Post
by Lavoy » Fri Aug 17, 2012 4:14 pm
Valve seat recession is a function of lead, which was pretty much gone by the end of the 70's other than avgas. Any of the rebuilds I do always get hard seats in the head to alleviate this problem.
I have dynoed more crawlers than I can remember that have been personally rebuilt by me. Not that my dyno is not off by a few HP, but running ethanol at stock timing, they have all been within 5% or less as far as HP per given model, and with a little bump in timing, more than a few will run 20% over stock as per my dyno. I expect on a rebuilt 420, 430, or early 440 at minimum to show 32HP on the dyno. They are rated at 25 HP PTO, so as I said, there could be some error in my dyno, but readout has been very consistent between engines.
My best ever was a 420 that I am fairly sure had a high altitude head. Setting carb and timing for maximum power at rated RPM by the dyno, it would consistently yield 37HP on ethanol. Once after a dyno run, I timed it with a degree timing light, and it was at 37 degrees at high idle, so 14 degrees hotter than stock. This crawler performed like it too, was truly a joy to run, but if you really let it pound, you could start to hear some detonation at the lower RPM's, so needless to say, no one but me ever ran it, and I never pulled it down too far for too long. I should note that it also had a brand new water pump, radiator, and updated 6 blade fan. I would never try this on a poor radiator with original fan.
By comparison, my non-rebuilt 430W would never make rated power no matter what I did to it so I always assumed that the dyno must be fairly close.
Lavoy
Lavoy
Parts and restoration for antique and late model John Deere crawlers.
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