MTFCA Forum

Getting ready to rehabbit and bore my block. How do you establish the location of the crankshaft with regards to block in the axial direction ? I assume that midpoint of any crank connecting rod journal has to match the centerline of that cylinder. This will determine the location of the thrust surfaces at the rear main. Is there a dimension from rear of block to the face of the crankshaft that can be used as a reference ? Any help would be appreciated. Thank you

Johnr

An interesting question! Perhaps something in this video series will answer it:

https://www.youtube.com/playlist?list=P ... 1nA0Yctp6G

A good block will have very little end play to work with as the 3rd saddle is the same length as a babbitted cap and crank length of 3-1/8" if the block has any wear, it will be in the front side so all that is needed is the cap to favor the front for extra thrust face when machined.

Crank should be centered on the center main saddle. If you do this, the rear main saddle will be centered on the crank thrust surfaces. The rear block saddle should not contact the crankshaft thrust surfaces if the crank is positioned properly.

Dan, that can't work using the center saddle, it has a variable of 1/32 to 1/16"for expansion, by the book, if the 3rd saddle has no wear there is only a several thou clearance on the thrust faces of the crank to block, especially if fitting a new scat. That's all you have got to work with for endplay and setting a center and .002 to .004" babbitt clearance.

I center the crank on the rear main bearing. Each thrust face is the same distance from the center of the bolt holes.

John:
Frank and Eric state in a simple and correct manner how to position the crankshaft in the model T motor block ... also as Eric states ,it is very simple to measure the position of the thrust by using the mainbearing bolt holes as a reference ... and while this may not take into consideration the effects of a very worn and re-ground crankshaft , it will be functional ...always an optimist ...Gene French

Regarding positioning from main bolt holes, does anyone have any reference dimensions that would allow one to check the saddle face front and back?
I like most centre the crank on the saddle. When using a good crank without too much wear on the thrust faces I find it works.
Tim

Another measurement I use is 2 5/16 from back of crank flange to the surface the field bolts to.

I will pull out of it, but maybe screwed up by cutting back the rear main in my block to just add thrust to the back/flywheel side of the block. Didn't consider using the bolt holes to base the distance on.

Mark- unless your installing a dry clutch/pressure plate, remember that the crankshaft thrust is toward the rear when the T trans is in neutral.

In motion it is to the front so that is where I added the extra thrust surface.