1. Husqvarna Motorcycles Made In Sweden - About 1988 and older

What the difference between 360 & 390?

Discussion in 'Vintage/Left Kickers' started by ruwfo, Jul 30, 2014.

  1. ruwfo Administrator

    Location:
    NJ
    Husqvarna Motorcycle:
    1980 390CR, 1982 430CR, 1984 400WR
    Other Motorcycles:
    1985 250XC, 2016 FJ-09
    What the difference between the 360 & 390?

    Ok, I know that a 2nd over (82.42) 360 is also a 390 std bore, but if you bore the 360 cylinder
    to a 2nd or 3rd over, do you now have a 390 not a 360? I guess you do right?

    The cylinder grew in height in 1977 when the 360 went to a 390 & gain an extra fin (8 vs 9),
    so I'm guess Husky lengthen the rod too? and that the piston wrist pin stayed in the same location
    as on the 360.

    I ask because, I'm getting ready to have my 360 cylinder bored, it's at STD bore now &
    I'd like to know my piston size options. I see Husqvarna-parts has 1st-3rd over , but I won
    a Wiseco piston on Ebay, which is a slightly smaller size then 3rd over (sort of a 2.5 over) &
    until I get it was wondering will that work too.

    Husky John
    ruwfo, Jul 30, 2014
    #1

  2. 390Dave Husqvarna
    A Class

    Husqvarna Motorcycle:
    83 250XC
    Other Motorcycles:
    80 Maico 440 84 IT490 84 MXC 250
    A 360 is basically big bore 250,a 390 is a bored and stroked 360,64.5 stroke for 250/360,71mm for the 390,all 3 use a 135mm center to center connecting rod,the 360/390 both have 37mm compression height pistons{centerline of pin bore to top crown}The 390/420 conversion{actually 412cc} is an 86mm bore for a 390,The 430 is a bored and stroked 390,74mmX86mm,same 37mm comp. height and 135mm rod,the 500 is a bored and stroked 430,88mmX88mm,with 145mm con rod.Kinda like the small block/big block chevy or Ford FE series of the dirt bike world.
    390Dave, Jul 30, 2014
    #2

  3. fran...k. Husqvarna
    AA Class

    Location:
    eastern ct
    Husqvarna Motorcycle:
    420ae 98wr125 2004wr250 others
    Other Motorcycles:
    electric freeride 1993 yam gts
    Post 2 pretty much cleared up the origional question but gets off track about the 500 it is 84mm stroke 86mm bore on a signigfincantly more massive piston but still same bore as 420. 420 piston is the same as 430 air cooled.
    fran...k., Jul 30, 2014
    #3

  4. 390Dave Husqvarna
    A Class

    Husqvarna Motorcycle:
    83 250XC
    Other Motorcycles:
    80 Maico 440 84 IT490 84 MXC 250
    whoops thought the 5 was square at 88x88!
    390Dave, Jul 30, 2014
    #4

  5. jimspac Husqvarna
    Pro Class

    Location:
    Connecticut
    Husqvarna Motorcycle:
    82 250WR, 82 430WR, 84 250WR, 85 400
    Other Motorcycles:
    86 400WR, 82 Montesa Cota 349
    Because the 420 was built over the 71mm stroke of the 390 and the 430 has 74mm stroke
    jimspac, Jul 30, 2014
    #5

  6. ruwfo Administrator

    Location:
    NJ
    Husqvarna Motorcycle:
    1980 390CR, 1982 430CR, 1984 400WR
    Other Motorcycles:
    1985 250XC, 2016 FJ-09
    Thanks Dave, that's answer the question , & also explains the 390 motor I got with a broken piston skirt, that I sold to Jim.

    He said it looked like the piston had actually hit the crank & broke the skirt & then the cases. Well that now makes sense, some
    knuckle head must have used a 360 piston in a 390.
    ruwfo, Jul 30, 2014
    #6

  7. jimspac Husqvarna
    Pro Class

    Location:
    Connecticut
    Husqvarna Motorcycle:
    82 250WR, 82 430WR, 84 250WR, 85 400
    Other Motorcycles:
    86 400WR, 82 Montesa Cota 349
    Actually I seem to recall the 360 has a 67mm stroke as I had noticed a 4mm change from 360 to 390 and 390 to 430.

    If you found a 390 crank, that may fit in the 360 cases but also remember that Husqvarna went from single point mounting on the front of the 360 to dual point on the 390. And as you reminded me that Husqvarna does everything for a good reason.....
    jimspac, Jul 30, 2014
    #7

  8. silverstreakNZ Husqvarna
    Pro Class

    Location:
    Christchurch nz
    Husqvarna Motorcycle:
    82cr500,76gp360,90wr250,81 420AXC
    Other Motorcycles:
    74 tm400 , 02 gasgas ec 300
    So can a 83mm piston for a 390 be used in a 360 engine ?
    silverstreakNZ, Dec 13, 2021
    #8

  9. motomwo Husqvarna
    AA Class

    Location:
    Imbler Oregon
    Husqvarna Motorcycle:
    Many vintage big bore and automatics
    Yes. 83mm 390 piston is the same piston for the 360.

    Marty
    motomwo, Dec 14, 2021
    #9

  10. 2premo Husqvarna
    Pro Class

    Location:
    Northern NV
    Husqvarna Motorcycle:
    98 WR360, 1987 WR430, 1988 XC430
    Other Motorcycles:
    Sherco 300, 2002 KTM 380EXC
    so stupid question as I am not well versed in this generation Husky
    typically when an engine is stroked as in a different stroke length, it also changes the piston height profile to compensate for the differ port timing from stroke
    later the 430 500 shared a bore size, but nothing else
    2premo, Dec 14, 2021
    #10

  11. motomwo Husqvarna
    AA Class

    Location:
    Imbler Oregon
    Husqvarna Motorcycle:
    Many vintage big bore and automatics

    When Husky went from a 360 to 390 they changed the stroke and the cylinder length and port timing. Used the same piston and rod.

    Marty
    motomwo, Dec 15, 2021
    #11
    2premo likes this.

  12. 2premo Husqvarna
    Pro Class

    Location:
    Northern NV
    Husqvarna Motorcycle:
    98 WR360, 1987 WR430, 1988 XC430
    Other Motorcycles:
    Sherco 300, 2002 KTM 380EXC

    that's a clever trick, but other makers just started over on stroke changes, so did Husky later, but still a cool trick
    2premo, Dec 15, 2021
    #12

  13. motomwo Husqvarna
    AA Class

    Location:
    Imbler Oregon
    Husqvarna Motorcycle:
    Many vintage big bore and automatics
    The 82-84 500 motor required a new rod, crank, piston, cylinder and head. 500's use the same cases as the 430. The 390 can also use the 430 pistons. The 1980 390's and 420 auto can go all the way up to 87.00mm bore!

    Marty
    motomwo, Dec 15, 2021
    #13

  14. ruwfo Administrator

    Location:
    NJ
    Husqvarna Motorcycle:
    1980 390CR, 1982 430CR, 1984 400WR
    Other Motorcycles:
    1985 250XC, 2016 FJ-09
    Yes, i made my 80 390 into a 420
    ruwfo, Dec 21, 2021
    #14
    Brad-in-STL likes this.