New cylinder heads, and compression goes DOWN?!

[kapnklug]

AARGH!
So just replaced both heads with rebuilt exchanges. With the old heads the compression test results were all 300-360 psi. The new head gaskets are Felpro 6.5 turbo gaskets, +.010 thicker than stock (trying to drop the compression a little, since I'm adding a turbo). I expected the compression pressure to drop a little because of the thicker gaskets. But with the new heads and gaskets the compression results are now 180-240 psi.
I've replaced heads before, the installation was not the problem.
1. Would a .010 thicker gasket reduce the cylinder pressure this much? I find that hard to believe. Will the motor even run with this little compression?
2. The thicker gaskets have the effect of reducing the length of the pushrods, meaning all the valves will open later, not as far, and close sooner. Some of the rocker arms seem a little looser than before. Could this cause the lower compression? How do you adjust the valve lash on these motors?
3. Or maybe the machine shop just screwed up the valve job?
Any advice appreciated, I can't continue with the build until I figure this out.

 

[dstang97]

you should have 400-425 psi and a good motor. sounds very low

 

[corelokt]

How hard was it to swap the heads? Looking at this myself.

 

[DavidJBlythe]

does your engine make any more noise when cold since putting the larger felpros on? Mine seemed to clatter more, which I figured could be from the pushrod length issue you described... let me know how it turned out.

 

[kapnklug]

Hey corelokt,
Ya I read your previous post about your situation. Maybe you should ask how hard the head swap is AFTER I get a running motor!
But anyway, if I didn't already have the hood and fenders off, it would be easier to just pull the engine. With the front clip off, it's still alot of work.

Hey DaveBlythe,
So you used the same Felpro +010 gaskets? Did you do a compression test after? I don't want to continue putting the motor back together until this is resolved.

 

[ODdave]

#3, Check the installed height

If you have access to a straight edge (a real one) Pull you rocker arms and set it across the valve stems. See if there all even. If there not you obviously have a problem, The intalled height could still be off if they are even, but check across them first.

 

[hardhead]

Try and put a little oil in the cylinders that happened to me long ago, I got too carried away cleaning the dust out and dried the compression rings

 

[kapnklug]

Hardhead,
Putting oil in the cylinders of a diesel with so much compression sounds a little dangerous. And it's not like I can distribute the oil 360 degrees with the heads on. I did however blow the cylinders clean with compressed air before installing the heads, which would have dried out the compression rings. Has anyone got any experience with this?

 

[diverman555]

In order to keep the same psI that you had, if you put gaskets that little amount thicker then you would have to have your heads milled the same difference as the gasket. I raced ARCA with 800hp motors and with just that little difference in height we would loose 50 hp. Just for cost sake I would put gaskets back on the same thickness as the old ones. Mark

 

[ODdave]

In order to keep the same psI that you had, if you put gaskets that little amount thicker then you would have to have your heads milled the same difference as the gasket. I raced ARCA with 800hp motors and with just that little difference in height we would loose 50 hp. Just for cost sake I would put gaskets back on the same thickness as the old ones. Mark

Works on gas, not on diesels........ Diesels do not have combustion chambers like a gas engine so milling them wont gain anything.

 

[hardhead]

The time that worked for me I wiped the cylinders with stodard solvent and a rag,, try one cylinder with the injector removed, (it should already be out for comp. test) use 1/3 teaspoon or less spin the motor over (excess oil will blow out ) don't glug glug the oil in the cylinder too much oil,as it will create a hydro lock. dstang97 is right,you should have 400 lbs or so compression you can check a TM to verify this
Also when the heads were removed did you micrometer the bore at BDC to check for cylinder elongation, or do a ring gap check??
Hope this helps

 

[kapnklug]

Is anyone using thicker-than-stock head gaskets to lower the compression, and do you know what compression test PSI is normal in this situation?