I have a bit of a curly one I need help with... or at least use the forum as a sound board.
I just got my heads back from the machinist, installed my new head studs, gaskets (corners toward the front) and torqued down the head (80ft-lbs 3 times as the ARP/Mummert guide suggests). I then installed my new adjusters and pushrods and went about setting the valve lash. I filled the engine up with new oil and installed a new filter and used a drill to prime her up.
Since I had the plugs out, I was blocking the spark plug holes with my thumb while turning the crank with a wrench to get the compression stroke. The passenger side (1-4) gave me plenty of pressure by feel of thumb when rotating the engine but when it came to no5 piston... not even a breath of air, but 6,7,8 all seem fine, Something is wrong, I have tried several times holding my thumb over the no5 plug hole but nothing. I tried a gauge on all other cylinders and got roughly 40 psi but 0 on no5 (keep in mind I’m hand cranking).
I did use a dial gauge on both intake and exhaust and compared it to no1 cylinder to make sure the valves are opening/closing all the way and it was ok.
I am leaning toward a ring problem, as I put some oil in no5 cylinder and got some pressure by feel of thumb over plug hole.
Bit of background-
The heads received
- new hardened exhaust seats
- full valve grind job
- machined head surface
- .530 valve guide cut and positive seals
The machinist has over 30years experience and was recommended by a reputable mechanic, so I don’t think it’s the heads or head gasket.
The 272 engine was sleeved after a failed cylinder boring attempt and 20thou pistons were fitted (didn’t sonic check and went for 292 std Pistons size) (different machinist)
Thinking about it, after the rebuild the engine has always sounded like it had a bit of a miss but I thought that was because I didn’t have the head work done but I was sure I checked the compression before and after the rebuild but it’s been a couple of years and only just got the heads done. The engine hasn’t seen many hours- less than 5 and most on an engine stand.
I did snap a piston ring when installing the rings, so there is one different brand ring but I can’t remember which piston it’s on.
On the weekend I’ll tear it all back down and pop out no5 piston and see what the story is. It’s a big hit to the morale having to pull it all back down again and discard the newly installed gaskets and oil but it’s all experience and valuable lessons.
56 F100 - 272 Y Block
Sydney, NSW, Australia.