470 Pro-circuit

No was going to use Walts 165 piston and stroke the crank.

What is walt 165 piston ?

Motocross Action did a small article on the PC 470. I might still have it. I will look for it and post it if I find it.

Walt, Wallybean on this forum does a piston for the 2000 - current 125/144's.

I had an 09 Husky I was going to 165 then get shorter rods through crank works to stroke it to a 175.

But crank works can do rods but you have to buy 4 in order for them to make them.

Now if you get 3 others on here, you could do it and then have them move your wrist pin out to stroke it.

Wossner will make a custom piston for $215.00. You could just have one made with the wrist pin hole a little higher.

Okay, I'm no engine guru, but that does not make sense to me? To change the stroke, total distance piston travels from bottom to top is affected by moving the crank pin further from the center of the point of crank rotation? To compensate, shorten the rod length. Hence longer stroke, more torque lower rpm, short stroke less torque higher rpm?

Been following this thread with much interest, so help me out here if I'm missing something?

Adam

That sounds to me strange the way to reduce the rod.
And it seems to be a hard work/ tuning on a rod.
Make directly a new shorter rod could be more easier, no ?

No, concept is like undoing a rusty nut.

Put a small wrench on it and it won't break loose.

Now, put a long piece of pipe on wrench for more leverage and it will break loose.

Plus your piston when it goes down in cylinder, captures a lil more fuel and air.

Hope this helps explain it better?

Also, when you change stuff around, added piston weights, crank weights, etc....

You have to balance the crank.

Guys that take the newer 125's and put the 144 kit on, feel more vibration in their bars.

After I did mine , I sent my crank off to have it rebalanced. Spooled up faster and didn't vibrate in bars any longer.

There a several ways to compensate for an increase in stroke, it really has a lot to do with where your port timing ends up after the stroke increase. You can move the piston wrist pin, space the cylinder, shorten the rod, or if you have enough meat in the head, you can let the piston come out the top of the cylinder and recut the head. You just can't let the rings come out of the cylinder.

As long as the lower crank pin is moved further from the crank center line you get an increase in stroke. It's that simple.

You have to remember that these motors were built almost 35 years ago. Finding someone to build a rod was a lot harder and much more work than it is today. There wasn't a guy with a CNC machine on every corner, like there is today.

Shrinking a rod is actually pretty easy to do, after you build a jig. It was also fairly reliable, but if it failed, it would probable fail at the shrink point.

Crank balancing is so often overlooked as a performance increase. A well balanced crank can do wonders, especially when you add bigger pistons, different rods and stroke.

A 430 cr 82 with a 470 kit for sale on subito.it !
http://www.subito.it/vi/102388992.htm

It is written 480 on cylinder.

You are not missing anything. The crank pin must move to get more stroke.
Perhaps ideal is to have rod at 90 degrees to line with main bearing center and crank pin center when pressure above piston is highest. I read that somewhere on this forum or another most likely. I think ocean going two cycle diesel cargo ships have long rods. Vibration of the third class is due to rod length not being infinate. An opposed design is able to cancel this out.

I havn't read the whole thread pertaining to over boring a lot whatever sort of swirl or direction of the transfer charge so as not to have massive amounts go out the exhaust or stuff like that the last bit of passage is lost and most likely some directional steering. Maybe similar at the holes on the piston on the intake side.

In Amateur hillclimbing perhaps 10 years ago there was a rule if you overbored 10% or more you could go into the next class. There was what was called a 540 kit to put on a Kawasaki kx500. The guys in the 750 class didn't have a chance unless it was a highway hill. No one was able to get faster with that set up, even the guys that had two bikes, virtually the same, actually the time difference was almost all the time more than you would expect.

Wally gets his blanks from somewhere, I asked him about the offset wristpin at one point as the origional 125 husky pin seems centered. He seemed happy with it that way but didn't say he sought out that on purpose.

We are almost in 2015, I read the whole thing now, Once the 500 came out or the 500 cylinder with the divided transfer ports, different reed cage, wouldn't carving that up, using the much lighter 430 piston, rod and crank mod discussed be more sensible at this time?

If the stroke is 6 mm longer ( with a shorter rod), must all ports
be bigger 6 mm down ?

You get the stroke from double the offset in the crank cheeks but you get the total stacking height from the length of the rod. Changing rod length does not change stroke, just piston height at TDC

My question was not right !
If the stroke is 6 mm longer ( with a shorter rod , a 3 mm crank pin move and no spacer), must all ports
be bigger 6 mm down ?

The 470 PC Kit is featured in the June 82 Motocross Action !
Someone has it ???

So you can change the location of the pin on your crank. Plug old crank holes. Have
machinist drill/bore pin location holes in direction wanted in crank halves.

So stoke is now longer and piston travels longer. So now we shorten the crank length but how much? It must only enough to match port heights? Because if it equal what have we accomplished.

Have an email out to guy who has sells old mags and see if he has that MXA issue

That is why the rod is shortened, so the port timing remains the same with the increased stroke.

A note on the Powroll rod modification, they did that for years, I have a '74 Honda XL175 with a Powroll 225 stroker kit and its rod was shortened with the "heat, crush, re-heat treat" method. I also have a 240 XR200 Powroll stroker engine (which they dont offer anymore) with the same "crushed" rod modification.