Help with Identifying twin cylinder heads.....

Yorkie · Post by **Yorkie** » Tue Jun 23, 2009 1:00 am

Hi All, i've got two pairs of cylinder heads for heavyweight twins but i only have parts lists for singles.... can anyone tell me which models they fit? The cast in part numbers are 026056 for one pair (maybe g12?) & 016433 for the other pair (G9 or G11?).
Also have two pairs of barrels, one pair with 8 fins & a bore of approx 73mm, the other with 7 fins & 73mm bore.....

ps. recently bought a '56 18S and my poor Bonnie hasn't been out of the shed since, what is it about old singles that makes you grin so much when you ride them......

wilko · Post by **wilko** » Tue Jun 23, 2009 1:00 am

This is Don's domain.

Don Madden · Post by **Don Madden** » Tue Jun 23, 2009 4:00 am

Ask quick, I'm outta here tomorrow for a few days in the desert.

Number cast in are always for the raw casting, which sometimes is machined into different parts. The casting number & the finished part are usually close & when the number first appears in the spares list is a clue.

1956 G9 & G11 heads are listed as the same part: 022234/5, so the 016433 is for the G9.

The 1960 G9 heads were 026695/6 & the G12 were 026697/8, but both sizes may have been machined from the same casting. What is the ID of the recess for the cylinder spigot? The 1959 G12 was 3in & the 1960 G12 was 3-1/16in.

Cheers, Don, signing off.

Yorkie · Post by **Yorkie** » Tue Jun 23, 2009 11:53 am

Thanks Don

The 026056 measures 3-1/16inch (78mm) across the recess so I'll assume are for 1960 on G12?

The 016344 measures 2-15/16 across the recess so does this confirm as 1956 G9

cheers, Steve

Don Madden · Post by **Don Madden** » Fri Jun 26, 2009 2:13 am

016344 would be for pre-1956 but I don't know which year. I don't have data for the head recess diameter of the G9 engines.
Cheers, Don.

SPRIDDLER · Post by **SPRIDDLER** » Fri Jun 26, 2009 11:22 am

quote:
ps. recently bought a '56 18S and my poor Bonnie hasn't been out of the shed since, what is it about old singles that makes you grin so much when you ride them......

I took my '54 350 single for its MOT last Wednesday. Grand sunny day. The tester (a modern motorcyclist) said "I'll just run it round the block (private Ind. Estate road). "You won't want come back" says I.
30 seconds later he reappeared, picked up his helmet grinning "Just need to give it a bit of a longer run to make sure".
It passed, of course.