9N head on 8N tractor

Yesterday I visited a used tractor parts place about 50 miles from here and found another usable head. From the casting numbers, I knew that I had a 9N head, but it looked good, and both are front mount anyhow, so probably no problem.

Today, I drained the gas, pulled the hood, tank and dog legs and then carefully removed the head stud nuts (I had put the studs in a few years ago) and pulled the head. But from careful inspection, I can see there is a volumetric difference in the cavity for each cylinder. Of course! The 9N has lower compression, and a lower HP (I'm reminded of how much by Farmer Dawn's post a few below this one).

How much difference in operation of the tractor does this lower comp head make? Much of the time this 8N is just used to go somewhere, as he is not allowed a driver's license, so less HP is probably not an issue for that use. But he does use a 5 ft hogg about a half doz times each summer, and that may be where the HP becomes a problem. The 9N head was the only good used one I could find ($75), and a new import is more than $150, and the FNH part is $400. If you have done this swap, tell me how it worked out.

Thanks!

Paul in MN

Thanks for weighing in on this. I knew when I bought this head that I wa going to get lower compression, but did not think it would be very noticable. However, Dawn's citing of the HP differences is significant. Almost 1/3 less HP. But this is a tired engine, needing rings sleeves, bearings, really a complete OH. My guess is that this one has never had an OH, but his grandpa was the first owner and used in vegetable gardening, so it had a pretty easy life. When Mark got it about 13 years ago, he liked to rev-rev-rev and drop the clutch, sometimes shearing off a rear wheel stud. I think the less HP might be just the right thing for him and making this now tired N live a few years longer.

He'll probably never know that it is less HP, as long as it starts and runs.

Paul in MN

The tired engine may give you trouble starting with the lower compression, 9N head. I have a good head from a side mount 8N I'll trade you straight across. You pay only shipping.

jim

Dan