3" belt or chain - primary drive

[simonDeuce]

The background:-

Have been in a development stage with the FXDX 124" project which until now has been happily running a Primo Brute III extreme enclosed belt primary. There is plenty of ventilation in the casing. During the latest stage of work, which has entailed work which I will detail soon, it has had over 100 dyno runs in the last couple of weeks.

Bearing in mind that the belts are supposed to be able to handle a large amount of power, I was somewhat surprised to find that the belt has stretched to such an extent that it is useless and needs to be replaced. We are not talking about a little bit slack but of the thing being totally knackered.

Whilst I accept that a dyno cabin does not have cold air blowing through it, and that performing that many dyno runs creates an extreme condition, I need to consider options.

So, input please...

1/. Do I simply replace the belt and have done with it?
2/. A 3" belt primary with outriggers bearing supports?
3/. Convert back to chain?

For now I will go with option 1 but over the winter, as the bike comes up to full drag spec, I think I need to choose one of the other options.

I have always liked belts for the following reasons.
A/. They are lighter, much lighter.
The rotating mass is far less than a chain setup
B/. Maintenance is much easier
No mucking about with oil and gaskets just to get in there and check it over properly.
C/. No compensator to worry about.
I want/like a direct power transfer and slick shifting.

Seeing that the bike still hasnt had any headwork so there is another 10% of the torque/hp still to come, do I go with a 3" primary or convert back to chain?

Thanks in advance.

[SX 150]

I put a Primo Brut 1V on my evo (softail) a few years ago, partly to make it easier to get my trans/drive belt aligned (I run a lot of off-sets), partly to to make removal of the primaries & drive belt, and party to allow for more HP and new motor.

I went for Primo over BDL,- it has a really good rep on the US boards & it has a split motor plate so the belt tension & trans position can be adjusted (to a certain degree).
I can now strip and replace the drive belt within an hour with the advantage of no oil leaks and lighter weight,-IMHO there's no negative points to it,- I have read silly claimed power capabilities of these belt drives/clutches from Primo probably well in access of any road bikes & that's without outer bearing supports.

Stock strait out the box


I've just fitted a Grandeur auto clutch (although Prime list there own now it looks identical) works virtually like a twist and go will sit in first gear, & will only engage when over a set RPM (adjustable). so you can sit in gear give it a good twist and it will wheel-spin. They claim it's been used on bikes on the drag strip up to 300BHP.
To me its the ideal combination.
& with the auto clutch fitted.

[Scotty]

Anyone i know who has used a belt whether on a Harley or old Brit has had nothing but trouble with em.
Not something i personally would go for, been running HD's with chains for many a year now and never had a problem.
Its mechanical, sealed from the elements (and your leg) lubricated and cooled by oil.
Nope not for me......Just my thoughts.

[the_monster]

Originally Posted by Scotty

Anyone i know who has used a belt whether on a Harley or old Brit has had nothing but trouble with em.
Not something i personally would go for, been running HD's with chains for many a year now and never had a problem.
Its mechanical, sealed from the elements (and your leg) lubricated and cooled by oil.
Nope not for me......Just my thoughts.

For once I agree with Scotty !!!

[simonDeuce]

Thank you for your input gentlemen.

I have run primary belts for many, many years in my harleys and my old british bikes. I recently found an old receipt for one I bought from Tony Hayward, to fit a Triumph Tiger 750 I had, back in 1985. This is the first time I have had a problem. I've always run enclosed belts and have been happy with them.

The points you have made for the chain are relevant and baring the additional weight factor, I seriously need to think about it.

I would like to run a 3" belt but if I'm honest, I really dont fancy running an exposed primary of that size with mid controls. Hence the consideration of reverting to chain.

[grbrown]

Simon,

Having heard a few of those dyno runs first hand I am not surprised your belt cried enough!

A wide belt is not in the running in my book, more for show than go. It is possible that a replacement for your current belt will survive far better in a less testing situation so is worth a try, simply because it is the cheapest way ahead.

However your bike is already seriously tuned and I doubt if you will find many vehicles running a primary belt. Harley used them in the original Sturgis model, which was the first they fitted with belt drive, but have not used them since. I know they are routine in historic racing, but those bikes, like your Triumph, are putting out far less power.

The torque fluctuations from your crankshaft are very extreme. I reckon a chain is the way to go, long-term. What do the extreme Harley drag-bike riders use?

[simonDeuce]

As you suggest Graham, I will run with a replacement belt on the current setup for the time being. I concur the conditions had a lot to do with the belts demise.

I'm taking it as a warning shot of what is to come when the next set of cams and head get done.

I'm not having any headwork done yet but when I do, I think it will be time to revert to a chain setup.