Farmall M vs Farmall MD (again)

TWheat · Dec 7, 2011

I'm trying to get my mind wrapped around this C-wise rotation on a M distributor and Mag, vs CC-wise rotation on MDs thing.
How is rotation reversed? countershaft in dist/mag?
I know there are different part#s for the M dist.
vs the MD and different advance degrees , but the mag is a H4 for both the M and MD , but the rotation is C for M and CC for MD.
I appreciate the replys from my previous questions but I still don't have a clear understanding about what is happening.
I used the CIH parts website and I&T Manual, but they don't answer my questions.
Thanks again for your input.

Janicholson · Dec 7, 2011

There is simply one more gear in the drive housing on the front of the engine. It just puts the drive in an appropriate location to clear the manifold. Jim

old · Dec 7, 2011

As Jim says plus to 2 engines are not any where near the same sort of like comparing a Ford to a Chev but in this case both engines are made by the same company just one is a true gas and the other is a gas start diesel run engine

Athol Carr · Dec 7, 2011

If my memory serves me correctly, in the M the camshaft is driven directly off the crankshaft and the magneto drive is from the camshaft. In the MD there is an idler gear on the opposite side of the engine that is driven from the crankshaft and that idler gear drives the both camshaft and the injector pump drive. This means that the camshaft run in the opposite direction to that in the M. The magneto drive is driven, as in the M, from the camshaft. As a result the magneto for the MD rotates in the opposite direction to that on the M.

D Slater · Dec 7, 2011

Like Jim said except I will add a little more detail. Gas engine the crank gear drives the cam gear and the cam gear drives the gear on the ignition drive shaft. MD block is taller and a little wider so to keep gears small enough diameter to fit in the space. Crank gear drives a idler gear, idler gear drives the cam gear, cam gear drives the ignition drive gear. Both gas and diesel also have another gear set in the distributor unit.

TWheat · Dec 7, 2011

Jim, so I take it that means the extra gear drive one on the MD is not the same as the 90* one where a mag. was modified to a dist. on a straight gasser? Tim

Paul from MI · Dec 7, 2011

The others have explained the rotation of the magneto issue very well. All that is need to make the magneto spark when rotated in a different direction is to make the impulse coupling trip when rotated backwards and change the relationship of the opening of the points to the position of the magnets and distributor rotor. So the same basic magneto can be made to spark when rotated either direction by interchanging some internal parts. Some mags have provision to rotate either direction without any change to the main case and all the electrical parts remain the same.

Janicholson · Dec 7, 2011

True.
This extra gear is in mesh with the cam gear on the front in the cam gear housing. Jim

TWheat · Dec 8, 2011

OK, That makes sense to me finally, thanks again to all . This site and the people here are great.
Tim

Farmall M vs Farmall MD (again)

TWheat

Member

Janicholson

Well-known Member

old

Well-known Member

Athol Carr

Member

D Slater

Well-known Member

TWheat

Member

Paul from MI

Well-known Member

Janicholson

Well-known Member

TWheat

Member

Similar threads