Technical info on Norton 850 Head

Hello to All,
I'm new to this site and am hopeful someone can help me out. I own a 1973 MK1 Interstate 850 (beautiful bike to ride). I am reconditioning the head (got smoky) and need to replace the valves and guides, I have the parts and the head man is ready to go but I need technical info.
My Haynes manual is limited use and does not have the information required, I need a measurement from the base - surface of the head (where the guide is fitted) to the top of the valve (when the valve is inserted home).

The valves were seated low in the seats suggesting they have been cut a few times thus the need for the requested technical information.

Regards

Vic

Hi Vic, welcome. You've come to the right place. I don't have the information you need, but there are those here who do, sit tight, they'll be along shortly. Perhaps fill out your profile (location, etc) so you can be directed in the proper direction.

If your cylinder head guy is not familiar with this you need to find a new cylinder head guy. A Norton head is not an automobile head. Jim

Appreciate the couple of responses I've had,

I was surprised by the No of hits to my question (I guess that highlights how little I sit in front of a screen). The head machinist bloke is well regarded but its been awhile since he's done a Norton head, my old Harley manual gives the measurement for doing shovel heads so I am hopeful someone out there can give me this tech info on Commando heads.

Vic

Well I would not be concerned about the valve stem height. Good valves will have a stellite tip and should not be cut to length anyway.

If he is cutting the seat with the correct 37 degree top cutter your valve stem length will be ok as long as the top cutter is not cutting into the aluminum. If the seat is worn or cut to the point that a 37 degree cutter cuts into the aluminum then the seat should be replaced. Jim

Vic H said:

My Haynes manual is limited use and does not have the information required,

Click to expand...

The factory manual is generally considered to be more useful than the Haynes.
If you don't have a factory manual, you can download a pdf copy from here: http://www.classicbike.biz/Norton/Repai ... mmando.pdf

I am reconditioning the head (got smoky) and need to replace the valves and guides,

Click to expand...

Be careful when replacing valve guides in '73 850 (RH4) heads. Many top Norton cylinder head machinists prefer to cut the old guide out rather than drive or press them out due to the thin wall around the guide and its tendency to crack. This results in oil being sucked into the cylinder. You should examine the port around the guide carefully.

Ron L writes:
"Be careful when replacing valve guides in '73 850 (RH4) heads. Many top Norton cylinder head machinists prefer to cut the old guide out rather than drive or press them out due to the thin wall around the guide and its tendency to crack. This results in oil being sucked into the cylinder."

I thought the more common problem was scoring the aluminum bore around the guide, not cracking it. Resulting in oil leaking between the new guide and the scored guide bore.

Stephen

valve-included-axis-angles-t18174.html?hilit=tuning

theres a pretty picture there ( cant get this machine to popy & caste ) .
Not entirely accurate etc , but gives the general picture .
Dont let any babbons with 12 Lb hammers at the head , only brain surgeons with 12 Lb hammers .

SOMEONE here NOTES Drilling out the CENTER of the GUIDE , 1mm under O.D. , concentric - then collapseing remains , so as NOT to gall / bludgeon the housing . Smart Move .

In General , New SEATS would be flush with chambers , not rebated - so valves not masked . A trifle oversize valves may seat further out on seats , if theres enough meat -
leaving nice concentric rebates from previous recession for edge of ' flare ' initiated on port with grinder - to improve flow .
Valve Edges ( I. & E. ) too close makes tangling a consideration - to avoid .

Toss the antique springs , or at least spec. them , while your at it .



The Dunstall & Norvil ( Thruxton Race Shop ) P. R. heads had reangled inlet valves , with the full Hemi Chambers ( as per picture ) if your feeling wealthy .

Hey Thanks Matt,

Appreciate the diagram and tech tips, will have a chat with my head machinist and see where to from here.

Cheers,

Vic