Inlet Valve Guide Angle ?

Not open for further replies.
Dec 24, 2003
Can anyone on the forum tell me the inlet valve guide angle off the machined head surface please ?

An inner valve spring broke on my 850 & it appears to have "hammered" the guide opening to a different angle.

What we thought would be a simple remove & refit, isn't.

The plan is to make a new blank guide & drill it out for the valve at the correct angle.

So, I am guessing someone knows the angle it should be.

Thanks in anticipation.
Hi Norton fan ,

8) The job should be easy to repair, but it dose depend on the amount of damage , worst case one should heat up the head to about 200degrees F to give the aluminum some expantion to loosen it's grip around the valve guide and drive the valve guide from the chamber side to the rocker cover side. There will be some resistance on the giude to come free but once it's brock loose it'll drive out. Any compatent engine machine shop will have the tools to do the job right , if you won't to do as much as you can yourself I can guide you throught the process. As far as angle this isn't something you should be worried about , there are self guideing reamers or just R&R the guide with a new one, hone in the clearance and do a valve job.

Johnny Rocket
Thanks for your reply Ronny Jocket.

It SHOULD BE an easy repair ... but this one isn't.

I have removed the guide & the head IS at the machine shop.

We have a problem........................

What the machinist should have done...he didn't do.......
That is to machine the oversize guide I gave him to fit the hole in the head. He tried to machine the head & %^&*() it up.
Just another "expert" costing me money !!

So, the question is,
"Can anyone on the forum tell me the inlet valve guide angle off the machined head surface please ?"

Then he can "fix" it..............

Sorry to hear about your troubles.

Looks like the valve guides are 30 deg from vertical or 60 deg from the plane of the head.
Inlet Valve Guide Angle ?

Hope it works out OK.
Dr Hiller,

You are terrific, :D as soon as I saw the diagram, I knew I had it in one of my books also.

Alas, I had only looked through the "technical specs". It is in the "performance section" at the back of the clymer publication isn't it ?

Thanks for taking the time to insert the photo also :D
Norton Fan ,

I understand your frustrated with so called " experts " but if the machine shop screwed up they should do the labour for FREE. I've been the customer on the other side of the counter and I know. From a machinest point of view even if there is half a degree of angle out the result is a valve grind way out on the seat, the most accurate way is to go off the old guide hole, you need to find a machine shop with special head equipment like a Sunnen VGS-20 or a Serdi head shop. These machines have multy axis beds, mount the head and machine a pilot if need be to fit the old guide hole , using the axis one can pin piont the angle with a bouble level . If the motorcycle industry can't do the job, try the automotive race industry. Its big in Australia , there is where you will find the experiance and the proper head tools to do the job right. Too bad that you don't live closer , I'd have you on your way in a couple hours and happy I mit add.

Johnny Rocket
Johnny Rocket,

Yes, you are correct about the frustration with the machine shop that has my head.

In all fairness the person doing the work has done an exhaust guide for me before & it is all good.

But it does appear that he has stuffed this one up in my 850 by reaming it at the wrong angle somehow. He is not admitting to it though. Anyway, the good blokes with lots of Norton experience are few & far between around here, those with the "right equipment" that is. Kelly Cork is an hour away & he is the one I will send any machine work to in future. I spoke to Kelly today about & it through his experience, it was he that said he would have never reamed the head, he always turns down the guide as it can't "stuff the head angle up". Makes sense to me.

I thank you for your offer/compassion & if you lived closer you could do the job. :D

I am just annoyed as I was supposed to be picking the head up today & would have been "snorton" this weekend on my 850 :x

Don't sell the 750! Keep both bikes so you have a spare. Very nice to have at times like this.

Good luck, hope it all gets squared away soon.

Since we're talking about valve guides here I've got a question: what's the concensus on the options available? The stock gudes are cast iron, there's a guide called Ampco 45 (bronze?) and some sold by RGM touted as Formula 1 type material. Soooo any opinions on whats the best choice?

Good silica bronze guides, whether they be Ampco45 or other, have higher lubricity and better heat transfer than cast iron. I would go so far as to say that any variant produced by a reputable manufacturer is an improvement over stock.

RGM and Kibblewhite both have very good reputations and I would easily use products from either. Though, in my case, I'm going on Keith Johnson (Johnson Cams) recommendation and using the Kibblewhite Ampco45's in my new motor.

As for the minutely different alloys, I would chalk that up to marketing.

I agree, having two nortons around is a handy thing :D

But once my 850 is sorted out & as "bullet proof" as a norton can be, I plan to sell the 750 to finance one of those late model Triumph Speed Triples. A mate has had one since 97(alloy frame) & I do like them.

I have been off work for some 11 months now because of a disc problem in my back. I was getting paid for 9 months of it by the insurance company, but no more...............

If I can find employment outside carpentry that I can manage, I WILL keep both nortons. But I am not having much luck just yet !

Thanks for your kind thoughts.
750 vs 850 Commando


Now you've started something between 750 vs 850 Commandos. This is all subjective of course. Keep the 750 and loose the 850. An 850 is just a detuned version of the original and is slower even if more displacement. I'm saying this to see the reaction, but I do believe it.

You said:
"Now you've started something between 750 vs 850 Commandos."

mmm... I believe you are the one starting it :D

So I will play the game with you & anyone else who wants to play.

My 1972 "Combat" 750 is one of the quickest, if not the quickest in our little group. It runs Ok but I have had quicker ones.

My "handbuilt" 1973 850 is the quickest commando in our group. It has a 750 crank in it, a Norvil profile 3S cam, 32 mm RH4 head that has been "shaved" a little, a 34mm Mikuni & a boyer o boyer ignition. And let's not forget the "Autolite" U Beauts platinum AP63s :D

The rest of the bike is "stock" except for the Brembo Master Cylinder & Caliper.

No one catches me now through the "twisties", ie: the 750 or 850 commados or featherbeds that are on our rides.

I love the 850 & love the 750 also, but if one has to go, it will be the 750 because the 850 goes better, sounds better & stops better 8)

Back to someone else..............

BTW, I have just purchased what looks like a complete RITA ignition for my 850. So I will be able to palm off the crappy old boyer :wink:

OK, I'll take the heat for starting something. There hasn't been much controversy on this forum for a while. I can believe an 850 can be made to go faster. Out of the box a 750 is a more exciting ride, particularly the combat.
Hi people!

Ha, now that's what I like about this forum: topics get mixed up...! Sort them out , baby, there are all in there!

Well, I have just been out on the road on my '69 750 S Type and I must admit that when I first hit the 5000 rpms I was astounded about the power kicking in (again!). Sweeeeet, beefy engine! The 750 wins in the "weight-department" as well (180kgs versus 211 kgs), while the power output is quite similar. Power-to-weight-ratio is better on 750s. On the 850 I rode I found the engine a lot lazier. Took ages to dash around the dial. Could not find the increased torque superior to the 750.
I guess, the only advantage of the 850 is its thicker crankcase. Horses for courses, that is.
I have been told, if you rebuild your 750 engine, you can find quite a bit of horsepower in there...

But anyway, a Norton Commando offers an outstanding riding- experience.

C'mon, let's have some controversy!!

Guten Tag from Hamburg, Germany

The 850 is "lazier" and heavier? Not in my experience. My old 850 felt identical to my current 750 (except it had a working front brake) and the motor was at least as strong. They both have/had similar power characteristics.

I've never ridden a Combat. Those may well be more "exciting". Particularly when the engine goes BANG and throws the rods through the cases! :twisted:

Though to be fair they probably don't do that anymore. By now, surely they've all been rebuilt with the good bearings etc.


Hi Debbie,

In the good old days ('72-'73) combats went bang because 19 year olds, like me, would rev them past 7,000 were you could feel a power surge. Actually my first combat never did go bang and wow what a ride. I owned a '74 850 in the form of a JPN a couple of years ago. Not bad but not as quick as the '72, except for top speed (22 tooth counter is stock on JPNs). I've traded off for several 850s on club rides so have ridden all years and most body styles.
Well, I got the 850 Head back during the week & have been very carefully putting it all back together.

The machine shop had to make up a new inlet valve guide & drill it to compensate for drilling the head at the wrong angle. I replaced the valve springs also as a couple were worn.

The bike started second kick & I have ventured further & further from home checking for oil leaks etc. I had my tacho drive drilled for a double lipped oil seal while it was off the road......dam thing still leaks :!:
What to do about that :?:

Apart from the tacho leak the 850 puts a real smile on my dial :D
Some of you should try the 750 crank in the 850 engine with a 3S cam with the RH4 head "shaved" a little. It goes alright & sounds wicked.

It is amazing how different it feels to ride with the roadster tank on it compared to my interstate comabt 750. When you have the roadster tank on, the bike just feels small but so much more "nimble". I can't wait for our ride down through the mountains tomorrow.

The sun is shining & there is blue sky everywhere, I am off for a ride 8)
I find little difference in high compression 750's and a good condition 850 in stock trim. The 750 will be geared a tooth lower, but with identical gearing, the slight increase in displacement compensates for the lack of compression. Trouble is, where do you find an 850 or 750 "in stock trim"? These things are too much fun to leave alone. Gearing changes, cam changes, carb changes, ignition changes, head work. When you add these items into the picture, the difference between the 750 and 850 is only 79cc! (828-749=79) Both are a blast!
Not open for further replies.