Commando Valves and Pushrods

TBolt

Joined
Jul 19, 2013
Messages
71
Does anyone know how long standard Commando valves and pushrods are, and how long standard Atlas and 650 ones are?
Thanks
 
Can we ask where this is going.
Or coming from ?

Some Atlas pushrods here are 8 & 1/4" and 7 & 3/8".
Top-to-tip.
I think these are the later ones.

Be warned that Norton pushrods are all over the place - there must be at least a dozen sizes. ?
Every bloomin model must have 2 different lengths of valves, and pushrods to suit...
 
Factory spec for Commando pushrods is 8.166/8.130” inlet and 7.321/7.285” exhaust.

For Atlas and P11 intake is 8.194" and exhaust is 7.351".

Ken
 
Ok so all Norton valves are the same length? I've got a spare 650 motor with no valves or pushrods in it.
So looks like I need Atlas pushrods?
 
lcrken said:
Factory spec for Commando pushrods is 8.166/8.130” inlet and 7.321/7.285” exhaust.
For Atlas and P11 intake is 8.194" and exhaust is 7.351".Ken
Click to expand...

I thought that all 600-850 Norton pushrods were the same length as long as they were from the same year. I don't have the information at arm's length, maybe it was in my Haynes manual, but wasn't the pushrod length changed across the board around 1965 or 1966 along with a corresponding adjustment to the length of the valve stems? Not counting even smaller Nortons that had shorter engines and pushrods.


Maybe if Tbolts spare 650 engine is from the later 60s then it's valves and pushrods would be the same as a 750 or 850, it is worth taking them out and checking them against the specs that lcrken has given to us. Someone may have replaced the pushrods in teh 650 engine in the past anyway.

In the end no matter what you throw in the engine you will have to turn it over and see if the rocker arms are staying in the right place on the valve tips, so the 650 pushrods might be good enough to throw in if to do nothing else but let you know if you need ones that are shorter or longer than they actually are.
 
Ok so Ken says that the Atlas pushrods are about 30 thou + longer than Commando.
Could this be to compensate for a higher lift cam in the Commando?
I don't have any spare pushrods or valves to measure off, and none in the spare engine.
 
TBolt said:
Could this be to compensate for a higher lift cam in the Commando?
Click to expand...

No.
The cam in the Commando has been quoted as being the same spec as the SS cam in the dommies.

A number of folks have commented here that valve and pushrod lengths in Nortons are a real can'o'worms.
There are at least 2 different versions/lengths of everything ... !!

Pushrods for Combats are, in theory, supposed to be 40 thou shorter than other Commandos too. ?
Headgasket thickness, rocker ratios and cylinder and cylinder head heights all come into it too.
 
Ok, looks like I'm up s&@t creek. I'll have to just put the head together and then go trial and error till I find the right set of pushrods, or make a temporary pushrod and shorten it until it's the right length, and use that as the measurement.
 
It is quite possible to shorten pushrods.
The steel ends can come off, the rod filed down to suit and the caps refitted.
Or so it is said, as I've not tried it.
 
Ok that's very good to know, because a person could mess around with head height, comp ratio and gasket thickness and still be able to maintain perfect rocker geometry by that method?
 
Rohan is quite right about shortening stock push rods. It's pretty easy. I've done it many times. The trick is getting the end off in the first place. I made a simple tool to do it, and I've seen some references here on the list to other folks methods. Try some searches here for pushrod length, etc.

About valve lengths, I don't have any factory specs, but I do know that Atlas valves are shorter than Commando. That's one of the reasons for the different pushrod lengths between Atlas and Commando.

Ken
 
Just went out to the shop and measured some stock Commando valves.

Exhausts were 4.023" and 4.024" OAL.

Intakes were 4.051", 4.061", 4.069", and 4.075" OAL.

Kibblewhite specs for stock size Commando valves are 4.015" exhaust and 4.065" intakes.

FWIW, the lengths on some drawings I have from a company that made oversize valves for Commandos with re-angled guides are 4.020" for exhausts and 4.069" for intakes.


Ken
 
Just a bit of update from a related post, which has a link to the Andover Norton valve specs, which include the length specifications. The current Andover specs are as follows:

Commando inlet - 102.3 mm (4.028")
Commando exhaust - 101.9 mm (4.012")
Atlas inlet - 100.2 mm (3.945")
Atlas exhaust - 99.5 mm (3.917")

The Andover table also lists overall lengths for earlier twins, as well as specifying the various valve diameters.

Note that these measurements are not the same as the ones I measured on old stock Commando valves. Andover lists their lengths as from the tip of the stem to the "bottom of the tulip", and I measured the lengths from the tip of the stem to the highest point on the bottom of the valve. Might be that Andover means something different by "bottom of the tulip". If you look at the valves, you will notice that the bottom of the valve has a rounded contour, and extends below the edge of the seating surface on the intake, and below the valve margin on the exhaust. I suspect that would account for the differences. Specifying the length as Andover does is more accurate in terms of the functional length of the valve, but it is more difficult to measure than the overall length.
 
For those who haven't already lost interest in the topic, there are some interesting comments in the following thread about pushrod and valve lengths based on serial number instead of model and year, in particular taking issue with the Atlas pushrod lengths I posted above:

norton-valve-and-pushrod-lengths-t18849.html

Ken
 
lcrken said:
For those who haven't already lost interest in the topic, there are some interesting comments in the following thread about pushrod and valve lenHi Ken,
gths based on serial number instead of model and year, in particular taking issue with the Atlas pushrod lengths I posted above:

norton-valve-and-pushrod-lengths-t18849.html

Ken
Click to expand...
lcrken said:
For those who haven't already lost interest in the topic, there are some interesting comments in the following thread about pushrod and valve lengths based on serial number instead of model and year, in particular taking issue with the Atlas pushrod lengths I posted above:

norton-valve-and-pushrod-lengths-t18849.html

Ken
Click to expand...
Hi Ken,
the page doesnt open.
Thanks.
Piero
 
Sorry, Piero. When I posted it back in 2014 that was a valid link, but it doesn't seem to work now. I have no idea where I got the link back then, so I don't know any way to see if it is still available.

Ken
 
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