• Husqvarna Motorcycles Made In Sweden - About 1988 and older

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How to: " stuff " a two stroke crank

Fritzcoinc

Fritzcoinc

Husqvarna
AA Class
I've heard filling the balance holes in a two stroke crank called " stuffing".
As I understand it, this reduces the low end area and allows for a quicker and lower vac signal as the piston moves up the bore.
I'm building/restoring am 87 430 WR and would like to plug/stuff the balance and crank pin holes of the crankshaft halves. The crank will be re balanced after re-assembly.
Because a motor like this needs more HP, right?
What material do you use? Aluminum? Titanium? Plastic? Epoxy?
If you have made this mod, what were the performance plus/minus?
Thanks in advance.
Photo of Crank:
IMG_1139-M.jpg
 
I have never done it, but I read an article many years ago, where they used epoxy to do the fill.
 
I have used cork as it is light weight and epoxied the cork plug in place. I think Bultaco used pressed in aluminum plugs or metal plugs on each side of the crank weight that look like small 'freeze" plugs.

Marty
 
Thanks, guys!
I had forgotten about cork with an epoxy seal. Cork is lightweight and resilient, and epoxy can easily stand the low heat in that engine area. A relativity easy job to do on a crank assembly with the added bonus of if it comes out, it won't trash anything.
But, since I'll have the crank apart, I'm leaning towards machining an aluminum barbell shape, mild shrink ( heat crank and freeze barbells) fit it in the holes with epoxy, and staking it in place with punch pricks.
So does anybody know how Suzuki did this for Roger DeCoster's bike, or better still, how did Yamaha do this for Kevin Schwantz's GP bike? lol
 
motomwo said:
I have used cork as it is light weight and epoxied the cork plug in place. I think Bultaco used pressed in aluminum plugs or metal plugs on each side of the crank weight that look like small 'freeze" plugs.

Marty
Click to expand...

Thanks Marty:
Did you just glue the cork in place or glue in place and seal over the cork with epoxy?
Thanks
 
I glued (epoxied) the cork in place and then sealed up the plugs on both sides of the plugs with a coating of epoxy. Worked good and never had the plug come out.

Marty
 
Over on ADV Rider I learned that there is a preferred ratio of engine piston displacement to lower crankcase volume. Somewhere around 1.4:1 is best for expansion pipe engines. Muffler engines or older engines may benefit from a ratio of 1.37:1. I measured the 430 cases, crank, rod, and balance holes then calculated the volume. It worked out to be 1.45:1. So, I have decided to leave good enough alone.
A big " THANK YOU" to all who chimed in here.
 
Just out of curiosity what would your piston displacement to lower crankcase volume ratio end up being if you did fill the crank weight holes?

Marty
 
KTM used aluminium plugs like welch plugs in their 2000 cranks.. i had one pop out and tap dance inside
 
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