you guys. There is so much fuel and fuel vapor going into the engine that some residual fuel would cause SOME kind of BANG.

How would one check and see of the oil pump is 180 degrees off?

What would be the symptoms and remedy if it were?

Thanks.

Post by **wesk** » Mon Jul 31, 2006 3:35 pm

This is where having an engine builder not familiar with the cam vs oil vs distributor drive arrangement gets you a ton of heartburn.

Let's slow this thread down and get some direct answers to a few important questions about this engine that you had overhauled several years ago and now that you have installed it it won't run.

1-Did the engine shop that did the overhaul completely set up the engine with a distributor installed and timed and test run the engine?

2-If not who installed the distributor?

3-When you did your compression checks did you go around a second time and squirt oil in each cylinder to help seal the rings then read the compressions?

A fresh engine with fresh bores and fresh (UNSEATED) rings will not give you 135 pounds.

qualityhardware · Post by **qualityhardware** » Mon Jul 31, 2006 8:33 pm

wesk wrote:This is where having an engine builder not familiar with the cam vs oil vs distributor drive arrangement gets you a ton of heartburn.

Let's slow this thread down and get some direct answers to a few important questions about this engine that you had overhauled several years ago and now that you have installed it it won't run.

1-Did the engine shop that did the overhaul completely set up the engine with a distributor installed and timed and test run the engine?

Negative.

2-If not who installed the distributor?

I did. Does this mean I'm toast?

3-When you did your compression checks did you go around a second time and squirt oil in each cylinder to help seal the rings then read the compressions?

Negative. Was unaware of this step. Do I need to remove the head to do this?

A fresh engine with fresh bores and fresh (UNSEATED) rings will not give you 135 pounds.

Well, I learn something new every day on this board. I'd be nowhere if it wasn't for this site. Thanks Wes

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Post by **wesk** » Mon Jul 31, 2006 10:44 pm

Now we really have a problem. The only way we can ascertain if the builder installed the oil pump correctly is to ask him or pull the front timing cover and check it ourselves. The pump must be installed with it's offset slot at the correct direction with the valve timing marks on the crank gear and cam gear aligned.

There are folks who will tell you just get # 1 top and install the plug wires where they line up #1 wire with the rotor. Thta can work occasionally but usually it leaves the distributor in a position that makes it impossible to rotate it ebough to set the timing correctly.

Let me know what answer you get on the oil pump installation.

You just fill a hand pump type oil can with 30 weight oil and pump some in eache cylinder throught the spark plug holes while she's be cranked over.

qualityhardware · Post by **qualityhardware** » Tue Aug 01, 2006 3:50 am

Wes,

OK. I will check that out. I'll take some pics and post them once I have the gear cover off.