and now a tranny swap?

Ok, I've ironed out the cylinder swap, now it's the tranny. The bike is a 75 wr250. I have an old lower end from a 77-79 CR390. Can I use that tranny in the 75 cases?

Yes, it will swap. I like the transmission in my '76 250WR even for MX.

Well lets see. The 75 250wr is the 6spd mag engine in an MK frame which means the shifter is mounted on the bottom of the clutch case. The 390 was in the GP frame which means the shifter is located higher on the clutch case. The 390, as with all early GP frame mounted motors, had a shifter linkage inside the clutch cover to enable mounting the shifting lever higher. I don't see a problem in this area but then I don't any personal experience with this type of trans swap.

I fit a 79 390 trans into a 76 360 without a problem so I don't see why the 390 trans wouldn't go into your 75 250wr mag engine. I think you'll find that the clutch gear and primary gear have different tooth sizes between the two. This will create a different gear ratio than if the 390 trans was running off the 250's primary gear and clutch combo. BTW, its my understanding that the 75 250 clutch is different from the 390's so you'll have to use the 390 clutch, and possibly the 390 primary gear.

An big improvement will be the use of the 390's shifting drum ratchet wheel as opposed to the 250's detent pin and spring. I think the shifting drums will interchange and that the 390's ratchet arm assembly will fit inside the 75 250 cases without a problem.

All in all I think the 390 trans will fit in the 75 250 cases. Whether or not it gives you the desired ratio at the counter shaft sprocket is another thing.

For a while now I've been contemplating putting the newer shifting drum ratchet setup out of a mag engine into an older 72 - 73 450 5 spd in order to get away from the stock dent pin setup. I think shifting would be crisper, would require less shifter lever travel, and eliminate episodes of going halfway into gear.

I'm counting on you posting pictures of the tranny swap, before and after so we can see the shifter ratchet setup in the 250.

Just swap the transmission, keep the 250 clutch and primary gears.

Maybe I should try the wr trans before I make any changes. What sprocket gearing do you use Kartwheel?

Since I don't have any first hand experience with this type of trans swap I referred to the Husky parts list and based on what I saw there the clutch is different between the 75 250wr and the later model 390's. I realize that the parts list is prone to inaccuracies so one must proceed carefully. The difference shown between the 75 250wr and later 390's parts list is enough to question the use of the 75 250wr clutch with a later model 390 transmission.

I believe that Kartwheel had success with his swap of a 76 250wr transmission and clutch with 390 parts since they're both from the same design but I question whether its going to be the same with the 75 250wr.

Here are my findings from the parts list. One PDF is the 75 250wr and the other is a 77 390cr.

The '75 250WR uses the '74 style Mag clutch, but the rest of the transmission is the same and can be swapped up to the last year of the non-primary kick engines in '80-'81. You will also need to update to the new clutch (I think) but one of the main benefits of going to the newer stuff is the much much better clutch in the '75CR/'76+ bikes so there is not really any good reason to keep the old style clutch.

Kartwheel. what gearing are you using with the wr trans?

I will have to look, I don't remember off hand.

I used to have a 1971 mh 400 . A previous owner had swapped in some cogs from a 250 to change the transmission gearing around to suit his needs . This may be something to look into , just change what you're not happy with .

and change primary gear and clutch basket will help start the mag style motors.

A lot of different models of Husky engines can swap transmission parts. I built a transmission for my '82 125XC like the ones the Husky factory riders put in theirs at the time. The 125XC used the CR transmission so it tops out at about 50mph. I took out the stock 5th and 6th gears and swapped in the '74 125SC 5th and 6th, which leaves a close ratio 1-4th and taller 5th and 6th. After that swap with the same final gearing the top speed went from around 50mph to around 62, a significant difference. You can mix and match any of the '75-'81 non primary kick transmission parts to build what you want.

I use 10\56 final drive and it is about right. My bike is the 75 WR 250. If you go much bigger on the rear, the sprocket might come in contact with the chain guide. I don't advise turning the brake stay arm around. The 10 on the front is smaller than I really like, but sometimes in woods riding you need a low first gear. My first gear is not a granny gear. Top speed is still pretty fast. I have never topped it out to find out. I like the stock 74 CR 250 gearing better. I just like close ratios. I think I read that in 1975 the WR's came with a few extra parts. Including a 10, 11, and 12 front sprocket. Jeff

Wow, 10 teeth? That's small. I'll get the bike together and try it before I decide what to do. I'm still finding top end parts for it.
Thanks for all the input. It's greatly appreciated.

I wasn't riding trails back then, so I don't know how gearing was for mid 70's enduros. I was into motocross. But the type of trails that are being used today, stock gearing was too tall for my taste. The only other vintage Husky I have ridden is a 74 250 Mag.

I believe I have 12/56 on my '76 250WR but I will have to check this weekend.

We rode mostly trails around here. I rode MX for a few years but I like the woods better. I think I'll go with a 12. I'll have to look and see what came on this bike, it's good enough to use for awhile. I'll buy new once I figure it out.