Hi guys, I am usually quite good with ford engines, however I wanted to get a second opinion on something before I tear into it. I recently purchased a 1975 F150 for $50 and I got it running and drove it to my parents place (250miles). It was able to make it there going 70mph most of the way, however it had a really wicked miss. I knew that either one or two cylinders were not happy. Anyhow I got it home and checked compression and found that the second cylinder on both sides of the motor (#2 and 6) had absolutely no compression whatsoever. I found this interesting, because I've had some very worn out engines, but never one with no compression at all and its wierd that they are the ones opposite of each other. I tryed to look throught the spark plug holes to see if the pistons were damaged, but they didn't look like it and I pulled the valve covers to make sure the valves were working correctly and they are definetly moving when they should. I would appreciate any advice on this, I was kinda thinking that it might be two completly fried exhaust valves, but not sure. She smokes badly too kinda a blue and white mix, so I was wondering if it was a bad head gasket, but not really using a lot of coolant. Well anyway hope to hear from you guys. thanks

 

I would suspect extremely burnt valves (or broken) for zero compression. I have never see a blown head gasket give zero.

 

Rings maybe? That might be where your smoke is coming from. Of course with that old of a motor, it could be anywhere.

 

With the valve covers off look to see if all the valve stems are the same height, maybe the truck sat a long while and two exhaust valves are hanging open. Any pushrods bent or lifters collapsed (reaching for straws)? Hole in two pistons? I would TDC each bad cylinder and add air with a leakdown tester or plug adapter to see where the air goes, tailpipe crankcase, carb (that would of popped).
.....=o&o>.....

 

I will have to look into that some more, because the truck had been sitting for a long time (couple of years or so). thanks