Mag rebuild with worn mains..

[Cadjin dex]

I'm an seeking your advice on a rebuild. The dilemma is should I install the magneto with worn babbit main bearings. The crankshaft was bent almost .02". Straightened and magnafluxed it. It's ok. The rear main is well worn in the block. Cap looked ok. On all three as well. I scraped the center to try and align The main bores. Got it pretty close but probably not perfect. Set up the clearance at approximately .002" on all three and it spins real nice by hand. Here's my conundrum: the thrust or end play is plenty good enough to install the mag, but I recall it being worse five years ago when I took the motor down. . The thrust is.005". I'm concerned the thrust might loosen up after it runs a while. Thrust surfaces looked fine.

[Gene_French]

Dex:
.005 clearance on the thrust is in a very safe range ... i set new bearings at .003 to .004 clearance ... run it and enjoy ...always an optimist Gene French

[Les Schubert]

I agree with Gene on the thrust.
Have you put a dial indicator on the transmission shaft?

[Cadjin dex]

Regarding the indicator, to detect run out?

[TonyB]

From memory, the high limit end play on the crank is 0.006” but I’ve had engines in for rebuilds up to 0.014” so you should be ok for awhile
As an aside, I remember in Milt Webb’s tuning book, he estimated that when run at high speed, he figured the wear could be as high as 0.001”per thousand miles. I always thought this was high but he use to run his coupe at 50 mph on a regular basis.
Any thoughts?

[Norman Kling]

Have you checked the fit of the timing gears? If you turned the mains, the timing gear will not be in the same place in relation to the cam gear. If I had the engine apart enough to remove the crankshaft, I would have the mains poured and line bored. That way the engine will last much longer before another major repair.
Norm

[Allan]

.02" is quite a bend, even without any twist. I would have like to have seen that shaft in the press when taking that much of a bend out, and having it remain straight. I am glad you had it tested afterwards.
If you have concerns with .005" end float, the thrust face on the rear main cap can be built up with whitemetal using soldering techniques, and then worked down by hand filing/scaping to get a closer gap.

Allan from down under.

[jiminbartow]

When I was 16 in 1970, and restoring my ‘26 T coupe all by myself with nothing more than the Model T Service Manual, the Model T Bulletins Essentials and the Model T Restoration Manual as my guide, I restored my T using common sense from my experience in repairing and rebuilding lawn mower motors and my $1.65/hr. wage as a part-time after school bag boy, I did things that would shock the members of this forum, but somehow, the things I did, successfully made my T run better back then than it does now when, in 2010 I re-restored my engine with an unlimited budget and doing everything right.

One of the shocking things I did back in 1970, was the way I confronted my worn main bearings. When I removed the crank shaft, I discovered that the surface of the babbits were soft, powdery and gray and could be scratched off with my fingernail. Of course I had no idea where to send it for rebabbiting and even if I did, I could not have afforded it, so I did the only thing I could. I took a straight razor blade and carefully and as uniformly as I could, scraped out the soft babbit until I reached the shiny hard babbit and did the cap the same way. I did one bearing at a time, after scraping each bearing and cap, I removed shims until the crankshaft was tight and added a shim until the crankshaft bearing turned. I would remove the cap and carefully stack the shims of the bearing I had just done, then do the same procedure on the next bearing, doing one bearing at a time until all the bearings were done.

Another shocking thing I did that most members here would discourage was to refurbish the magneto myself. It was in bad shape with missing insulation with many of the coils showing. Again with no knowledge of where to send it to be rebuilt and no money to get it rebuilt, even if I had, I did the next best thing. Using a round container the size of the mag coil, I soaked the entire coil ring in mineral spirits, which turned the mineral spirits black. After several changes of mineral spirits it gradually started to become clear. When it was clear, I let it sit in the mineral spirits for a week so as to soak out the deep seated oil, which, after a day, turned brown from the old oiled down deep in the coils. Finally, when the mineral spirits stayed clear and I was satisfied that all the oil was out of it, I hung it up and let it dry for another week. After it was dry, I applied 4 coats of red Glyptal and let it dry. During all this, I was rebuilding the transmission. When I assembled the engine, I was too ignorant to know that my chances that the magneto coil would even work were very slim, but ignorance is bliss and I did not know to be worried. When I got the engine on the chassis, wired it up, and rigged up a fuel source, it cranked on the second try and amazingly, the magneto worked and the engine ran without a knock. I was incredibly lucky, but it is proof of how resilient the Model T is to have run so well after having been worked on by such a novice, just like the new Model T owners back in the day, that knew as little as I did as they embarked on repairing their T’s on a shoestring budget, just like me, because they had no other choice. My first restoration was completed in 1972 and my T ran beautifully for 38 years until my second restoration in 2010.

Bottom line is, if you have the money, by all means, do it right, but if you don’t, don’t give up, do it anyway you can. If you use common sense and have a copy of the T-1 Model T Service Manual to guide you, chances are, you will be rewarded with success. Jim Patrick

[Cadjin dex]

Jim and Norman, thanks for the replies. It's good to see you all are still active here.

Allan, the crankshaft was on some homemade wood V blocks when we straightened it. The force applied deflected it approx. .4 inches then we shocked it with a pieces of brass and a hammer. It took 3 or 4 try's. I didn't want to deflect it any more than that. It was kind of intense. It runs out at least. 001" but that's good enough for me.