Belt or chain

So far this is just daydreaming, but who knows.

If you found the need to divorce a Harley engine (OK, it's an S&S) engine by about a foot from the transmission could you use a drive belt instead of a chain? Chains make me nervous and since the belt works on the wheel after the transmission with all it's torque multiplication it just seems that it would also work to attach the engine to the transmission.

Gears are out mostly due to power loss, noise and cost, but is there something else I'm not thinking of?

You mean the primary drive right? I'm not an HD guy, but I'm fairly certain that belt drive primary kits are available. I'd guess that you'll be on your own for the stretch part though.

I believe several HD's have a belt driven primary already.

IIRC those are aftermarket belt drive kits, although there was the "Sturgis" special edition/model that came with dual belt drive from the factory.

The transmission is right behind the engine. There is not a foot to lose. But, yeah, primary belt drive kits are all over. Primo is a name that has been out there making them for decades. Harley even had a bike with a belt primary in the 80's called the Sturgis.

Keep in mind, though, that while they look cool when open, not that many people run them and over the decades, I have seen A LOT of people with those have problems, including a guy stuck on the side of the road with one a couple months ago when I was on the way home. It is VERY RARE that you see ANYONE with problems with a primary chain.

Well I guess that settles that, it can be done. I won't be losing a foot (human or space wise) I need to add a foot between the 2.

And there's a cool tensioner too.

You know I look at that big old wide belt hanging out there and my ADD kicks in and I think about the forces transmitted through the crank by it. What makes me think of that is that for everyone who has tried to adapt the Harley engine to a Bike Engined Car has had crank issues. They've had to add long and well double supported jack shafts or the bottom end falls out.

I know the S&S has a better bottom end, but it just seems like they'd have put that in double shear. Could the width and the longer lever arm be what's causing the issues you've seen Dr. Hess?

Or have you seen things like toes getting stuck in them?

I've not seen crank issues with the belt primaries. There should be no extra stress at that point, as the 3 axes (with tensioner) are supposed to be parallel. Actually, crank issues are very rare on a Harley, so I would guess that the BEC people are putting some kind of extra stress on it. The problems I've seen with the primary belts are usually things like the idler bearing going bad, which then destroys the belt, leaving you stranded, or the teeth shear off the belt (what happened to that guy a couple months ago), or the belt breaking on it's own, leaving you stranded. Open belts look real cool and all, but I've seen a lot of guys with open primaries and shredded pant legs, and duct taping their left pant leg before they go riding.

If you're going to use a chain, do keep in mind that it needs some lubrication. I don't know if regular motorcycle chain lube would be enough for that or not. I've known some guys that used open primaries with a chain with varying degrees of success (usually "not very.") Don't know how religious they were with the chain lube. You can buy master links for the primary chain and get the chain in bulk or in a custom length. They were using the master links and chain from who knows where. They would have to go out in traffic to pick up their chain after it got spit out. Didn't say they were the brightest, and the master links may have been well-used or salvaged from heavy equipment. Those bikes were probably doing a third of the HP that the S&S is capable of.

I don't understand why anyone would want an open primary other than the "Bro" factor. Modify a part so it is more likely to fail sounds like a great idea. I was selling a rear harley rim and some guy chewed up a new secondary drive belt by not tensioning it correctly, he was asking me about gearing and sprocket, basically told the guy to stick with stock parts installed correctly.

There have been stories of crank problems with the twin cam engines. Somewhere along the lines Harley changed the way they make the crankshaft, making it weaker. They also relaxed the tolerances, meaning some have more runout.

That might be what you're hearing about with regards to crankshaft problems.

For clarification, the '81 Sturgis had the twin belt drive, but I don't think that the '91 Sturgis did.

You can get primary bearing supports to help extend the life of the bearings by keeping everything lined up and parrellel