The Engine - Crankshaft & Flywheel

The crank on the left is the one that came on the bike. Notice the length of the shaft closest to the bottom of the picture for the flywheel: it is far longer than the original crank on the right. The crank webs are a different shape. Also, the thread is a conventional RH thread onto which a standard nut was used to bolt on the flywheel without the LH threaded retainer ring. The second photo shows the crank with the nut covering the sludge trap removed and the welded up crank pin clearly visible. Heaven knows what happened to this crank to cause such destruction that the pin needed to be welded up! Jerry Kimberlin had an extra crank in excellent condition which is the one on the right in and that went in perfectly.

While I did not have to do this for Jerry's crank, on the old one I removed the safety wire and unscrewed the sludge trap on the flywheel side crank cheek. I cleaned out the inside and then shot compressed air through the hole in the crank shaft on the RH timing side to blow out any residue.

The way to assemble the big end is to clamp the rod in a vice with the big end bottom half of the bearing facing up. Coat the rod bearing with thick oil and lay the rollers into the curved half. Then lay the crank journal on the rod, coat the journal with thick oil and lay the remaining rollers on the journal. Put the con rod bottom cap on the journal and tighten the new bolts. Tighten it just enough to make the mating surface of the bottom cap lightly touch the con rod. With a wooden mallet tap the big end of the con rod to settle the rollers. Move the rod laterally to align the rollers. Then alternatively tighten the two bolts till the two split bearing faces are tight up against each other. Safety wire the crank weights and the sludge trap cover.

The crank tolerances are as follows:

Plain bearing big end : 35.05mm +0.000mm, -0.015mm
Crank pin journal dia : 29.00mm +0.010mm, -0.005mm
Big end rollers: 33 rollers with a dia of 3.0mm
Small end bronze bush: 20.00mm +0.007mm, -0.028mm
The bush extends 0.50mm on either side of the small end faces.

When these tolerances are exceeded and the crankpin & big end need to be reground:

First oversize:
Big end : 35.30mm +0.000mm, -0.015mm
Crank pin journal dia : 28.75mm +0.010mm, -0.005mm
Big end rollers: 31 rollers with a dia of 3.25mm

Second oversize:
Big end : 35.55mm +0.000mm, -0.015mm
Crank pin journal dia : 28.50mm +0.010mm, -0.005mm
Big end rollers: 28 rollers with a dia of 3.50mm

Con rod center to center length : 156mm
Con rod big end thrust face width: 23.8mm + 0.02mm, -0.02mm
Crank pin length across thrust faces: 24.0mm

The dia of the crankshaft journals that sit in the main bearings: 35.0mm, +0.01mm, -0.000 mm.


The Flywheel

Though this part came later after the gearbox was assembled and the crankcase closed, I am including the flywheel here as it is in the parts diagram above. My flywheel saga will take up a number of blog posts but it is not of any interest to anyone who has an intact flywheel. My flywheel seems to have suffered catastrophic damage at some point in its life and the taper had been rewelded with a much larger boss. This resulted in the flywheel protruding far beyond the crankcase, fouling the flywheel cover. The LH tread had long gone. Jerry Kimberlin's flywheel measurements were emailed and after a trip to two machinists - one to cut the taper and the other to cut the large LH metric thread for the retainer ring nut- the flywheel was ready for installation. I used Loctite Clover 280 fine grit lapping compound to lap the taper onto the shaft rotating the flywheel till I got a smooth finish on both the shaft and the taper. A dab of Loctite 609 retaining compound to take up any remaining slop between taper and shaft and the flywheel was mounted on the shaft.

The conventional RH threaded nut was bolted on and then the LH retainer ring spun on using a special tool from Guzzino. The tool is basically a pipe with tangs cut at one end to match the slots on the flywheel retainer nut. The way to tighten it is to hold the flywheel with one hand and tighten with the other using a foot long rod inserted through the special tool. Then, insert a piece of rope about the size of the spark plug hole into the spark plug hole and slowly bring the piston up to TDC. Somewhere along the way, the piston crown jams up against the rope effectively locking the engine. Then, as they say in the old restoration guides, fetch the rod a couple of whacks with a hammer to finish tightening and you are done. To remove the flywheel, first loosen the conventional threaded nut and then using the special tool, turn it clockwise to loosen it - it acts as its own puller to detach the flywheel from the taper.