Cylinder head for spigotted barrells

pierodn · Dec 19, 2016

Hi.
How do I recognize if an Atlas 750 cylinder head is the one that fits the spigotted cylinder?.
Can this cylinder head be mounted on a later not spigotted 750 cylinder?
Thank you.
Piero

robs ss · Dec 19, 2016

Piero
Attached is a photo of my 650SS spigotted head. You can see the stepped recess around the outside of the combustion chamber to accept the spigot protruding from the barrel.
The non-spigotted head does not have this recess.
Hope this helps
Cheers
Rob

texasSlick · Dec 19, 2016

Piero

If you mount a spigotted head on a non spigotted barrel, there will result a large drop in compression ratio.

Slick

Beach · Dec 19, 2016

pierodn said:
Hi.
How do I recognize if an Atlas 750 cylinder head is the one that fits the spigotted cylinder?.
Can this cylinder head be mounted on a later not spigotted 750 cylinder?
Thank you.
Piero

There are spacers made to mount in the recess of spiggoted heads...I bought some from Ebay...

pierodn · Dec 19, 2016

Hi,
thank you to all.
Piero

dynodave · Dec 19, 2016

IMO showing a 650 head will only confuse...

the following are atlas
spigot barrel head

spigot barrel head with steel conversion rings for flat barrels

flat barrel head

pierodn · Dec 19, 2016

Hi.
Thank you.
Work well the recess rings?
Piero

Beach · Dec 19, 2016

Just like it is made for it...I've been running for 3 years with the rings...No problem

dynodave · Dec 19, 2016

Hi Bill
Shrink fit steel/iron rings or aluminum?
Install and go or machining needed?
thanks

Beach · Dec 20, 2016

Hey Dave,

Install and go..Aluminum I believe...

pierodn · Jan 5, 2017

Hi.
Is better to join spigotted barrells with his spigotted head or join this head with rings with flat barrells?
If i skim the spigots the barrells are the same of the flat one?.
Thank you.
Piero

Bernhard · Jan 10, 2017

pierodn said:
Hi.
Is better to join spigotted barrells with his spigotted head or join this head with rings with flat barrells?
If i skim the spigots the barrells are the same of the flat one?.
Thank you. Piero

re;
If i skim the spigots the barrells are the same of the flat one?.

No.

pierodn · Jan 10, 2017

Bernhard said:
pierodn said:

Hi.
Is better to join spigotted barrells with his spigotted head or join this head with rings with flat barrells?
If i skim the spigots the barrells are the same of the flat one?.
Thank you. Piero

Click to expand...

re;
If i skim the spigots the barrells are the same of the flat one?.

No.

Hi.
Why not?.
Please, could you explain?
Thank you.
Piero

dynodave · Jan 10, 2017

I'm always willing to learn something... Whats differrent?
data points:
casting 24237 used from atlas beginning through the end in 73-750
early atlas/ spigot/ 5/16 bolts
late atlas /no spigot/ 5/16 bolts
early commando/ 3/8 bolts
72 combat/ shorter lifter bores to accommodate 2S cam
unable to confirm barrel height for the whole 750 run without disassembly of 6 engines
I believe only my dunstall modified barrels are shorter than production stock-verified -.030" from stock

texasSlick · Jan 10, 2017

pierodn said:
re;
If i skim the spigots the barrells are the same of the flat one?..

IIRC, the pistons at TDC are flush with the top of the spigots. Therefore if you skim the spigots, the pistons will then protrude about 1/8 inch out of the cylinder bore.

The non spigotted cylinder barrels must be about 1/8 inch taller than spigotted barrels.

Slick

dynodave · Jan 10, 2017

As far as I have seen all 750 commando pistons are above deck and partially fill the .120" squish band. Still no problem with the combat head...With .070 squish band because the head gasket adds .034" (to both kind of heads, std and combat)
How different for the atlas? I would have thought and expected the same from atlas and commando pistons both are 1.200" pin to piston top.
I also just measured 750 command barrels and atlas no spigot barrels and they are the same +/- .010

May be unrelated but I just measured my 650 spigoted barrels and it is 4.55x" therefore the same as unspigoted atlas and commando. Additional spigot is about .145"....subtract .030 for the headgasket and you have .090" into the squish band (.120" typical).

Was only able to rough it for my assembled 63 engine, but the calipers don't seem to be off, and I think I could see 1/8" if it was there

pierodn · Jan 11, 2017

hi.
i understand that you can skim the spigotted parts and use flat with non spigotted head.
thank you.
piero

texasSlick · Jan 11, 2017

I just measured my spigotted Atlas barrels. I have 4.590 inches between base gasket surface and head gasket surface. (a good measurement as the barrels are off the bike) @DynoDave: How does that compare to non-spigot barrels?

My spigots extend from 0.140 to 0.169 inches above head gasket surface ... not at all uniform.

So, if Spigot and non-spigot barrels are the same height (pending reply from Dave), then it must be that pistons at TDC extending above cylinder bore in non-spigot barrels is the normal configuration..... not what I would have expected, but on further consideration, it would have meant Norton would have had to make major changes to the head castings to keep the pistons in the bores and have the same relative combustion chamber configuration.

Slick

dynodave · Jan 11, 2017

I do wonder that the 650, atlas no spigot and commando are all the same 4.55" and only your spigot barrel is 4.90" plus .145/.165" for the spigot? It almost sounds like your top piston ring would come out of the bore in one of my no spigot barrels.
My 63 ran with rod knock so that engine was parked and that "should" be a spigot barrel/head and will be OK to come off for measurement. Last time I had it apart was a LONG time ago so I can't recall.

I'll take it off tonight.

texasSlick · Jan 11, 2017

Ooops! I made a typo. 4.90 should have been 4.590. I made an edit to my previous post.

I dont think 0.040 makes much difference, thus we can take spigotted and non-spigotted as the same height.. Then can we tell Piero to mill off his spigots with no fear?

Slick

Cylinder head for spigotted barrells

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