I recently picked up a custom chopper and was told the engine is from a 1971 Sportster XLCH. It's definitely an Iron Head with right side drive and shift, but the serial number on the block doesn't make sense. It is 6A10419H1. Everything I read online says the format shown on my engine started in 1970 and that the "6A" is a SS-350 Sprint, although the H1 seems to match the 1971 year I was told the engine was. I just don't see how the "6" could be anything but a "6" (see picture). Any ideas?

 

Interesting. If an XLCH it should have a number starting in 4A. The last 2 characters H1 do indicate a 1971 year.

XX 12345 XX
Model - production number - year

Post a picture of the full engine. The pic provided looks like a regular nose cone vs a sportster cover.

 

Here's a full view of the engine and bike...

 

See attached

...

 

You're correct, the prefix "6A" doesn't makes sense on a 1971 motor.

• "H1" suggests 1971 for sure
• Combined with the sequence number "10419" suggests an early 1971 motor.
• "6A" suggests it has been altered from original.

In 1971, it would be either "3A" (xlh) or "4A" (xlch). I won't speculate on how the "6" got there..... but leave that for your imagination.

There are some other minor tells on a unaltered OEM 1971 motor..... a few more pics:

• left side case
• mounting bolts for the oil pump
• cyl head bolts

might reveal more. Or not. But does it matter ? Up to you.

 

 

Man, that's a head scratcher. Nice looking bike though.

 

The pics reveal:

• left side case is from a 1000cc motor. That rules out a '71 900cc (actually 883cc) motor.
• cyl head bolts suggest the cyl heads are from a 1000cc motor. Further confirmation we're not looking at a '71 900 cc motor.
• right side case is of unknown origin at this time.

A clear pic of the "Belly Numbers" (both left & right sides) will provide an additional tell (aka the year of the left & right side cases & maybe the production date of the cases), if you choose to go down that path.

To find & interpret the numbers, this reference should help (scroll down to belly numbers):

https://sportsterpedia.com/doku.php/...:ih:engmech01b

Fingers crossed the belly numbers haven't been ground off or altered.

 

Not so. '71 was the first year for "nose cone" and a wet clutch and was still a 900cc bike.

1971 Harley-Davidson XLH Sportster | HowStuffWorks

 

ahhhh...... I guess you're thinking "primary chain case cover" and "cam cover" ? I am NOT. I'm focused on the the engine castings..... left & right side

So I guess I should have been much more explicit and said:

• left side ENGINE casting is from a 1000cc motor. That PRETTY MUCH rules out a '71 900cc (actually 883cc) motor.
• cyl head bolts suggest the cyl heads are from a 1000cc motor. Further confirmation we're not looking at a '71 900 cc motor.
• right side ENGINE casting is of unknown origin at this time

I'd edit my original post and make the changes, but not possible on this site. (I think that has to be done within an hour of posting)