Small bolt pattern head/ID?

I though 1-1/2" manifold bolt spacing was early and 1-5/8" was later heads?

I'd be shocked if they don't both have 1.4" intakes. I only have 1 alloy head with 1.3" intake but it is a small fin head...not medium fin like the one I am asking about...?

I can't actually measure the valves yet. every bolt and stud/nut is off, but they are glued/corroded together and will require violence to get the head/barrel lump apart.

Previously Phil Hannam wrote:

Previously david_comeau wrote:

This is the first head like this I have seen. Of course here in the US we have very few pre commando bikes except atlas.

looks like this head , which is a 1-1/2" bolt spacing:

BUT This new head is definitely 1-5/8" What is the time frame for this head? 1960 and after???

thanks Dave

From March 1958 on the Nomad 500cc Twin Scrambler was produced, mainly for the export market. The engines on these machine were seriously uprated in a number of ways, including high comp pistons, polished internals and twin Amal 276 carbs of 1&1/16" bore. The cylinder heads, on many of these engines, had 1&5/8" manifold bolt spacings which then became the norm for road bikes, the following year. However, the 1958 heads kept the T2225 casting finning whereas the 1959 heads had the 22707 type.

Robert I finally got the head off of the barrels. Wood and a BIG hamer.

Phil - Re joined NOC after a few years of very busy non motorcycle activity.

Did some tests to compare to my first medium fin head, which I acquired since we last emailed. I'm convinced these are both the same casting and final machining except for the manifold bolt spacing. Same squish band/spigot groove, depth within a few thousandths(,140" v.s. ,142"), and 51.3cc volume V.S. 51.8cc for this new one. The new one has slightly sunk exhaust valves, so it shows the bigger volumne. It's pretty ugly otherwise.

I have never seen a 500 nomad so your explaination sound good to me. I have seen pix of the slab of metal manifold with machined ports that splay...99SS manifold? So these head run in the same time frame but just different application.

The good part of all this... is I get some pretty nice standard bore 88 barrels because I'm converting my 63 atlas into a 88SS.

Thanks guys

Previously robert_tuck wrote:

Seems like an odd choice of direction, what with the shortage of reliable 88/99 rods. I would have swopped the barrels/crank and bult a 650 with new rods. But I do like the 88 motor too.About time the poor old dommies got a supply of new rods, I thought that was what the club spares was set up to do. Considering the dommies form such a large part of the Norton scene after the Commando (,which is well provided for).

On this side of the pond any slimline drivetrain, except atlas, is incredibly rare. A complete 650 of any type regular or SS, which is what I originally was tradeing for, ended being empty cases no crank, rods, pistons, barrels. head, timing chest components. I do have a regular 88 engine which I can use with atlas cam and downdraft SS head and now have std bore barrels. The 1-5/8" head I am asking about is pretty much junk. My 1-1/2" head is almost perfect as is.

I've got 3 MKIII and at least half a dozen commandos and am mosty bored with them. The commando scene not the bikes.

Got a 51 and a 52 model 7

3 slimline featherbed plus a 68 Dunstall atlas

Dave