Compression

[12B]

I have a problem I hope someone can help me with. My modified M 38 has a Supersonic engine it, which ran fine until Father's Day weekend when it lost compression on #2 cylinder. I took it to a friend of mine, a retired mechanic. He adjusted the valves, which initially seemed to fix the problem as we were able to drive it into the shop. But compression problems continued on #2 (the other three cylinders read between 110 and 120) so he pulled the head and ground the seat and the valve on #2. He put it back together (new head gasket) and now it won't start. Also, and I think this has him stumped, the compression is low now on all cylinders - and it varies in unequal amounts on each cylinder. He said the intake is opening and closing okay and that the timing is right on where he set it for me last winter. We went through the carb and it seems okay - I am definitely getting fuel. Plugs are fine. Anybody have any ideas?

[wesk]

It's a safe assumption that something the mech did has caused the engine to not start. He needs to retrace each step he did to isolate the cause.

Unless your description of the troubleshooting that brought you to a head removal was overly abbreviated I don't understand why this Old Retired Mechanic didn't start with the basics and do a pressure leak down test when #2 came up low on compression to ascertain exactly where you were loosing the pressure. Loose worn guides and sticking valves will also cause the pressure loss.

There was no reason for him to disturb the valve or ignition timing just to grind one valve & seat. Did he pull the exhaust/intake off the block?

There are several head gaskets for the L134's. Did he err and use the WWII MB head gasket?
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[12B]

Thanks Wes for responding.

Well, according to my mechanic the guides are a little worn, but not to where he thinks it's a problem and the valves aren't sticking. He said he got the correct head gasket, too. He did have the intake/exhaust off the block. I don't know exactly what or how a pressure leak down test is. Can you fill me in there? He did not do this.

Isn't it strange that we had good compression on all four after the first time he adjusted the valves, then lost it? Then we had compression after the valve job and lost it on all cylinders again once everything was back together? I'm in over my head here and appreciate your advice.

It had been running fine and then all at once when I was driving a couple weeks ago, it back fired and started missing - acting like it was starving for gas. Would barely start, idle real slow, and die out if I tried to give it gas. I went and got my old farm tractor and pulled it home. That is when I initially found the low compression on #2. Then I took to my friend.

[artificer]

You need to go back to your "mechanic?" & ask him to list everything he did.
You don't just loose compression when you grind a couple of valves & replace the head plus he should be able to diagnose what is wrong.
He should have done both a dry & wet compression test before pulling the head to establish valves [or rings] to be the trouble.
If you correctly describe "no compression" on all cylinders valve timing may be incorrect, but there will be other pointers, if that is the case.
Ignition timing has absolutely no bearing on compression pressure
_________________
John GIBBINS
ASE Master Medium/Heavy Truck & Auto Technician 2002 USA
Licensed Motor Mechanic NSW # MVIC 49593 Current
YOU CAN'T TROUBLESHOOT WHAT YOU DON'T UNDERSTAND

[wesk]