Latest info on Project to eliminate two Peice Crankshafts

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Model T Ford Forum: Forum 2005: Latest info on Project to eliminate two Peice Crankshafts
Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Houston, Broken Arrow, OK on Thursday, February 07, 2008 - 12:25 pm:

It's not the final copy yet, and not on the Tulsa website, we'll share with you what we have and put the final version on, hopefully in a couple of weeks. This posting was triggered by Erik Barret's recent posting regarding his brand new two peice crankshaft.

Aligning and Balancing the Model T Ford Engine and Transmission

Fred Houston and Mike Bender February 1, 2008

THE CAREFUL ALIGNMENT AND BALANCING OF THE MODEL T FORD ENGINE AND TRANSMISSION will significantly improve the life of the engine, transmission bearings and the crankshaft. Over the past 30 years or more, we have been besieged with broken Model T Ford crankshafts. Why not, the Model T crankshaft is small for the work it does and some are approaching 100 years in age. Having said that, it is our belief that much of the problem has to do with the lack of good alignment and balancing techniques used in the rebuilding process. Further, we believe if one starts with a magnafluxed crankshaft and properly aligns and balances the Model T engine, that the crankshaft and bearings will be long lived. Also there has been considerable interest recently on the MTFCA Forum in new light weight bolt-on counter weights similar to the bolt-on counter weights available in the Model T era. Since “all” Ford four cylinder engines had counterweights starting in 1931, we believe that a carefully designed set of counter weights could also help eliminate the possibility of a broken crankshaft.

The basic design of the Model T Ford engine/transmission “demands” careful alignment and balancing. Differing from most others, the Model T Ford engine has an 85-pound rotating mass transmission bolted on the rear of the crankshaft that must be aligned and balanced. Since there are four different ways the transmission may be assembled to the engine (both the transmission main shaft and crankshaft flanges may be turned 180 degrees); any time the Model T transmission is removed from the engine for maintenance, an opportunity for misalignment is introduced. Over the life of an engine, several such opportunities may have occurred perhaps accumulating and resulting in severe misalignment. Crankshaft regrinding, re-babbiting, parts used from other transmissions, and/or assembly errors may unknowingly introduce misalignment. For example, a rather common occurrence in the crank shaft re-grinding process is grinding the main bearings off center from the alignment pins. Another common practice is to have one craftsman rebuild the transmission and another rebuild the engine and the two simply bolted together upon return; completely skipping the alignment process! All such problems must be resolved during engine/transmission reassembly procedure. Misalignment will severely drain horsepower from the engine. We only have 20 horsepower or so and we need all of it.

A good foundation is required. The path to a correct running fit on the tail shaft starts with the crankshaft. Concentricity must then be maintained starting with the crankshaft and carried through the transmission main shaft, flywheel, brake drum and sleeve and drive plate and sleeve (tail shaft). The distance from the back of the crankshaft flange to the rear-most tip of the tail shaft sleeve is approximately 11½ inches; thus even a slight tilt or off-set will introduce a wobble at the end of the tail shaft.


Alignment is Critical – We believe it was Ford’s intention that the crankshaft crank pin bearings and main bearings be ground at the factory aligned with the alignment pin holes in the crankshaft flange. The alignment pins have a snug fit in the crankshaft and the transmission main shaft flanges and are a press fit into the flywheel, all well designed to carry an accurate alignment to the rear.

Indexing a crankshaft grinder on the alignment pins requires a special fixture – Crankshaft grinding machines have lathe chucks on either side, plus the capability of using the lathe centers on either side. For example, the front end of the Model T crank may be chucked on the right side of the grinder, with the surface under the crank gear providing an accurate attachment surface. Since all surfaces on the used flange end are suspect, a fixture made from an extra transmission main shaft will assure the bearings will be reground aligned with the alignment pins as the factory originally intended.

Making the Fixture – Select a transmission main shaft in nice condition and cut about 3 inches off the shaft leaving the flange with about a 3 inch stub shaft. Drill out the four bolt holes in the flange to ½ inch. Prepare four ½ by 20 thread bolts, short enough so they will not protrude beyond the crankshaft inner flange surface when the fixture is attached (this to allow grinding on the front surface of the crankshaft flange).

Preparing the crankshaft to be ground – The four bolt holes in the crankshaft flange must be threaded ½ by 20; the alignment pins inserted, and the fixture bolted the rear surface of the crankshaft flange. Next chuck the rear crankshaft flange in the left side chuck of the crankshaft grinder and index on the shaft of the new fixture. This procedure will provide a very accurate crankshaft…….UNLESS…the crankshaft has not been correctly ground at the factory (aligned with the alignment pins). In this instance, if you choose to use this crankshaft, the crankshaft may be ground aligned on the least worn main bearing and the transmission alignment procedure used to align the transmission, plus your crankshaft, transmission main shaft and flywheel must be dynamically balanced as a unit.

Alignment tasks are accomplished by placing the engine block with the installed crankshaft nose down on an engine stand. The transmission is then assembled piece by piece onto the engine. This method removes the gravity component from all measurements, plus all measurements are made with a dial indicator mounted on the block allowing concentricity to be measured by turning the engine and transmission components in exactly the same manner as when the engine is running.

Step 1 – It is critical that the transmission main shaft be aligned with the crankshaft main bearings to a high degree of accuracy. Usually the crankshaft is freshly reground, but any time the engine is removed, alignment and balancing should be considered. Remove the crankshaft from the engine and use V blocks with a surface plate and dial indicator to check if the crankshaft is straight.

This Crank grinding procedure will work equally well on a Model A crank shaft.

Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce on Thursday, February 07, 2008 - 12:41 pm:

Nice article Fred.
Obviously I agree with assembling the transmission with the engine on its nose.

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