As you noticed by the number of posts I already published, open belt drive systems find their place in more and more bike models, in many widths and designs.
This latest release comes from Ultima Products, a company already offering an old school 2″ primary belt drive system for Harley Dyna (left picture).
Ultima just added to its line-up a new 3.5″ system for both Evo & Twin Cam Dyna models from 1991 to 2005. You can install it with no modification. Available in 2 versions, Street or Drag Style (right picture) both with outboard supports in 3 different designs. Backing plate is billet 6061-T6. Front grill guards and side covers are also available. All Ultima Products are distributed exclusively by Midwest Motorcycle Supply. Retail clients must order through a Dealer. All designs & options can be seen at Ultima Products.
i am a big Dyna fan so good news.
But wouldn’t you want a strong link between the transmission and engine to hald all that rubber mounted vibrating mass in place? I thought the stock inner and outer primary covers also served as a structural link between the two.
My students used an Ultima 2″ open belt drive on the bike they built last year. Looks great and performs well. There is a lot quality in these value priced primaries that I did not expect before we used one. I am very interested in this new offerring. Great product. Thanks.
-Darin
I’m not sure about my facts, But I would bet that the “open belt” concept has been around longer than I have been alive, and if thats true, I would also bet that the “open belt” has been proven to be strong and reliable.
These belt drives not only look good but they work as good as they look.
These type comments just kill me, If the motor and tranny are bolted down well enough, and aligned correctly, one could use a paper plate as an inner primary .
Steve Carr
But the engine and tranny are not bolted down to the frame. They are rubber mounted. What else holds the engine and transmission in line on a dyna? Even the factory sells an accessory “race brace” to tie the engine to the transmission. By going to an open belt drive, your removing much of the bracing on the left side of the drivetrain. Yes, you can get by with it on an old shovel or pan where they are both bolted to the frame. I run belt drive on two of my bikes, but not my Dyna with the swingarm pivoting off the end of the transmission and everything rubber mounted. And to make things worse, the Dynas do not vibrate on one plane like rubber mounted buells. That’s why companies like Sputhe make a kit to fix that problem. So why would anyone want to weaken things further. Maybe I’m wrong but I would like to hear some opinions from folks that know Dynas and not just old 4 speeds…..But I don’t think I’m wrong.
Lyle,
Think about this a minute…… there is a 1″+ thick piece of billet aluminum connecting the trans and engine with the open belt drive where as with the inner and outer primary you have 2 “Cast” aluminum pieces that may be 1/8″ thick each with some casting webbing thrown in connecting the two components. You thesis is completely wrong! You are adding a tremendous amount of strength to the engine/tran’s combo with the Big Chunk of Billet Aluminum on the open belt drive.
Over & Out,
Jeff
Ok, that’s a start and the article didn’t say anything about a 1″ thick piece. It said “open belt” and the photos show a piece of aluminum keeping the shafts spaced with no mention of thickness. You also need to remember the 1/8″ thick or so stock castings are further apart and on each side of the belt keeping the neutral axis more in-line with the primary belt which is better than just on one side of the belt causing a bending moment. Of course, I’ve seen broken cast primarys too. That 1″ thick plate can’t be 1″ thick everywhere. Else, you’d need to lengthen your shafts. It’s good to hear from someone who’s used these on Dynas.
good posts – i use rubber mount HD engines in a rigid frame and use rose joints for flexibility (where the swing arm would go) – you get a nice ride from it – so maybe i will have a go at these open primary’s too – and i like budget stuff.
drag raced a dyna last week, ran 10.80’s in the quater, 124 h.p. street bike..broke the inner primary on the second pass…cracked the bottom and leaked all over, big hp dynas need a belt drive and a tourqe arm on the other side to keep things aligned..i know putting incredible stress on street bikes is my job..1.60 second shorts with a 150 rear tire is getting after it…stock inner primary with no tourqe arm on right side will break your inner cast primary every time…rubber mounts rule but its tough on them when you hook them up at the track
a1: You’re talking of an EVO right? I think the confusion of some here is the difference between an EVO and a TwinCam and the motor/tranny orientation.