Rear main cap removal advice

[Bruce Compton]

My crank has almost 1/8" end play so the mag is weak and the car won't idle down on Mag (it's fine on battery). I tried recharging the mag but soon discovered the excessive end play so now I'm wondering....are there any secrets to making the rear main removal easier than it appears??? It's a '26 so apparently it's possible to get it off with the engine in the car. Thanks in advance; Bruce

[Norman Kling]

It is difficult on a 4 dip pan, but I have never tried it on a 3 dip pan. It would be easier to put a spacer between the front of the crankcase and the pulley until the time you need to pull the engine for some other reason. If you can get to the cap, you can add babbit to the front edge to pull the flywheel closer to the magnets. You might need to try it on and remove it for fitting, but try to get it close to the clearance you need before you attempt to install it. If you do it with the crankcase in place, it is best to put some rags between the flywheel and the magneto ring at the bottom of the area just in case you should drop a shim or a nut or a cotter pin, it won't get into the magnets. With a 4 dip pan it is possible to do, but not easy. Be sure to remove all rags before you button things up.
Norm

[Joe Bell]

I would pull it and do it right, would be really hard to set the thrust in the car, not knowing where the magnets are to the field coil? I have done a few rear main fixes and would never try it in the car!

[Joe Bell]

You have to remove a flywheel bolt to drop the main and chances are some thing will fall down in.

[Bruce Compton]

hanks Norman; The spacer between the pulley and front of the block sounds interesting. Is that a normal practice, and what would you suggest for material? I have access to delron, hard nylon and brass but would be concerned with the rough casting at the front of the block/timing cover. If I pull the rear main cap, is it possible to use solder to add some thickness to the thrust surface as I don't have ant babbit.

[Bruce Compton]

Thanks Joe . I hear ya. That's why the spacer at the pulley sounds enticing (for a while anyway).

[JTT3]

I believe some of the vendors sell a brass fittings that fits between the block and crank pulley

[JohnH]

Some years ago I did remove the 3rd main with the engine in the car. It required first removing the safety wire from the flywheel bolts, and then removing one flywheel bolt so the the bearing could drop down. It's tricky and requires good dexterity, but can be done. Best to remove the radius rods to get better access to the whole thing.

[John kuehn]

The Model T Ford Service manual chapter 7 page 110 has some information about taking up the mains while in the car but it’s not real easy. It can be done if they aren’t worn to bad.
Lang’s sell an old time end play fix that’s been around for years. It’s called a crankshaft shim
no. 3030SHIM.

[Gene_French]

Bruce:
this can be done ... moderate difficulty ... 1 flywheel bolt is removed so the rear cap can drop down for removal ...you will also have to push upward on rear main bolts to allow cap to drop down ...
the thrust flange may be built up with babbitt or the cap replaced ... it will be a good idea to measure the amount of wear on cap before removal ... this will allow you to accurately fit the cap or to face the thrust on a new cap ... i have measured by inserting feeler gages between crankshaft thrust flange and babbitt thrust surface on the cap ... you will have to hold the crankshaft forward to do this ... hope this helps ...as stated above , it is best to do the job right ... if the thrust is bad on the mains , then it is probably time to re-babbitt and do any other work needed to assure good service ...always an optimist ...Gene French

[Russ T Fender]

I ran a T with the shim the venders sell for use behind the front pulley for years. Wore one out and replaced it with another one until I pulled the engine for a complete overhaul. Just wondering if it would be possible to use the center main to take up end play. That would seem to be a relatively easy and quasi permanent fix if it can be done. For that matter I wonder why it would not make sense to do that as part of a total rebuild so you would have double the thrust surface out of the gate.

[RajoRacer]

I have several different types of era accessory center main caps that do just that - much easier to adjust the thrust.

[Jim Eubanks]

It can be done and does require patience. IMHO the fix is determining first what the gap is before pulling the cap then after the cap is pulled, make a c shaped brass wear plate the correct thickness and pin it to the cap with countersunk brass screws. I speak from experience and have one of my Ts fixed that way that has run for years.

[Bruce Compton]

Wow, Thanks for all the great advice everyone. I have ordered the crankshaft shim from Langs and will give it a try. I just bought this '26 Coupe that is a 3 owner car that was "restored" in 1965 with a "used car" paint job without removing ANYTHING and at the same time was re-upholstered and had the original bumpers re-plated. It's very low mileage and has an amazing original unmolested body so I just want to drive it for a while to get a feel for what the future holds and which direction to take. The motor is original so a total rebuild will probably happen next fall but I'd rather drive it for a while before tearing everything apart. Thanks again : Bruce

[Allan]

Any in car fix involving the rear main is dependent on the crankshaft thrusts also being in good order. If there is a wear groove in the crank thrust faces, no amount of added Babbitt will totally compensate for wear.
I would be interested in the centre main fixes. As there are no thrust faces on the crankshaft journal, how do they work?.

Allan from down under.

[Craig Leach]

Allen
The cap is brass so it gives a more robust surface to wear against. It alos has a way of locking it in place to get the mag ajusted.
Made by the Hayward bearing and casting Co. Called the "Stay Put" adjustable center main bearing cap for ford motor.
I'm having trouble sending pictures to my comtuter.

[Allan]

Craig, I was not aware that the cap was brass, but it still does not compute with me. You report that it is stated that it wears better, but in the absence of a thrust face ground on the crankshaft, what does it wear AGAINST? There is no thrust face on a centre main cap and no thrust face ground on the crankshaft. I must be missing something. Or does it just fill a gap like the temporary brass item sandwiched between the fan pulley and the front of the block, and wear against whatever?

Allan from down under.

[Don Conklin]

What about slotting the holes in the cap so the cap can move forward to reduce the end play. Ref. Ted Aschman’s “Tinkering Tips” volume 2, page 2

[speedytinc]

Center main fix isnt a great idea. In operation the flimsey T crank will "grow" in length. Big problem for go fast guys. If not enough clearence is given to account for the that growth in the center & front main caps the force can lead to a broken crank. Thats usually the cause of a frontal area crank break.(barring removed radius's on journals).Rear area breaks are usually from pan/4th main misalignments. One old timer racer buddy told me to allow at least 1/8" @ the front main for crank growth. If the t was originally center thrusted, the magnet/field coil clearance would change @ speed. "widen"

In regard to in car or engine out fixes. Were it a new acquisition to me. Unknown.
If the rear main is worn out, there are a bunch more mechanical issues to be found. Do it right. Pull the motor. Even if i thought(over optimistically wishing cross my fingers & toes) there was no other issues, i would consider the total PITA job of going from the bottom side to patch it, & still probably pull the motor. That bit of overall extra time will save big $$$'s in chiropractic visits.
Front thrusting behind the crank pully is so 1/2 A%&. But if you are occasionally driving to the donut shop & have no serious touring expectations. Thats a painless patch.

[Craig Leach]

I would assume that there is enough suface in & past the radius of the center main journal to hold the crank in place. Don't think it would be wise to set it up any tighter than you would the 3rd. main. This is just a stop gap repair I would not think it smart if you are not sure the rest of the engine is up to the task. As I understood this was intended to keep the Mag. working? When I purchased the engine in for My speedster I was told it was probably
rebiuldable. I didn't. In the next 7 years I replaced the valves, lifters, head, 2 rods, and the bands. ran the cr@p out of it but didnt pull the engine untill I cracked the low drum. The more knowledge I gain from working on T's the less fun & more worry I have. Some times I think we over complicate one of the simplest cars ever made.

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