Crankshaft / Flywheel ID

[RichardS]

I have some flywheels in a case marked '51/G3LC, can anyone tell me any definitive feature (like weight, balance, dimension) that will confirm they are 350 wheels.

I ask, as the engine currently has a 500 top end, but I intend to make it a 350.

There are 4 different flywheels listed 350/350C/500/500CS - I assume it's 'just' a matter of balance and probably total mass, but have no idea of anything specific.

[dave16mct]

350 flywheels are stamped G3, 500 are stamped G9, which is a bit strange!
Dave

[RichardS]

Champion, thanks!

And odd, as you say.

[dave16mct]

If you look at this set on ebay you can clearly see the G9 on the one on the left.
115857089233
Dave.

[SPRIDDLER]

I have some flywheels in a case marked '51/G3LC, can anyone tell me any definitive feature (like weight, balance, dimension) that will confirm they are 350 wheels.

According to the the Archives the 350 and 500 engines from '48 onward used the same c/case and flywheels although the article doesn't differentiate between road and comp models so presumably comp engines used the same as the road models.

Changes. Singles b.jpg

Full details of all changes here:

https://www.jampot.com/article_read.asp?id=28

Balance factor (apparently for both 350 and 500 engines) was 62%. See interesting article re. balance and flywheel design in an interview with the AMC engine designer here:

http://archives.jampot.dk/editorial/Roa ... _Baker.pdf

Edit:
Looking at the 1951 factory Spares List ALL 350's (i.e. road and comp models) use the same flywheels. HOWEVER, contrary to the 'Changes' info in the Archives the 500 's have different part numbers for the flywheels, probably because the 500 has a heavier piston than the 350 and need to be machined differently from the 350 to obtain the same 62% balance factor. (The 500 has G9 included in the old part number so maybe that's why they are stamped with G9).

This is the AJS Spares List but the Matchless is exactly the same:

Spares List front cover 1951.JPG

Flywheels. Singles 1951 b.jpg

[RichardS]

Thanks for all the info.
So it's pretty probable that the flywheels in the cases are for a 350 and, even if they're not, it's not likely to be big issue. I had not intended to split the cases, just change the top end, but it's over 40 years since I rebuilt it (Jeez, I must be gettin' old) so I guess a little look-see wouldn't hurt.

[mdt-son]

Some of the differences between 350/500 and STD/C/CS are rather superficial. The proximity in spare part numbers tells me the only difference between 350/500 flywheels is the balance factor drillings.

- Knut

[mdt-son]

350 flywheels are stamped G3, 500 are stamped G9, which is a bit strange!
Dave

Generally speaking, stamping was performed late in the manufacturing process to either differentiate parts (example: pistons classified in tolerance groups), or to sign off approved parts by the quality inspection department (example: crankcases). G3/G9 stamping appears to belong to the former group, and as bare flywheels are identical from 1948 onwards, stamping can only serve one purpose - the balancing. Apparently a "G9C" stamping is found as well, and I can only surmise it designates a crankshaft for a heavier piston, maybe for an early G80C/CS engine, which required a different balancing counterweight.
Remember that for a large operation such as the Plumstead factory, parts were manufactured in batches in advance. A pallet of crankshafts for the G3 would be delivered to the engine assembly line, succeeded by another pallet for the G80, and so on. There was one engine assembly line only. During times of switch-over assembly, e.g., from G3 to G80, picking the correct part was paramount, hence the need for stamping.

- Knut