470 Pro-circuit

Does someone know what is the bore x stroke of the Husqvarna 470 pro-circuit Kit ?

ii was a long time ago, but i am pretty sure it was the standard bore but they lengthened the rod. I dont remember what they changed on the cylinder/head to accommodate the longer stroke.

Here's pics of a bike sold in France with a 468 cm3 (B.MILANI). I don't know the modifications.
Surely an HUSQVARNA 470 Pro Circuit KIT

For a standard 430:
-bore x stroke: 86x74 =429 cc
So, for a 470 it could be with a longer stroke:
- 86 x 80.5 = 467.37 cc
-86 x 81 = 470.27 cc
For a 470 with a bigger bore:
-90x74 = 470.52 cc

I was thinking the 81mm stroke was right, but I think they used a Honda rod and / or piston to compensate for the additional 3.5mm coming out the deck. I don't think they used a spacer, but they may have.

Ok Motorhead !
Do you know if there was a Husqvarna ProCircuit 470 Kit sold in these days ?
Or was it only a limited number of 470 PC bikes produced for the PC racers?

They were for sale, but I don't know how many, if any, were sold. I don't remember how much they cost, but it was pricey for that period, because you had to send them your motor to have it done.

If a bike has been in the adds in France, it is because some 470 Pro Circuit Kits have been sold there.

I sent my crank and cylinder / head to them so it really wasn't a "kit"

I'm curious as to "why" Pro Circuit would offer a 470? I wonder what performance they were trying to achieve? Husky had a 500 available.
Maybe just to give 430 owners more power?

Also, isn't the 500 essentially a 430 bore with a longer stroke?
And riders didn't like the vibration of the 500 due to the longer stroke and they tried all kinds of tricks to balance it?

I might modify my 430 if there was a good reason. A 470 might be cool.
Dave

Interesting, Factory 4510 !
Do you remember what has been done ? Porting ....?
I have heard of longer stroke and Motorhaed think they used Honda parts ( Piston and rod) in it !

I did my 430 just before the Silver streaks came out. And the early 500 CR's were 4 speeds. I switched from a YZ 490 (4speed) to the 430 mostly because of the stability, but the 6 speed sure made the bike a lot more flexible. At that time we were transitioning from all natural tracks to a lot of SX type stuff. The Husky was perfect for the natural terrain tracks, but if sure wish I could have had the Yamaha brakes.

It was definitely the stock piston, and I thought I remembered the weld were the rod was lengthened. I think the reason they need the cylinder was to put a relief cut in the bottom of the liner to get more clearance for the rod but I sure don't remember how they allowed for the increased stroke. I also had a Can AM 250 GP (rotax rotary valve) and between that engine and the 470 those were about the two best engines I have ever ridden. The 470 conversion did make the weak brakes feel even more inadequate. I had ridden a 500 CR with the dual leading link front brake, and with the shoes properly arced in and adjusted it stopped much better. If I was to build a vintage MX bike, the 470 would be a good choice to go up against the Maico's and Honda's.

Pro Circuit did the porting,but the crank and rod work was subcontracted to Klemm Research,www.klemmvintage.com.Excellent tech articles on their website pertaining to engine preparation,compression and leakdown testing,2 stroke oils.

Thanks for all datas.
But with a HVA standard piston and cylinder, but with a longer stroke,
you need to put a spacer, no ?

Did a little checking, the crank work was done by POWROLL. The crank was stroked 7mm and the rod was "shrunk" 3.5mm to accommodate the increased stroke. The rods are placed in a jig, on a press, and heated in the center. Then compressed in the jig to make them shorter. There is a fat spot in the rod after this is done, from compressing the metal. That is probable what Factory4510 remembers as a "weld', but the rod was actually shortened, not lengthened.

The porting and head work was done to bring the port times back in line with the new stroke.

If you have a shortened rod 3.5mm and 7 mm stroke more, the piston
goes down 7mm more in the cylinder ( and 0 mm up).
So you must do the porting and go down all holes in cylinder of 7 mm.

Yes, that is correct on the stroke. But, you may not have to lower the port windows. Only if you need the extra port time / area. In most cases where you increase the stroke you are looking for more torque, and that's achieved with the mechanical advantage of the stroke increase. Or, you need a big increase in port time / area that you can not achieve with just porting.

The increased stroke will yield a substantial increase in time / area with the standard port configuration, but you still may need to adjust the timing of the ports to suit your needs.

Another option is to contact crank works. They can make you 4 custom sized rods.

Minimum order is 4 for like $ 250 each.

Then get them to move your rod location on crank.

I almost did that to make a true 175 newer husky.

125 bore x stroke are 55 x 52
175 bore x stroke are 64.75 x 52
So, to make your 175 you kept the 55 bore (125) with a longer stroke ( 52++ ?)
How many ?