Farmall Cub

by **WKPoor** » Tue Apr 08, 2008 9:20 pm

Some may remember a few yrs back a problem I was having with my H fouling plugs after a rebuild. Well I may know why in a round about way. Recently I was trying to diagnose a chainsaw problem using my compression tester (2 cycles are very compression sensitive). I wasn't getting a very good reading and it was suggested my gauge might be off. So Monday I had an opportunity to check my gauge against another and found it to to be reading 40lbs low. WOW!! That means the reading I was getting on the H of 180lbs was really 220lbs. Man thats alot of compression and explains all the fouled plugs. Actually it just might explain all kinds of issues I was having. Rough idle, starter failure,wrist pin failure, and fouled plugs to the point it will only run on racing fuel or AvGas. We had milled the head and reshaped the chamber to except the high toppers leaving about 25thousands clearance. Yep it ran good and strong but all the fuss over why it was fouling plugs so bad on pump gas may now be explained. It just had too much pressure!
Its still apart from the wrist pin episode and I remembered I had the head redone and the guy said he took a little more off it again. Oh no hope I can still use it as I've got a pile into that head now. More than I originally paid for the tractor.

by **NawlensGator** » Wed Apr 09, 2008 10:31 am

220 psi - WOW. That's a compression ratio of 16 to 1. Maybe you could shave a little more off, get the pressure up to 280 psi for a 20 to 1 compression, and make it a diesel. What about a thicker head gasket? Once you get over a 10.5 to 1 ratio (around 140 psig) you start needing high test.

by **KETCHAM** » Wed Apr 09, 2008 1:09 pm

What now???A new head.that sucks!!!Kevin

by **WKPoor** » Wed Apr 09, 2008 1:50 pm

When I get around to putting it back together I'll check it again and see where I'm at before I make a decision. The pullers have more compression than that. A friend of mine has a 300 Utility with 300lbs compression. Over 100 HP too.