Don't destroy your crank with your starter.

[xjwmx]

Somewhere I read a story of a guy in the old days who laid an XS650 crank on the counter at a dealership, and the old guy behind the counter knew immediately what had happened, without asking any questions. The starter can catch wrong with a big loud "THUNK" and cause the crank to separate, in effect to bend. Very significantly. Happened to me, just like I read about it in the story later.

I don't know exactly what happens, but I have a theory, a feel for it, say. When you use the starter, do not release the button as soon as you think the engine has fired up. Keep it down until the engine is fully running, at which point the starter/headlight dual relay board will have already turned off the starter.

 

[Superjet]

Good advice XJ but are there any other known cases of the crank splitting into singles?

 

[xjwmx]

I don't know what you mean.. When it "separates" in the case it bends and the ends outside the case show a wobble. It puts a big strain on the bearings and makes a whirring sound.

 

[Superjet]

XJ i misunderstood your meaning of seperate. Thought it meant break.

 

[xjwmx]

I tried to find that article or story again for the umpteenth time yesterday. I guess I just got lucky the day it turned up. In my situation, when you turned the crank with the case together, the right side would wobble visibly. But when you turned it with the cases apart, that end and the bearing would actually lift out of the case a quarter inch or more.

 

[Superjet]

Oh wow. If you do stumble across the article, please post. J-C

 

[TwoManyXS1Bs]

Historical postings of starter-related crank twisting.

Post ##23.
http://www.xs650.com/threads/crankshaft-split-overhaul-assembly.31213/page-2#post-388170

http://www.xs650.com/threads/1973-tx650-starter-replacement.44248/

Justa theory.

The starter works on the far right crankwheel. Any opposing forces from the right cylinder will go direct to the right crankpin, direct to the right crankwheel.

Any opposing forces from the left cylinder will go thru the center crankpin, then to the left crankwheel of the right crank half. From there, those forces have to travel thru the right crankpin, in a twisting fashion, to get to the right crankwheel.

This means that the left cylinder would be responsible for undue crank twisting, of the crank's right side. So, let's put a compression release on the left cylinder.

Of course, you'll see similar crank twisting loads when dumping the clutch, or doing the lurch/snatch thing in high-gear low-speed cruise. BUT, those loads have to pass thru the small diameter primary gear (small torque values), and are dampened by the clutch basket's damper springs. Damping of the starter mechanism is different, and operates on the large diameter toothed crankwheel (larger torque values), and may allow higher shock loads to get to the right crankwheel...

 

[arcticXS]

So this would be a good reason to weld the crank pins?

 

[Paul Sutton]

Interesting, a subject I have been thinking about lately but in a different context. On a rebuild with a PMA where do we take the sensor signal from to auto shut off the starter motor?

 

[xjwmx]

^I think you could reuse the same dual relay board for both the starter and the lights. I'm not sure where the yellow wire comes from, but I think there's only 6V on it and that it's a 6V relay. I might look it up later. If the PMA is three phase like the original, and the voltages are similar, and the yellow is simply one of the phases, there you go.

P.S. Okay....I looked it up. The yellow comes from the common connection point of the three coils in the stator and the only place it goes to is that relay. The PMAs probably aren't going to have that since it's special just to operate that relay. But you could run the relay if you could get about 6V from somewhere that's only present after the engine starts. If nothing else, you could make a little circuit that's connected to one of the legs and kept separate by a diode in series with it. Or maybe some PMA maker has the foresight to bring out that connection, since it could be useful in various ways. Or if that point is accessible in the stator due to luck, bring it out yourself. I'd never thought of this -- another strike against PMA maybe.