Hi Guys. Im new to the forum and new to a Model T. I have been a mechanic all my life. I am rebuilding a 25 T engine. The engine still has std bores and crankshaft and rabbit is in great shape. My question is how much crankshaft endplay can you have? I know the spec is .003-.004 I have .008. Twice as much as allowed! Should I be alarmed? I read in one place some one had .018 and had no problem. someone else had .074 and did have magneto issues. I guess I am wondering if need to address the issue.....will I ever wear it out?????? I do have the engine apart now so now is the time to do it but do I really need to bother?
The engines I have torn apart for rebuild have on average .012 end play. Apparently they ran that way for many years.
I don't think the .074 is the truth. We set at .030, and .074 is over half of that. The flywheel should have taken out the coil ring, flywheel, the block, Hogs Head, and maybe the Guys feet, long before that.
Excessive end play does a lot of damage.
It can makes the fan belt unstable.
Makes the front seal leak.
Cuts the 3 main backside clearance and runs the crank in to the block.
Throws the rods out of alignment with the block.
Can explode a Mag.
Changes wear position on the tail shaft, and will pump oil to the drive shaft tube.
Ford said any end play over .004 thousandths , should be fixed.
As for the Mag. working properly, a flywheel that has to much clearance, the flywheel runs to, and away from the coil ring, sending the out put up, and down, causing stronger, and weaker spark.
Ford said any end play over .004 thousandths, should be fixed.
That is true when doing a proper full engine rebuild.
Ford also said, if there is more than .015" end play in the shaft then it's time for a new cap.
Your .008" will see you though to the time your engine will need a full reconditioning.
Excessive crankshaft end play can be a problem when using neutral or low gear because the high gear clutch fork is pushing the crankshaft forward and can cause the magneto magnets to contact pickup coil ring, shorting out the magneto. Brad
I have never seen a rear main worn as to let the flywheel move forward and hit the coils. Always worn to move the flywheel further away from the coils.
Kelly - Nobody said it, but let me be the first,....welcome to the forum! You have come to the right place,....lots of helpful people and information here, and all you have to do is ask!
Herm - Just trying to help,... You said,.... "I don't think .074 is the truth". I'm thinking that you might have mis-read part of Kelly's original post. He said,..... "someone else had .074 and did have magneto issues".
.....and then again, maybe I just don't understand,.....harold
It can be fixed without much of a problem anyway. Careful addition of new babbit material to the thrust face on the rear cap using a soldering iron can be achieved. All that remains is to hand file/scrape the trust face back to give the desired clearance. The process is detailed in one of ted Aschman's Tinkerin' Tips compendia.
Hope this helps.
Allan from down under.
Thanks guys for the quick response! I agree there is lots of good information here on your site. I think since I am in the process of the rebuild I will take the time and do it right. IE build it up and machine the two faces. I have machine shop capabilities. I talked to a fellow on the phone today that for only .008 to just shift the cap and see if that takes up the clearance. Since I would only be building up the cap surfaces I would only have 1/2 of the thrust surfaces in contact with the crank anyway I might try that. I guess I would end up with thrust on the cap from one end and on the block thrust surface from the other. He did say everything you can do to help the magneto is a good thing. He has seen very few failed magnetos mostly coils adjusted to draw higher amps that the mag was designed to supply.
So to sum it up.....Im gonna shift the cap and see what it looks like. If I don't like it I think I will build it up and remachine the two surfaces in the lathe on a mandrel.
IMHO shifting the cap is not a good idea if what you mean is reversing the cap on the crankshaft. Your cap had achieved a good fit with with the crank in the position you found it. It would be like reversing a rod cap. Bad practice.
I once elongated the bolt holes on the cap so I could move the cap closer to the crank flange. Another bad idea. I found it difficult to tighten the cap without distorting the position resulting in a bad fit on the crank and uneven wear on the cap babbitt.
I like your idea of building up the thrust surfaces and machining them on a lathe using a mandrel. I've done that myself with a jig that allowed me to accurately take the same amount off each side. You can also purchase a new babbitted cap, fit it to the crank by scraping and the use of Timesaver and set the thrust on a lathe like you said. I've also had success with that approach.
You will most likely find that the thrust surfaces on your crankshaft are also worn. There tends to be a groove worn into the fore & aft thrust surfaces. A widened cap will not pass the high ridges on the outside of the groove and narrowing the cap to do so will only put you right back where you began when the cap is bolted down. In other words, the cap is only half of the equation. You've got to address the crankshaft wear as well. I have put my crank in my lathe and carefully re-cut & polished those surfaces. Then measured the resulting gap before sizing the main cap.
No, Harold, I got it the first time. Kelly said he had .008
Herm - Yeah,....It's ME that "mis-read"! I need to learn to read the WHOLE THREAD before commenting, right? Sorry,.....harold