Jerry Kieffer's 1:8 scale D John Deere

[Forrest A]

I posted a video I shot of Jerry's tractor driving on You Tube.


http://www.youtube.com/profile?user=mascobe

Forrest A

[gbritnell]

I've seen Jerry's tractor on several occasions. Extremely impressive, all of his work is.
gbritnell

[maryjane30]

thanks for the clip, first time i've seen this running.. now a question.. is it timed right? maybe its just running fast, but sounds a bit regular for a johnny popper? what does everyone think?

M-J

[gbritnell]

Hi MJ, having built some very small engines I can tell you that they have to run faster because they don't have enough flywheel weight to keep them going. You can increase the size of the flywheel but then you can't build an engine to scale. That's one of the physical problems in scaling down full size machinery. You can build everything in miniature but things like carburetion, ignition and physical forces can't be scaled and still work properly.
gbritnell

[Benjamin Roth]

Yes, it runs fast. I remember Jerry talking about lowering the compression ratio so he could still have a scale flywheel and not some big ugly thing hanging there. It runs a little slower now that it is getting broke in.

Benjamin

[Kelly Tytlandsvik]

I e-mailed Jerry a few months ago to get an update on the Harley he is building. He told me the Harley will be on the back burner for awhile as he plans to cover up that beautiful machining job with some green paint. He said he does have it slowed down more now that he has tweaked a few things!

It is a Museum quality piece! He had it here in Estevan at the show twice and was a real show stopper! It is perfect........right down to the proper number and size of holes in the aircleaner stack!

Kelly T

[Forrest A]

A note about the RPM and the comp ratio, the RPM has slowed the more it has been run. It will however never run at the rated 900 rpm reliably due to the laws of physics. As for the compression the real tractor has a 4:1 compression ratio and Jerry, initially had too much built into tne tractor. It does fire correctly and would sound just like the full sized tractor if it did run at the same speed.

I know a fare amount about the model D and have been a reference for Jerry, he has a real 1936 D and I have one as well. The tractor was designed to run on kerosene/distillate and so the compression ration needed to stay low or pre-detonation would occur. A water injector was used to dampen the mixture enough to prevent pre-detonation as well.

I had my D on a dyno last fall and it was putting out 47 hp at 900 RPM which is 5 hp higher than rated. I always wondered what it would do with compression boost. There is ton of space left in the cylinder when the piston is at TDC, as much volume as some small car engines displace.

Forrest A

[ronm]

Hey Forrest, somebody builds "donuts" for the tractor pullers, it's a ring that fits in the combustion chamber above the piston, has a flange that lets the head hold it in place. Raises the compression a lot, I don't know exactly how much...I suppose you could specify what you want. I think they pretty much make an electric starter necessary...There's a D around here that has the spark plugs in the head, which would seem to imply "loooong" pistons... the guy claims "lots of mods" but won't really tell anybody what's in there...It didn't seem to me it pulled that much better than a stock D...
Ron in CO...

[Forrest A]

Ron,

There is more to making horse power than just boosting compression. My guess is he hasn't done much to help the air enter the engine quicker.

I have seen the doughnuts and also the 0.125" over AL high compression pistons (which is a HUGE jump in displacement), some were just on eBay.

Forrest A