A primary drive conversion kit is designed for those who push the limits. Maybe you spend your weekends at the MX track, sending it big over jumps; maybe you’re in the learning stage of racing, or you just demand your bike holds up to anything you throw at it.
If you like meandering down tracks and stopping to smell the roses, then you probably don’t need to upgrade your belt drive, but I bet that isn’t you.
The primary drive is the first stage from the motor to the jackshaft, which in turn delivers power to the rear wheel via the big, obvious chain! Some e-motos run a belt system, some run a chain system, and others run a gearbox.
Here’s some further info on the gearbox:
Today we’ll discuss upgrading from a belt system to a chain system, why you would do that, and the options you have – and why we decided to make an in-house kit which we believe is the best option in most cases.
Here’s why we made our own kit.
Like most of the products we’ve designed ourselves, the primary drive chain conversion came from us needing a high-quality race-level component on our own bikes.
When we first started looking into other brands, we noticed many of them had flaws. We tend to look for high performance, not necessarily a pretty part that’s not quite as functional. And frankly, that was most of what we found.
We found that many aftermarket primary chain conversions had inconsistent shim alignment, and the sprockets didn’t always run true. Not really an issue on a belt system where there is room for movement, but when you run a chain, this all needs to be really accurate; otherwise, you get uneven wear and premature failure. Add in some big power mods, and seemingly small issues can turn into day-ending breakdowns. We know this because we broke competitor’s kits throughout the process of designing our own.
There was still more to fix.
When you design something in-house, you have full control over the quality, which eliminates inconsistencies like wobbly sprockets and bad shim alignment.
We also didn’t want to include the rubber isolators. While they do make the system slightly quieter, the trade-off isn’t worth it.
This is what our R&D lead, Rusty, had to say: “Think about it: you lube a chain, chain lube is sticky, then you ride in sandy conditions and everything sticks to it. Now your chain is running on a rubber shelf where the teeth are.
All that sand and debris compacts and compresses between the chain links, which causes early-on failure because you’re forcing stuff between your links. More binding, more heat generation.
The chain can’t properly clean itself because there’s a shelf where the teeth should be clearing. So the small amount of noise reduction isn’t worth what you’re sacrificing.”
Now that we knew our main design and engineering targets, it was only a matter of doing the work.
Why upgrade to a primary drive chain conversion?
For something a bit different, let’s start with why you wouldn’t upgrade.
The trade-off to changing to a primary chain conversion is the added weight. The chain and sprockets add weight, and due to the characteristics of the chain needing a little slack, there is a millisecond’s worth of delay. And yes, I’m talking about such a small amount, but some riders notice it – and they’re the ones who know they need the chain conversion!
So, why get the chain conversion? Well, it’s simply because the chain is stronger and more reliable. It is way more likely to survive a hard, flat, full-throttle out landing than a belt will. It won’t come off if the usual amount of dirt and sand gets trapped between the belt and the sprocket. It’s a performance part for performance riding.
Heavy Hitter 420 Primary Chain Drive Conversion Kit
Rusty and his R&D team have designed both a 420 primary chain drive and a 520 primary chain drive, and they’re both slightly different.
Firstly, let’s look at the 420 Primary Chain Drive. It’s designed for the smaller e-motos. Think the Surron LBX, E Ride SS, Zero XB type. It uses a chromoly front motor sprocket and an aluminium rear sprocket. Chromoly is used for the front motor sprocket as it’s better at being heat resistant. The rear sprocket is aluminium as it’s lighter. As far as we know, it’s the lightest on the market currently, which means it keeps the rotating mass down. Aluminum does wear faster, so that’s why we went with aluminum on the rear and chromoly on the front, but I’ll get into more detail on that in the next section.
One of the clever design factors for this primary chain drive conversion is the ability for this kit to fit many different types of e-motos. This is done by using shims on the sprockets and also installing the sprockets in a certain direction. They are all clearly marked with instructions on how to install them on your bike. Ultimately, this also keeps production costs down, which means we can stock these kits at a lower price for you. Just some of the cool stuff that Rusty comes up with!
Heavy Hitter 520 Primary Drive Conversion
One question I asked Rusty was what’s the difference between the 420 and the 520 drive conversion, and I thought this was going to be an easy one – just bigger – but I was very wrong! This is what he said:
“The motor sprocket is similar to the 420 in that we include a shim spacer. But the jack shaft sprocket is different. It’s a dish-style sprocket — there’s a hub that mounts to the jack shaft, and then the actual sprocket ring mounts to that hub. Two-piece design. The reason we did that was to offset the chain line so the 520 chain clears the frame.”
In other words, the 420 chain clears the frame, but the 520 wouldn’t if it were simply a bigger version of the 420 design. Other companies haven’t factored this in, meaning you either need to run the chain really tight – which causes other issues – or have it contacting the frame. Our two-piece dish design avoids this compromise.
Heavy Hitter Zero XB 420 Primary Chain Drive Conversion Kit
The primary Chain Drive Conversion for the Zero XB is slightly different from what I mentioned above, so it’s got its own kit! It has all the high-performance features the universal 420 Primary Chain Drive Conversion from Heavy Hitter has, but the Zero XB has a completely different offset, which needs to be addressed.
If you ride a Zero XB and are looking for the Primary Chain Drive Conversion, click here
Engineering the Heavy Hitter Primary Chain Drive Conversion
Rusty and his R&D team worked through many obstacles to bring you the highest-performing drive conversion we’ve seen. Here are a few interesting things the team worked through:
Material choice
I’ve already mentioned the sprockets are chromoly on the front and aluminium on the rear. You may be thinking, why not aluminium for both as it’s lighter, and originally Rusty tried this. However, during testing, it was found that aluminum on the front would wear too quickly. This is due to the heat from the motor, as when aluminum gets hot, it goes softer and wears more quickly. This sprocket was switched to chromoly so that it lasts longer when heat cycles are applied. The team found this was the perfect balance between weight saving, high performance, and longevity.
Alignment
This is possibly the biggest hurdle Rusty and his team were up against. It was found that even the smallest variations could occur between the same bike models due to manufacturing differences. For example, Bullet found up to 2mm variance across ten E Ride 3.0 frames. It might not sound like a lot, but when a chain is riding on a sprocket, the tolerance is very low, under 1mm. If it’s more than that, the chain will start to ride on the face of the sprocket, quickly causing uneven wear and ultimately premature failure.
Rusty and his team factored this into their designs, as well as making sure that everyone understands that this kit needs to be installed correctly. With a basic mechanical understanding, the kit is easy to install; it just needs to be aligned right!
Check out Rusty’s video where he explains this in lots of detail.
Maintenance
Chain tension is the biggest thing that we’ve seen cause issues with the primary chain conversion. It needs to be looser than most people expect. It’s recommended to have about 1 inch of up-and-down play. If it’s too tight, it can cause excess heat generation and add stress on the rollers.
Click here for more detailed information
The Primary Chain Drive Conversion
As Bullet says: “I think the primary reason someone buys a primary drive kit is not longevity. If you want longevity, you go with a belt. If you want durability and performance, you go with a primary drive chain.”
For that reason, this isn’t a mod that I would recommend for everyone. For those who don’t ride hard, a belt drive is quieter, and you don’t have the tolerance issues.
However, for those who do like to ride hard and need their bike to hold up to their riding style, the primary chain drive conversion is definitely worthwhile. So, if you spend your weekends on the trails with no chicken lines – jumping, racing, or just pushing the bike beyond what is intended – this is one upgrade you definitely don’t want to miss.
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