Magneto Clearance

[BarnesvilleT]

A bit new to all this. Engine was vertical on the engine stand when I put a new magneto on. Put the transmission assy on to measure the gap. Too big, so I put shims under the Magneto and put the assy back on and checked the gap. All the gaps were anywhere from .035 to .042. A little wide but I figured I would give it a try. Once I buttoned everything up and rotated the engine on the stand to horizontal the rear was lower than the front and I heard a little click. I quickly figured out that the crankshaft side-to-side clearance came into play. It is a hair over .015 so when that happened now the Magneto gap got larger. Is this a concern for the Magneto to work properly or do I have to take that into consideration and re-gap it?

[Jerry VanOoteghem]

What you may need to do, is work on the .015 end play in your crankshaft.

[speedytinc]

What you are saying is the main cap has .015" play?
Fix the excessive wear.
I have done this by melting added babbit to the cap & resurfacing CAREFULLY to not melt/ruin the original babbit.
Then reset the magneto clearance to the service manual specs.(T1)

[Norman Kling]

It's a little hard to understand what you mean by what you posted. So I will explain 3 things which affect the magneto clearance. It could be any or all of them. First I will recommend the booklet published by the club "Electrical System". It has an easy to understand with pictures of the magneto system and a do it yourself explanation of how to accomplish it.
The first thing which affects the clearance of the magneto is the third crankshaft main bearing thrust surfaces. That is the flat area in front and in back of the 3rd main bearing of the crankshaft. You should have minor endplay. The manual says with new bearing endplay should be .006-.007. Servacable .016. Anything more than .016 should be repaired. This can be done by building up the flat surface of the bearing on the front side of the bearing or re-pouring the bearing. If you have excessive endplay, every time you push down the clutch to neutral or low, you will move the crankshaft farther away from the coils and decrease the output of the magneto. However as you drive the flywheel will move back, moving the magnets too close to the coils. So be sure this thrust surface is within clearances before proceeding with the magneto.

The next thing is to be sure all magnets at the outside end are equal or almost equal height. The book says hammering the end with a brass hammer. (not iron). If you are replacing the screws and they have not been staked, it would be better to grind off just a very small amount from the little brass or aluminum spools at the end of the magnet.
Then the final adjustment is the shims under the magneto ring which need to be placed to get the same clearance all the way around and be sure to rotate the crankshaft to be sure it is the same all the way around. Must be between .025 and .040. Ideally all should be at .025 or close to that. However if one or more is not quite exactly same distance from flywheel, you can leave alone as long as the closest is not less than .025 nor the farthest is not more than .040.
Anyway, I hope you get it to work very well. It is fun to run on the magneto and is one of the unique features of a Model T.
Norm

[Steve Jelf]

You can adjust magnet height by grinding some of the spools shorter as Norm described, or you can raise the short ones with shims. I use shims of .003" and/or .005". I call a gap of .025" to .028" close enough for gummint work.

I know some people do it, but the idea of beating the magnets down with any kind of hammer makes me cringe.

[John kuehn]

When aligning magneto clearance you need to allow for the weight of the transmission when you rotate your engine to horizontal. When the engine is vertical you’ve got it set how you want it. But rotating the engine the transmission weight may cause a few thousandths sag.

That’s went you rotate to vertical an add a shim or to to level it up when it’s turned back to horizontal.

As mentioned in the above posts the crankshaft end play has to be dealt with first of course.

[Scott_Conger]

William

I think folks are not fully understanding what you're describing, but if I am correct in my reading, you set your clearance with engine "nose down" and then in the process of bringing it back to horizontal, it went a little past horizontal and the crankshaft moved backwards .015", thus increasing your effective magnet gap. This is not good. Your 3rd main bearing thrusts are worn out to twice the accepted "worn out" value.

The only permanent fix for this is to fit a new 3rd main cap or build up your old cap. Neither is particularly simple and in fact you will likely find that the crank itself is worn a bit. At the very least, when building up the old cap or fitting a new one, you may have "zero" clearance until it's pushed home and bolted in and then you may find that once again the crank moves some, or too much due to wear on the cheeks of the crankshaft.

A very long term "temporary fix" is to buy the Lang's crank shaft shim which is fit behind the crank pully and keeps the crank "forward" like it was when the engine was vertical. https://www.modeltford.com/item/3030SHIM.aspx

Yours is a common problem when freshening up part of an engine and there are almost always multiple unforeseen issues.

[Norman Kling]

I would use the Langs shim in front of the engine if I discovered the end play while the engine was assembled and in the car, however, with the engine out, it is better to re fit the rear bearing cap. it will be a more permanent repair. This endplay usually occurs on cars which are driven a lot in low gear, such as in the mountains. It will last longer if in that case you use an auxiliary transmission with a lower range. Most hills can be climbed in low range of auxiliary without using low T gear.
Norm

[Matt in California]

William,
Just to clarify you have mounted the pan and fourth main? And the pan has been verified to be straight?

I am no expert here, but it sounds like your transmission is sagging. The question is why. It may be more than acceptable for a rebuild, but the reality of the engine you have. I will let the experts respond to how much sag is acceptable without a fourth main.

Matt

[Allan]

Scott raises a point re wear on the crankshaft flange. If the bearing cap has worn the forward face on the flange, replacing/rebuilding the rear main cap may not solve the problem of crankshaft end float. A .005" deep wear groove will leave .005" of end float in the shaft. You might pick up a little of this discrepancy in slop in the cap mounting bolts, but there will still be some end float. just take out as much as you can.

Steve's suggestion that you shim the magnet spools to reduce the differences in the magneto plate heights is a good one in an already built coil plate.

You are assembling the whole thing correctly by doing so on the vertical. However, the weight of the transmission will inevitably open the gap at the top of the coil plate and close it at the bottom when turned to the horizontal. There is nothing to stop you compensating somewhat for this sag by making the gap at the top narrower, when you have the assembly vertical.

Did you have the fourth main cap in place when fitting the pan? If it was, and the clearance between the bearing and the trans shaft was OK, the trans should not drop too much at the rear before it is supported by the bearing. This will help maintain an even gap between the magnets and the plate. You can check to see if the top clearance has changed appreciably.

Hope this helps,
Allan from down under.

[BarnesvilleT]

I think we are going to try Scott's suggestion and put the shim in. Hopefully it is in stock. This engine might not be in the car very long once we get it on the road. Just want to drive it a bit and then swap it out. We acquired another block with a 1926 Ser. number and are going to rebuild it from the bottom up. The engine that came in the car when we bought it has a 1922 Ser. number. I also have a 1926 Hogshead that will also be used with the '26 engine. There is a lot of great information from this post that we will soon use.
Thanks to everyone that posted.

Bill

[Jerry VanOoteghem]

I think we are going to try Scott's suggestion and put the shim in. Hopefully it is in stock. This engine might not be in the car very long once we get it on the road. Just want to drive it a bit and then swap it out. We acquired another block with a 1926 Ser. number and are going to rebuild it from the bottom up. The engine that came in the car when we bought it has a 1922 Ser. number. I also have a 1926 Hogshead that will also be used with the '26 engine. There is a lot of great information from this post that we will soon use.
Thanks to everyone that posted.

Bill

When you swap over to the '26 block & '26 transmission, be sure you also use a "4 dip" pan, (which is also 26/27). Three dip pans will not have enough clearance for the wider '26 brake drum.

Since you're new to this, as you say, a "4 dip" pan has 4 "dips", or troughs", in the lower inspection cover, while the "3 dip" pan has 3 dips, (I'll bet you guessed that part already...)

[BarnesvilleT]

It turns out that I do have one of each but did not know that until today. I just went out to look at both pans and sure enough 3 on one and 4 on the other. Thanks for that. Still new but learning.

Bill