5/8" inlet guide

having just bought an 850 head with one valve guide missing i have just noticed the valve guide hole is 5/8" diameter ,is this a common mod? are the valve guide availiable or are they specialy made? ............baz

Sounds like specialist machine-shop time. How are the exhaust port threads as it might be a good time to check them too ?

baz said:

having just bought an 850 head with one valve guide missing i have just noticed the valve guide hole is 5/8" diameter ,is this a common mod? are the valve guide availiable or are they specialy made? ............baz

Click to expand...

Baz
That’s not a mod. Kibblewhites measure in at .6255" to .6250" for 850 heads std. You can get oversized guides if need be.
Check for cracks around that valve guide holes and area. What is your intake port size in millimeters?
Check for an RH number stamped on the head. RH4=73 850, RH9, RH10 =74 850 and report back. edit.
here is some good info http://atlanticgreen.com/nhth.htm
Cheers,
Thomas
CNN

CanukNortonNut said:

baz said:

having just bought an 850 head with one valve guide missing i have just noticed the valve guide hole is 5/8" diameter ,is this a common mod? are the valve guide availiable or are they specialy made? ............baz

Click to expand...

Baz
That’s not a mod. Kibblewhites measure in at .6255" to .6250" for 850 heads std. You can get oversized guides if need be.
Check for cracks around that valve guide holes and area. What is your intake port size in millimeters?
Check for an RH number stamped on the head. RH4=73 850, RH9, RH10 =74 850 and report back. edit.
here is some good info http://atlanticgreen.com/nhth.htm
Cheers,
Thomas
CNN

Click to expand...

ok thanks for that info i had thought the valve guides were the same size as the 750 head, the 850 head i have just bought is an rh4 32mm inlets it is from a norton wasp standard valve size it has a stud conversion on the exhaust ports the 3 existing valve guides are all loose there are no cracks that i can see (i do have another 850 head up the back of my shed somewhere that was cracked around the valve guide boss i attempted to weld it but i found another one that was better ,i was told at that time it was impossible to repair this was 25 years ago) cheers baz

Hi Baz
Is the head for use on an 850 or 750 as they have different bolt spacing!
Not sure where you are located, Andover Norton do the guides upto +6thou if you need oversize ones, and SRM do them even more oversize.
Cheers
JohnT

its an 850 head for a 920 barrel cheers baz