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Air Randy
12-13-2008, 06:01 PM
I ran a compression check tonight on my 1974 FJ40 with the F.5 engine.

Some info: Since I am waiting for my carb to come back from Jim C, I couldn't run the engine first to operating temp before checking the compression. But it has been parked in a garage that maintains 65 degrees, so not ice cold.

And the carb is off so even better than WOT, all the plugs were pulled. It was just me so I couldn't see if the compression jumped up then topped off slowly or built up slowly, but I cranked each cylinder about 20 revolutions.

All of the cylinders were 90-95 lbs except for #4 which was 40 lbs. I gave #4 several good squirts of oil and checked it again and it only came up 5 lbs.

I live at almost 6800 ft elevation so I'm thinking 90-95 works out to around 110 to 115 at sea level. What should I be seeing on this F.5?

What do you think about #4. Burned valve or cracked seat? How big of a job is it to pull the head? Any recommendations on who to send the head to for a valve job (I live south of Parker)?

One more question: I have a 6-1 header for this. If I'm going to have to pull the head I'll wait to install it then. But, I've read that you have to get the intake "shaved" to match the thickness of the header flange. Is that corrent or is there another way to make sure it goes together right? And if I have to have the intake machined, any suggestions on where to get that done?

60wag
12-13-2008, 06:12 PM
Before deciding that a valve is toast, adjust or at least check the valve lash. You want to be sure that the valve is seating completely. I tend to set the clearance a bit tight and nearly freaked out when my 2F was showing low compresion on one cyl. A valve adjust brought it back up where it should have been.

As for the intake, it'd be best to have it the same thicknes as the header but if they are too far apart, some custom shims can make up the difference. The machine shop that flattened my maifold is gone but they used a giant belt sander to surface it.