• Husqvarna Motorcycles Made In Sweden - About 1988 and older

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Installing a 390 jug on a 250?

Bigbill

Bigbill

Husqvarna
Pro Class
Has anyone ever thought of installing a 390 cylinder '82 on a '84 250wr?
I believe the difference in the stroke is around 7mm. So the cylinder height may need machining. To get the ports in there correct position. The cylinder stud location should be ok between the 82 390 and the 84 250. The 390 transfer ports on the bottom of the 390 cylinder needs to be ported. I'm thinking the bottom of the piston may need to be cut for clearance.

Ever think about this?
 
Well you probably could and why I say this?

I bought 82 cr 250 and it had the 79 250 jug on the newer 82 bottom end. It also had a space and adapter plate below jug and used two gaskets.
Not sure about rod though?
 
The motor would be so over square not sure how it would run.What exactly are you trying to accomplish?
 
Over 330cc' s?

If we turn 7mm off the bottom of the 390 jug. Estimate, The height or stroke should match the 250 jug but we have the 82mm bore by the 250 stroke. The newer 390 jug uses a similar base gasket. I believe the cylinder tie rod is the same distance apart.

I'm just thinking out loud here and wonder if it's been done before.
 
I bet Tinkens got some fancy computer program that would figure that all out mite be cheaper than an HVA300 or go the other way don't forget the 360 I bet you could mix n match a lot of that with a little work and build some real screamers
 
ol mate here has a 290 maico built by some similar witchcraft thinking so who knows what crudzilla could result.... my thinking, if it was a good option, husky would have thought of it....they didn't miss too much.
 
I just purchased what the seller called a 250 head with a compression release added in it for $30. I'm looking at his add for the same parts there's a cylinder $30 plus a 390 flywheel and 390 clutch cover. These parts marked 250 are from a late model 390. If this big bore kit can be fabricated at little cost it just maybe a fun ride. I received the head and it's from a larger bore than a 250.

Even if the cylinder sleeve or piston is too tall we can adjust that too.
 
price is good that's for sure...Face it, there isn't too much more fun than mucking about with old Husky's:thumbsup:
 
I think the 78/79 husqvarna 390 is one of the fastest huskys ever made. With its 43hp at the rear wheel I never had the rear wheel stop spinning. You could follow me by the rips. The wheel only stopped spinning is when I shifted.

I had husqvarna 250's, 360, 390's, 400, 420, 430s. I had a '85 500cr but never put it together I regret that to this day. The 86 400 lc was a quick one too. The 83 430wr was like a tractor.
Even there transmissions were well built. The Swedes knew what they were doing.
 
suprize said:
ol mate here has a 290 maico built by some similar witchcraft thinking so who knows what crudzilla could result.... my thinking, if it was a good option, husky would have thought of it....they didn't miss too much.
Click to expand...

so how was that 290 Maico built and howd it run?:banana:
 
Another option is a 430 crank and a spacer on the cylinder base gasket. I hate to see parts sitting idle when a frankenhusky is possible.
 
I rode the maico and found it to be a strong 250, bit like a kato 300. I cant remember what the combination was of motor bits but I will ask again nxt time I see him.
 
The most common Maico conversion between 250 and 400 is the 326, which is a 250 crank in a 400 engine, a 250 bottom end with either a 400 top end or a 400 sleeve in a 250 cylinder. Maico even used that configuration in the early 90s and sold it as a 320.

There was no 390 in '82 the last year of the 390 was '80, and the '80 390 cylinder is the only one that has the same cylinder stud spacing as the 430 and '82-up 250. There is not really any reason to limit it to just the 390, the 420 and 430 are all almost identical to the '80 390 other than bore size, the port layout is the same. The biggest problem is the Husky 250 is already short stroke and very over square, which means the port misalignment will be large, if you align the piston/deck height the bottom of the ports will be far below the top edge of the piston at BDC. With some work though, you should be able to make a 390/420/430 cylinder work on an '82-up bottom end.
 
Just thinking out loud. What if I used a 430 crank with the 390 cylinder using a base spacer?

What's the stroke on the 430?

Looking for ideas for a Frankenstein husqvarna ripper.
 
buy a folan thingy ... plenty of rip there im sure!

from memory, the maico was a 320 conversion (Alzheimer's)
 
That should be pretty easy to do, only 3mm difference in the stroke of the 390 and 430, 71mm vs 74mm. The LC 400 has a 430 stroke and 390 bore size, so that is basically what you would be building in an air cooled version, I'm not sure that is worth the effort with 430 top ends so easy to get.

I like the idea of building something unique, but if I was going to do it I would want a displacement not found in a stock Husky, something in between sizes like the Maico 326. The problem is the Husky 250 is already too oversquare, so going bigger bore would not be as good as longer stroke, something like a 430 bottom end with a 250 top end, should give you an undersquare engine at 74x70(69.5)mm or right around 300cc. I dont know what the stoke of the 240 crank is, but I know its longer than the 250 because that is what HVA uses to make their 300. I doubt the 250 ports could be lowered enough to match the piston at BDC with the 430 stroke though.
 
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