175 / 390 Build

Looking to put a 1978 390 motor into a 1975 175 frame. Other than the motor, electrical, carb, and exhaust any roadblocks ahead? Maybe the motor mounts?

bet it bolts right in but what do i know i was 9 in 75

You may need to reject the carb or change it to a mikuni 38'm if it's not.
Take it easy with the 390 for a while this engine has lots of power over the 175.

I look at the older 125/175 pictures without ever seeing one in person and the frames all look the same size?
Did husqvarna use the same frame for all the bikes of that 70's decade? If so was the bike under powered became of the weight of the frame with the 125/175 engines? If so that 390 engine your going to feel like your riding a rocket. To me the 390 is one hairy and wild ride, my 79 390cr was.

Most ML frames are very similar. The early ones used a 'loose ball' head stock bearing (which can be a pain). This was up to late 76/77 on some models.
From about 77/78 on they used a taper roller bearing here. There were variations in headstock angle too between the CR, WR and OR models.
I think the 125's had a "short tab" mounting plate where the swing arm pivot goes through the frame.

To fit your 390 into that early frame I would think all you need to find are the engine mounting plates front and rear. As well as the parts listed above.

I am sure Claude will be able to shine more light on this than me.

The 175 is probably a smaller bore 250?

Looking at the rear swingarm. The stock swingarm probably needs to be longer for more stability. The made them longer after 76 and longer again in 80. I will have to get some measurements posted up to see what fits my frame. Also thinking about a more modern rear shock setup. Maybe a 82 Ohlins piggyback pair. This might work for the longer swingarm. If not, I have a pair of remote resiviour Ohlins shocks I can have rebuilt.

I have a dumb question sorry. In another post why do they shorten the longer steel swing arm on the '83 milk truck bikes? Is the wr frame is the swing arm longer than the cr swing arm?

Would the shorter swing arm, with the shorter wheel base turn quicker in motocross and the tighter turns in the woods during hare scrambles? Is there an advantage with the shorter swing arm over the longer one?

The CR/XC swingarm is longer than the WR swingarm by at least about 1.25" for the 1983s About the same as the 1982s except the 1983 shock position is further forward on the 1983 swingarms