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Thread: Blast primary question: What is this?

  1. #1
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    Blast primary question: What is this?

    In continuing my work on this Blast, I just pulled the primary cover off the bike, and I'm a bit confused by what I'm seeing. It appears to me that there is some vestige of what might have been a 'manual' type primary chain tensioning device left in the primary cover. What I'm referring to is the large bolt that is threaded into the bottom of the primary cover and directly beneath the 'spring loaded' chain tensioner when the cover is in place. This bolt has both a spacer sleeve of sorts on it, that fits over the bolt like a horse-shoe of sorts, then a 'lock-nut' where it tightens to the primary cover. And, there's a fiber-washer seal between the lock-nut and the primary cover itself. So, I'm just guessing here, but it looks like maybe at some point in the past, this bolt was used in a similar manner to what HD did with the primary chain tensioner on some of it's other engines.....where you tightened up the bolt putting pressure on the tensioner shoe until you reached a proper tension level, then locked it in place with the lock nut. However, that's a rather antiquated design, as most engines are now equipped with a self-adjusting tensioner....which I think is the case with this Blast motor and the spring-loaded tensioner that is attached to the inner case. If so, then what is the purpose of this bolt, spacer & nut? Is it basically just a 'plug' in the case? Basically I'm just trying to find if this thing serves any currently necessary purpose other than just being a remnant of the past? If so, what does it do? It looks to me like when tightened all the way up, and with the seal stopping any leakage of fluid from the primary case, with the spacer in place, it can't be anything more than just a glorified 'plug'! But..... I've got little to no experiece with this motor, and I don't like 'guessing' about anything!! So, if someone can help me here, I'd REALLY appreciate it! If it does still serve a purpose, I'd like to know what that is? Many thanks!! Tom D.

  2. #2
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    OK, a little more 'on-line' research, and I may have answered my own question here. It appears that the 'horse-shoe' spacer I referr to above is a 'production' technique used for assembly of the engine, and a component that is to be discarded upon the first service of the motorcycle primary case. According to what I found on the internet, that 'spacer' was used at the factory to quickly make the adjustment for production and shipping purposes, but it is NOT an on-going part to be used. Instructions indicated removing this spacer at the first service (which one might consider to be the 500 mile service though that is not stated in what I read) and then making a proper adjustment. That is indicated as being to tighten the bolt to 24 INCH pounds, then back it off 3/4 of a rotation, then tighten the lock-nut. Simple enough, but it requires both an inch-pound torque wrench, AND..... you clearly have to remove the muffler (entire exhaust system) to do this properly. Otherwise, I guess you use your calibrated fingers and set the tension by 'feel'! Those of us with 50+ years of 'wrenching' might feel comfortable doing that, while others may want to go the full-factory route, pull the muffler, buy the inch-pound torque wrench, and 'do it right'!! Anyway, this would appear to solve the question of what this bolt and spacer is all about. Appears the unit DOES still use this tensioneer technique, although they now refer to it as being a 'limiter' vs a 'Tensioner'. So, clearly the spring mechanism is doing 90% of the job, and the 'limiter' is for the extreme case of slop under a REALLY high load! For future reference for any one looking........... Tom D.

  3. #3
    Senior Member 34nineteen's Avatar
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    I'd need to see a pic of what you have for the peanut gallery to comment on this.

  4. #4
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    Hi Tom! I don't really know what's doing the lion's share of the work in the tensioner mechanism, but what I do know is that it's really, really, REALLY important to make sure it's adjusted correctly.

    There’s another way to adjust the primary that doesn’t rely on a torque wrench OR highly-calibrated fingers! Instead, it relies on your ears! The steps are as follows:

    1) With the bike idling (ideally at operating temp), slowly loosen the tensioner bolt until the primary starts making noise (should be a “rattling” noise). This noise indicates that the primary chain is too loose.

    2) Slowly begin tightening the tensioner bolt. The rattling noise should go away.

    3) Continue slowly tightening the tensioner bolt until you start to hear a new noise. The new noise will be more of a “whirring” sound. This sound indicates that the primary chain is too tight.

    4) Loosen the tensioner until the “whirring” noise stops and then loosen an extra 1/2 turn.

    5) Hold the tensioner bolt in place while you tighten the tensioner locknut/jam nut. Make it snug. Doesn’t need to be 500-pound-gorilla tight. Just snug. If you’re worried about it loosening up, give it a check after an hour of riding.

    Aaand you’re done. That’s how to adjust your primary without any torque-wrenches, flat-counts, or calibrated fingers.

    As a final thought, a wise man once said:

    “It is much better to have a primary chain too loose than even a little too tight.”

    (That wise man may or may not also be the one I plagiarized the whole adjustment procedure from. )
    Last edited by DozerBoy; Yesterday at 03:03 AM.

  5. #5
    Senior Member Cooter's Avatar
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    That there is a completely perfect description on how to do a fail safe primary chain adjustment. Well done!

  6. #6
    Senior Member Barrett's Avatar
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    Next Up: the incomparable John Vreede and his doctoral thesis on "grounds".
    PS-LunticFringe aka user_deleted also quite windy and flatulent.


    https://www.buellxb.com/forum/showth...ms-Why-and-How



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