crankshaft

Eric · Post by **Eric** » Mon Oct 06, 2008 3:34 pm

I think the differences are all to do with the throw of the crank not its width. As far as i know the bearings are the same for the 500 as the 650. One thing that was changed around the time of 1959/60 models was the use of SG iron (Spheroidal Graphite) so the cranks became known as nodular or noddy cranks. This was done to overcome an increase in breakages of the cranks on 650 engines particulalry those with alternators the 500 was and is almost bullet proof in this reaspect given normal use of course. Thesre is a difference between cranks for alternator & dynamo use but I dont know how to describe it also have just found that 650 has a stroke of 79.3mm whilst 500 is 72.8mm so measure the crank throw and double it to find out what you have

By the way just realised you have posted this in the frequent questions section you may get more help in the "Help" section.Edited by - Eric on 06 Oct 2008 2:48:57 PM

Don Madden · Post by **Don Madden** » Mon Oct 06, 2008 5:18 pm

Since the question is here, I will respond in the frequent question sublist.

The easy way to tell is measure from the outside of one rod journal to the edge of the adjacent flywheel: 1-1/4in for 500/600 & 1-1/8in for the 650.

Up to 1956 a cushion drive sprocket was fitted & the drive side axle is 2-3/4in long. 57-up the cushion was deleted & shaft is 1-3/4in long.

SG iron was introduced in mid-1961 & may have been used only on 650cc. Hold the crank in the air & rap it with a hammer. Mehanite goes "thunk" & SG "tink". Sounds objective but very distictive side by side. If testing only one, the SG will ring like a bell with the sound fading, mehanite sounds dead.

Cheers, Don.

becks · Post by **becks** » Mon Oct 06, 2008 6:26 pm

I posted this message in the wrong section of the forum and have been advised to post it in this section.can anybody tell me how i can determine if i have purchased the correct crankshaft for my 1959 5oocc model 20 alternator twin . I have been told that all i have to do is measure the opposite side of the crank where the pinion connects to the crankshaft by taking a measurement from the center of the pinion retaining bolt to the outside of where the main bearing seats. If it measures 19mm from center to outer side then its 500cc if it measures 21 mm then its 650. Is this correct and if it is the latter then is there any thing stopping me taking the crank to an engineer who could machine the crank down to 19mm or will this render the crank useless as i have been told that my only other option is to convert the bike into a 650cc thanks becks.