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casting marks

Submitted by steve_adkins on Sun, 09/04/2017
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Heavy Twins

Greetings,

I have two SS heads; one I believe is for an 88 SS and the other for a 650 SS, which is currently nearing completion of a ground up restoration. The casting number is clear on both heads, on-top by the inlet rocker box. Both heads have the number cast in '22707' but the 1 1/8" inlet (650) has the suffix "R" and the 1" inlet bore, (I believe is for an 88 SS) has a "W" (or maybe âM?â) suffix.

This one the âWâ (or maybe âM?â) also has a machining mark about 3/4' into the inlet tract? The "R" suffix inlets are conformal, with a very clean and smooth-bore, no evidence of this 'step down feature.' Itâs not much of a reduction, maybe 1/16â?

Anyone out there provide me with other guidance on this. There are no casting marks elsewhere on the 1â inlet head but not sure about the 650; as itâs fitted now, bit difficult to interrogate! I have looked at the 'Atlantic-Green' web site too, but there is no discussion regarding this feature.

Thanks Steve

Submitted by david_comeau on Sun, 09/04/2017

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It appears you have two NORTON heads.

On the surface, it sounds like you have an early head used on 61 88SS(and others).

Then you have a later downdraft head introduced on the manxman/650SS/Mercury and also used on the second generation 88SS (62).

All the marking you quote are casting molds of portions of the heads and with minor revision letters. These alone... do not identify the heads.

If you care to look at my web page for norton heads you may improve your insight into the specifics.

I have been researching in the USA for the last 15 years and with help from others have improved my coverage. However it is not 100% complete or totally accurate. Improvements will likely follow.

However, I have not seen anything better yet.

http://atlanticgreen.com/nhth.htm

1. On your early head, does it have small, medium or large fins?

2. What is the vertical spacing of the manifold mounting studs..1-1/2" or 1-5/8"

Submitted by anthony_curzon on Sun, 09/04/2017

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The letter stamped on the under side of the cylinder head is the letter M. This was done on the hybrid 750 cylinder heads for the G15, N15, and the P11 series of engines. The letter M standing for Matchless.The later cylinder heads hadan O6 part number cast into the under side of the cylinder head,as the cylinder head casting could be used for either the 650 or 750 engines as the castings were the same but machined differently.

Submitted by david_comeau on Sun, 09/04/2017

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PER Steve:

"Both heads have the number cast in '22707'"

These 22707 are not late heads wouldn't you agree?

The only downdraft heads that I have seen with 22707on top are small bolt pattern, with 23166 on the bottom...88ss or 650SS

This is of course not conclusive since my research pool is small here in the USA. Very few featherbeds are here in east coast north america except Atlas, surviving hybrids are rare too.

1. I have a variety of different vintage spigot and nonspigot atlas heads and none have 22707 on top but do have 23166 or 25319 on the bottom.

3. Wouldn't any head with top oil feed, small bolt pattern 06-0380 be a very much later like 67-68 mercury? (shown on my web page)....

of course neither of these 2 helps with Steve's question.

What feature? minor step down in the intake bore of a 25mm port?

Submitted by david_comeau on Mon, 10/04/2017

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The numbers don't say all that much beyond a small group of heads, the cast letter probably does not say much either.

Full front/side and full rear/side pix. helps the most

measured vertical stud spacing? 1-1/2 or 1-5/8"

Submitted by steve_adkins on Mon, 10/04/2017

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Hi David,

The 22707 âWâ cylinder head appears to be a non-downdraft head, with vertical manifold threads 1 5/8â apart and the strange counter bores in both inlet ports. The 22707 âRâ head has horizontal manifold threads 2â apart and is down-draft. So it would appears the âRâ one is a 650 SS head and the other? Both are configured for spigot barrels.

I will post additional pics later as not sure regarding fin sizes etc.

Rgds Steve

Submitted by gordon_johnston on Mon, 10/04/2017

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The head in your pictures is a pre-downdraught head, probably 1960 or later as fitted to 88 and 99 models. This would normally have a manifold and single carb fitted. Not what I would associate with an SS which I would expect to have a downdraught head and twin carbs. The Mercury models of course had downdraught heads and a single carb just to add a spot of confusion.

Submitted by anthony_curzon on Mon, 10/04/2017

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This is as per Phil Hannam who has written at length on this subject in the past.Fact.......the 22707 casting number was used cylinder heads for two completely different models of bike.The pre-1960 head had forward facing 40* splayed exhaust ports. For road bikes such as the 88 and 99 it was fitted with a single carb on a2 into 1 manifold.The Nomad, 99SS and early 88SS engines had a special twin carb manifold fitted.Fact.......From 1960 onwards a second version of the 22707 headbecame available. This was known as the SS head and was specifically designed for the 650 engine.In the 650SS version of the bike it was generally fitted with twin 376 carbs. The Standard, De-luxe and some Manxman versions of the 650 bikes had a 2 into 1 manifold and bigger single 389 carb.Fact........The second generation of the 22707 cylinder head also had 23166 stamped on its underside. This casting was usedfor both the 650 and 750 engines but is not interchangeable between them due to the head bolt hole spacings being different.This head was first used on about 100 Bracebridge built Atlas 750 engines and a version of it later manufactured at Plumstead, London when production was moved.The early Plumstead heads were a disaster withhundreds having to be scrapped due to porosity and bad machining.Later Plumstead castings just had 23166 stamped on each underside.Those used for the Hybrid machines generally also being stamped with the letter M.The casting letters found above the inlet cover (Eg J, M, W, Setc) refer to specific batch production. They are similar to shop numbers andrefer toa particular mould used in the casting and later machining process. This was to help the factory quickly find out the source of faulty castings.At one point the casting foundry had 6sets of moulds blanks all in use at the same time.One of themost commonproblems being a failure to properly clean the mould sections in between each casting. This then led to overspills of metal which then needed extra machining to clean it off the heads.

Submitted by gordon_johnston on Mon, 10/04/2017

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One small observation Anthony. In 1960, the non-downdraught head was changed to larger inlet valves (prior that inlet and exhaust were the same) and a higher compression ratio. They also had the ribbing on the casting between the rocker spindle holes. Prior to that there was no ribbing. The inlet manifold mounting remained the same, i.e. studs in a vertical plane. I don't think the downdraught head with horizontally placed inlet studs appeared before 1962, or even later.

Submitted by david_comeau on Mon, 10/04/2017

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Previously steve_adkins wrote:

OK here is some further info on what appears to be an early head.

Your head pix is a D12-2/136... just as shown on my site, except my head does not have the minor intake port mod. 1.625" stud spacing makes it ideal for 61 88SS and all 99SS with the splayed slab dual carb setup. There is likely other uses and times used.

Submitted by david_comeau on Mon, 10/04/2017

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Previously steve_adkins wrote:

And the down-draft head; any comments on the fin sizes as per previous posts:

This head is a S650/136 just as shown on my site. I was used on manxman and 650SS and the (62) 88SS, the use continued here in the USA but seem to be much more rare here. The casting may be the same for later atlas, however the atlas got 1.5" intake and the 500/650 retained the 1.4" intake valve. All my research is based upon north america nortons which is obviously much smaller fleet until the commando era where we got over 50%. Your machinery could well be more varied then what we got.

Submitted by david_comeau on Mon, 10/04/2017

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Previously anthony_curzon wrote:
This is as per Phil Hannam who has written at length on this subject in the past.snip
Yes Phil has been very helpful in improving my cylinder head web page which has been online since 2000. In October 2012 we colaborated on his article which later came out in Roadholder 302 Jan 2013.You might have seen this at the end of the articleContributions for this article have come with permission from Dave Comeauâs website http://www.Atlanticgreen.com , Dale Middlehurst, John Dunn, Ken White and Anna Dixon.Despite lapses I've been a member of NOC since 2000 and INOA since 1988cheersDave Comeau2 gardengate4 featherbed10 commando4 MKIII Commandoinclusive of basket cases

Submitted by Xanna_jeannett… on Mon, 10/04/2017

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Previously steve_adkins wrote:

OK here is some further info on what appears to be an early head.

Hello this head is NOT a Downdraft head and its a M not a W yours Anna J

Submitted by steve_adkins on Wed, 12/04/2017

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Greetings,

Just confirming that the valve sizes are inlet = 1 3/8" exhaust 1/1/4".

Not much room for anything bigger either, is this normal?

Thanks Steve

 


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