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Low Compression, Dead Cylinder, What To Do?
https://slantsix.org/forum/viewtopic.php?t=47157		 Page 2 of 2
Author:  Reed [ Fri Dec 02, 2011 4:41 pm ]
Post subject: 
So it is beyond "slightly dead" and has progressed to "mostly dead?" (This is a Princess Bride reference for anyone else who grew up in the 80s).

I once had a daily driver slant that wheezed along for years with compression in all cylinders between 95 and 105. If you don't have the resources for lots of machine work, I say (1) see if the low compression is just a couple bad valves (2) if it is, source a decent used head (3) if it isn't, source a decent used motor or plop the head back on and run it until it is "completely dead."
Author:  63valconvert [ Sat Dec 03, 2011 10:36 am ]
Post subject:  Used Head?
Ok, we're still in "Hope Mode" here, because I haven't done the Oil in sparkplug hole test yet. But, curious as to thoughts on "Remanufactured Heads", namely those from Moore's Engine.

Thoughts on these guys? Anyone have any experience? I figure if I can get a 1972 head, I'll actually get an upgrade in the deal with the revised combustion chambers.
Author:  supton [ Sat Dec 03, 2011 10:51 am ]
Post subject: 
Wouldn't bad rings get dirty oil fast? I'd think the blowby would dirty it up reasonably fast, even if it's just one bad cylinder.

When you did the lash, did you verify that the rockers all moved 'bout the same? Just want to verify no dead lobes.
Author:  63valconvert [ Sun Dec 04, 2011 3:07 pm ]
Post subject:  Good News?
Did as many members suggested and took compression, then put about a tablespoon of oil in the sparkplug holes and rechecked.

No discernible difference. Good signal that this is a head problem? Or is there something else I can do to check for Cylinder issues?

I'd like to know because I'm already looking into a used engine, but I'd like to NOT go that route if possible.
Author:  63valconvert [ Sun Dec 04, 2011 3:22 pm ]
Post subject:  Another thought.
Could this just be a head gasket?

I am looking at the fact that the engine was rebuilt less than 30,000 miles ago. Probably more like 15,000. Potential damage would have come from the intense heat of a closed heat riser valve.

I like the idea of "upgrading" the head to a 72-73 head anyway, with the better combustion chambers.
Author:  Reed [ Sun Dec 04, 2011 3:30 pm ]
Post subject: 
I believe you have a head and/or head gasket problem since (a) you say the motor was rebuilt fairly recently and (b) adding oil didn't change compression. Pull the head and look closely at the chambers with low compression.
Author:  SlantSixDan [ Sun Dec 04, 2011 3:37 pm ]
Post subject:  Re: Another thought.
Quote:
Could this just be a head gasket?
Potentially, but probably not. Not if you haven't found wild overheating/overboiling symptoms (combustion gas getting into coolant), water in the oil, or oil in the water.
Quote:
Potential damage would have come from the intense heat of a closed heat riser valve.
No, it wouldn't have.
Author:  63valconvert [ Sun Dec 04, 2011 4:07 pm ]
Post subject:  The Misdiagnosis blues
Ok, so I rechecked with the Oil test and turns out my bad, I was using a Oil Additive (Rislone Compression Helper) as opposed to oil.

Once I put in oil, compression went:

#1 90 -> 120
#3 30 -> 50
#6 105 ->125

I stopped once I realized this thing was not looking good. Somebody give me a reason why I won't be putting in a new engine.

I can't see one myself.
Author:  supton [ Sun Dec 04, 2011 5:55 pm ]
Post subject:  Re: The Misdiagnosis blues
Quote:
I stopped once I realized this thing was not looking good. Somebody give me a reason why I won't be putting in a new engine.
Err, 'cuz you decided to rebuild the one you have?

Sorry man, it don't sound good. About the only thing I can think of is two-fold:

1. Find someone close by, who can validate your results. A slant member, or even just a good trusted mechanic. It sounds like you are doing the testing right now; but, it can't hurt to have a second diagnosis.

2. Depending upon how much time you have to kill, you could pull the head first. Look at the valve seats, and the crosshatch pattern on the cylinders. If the crosshatch looks bad--then keep going...

But I'm going to guess that swapping motors at this stage is probably fastest, cheapest and easiest solution.
Author:  emsvitil [ Sun Dec 04, 2011 8:30 pm ]
Post subject: 
Try a leakdown test.

You can listen for where the air is escaping. (when the compressor isn't running)

(or at least pressurize the cylinders and listen)
Author:  SlantSixDan [ Sun Dec 04, 2011 8:44 pm ]
Post subject: 
Well, gee…Here is a 1963 slant-6 engine with just 17k miles on it about to go begging.
Author:  63valconvert [ Sun Dec 04, 2011 9:40 pm ]
Post subject:  Thanks, Dan
Thanks Dan, but saw it. The problem? Maryland. I'm in California, so the distance is a little extreme.
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