Roy, your grandson is very fortunate to have you for a grandad! Really neat project.
Chim,I feel I am the lucky one, kid is just fun to be around and as we have the same interests it just never gets old.
To the build, one point I would like to stress on this unit is the beauty of welding the spiders in a front wheel drive trans-axle. What a game changer. The second home-built I have done this with. It not only gives you a transmission with an additional 3.5 to one reduction unit built in it shortens the power train up as the powerflow doubles back on itself. Compare this with using a conventional car engine with a conventional transmission and then having to put a second transmission behind it. Things get so long you simple do not have room for it.
By welding the spiders and using only one drive axle to power the unit you have the ability to locate the engine were you get the best fit and balance.
Now the question is, how strong will it be? Stronger than you think. In my first homebuilt I used a little 96 cubic inch Nissan Sentra motor with the five speed trans-axle. On this unit the clutch is about the size of a pie plate, the spiders gears the size of fifty cent pieces. It has been in operation for 25 years, we used it to spray 2-4D on lawns yesterday. We play with it at tractor pulls. In all the dinging around and pulling we have done it took twenty years to wear out the first clutch and the welded spiders have never been an issue. on the other hand the nine inch Ford rear end we use with adaptors and semi truck tires has had the spiders fail three times.
Yes, the one thing I did not think would give any trouble has let me down three times, every time on a tacking pulling track. The little Nissan motor will simply crack the spiders like walnuts on a hard pull. Why? Every time you slow it down by half you raise the torque applied by two. Think of it from those broken spiders point of view, there is a 3.5 to 1 reduction in the trans axle final drive, then a 2 to 1 reduction in the transfer case I use, then a 5.38 to 1 reduction in the 9 inch Ford. Now hang some semi tires on it, think of them as a big long pry bar on the axle. All that torque is caught up in the 9 inch's spiders.
I have no doubt there will be some weak links in this latest project we have. As to the little three speed GM trans axle? I have high hopes for it as the closer to the engine the less torque there is. Little nervous about the welded axles, afraid the truck spindle we used for the front pivot will not be strong enough and have to be re-designed, Worried about the welds on the welded sprockets, lot of torque there. Also concerned the pull from the drive chain my simply rip the nose off the back differential.
But this idea of using a trans-axle with the spiders welded solves a lot of builder issues. Anyone considering building a home built tractor should take a good look at it.
