Forum

[Allanfox]

Whilst the AVL Electra X is being worked on IN have been putting some miles in on my 2003 350 iron barrel. Lovely bike and really enjoying it but like all 350s could do with a little more umph. Lots of options how to do this but got me to thinking a 500 conversion would be one way to increase the torque and top speed. What is involved? I think the cranks are the same but the crankcase mouth is wider on the 500?

Just looking at options really as platy of 500 parts knocking about!

[Allanfox]

take it back, looks complex and a waste of time, want a 500 get a 500!

[Wheaters]

I’ve rebuilt quite a number of engines of different types over the years and always like to spend time to ensure I remove any steps or roughness which might reduce performance.

I had to do a top end rebuild on my 350 Electra iron engine (TCI electronic ignition, kickstart only).
I was quite shocked to see how badly the ports had been finished (or rather, not finished) from the factory. There were big steps, especially between the back of the the original valve seats and around the guides, worse on the inlet side and also a badly matched carb mouth. I sorted those out with my Dremel tools and also opened out the inlet to suit a 26mm concentric carb and foam filter. With a less restrictive exhaust, the bike runs very well. I’ve since fitted a five speed box with very slightly higher than standard 350 gearing and I’m now happy to use the motorways where necessary because the bike is able to keep up with and overtake HGVs (although tbh I wouldn’t plan to go very far on those roads at busy times). I certainly wouldn’t have done that before; I tried but was being crowded by HGVs because they were faster than the bike.

[stinkwheel]

Machine crankcase mouth, re-drill and tap wider spaced stud holes, plug old stud holes with insert or weld. Bigger barrel, piston.

Exhaust header is different, as is carb and inlet manifold.

Crank isn't actually exactly the same but I think people still use the 350 one.

Then the question is... If it takes a 500, would it take a 535 barrel?

Another option, not heard of anyone who has one... Our host does a 400cc longstroke crank for the 350...

[Bullet Whisperer]

With suitable and inexpensive tuning, a 350 can be made to out perform a standard 500.

[Adrian]

The Tollgate Classics 450 conversion for the 350 Bullet is also still available, it uses the 350 barrel but re-sleeved with a larger 79mm bore liner and BSA Victor piston, the crankcase mouth has to be bored out too, but the original cylinder stud position is kept.

A.

[Duke of Wybourne.]

Second the tuned 350. If you're not a "Porker" so you've got good power to weight, a 350 can be made quick without taking the motor out of the frame. Cams (own profile), piston, and some head work, and some other simple mods. I had one of our hosts rear hubs/drum which allowed the changing of rear sprockets, and ended up using slightly lower than standard gearing, because the engine RPM was considerably higher. Worked well for years with no explosions. Bottom end/crank was bog stock too.

[Wheaters]

I’ve found the 5 speed box works very nicely with the 350. 1st gear is lower than that of the 4 speed box and the extra ratio means that there are no big gaps, unlike the very noticeable one between 3rd and 4th of the older design. I’m sure that gap isn’t so critical for the 500 but I often found myself rowing between those two gears.

I discovered that the engine will now rev till the valves bounce, but obviously having found that limit I make sure I don’t let it do that now.

I also have one of the modified rear drums and run the sprockets at F18/R42. This is almost identical to the 16/38 which is standard for the 350.

[Daiwiskers]

I have only ridden one 500 and all I can say is it felt sluggish compared to asbo30, and the vibration was pretty horrible.
Undoubtedly the 500 could be made far better than the one i tried but my bike felt nicer than the 500 even before it became asbo30

As a starting point i would recommend retarding the inlet cam and fitting the close ratio gearbox mod

[PeteF]

I’ve found the 5 speed box works very nicely with the 350. 1st gear is lower than that of the 4 speed box and the extra ratio means that there are no big gaps, unlike the very noticeable one between 3rd and 4th of the older design. I’m sure that gap isn’t so critical for the 500 but I often found myself rowing between those two gears.

I discovered that the engine will now rev till the valves bounce, but obviously having found that limit I make sure I don’t let it do that now.

I also have one of the modified rear drums and run the sprockets at F18/R42. This is almost identical to the 16/38 which is standard for the 350.

Most of the above can be achieved with a close ratio conversion without spending (probably) more than a 350 is worth