Switched heads and lost compression

JasonNC
JasonNC Expert Adviser
in HUDSON
I have two 262 engines and I traded them out because one had 100 lbs. of compression in all cylinders while the other had 100 lbs except in #6, which had compression of 60 lbs. I took the original head off the the motor with the proper compression and replaced it with the "500" head from the second engine. Now I have 100 lbs in all the cylinders in that engine except # 4, which has dropped to 90 lbs. I'm planning to put the original head back on that engine. Any ideas as to why the drop in compression after the head swap?

Comments

  • Geoff
    Geoff Senior Contributor
    Are you checking with hot motor, throttle wide open? 500 head is off a 232 motor, so theoretically compression should be higher.
  • JasonNC
    JasonNC Expert Adviser
    I warmed the engine up before I checked the compression. Not sure what you mean by "throttle wide open". The reason I switched to the 500 was to get higher compression. I notice that there is an exhaust leak near where the manifold is attached to the head between plugs 3 & 4. I can't seem to cure this problem on either engine with the 500 head. This leak didn't exist with the original head on the motor with the normally good compression.
  • Geoff
    Geoff Senior Contributor
    When doing a compression check you need to open the throttle when cranking the engine over, so it gets maximum air in for compression. Exhaust leak has nothing to do with cylinder head. Manifold is attached to the block, not the head. You need a new gasket. I wouldn't worry about the 10lbs difference, it will not affect the running of the car to any degree.
  • JasonNC
    JasonNC Expert Adviser
    Thanks Geoff.
  • Nevada Hudson
    Nevada Hudson Senior Contributor
    Is the 500 head narrow block and the 262 wide block?
  • Geoff
    Geoff Senior Contributor
    Yes, that is correct about the lower compression in No. 6. According to the report, the knock went away in later models, so no actual cause or fix was come upon. Probably better fuel.
  • JasonNC
    JasonNC Expert Adviser
    Nevada Hudson said:

    Is the 500 head narrow block and the 262 wide block?

    There are two block sizes for 262. 500 fits the narrow block 262, 232 fits the wide block 262 from the later model engines. Ask me how I know.....

Categories

In this Discussion