Engine number help please

[Slakewell]

What year is  #2077

[Mike52]

Should be a 1980 390ACC whatever that is.
Frame MN-1001

[Slakewell]

Bugger was hoping it was 1977 390 auto cases

[bigk]

I know some people say that the 390AMX was available in 1977, but there are no identification numbers listed in ANY published or otherwise literature to support this. Maybe you can find a magazine test in late '77 but I believe it will be a test of the '78 model. The earliest listed is 1978 390AMX with an engine prefix of 2070. 1978 model Husky's are generally not accepted as pre '78 legal bikes although the 3 major differences, 1: tapered steering head bearings,2: slightly different swing arm (no reinforcement plates on front cross section), & 3: slightly different rear hub, in my opinion hardly make them vastly improved over the '77 model. The '77 390 manual engine (2061) ran till 1979 unchanged & the 1978 CR125 uses the '77 chassis (all capacities), same part number, but will have a 1978 series frame number. The 125 engine ran from 1976 t0 1981.
Another can of worms if you want to run a 390AMX in pre '78 where it belongs.
Oh, by the way you'll still have to restrict the standard 1977/78 suspension travel to comply with the pre '78 rules as well. Don't understand that one myself but them's the rules.
K

[PEZBerq]

78 AMX is different to 78 CR Huskys. My AMX does not use tapered steering head bearing, it also use the 76 CR swing arm.  I believe they would be pre 78 legal with the suspension travel limited. Unlike a 78 CR.

[Slakewell]

This is what the seller sent me.
The number plate was on the countershaft support case, that's gone. No stamped numbers on the main cases like a normal Husky motor. Might have a casting number inside, but I think its going to be common to all the auto cases.

We know that the cases are the same from one year to the next. If the cases have no numbers on them then they should be able to be used in Pre 78?

[bigk]

I have all the parts books Mick, can check part numbers if you like? I'd use them, it's not the cases that will cause an issue with eligibility.
I haven't checked but perhaps like the 125, the '78 390 AMX uses the '77 chassis? '77 swing arm is different to '76 though.
I'll check the photo's of my 390AMX, a '77 swing arm is easy to spot.
Cheers,
K

[PEZBerq]

This is the 78 AMX swing arm. Quite different to the 77 CR. Seems to be very much like the 76 CR arm to me. Poor old autos always got the leftovers from earlier years bikes 

[bigk]

Umm, sorry to disagree Pezberg but that's a '77 swing arm. Both '77 & '78 swing arms are listed as new parts for the model year. '76 is smaller diameter tubing & doesn't have the side stand bracket. '78 swing arm is pretty much the same without the triangular shaped gussets. Looks like a no brainer that a '78 390AMX should be legal for pre'78.
K

[grouty]

This is what the seller sent me.
The number plate was on the countershaft support case, that's gone. No stamped numbers on the main cases like a normal Husky motor. Might have a casting number inside, but I think its going to be common to all the auto cases.

We know that the cases are the same from one year to the next. If the cases have no numbers on them then they should be able to be used in Pre 78?

There were two different 390 engine cases to fit two different types of frame. The 2070 was a short motor to fit the standard frame. The 2077 was a long motor to fit the "short tab" frames. I think the only other short tab frames housed the 125 motor from 77/78. As Big K said, the early ones (77) had the non taper roller headstock. The later 78 ones did. Both my 78's have the shorter earlier swing arm (I think 77 type). The housing that has the engine number can be swapped from engine to engine ! (seems a daft idea).

[grouty]

Picture shows a "short tab" frame with the long 2070 engine.




This shows the standard frame with a short motor 2077