What year engine?

[big danno 1970]

Just wondering if there is a way to find out the year an engine is by the serial number or something.Engine is a 340 liquifire.
Thanks

[harleysportster]

Possibly narrow it down by the ignition type. The 76 had retangle plugs, the mid 77 thru 78 had round plugs.
If you still have the carbs:
76 340=VM34-79
77/78 340=VM34-122

[big danno 1970]

76 it is then,rectangle plug
Thanks harleysportster

[big danno 1970]

Next question then,did they use the same bottom end as the 340/440cyclone?
Thanks

[harleysportster]

There were changes thru the years. Here is a break down in part numbers.
AM53984 CRANKCASE 1 (BEGINNING ENGINE SN 741,200,000) (340)
AM53984 CRANKCASE 1 (BEGINNING ENGINE SN 740,200,000) (440)
AM53522 CRANKCASE 1 (BEGINNING ENGINE SN 5,600,000) (340)
AM53522 CRANKCASE 1 (BEGINNING ENGINE SN 4,400,000) (440)
I believe the change was in 77 when the compression ratio was lowered.