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Friday, September 23, 2011

Long Rod XS650 Crank - We can do that!!

I've been wanting to build one of these for a good long while.  I have a customer in the UK who has contacted me to build him a Long Rod XS650 Crank. 

Here you can see the difference between a standard 447 Rod from MikesXS, and a CR500 Rod from Hot Rods - much longer, and much better quality. 

A better view of the rods for comparison....  CR500 Hot Rod on top, Stock HP replacement on bottom:

The Rod Pins that come with the 2 rods are a bit different as well.  The 447 Rod Pin being shorter than the CR500 Rod Pin...  I've machined the CR500 rod pin down to the proper length..

The CR500 Rod Pin is also hollow, which is a nice weight saving feature seeing as how the CR500 rods are slightly different in weight than the HP 447 Rods. 

The small end of the CR500 Rod is much larger, and supports a roller bearing (which I think is a huge upgrade compared the stock setup).  To utilize this bearing, the pistons will likely need to be modified a bit to fit the bearing width.  Most folks are making bronze bushings to size, but I think I would keep the roller myself..

So I start with a very clean and degreased crank that has been fully disassembled.

I press in the Rod Pins, check them for square and fit, and then full TIG weld them into the flywheel.

Fit up the shims and bearings...

Align the camchain sprocket and press the 2 halves together in the proper location (This crank is also being rephased, keep that in mind)

I ALWAYS weld a crank that is being used in a performance application.  I see more crank failures from cranks walking apart than you could imagine.  If you have problems with your charging systems and/or you are getting lots of aluminum shavings in your oil, then this is likely your problem...   I see failures in stock engines just as often as in Big Bore engines, so do it once, and do it right... 

This crank is welded in the center, notice I didn't weld right at the bearing surface for the rod thrust washer.  Keeping the crank together is one thing, but you gotta keep those rods happy as well. 

The CR500 Rods share the same width in the small end as the XS650 Rods.  But, the XS650 Thrust Washers are narrower than the CR500 Thrust Washers, so I will be installing the XS650 Thrust Washers just as they were in the stock configuration.  Keeping the crank operating in the cases as close to stock is important, and even something as small as .022" could get things really out of wack!

Stock XS650 Thrust Washer:

CR500 Thrust Washer:

If you kept the CR500 Thrust Washers, you crank would be almost .100" wider than stock, I don't think that would do your cases any favors... 

Install the rods:

Get those outer flywheels on, true em' up and weld the pins...  Sounds easy right? 

Well there you have it, a really great looking setup for a long rod conversion.   If you are thinking of doing this modification, know that you'll be modifying other parts of the engine to take advantage of this setup.  Piston heights will have to be modified, clearances checked, etc... 



  1. Damn that thing looks awesome Hugh!

  2. what are you using that lucas oil for? quart sized assembly lube?

  3. Fraser Todcd - the stroke of the OEM crank has not been changed, just the length of the rod. The displacement will be based on the bore of the cylinders, just as with any XS650.

    1. That is dum, dum, dum. A longer rod will allow the piston to move further down ,as well as up, in the cylinder. Thus the need for redecking the pistons and the cylinders will probably need some relieving at the bottom. Have you ever heard of bored and stroked.This increases the total usable length of the bore the piston travels up and down in so more cc's. You need to do some study before you comment or you'll just look dum and you do.Less strokin' on your part and someday you'll be able to hang with the big guys who know WTF they are talkin' about.

    2. Mack, I don't usually post replies but your arrogant misinformed comment is what's wrong. To those that don't know and may be reading this, more cc's (volume) are gained by increasing the bore or increasing the stroke. The rod length merely dictates where in the bore the piston will go up and down, it doesn't dictate how far up and down. That's done via the stroke. Simple geometry will tell you that.

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  5. Mack, you're not too bright are you? The longer rod can't ever let the piston move further down. The stroke of the crank controls that. All the long rod does is change the rod angle and lengthen the dwell of the piston at TDC and it's a bit complicated so I won't waste my time explaining what the extra dwell does. The extra length of the rod is compensated for by using a piston with a higher pin hole. "You need to do some study before you comment" . If the hat fits.


Checkout the online shop for new parts and service for you ride!

Click Here for more info on parts! Thanks - Hughs.