My magneto was gapped well until I put the motor in my car there was enough play in the crank shaft to where my transmission shifted forward and closed the gap. Is there any way to shim the crank shaft back or do I need to re do it all? I know the parts suppliers are shims to move the crank forward, how can I move it back a hair?
Replace rear main cap. Bob
How do you know it shifted forward?
When I set up a mag I do it with the engine standing on its nose. Now, when placed in the car, assuming the 3rd main had .003 end play it can only move to the rear and only by the amount of end play in the bearing. Most of the wear on a 3rd main is on the front face caused by the pressure from the clutch spring while in low or neutral trying to pull the flywheel away from the field coil. When the wear becomes too great the gap increases and the mag output is weak.
To verify you need a 3rd main cap. I would mount a dial indicator to read off the front of the crankshaft. With the hand brake set (forcing the spring to pull the flywheel away) take a reading. Now, using a large screwdriver between the pulley and block, try to pry the crankshaft forward and see how many thousands it moves. If its much over .005, do as Bob suggested and fit a new cap to it.
Wouldn't it be nice if somebody would make a sealed bearing set up with shims that fit between the block and the pulley? Sort of like a clutch release (throw out) bearing.
Used to be that there was an after-market adjustable (for crankshaft end play) rear main cap that somebody made. Don't think I've ever run across one at a swap met though. Must be a pretty rare and hard-to-find item nowadays.
End Play....I got slapped once for end play...nice and firm and well worth the welt on my cheek.
Daniel, your rear main bearing cap is flanged to give end float in the crankshaft. If your magneto clearance has disappeared, the main cap thrust faces need attention. Bob suggested a new rear main bearing cap. This would work if you can buy one to suit your existing crank journal and it had the correct clearance for your application.
It may be far easier to fix your existing cap if the crankshaft bearing is good. In one of Ted Aschman's Tinkerin' Tips volumes I suggested a satisfactory method to fix excessive end play by rebuilding the thrust face on the bearing cap. It involves soldering bearing material to the thrust face and then re-working that face to eliminate the excessive end float. See page 3 of Tinkerin' Tips volume two.
If you cannot access this, I could photograph it and post it here.
Hope this helps.
Allan from down under.
I once bought a TT that the seller said he had a professional overhaul done on the motor . But when he installed it in the truck , he found that it had a knock and gave up and put it up for sale. I found that end cap needed to be reworked . I toke some of my old main caps and melted the Babbitt out and added it to the face of the cap . I failed it fat with a large fail . I drove that truck for years with that fix .
Perry- "I failed it fat with a large fail . " Can you explain?
Thank you for all the advice. I now have some direction and am going to explore my options.
I did that rebuild on my rear cap, not that hard and I am so-so with soldering. I to filed it flat with a big file!
After you add Babbitt the to the cap it looks like a mole hill . kind of arch shaped ,so you take the top off the arch with the file . This gives you a more or less a flat serves . Before you remove the cap you take a leaver and pull the crankshaft forward this will tell you how much babbitt you need to add to the cap more or less . If you have a will worn motor in your T you can pull the crankshaft forward which moves the magnets closer to the mag rind so the car will have more voltage to start the car . Just a little Model T trick .