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Long Rod Conversion? I think so!

Discussion in 'The Garage' started by Punkskalar, Sep 23, 2011.

  1. Punkskalar

    Punkskalar Hugh's HandBuilt

    * For high resolution photos and details - this same post is on the Blog - http://hughshandbuilt.blogspot.com/2011/09/long-rod-xs650-crank-we-can-do-that.html

    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. I'll be using a set of CR500 Rods for this conversion.

    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. Surprisingly, the Hot Rods are cheaper to get than MikesXS rods are as well :laugh:


    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.. After seeing how abused the 2 stroke engines get by with, I see this as a nice touch :thumbsup:


    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... More information on that here:


    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? Getting the flywheels trued up properly is the toughest part of the job - I go more into depth on that in the last issue of RustyMetric Magazine (Online Magazine, only $1 for a download - check it out!)


    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... If you folks are lucky, maybe Jack will drop in and give some insight on getting the right pistons for the swap, but this one is headed to the UK for a guy that already has it figured out :laugh:

    Last edited: Sep 23, 2011
  2. xs650nutt

    xs650nutt XS650 Enthusiast

  3. hotdog

    hotdog XS650 Guru

    Beautiful, more info on the pistons required please Jack..?? & the modifications required.
    Going to be doing a crank rephase for a friend in the not too distant future & always looking for new ideas..??
    Will probably even do one of these for "numero uno".
  4. Punkskalar

    Punkskalar Hugh's HandBuilt

    Some folks are using SP360 Pistons, others are using modified Virago Pistons and Liners. Either way, its an intensive modification, requiring mods the the pistons, liners, etc...
  5. littlebill31

    littlebill31 Smells of Raw Fuel

    Very nice Hugh, as usual!!!
  6. Ironsled77

    Ironsled77 XS650 GRAND HACK

    Top of the game, no doubt

    Posted via Mobile
  7. racerdave

    racerdave ^ Gone not forgotten ^

    Hugh, many years ago I went flattrack racing with a buddy to help him with gear changes,etc. He had just gotten a tt500 based flattracker. Champion frame'd, etc. When I seen it, the first thing I said to him, it's stroked, because I seen a spacer under the cylinder. He told me it was a long rod. I'm still not sure exactly what it accomplishes? More torque? I think he also said something about it putting the power to the wheel with less shock or something. Can you explain a little please.
  8. August

    August XS650 Member

    I'm not Hugh, but I do believe you're right on with it increases torque.

    If it's like stroking a V8, typically what happens is that you'll gain torque (and plenty of it), but you'll lose your top end reving that these engines have. Though since these can rev higher than a stock American V8, you may not notice the lose on most (not all) street driving.

    The torque is increased because on the longer travel of the piston (this also increased cubic inches as well. I was going to stroke my Magnum 360 to 426 with the appropriate crank, rod, and piston combo but it's a bit pricey for me right now.)

    A stroked XS engine on a flat tracker...damn that will be one fast bike out of those turns! :bike:
    CC1 likes this.
  9. gruff54

    gruff54 XS650 Enthusiast

    Been looking at building an XS800 (CR500 rods/Virago 750 piston & liners) for several years. Have the parts, lack the time. CrazyPJ over at the 650 garage came up with this combo years ago. This isn't a stroked motor as the stroke is unchanged. Not sure of the physics, but I think I remember Jack saying that to take full advantage of the long rod concept, you really needed to rev the motor. In that sense, a long rod/rephase combo should work well. Hugh, another thing I remember. The Yamaha built the original XS's with needle bearings on the wristpin(a carry-over from their 2-strokes). The early XS's had problems with those needle bearings and switched to bushings.
    Disclaimer: This is based on my memory, which doesn't work as well as it used to!
  10. racerdave

    racerdave ^ Gone not forgotten ^

    August, the way it was told to me it was not stroked.
  11. Tia813

    Tia813 XS650 Addict

    I'm sorry fellas pulled an all nighter pulling the carpet out of my living room so I can lay down some wood. So my thought process is not all there. ANYWAY on a stroked motor you have a crank that has a longer travel than stock and a longer rod. Produces a butt load of power. With a stock crank and a longer rod the travel is shorter. So this motor would have live up top to produce some power? So would this be considered a de-stroked motor?
  12. ippytattoo

    ippytattoo Just another grumpy old hack.

    This is just a long rod mod, it doesn't change the stroke at all. It increases the distance between the crankshaft journal and the wrist pin to change the angle of attack of the connecting rod and piston in the cylinder, effectively reducing side load and wear on the pistons and helping to change where the harmonic vibrations will be (RPM range). If done right you can also use a long rod mod to increase compression ratio and quite possibly a slight increase in torque delivered to the rear wheel.
  13. Tia813

    Tia813 XS650 Addict

    Thank you I was focused on the length and not the position of the rod. Now it makes sense
  14. Jack

    Jack XS650 Junkie Top Contributor

    WOW!!!!! "Rod porn" I knew this forum was more opened mined but openly showing the public whose rods are the longest:doh: :laugh:

    Hugh,your tig welding work is just beautiful :thumbsup: but to what method would be best for the small end,typically a bronze bushing will offer a tighter inner fit in keeping the piston stable and spread the load tension more evenly throughout the bushing over a roller type. These are just my opionions as to why I'm installing bushings.

    For those wanting to know what pistons are available for the L/R conversion,personally I would steer away from any piston compression height that requires a block spacer,reason being to lighten the small end mass to reduce rod and crank stresses and to reduce excessive inertia loads that can cause rod small end breakage as RPM's are increased.

    Through PJs and my research,you can use the Virago 750 pistons but require machining the dome for reducing combustion chamber volume to get the compression up to par and these pistons also require mods to open the case spigots for fitment. There are photos of PJs piston mods over at the" Garage". Another option would be the Virago 700 piston,same as the 750 piston mods but this piston is 80MMs in bore.
    For a near true zero deck height ,the GSXR 1100 piston would be the way to go,if you were going to turbo,just not enough dome height for compression as I've already been through that trial and fit process. Other piston options and the way I'm going is by using the KZ 900/1000 or KZ1100 style pistons. They're a two valve dome configuration that would need the valve reliefs cut to Xs valve dimensions with some slight dome machining for combustion chamber fitment or the JE early style KZ piston that would require combustion chamber to be welded up,much lighter piston over the KZ1100. The ideal compression height your looking for is .995 to 1.000. If some of you have any suggestions on what pistons might work post your ideas. Later!
    Last edited: Sep 24, 2011
  15. hotdog

    hotdog XS650 Guru

    Just read a lot about this mod over at the xs650 garage, a lot of mods to be done....std rods & 700/750 kits are far easier IMO after doing a bit of research.
    Thanks Jack - did PJ end up getting his long rod motor totally sorted..??
  16. Jack

    Jack XS650 Junkie Top Contributor

    Late time I talked to PJ he was recovering from some hand injury and was about to install
    the 256 cam I sent him. I miss that guy,truly inventive when it comes to odd ball engine combinations with little to do money.
  17. Punkskalar

    Punkskalar Hugh's HandBuilt

    I can agree with that. But I wonder about how much stability can be required with a shortened dome height. I might just try a build with the rollers in it, what have I got to lose right? :thumbsup: Thats the fun in building these things, and learning from folks like Jack...

    Of course, I tend to operate in this manner: Build, Make Mistakes, Rebuild, Repeat :laugh:
  18. Patches

    Patches XS650 Junkie


    I too will be working on a CR500 swap. I have to get a meeting arranged with several local flat track guys that have built many of these engines successfully. I have a little bit of piston info, but nothing concrete yet. Hopefully I can get together with these guys, buy them a couple of beers and we can swap some info and ideas. From the bit that I'm told we're talkin' endless possibilities. Think: 800-880cc, long rod, rephased beast......

    Now I don't want to put the cart before the horse, but once I know more I'll be shooting you and Jack some PM's.
  19. August

    August XS650 Member

    :doh: Yeah, now I see it. :banghead:
  20. hotdog

    hotdog XS650 Guru

    Patches, this is the sort of info I'm chasing - Hard facts & good solid info about all the mods required to do such an engine mod including hi-res photos.
    Lets face it - the crank is the easy part. The finer detail is required on the top end mods required & the pistons combos that work best with the least amount of work & costs involved. Looking forward to what you find out.

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