Norton comm 750 1972 valves springs shim or washer?

Hi there,
here I am asking again. Today, I was working on removing the valves from my norton commando 750 1972 200000 onwards and I found the following washers under the valves springs collets.

Are they the famous heat washers or simple shims? there is stamped on the top 100





Does anyone know the code for this replacement????

Thanks a lot in advance

Not the heat insulater. Probably a shim to adjust valve height.
You haven't identified this bike as a Combat, have you?

No I did not! but it is a combat!!! is it a shim then???

chiccogarz said:

No I did not! but it is a combat!!! is it a shim then???

Click to expand...

Hell, I don't know. Everytime I make an educated quess, I find out how ignorant i can be. :?

The reason I ask about the Combat head is that many were machined, for the lack of better words, haphazardly. Drill presses with little jigs made too deep spring pockets, guide hole with bad angle and porting perform by eager beavers with coke bottle bottoms for glasses. This may also pertain to other heads but particularly with the "C" stamped head.
Do you have one of these?

Combat may be quite desirable but some aspect really suck.

Here's my C stamped paper weight.

it is a spring shim NOT the factory insulating washer. where did you find them? under the intake, exh or both? did you find the insulators and these?

It's kind of hard to get an idea of the size. It's probably a shim used to adjust spring pressure. Does it have the thickness stamped on it? Does that say, "This Side Up"? Heat insulators aren't metal. I think they're the same stuff as the insulators on the intake manifolds.

'I found the following washers under the valves springs collets' Guessing you mean "collet retaining Plate" that locates the top of valve spring.. Thats unusual to me, is the writing stamped in or embossed.. Not knowing what there for, i can only assume that they are there to increase v/spring tension... IMO they would do nothing else. Are they all the same thickness??.. Be good to know there real purpose !!!

They are just shims.

They are thicker than the standard ones and you use them under the bottom spring retaining cup next to the head.

I have a box of different thinkness shims and these are pretty commonly used. I have personally used them in my race bike for more than 10 years.

If I have room I use a heat insulating washer on both inlet and exhaust and then shims as required for seat pressure.

You must also check for spring bind of course.

johnm said:

They are just shims.

They are thicker than the standard ones and you use them under the bottom spring retaining cup next to the head.

If I have room I use a heat insulating washer on both inlet and exhaust and then shims as required for seat pressure.

You must also check for spring bind of course.

Click to expand...

Im a SOC so give me some grace.. Why would you use washers and shims ......... Is this not just to get "seat Pressure" as you say, or increase the tension on "weak" springs..... Why not go buy new/rated springs and chuck the patchup remedey.. Or am i missing something.... Also how does the DIY bloke measure "seat pressure"???

We generally trust the spring specs.
The issue is, not all spring pockets are machined equally.

Valve height is known spec. I measured mine by making a short tube being the same diameter of the spring and exactly 1.000" long. You assemble the parts minus the spring and include the 1.000" spacer.

Measure the top of the valve in the seated position and while sitting down on the spacer. Add 1.000" to this reading to get your valve height and add shims, if needed, to bring to spec.

olChris said:

Im a SOC so give me some grace.. Why would you use washers and shims ......... Is this not just to get "seat Pressure" as you say, or increase the tension on "weak" springs..... Why not go buy new/rated springs and chuck the patchup remedey.. Or am i missing something.... Also how does the DIY bloke measure "seat pressure"???

Click to expand...

They shim the valve springs to equalize the spring pressure between the cylinders. The spring manufacturers could produce springs that would meet the spec's but you wouldn't want to pay the price for them, and most people wouldn't need them anyway. You would have to take it as an article of faith that the action of the valve doesn't correspond exactly to the cam lobe. Valve trains flex and all the components want to sail on you. It can't be helped but at least you can get all the cylinders doing the same thing so the output between cylinders is equalized. It really only matters to people who race with engines at or near redline who need the HP and reliability. Valve spring measuring devices measure pressure at different heights to set up the shimming.
There's a good book Four Stroke Performance Tuning by A. Graham Bell. (Yes, his first name is Alexander) That spends more time on valve springs than most. But there's a lot of engine building books out there that explain it. Redine's are defined by valve trains so racing forces builders to push them to the edge.

P.S. This Youtube video is good at show valve spring measuring.

http://www.youtube.com/watch?v=3Hyw3fantpk

Somebody told me this didn't make sense. I should have said, " It can't be helped but at least you can get all the cylinders doing the same thing so the output between cylinders is equalized, by matching up the springs.

bill said:

it is a spring shim NOT the factory insulating washer. where did you find them? under the intake, exh or both? did you find the insulators and these?

Click to expand...

I found one shim per valve just under the valves springs discs so in total 4 ! there was no insulators...

rpatton said:

It's kind of hard to get an idea of the size. It's probably a shim used to adjust spring pressure. Does it have the thickness stamped on it? Does that say, "This Side Up"? Heat insulators aren't metal. I think they're the same stuff as the insulators on the intake manifolds.

Click to expand...

I think the thickness is 100 (or 1 mm) and yes there is stamped on one side "this way up"

does anyone know where I can buy them???? I checked around but I could not find anything

chiccogarz said:

does anyone know where I can buy them???? I checked around but I could not find anything

Click to expand...

What's wrong with the ones you have. I doubt they wear out. If you feel you need to add, you can alway put in the heat insulaters that you don't have. NM23392

'72 combat used no insulators. It's British so the Blokes were accustomed to shimming just about everything you can think of. That's why the industry expired : too much shimming time in between cuppa teas.

rpatton said:

olChris said:

Im a SOC so give me some grace.. Why would you use washers and shims ......... Is this not just to get "seat Pressure" as you say, or increase the tension on "weak" springs..... Why not go buy new/rated springs and chuck the patchup remedey.. Or am i missing something.... Also how does the DIY bloke measure "seat pressure"???

Click to expand...

They shim the valve springs to equalize the spring pressure between the cylinders. The spring manufacturers could produce springs that would meet the spec's but you wouldn't want to pay the price for them, and most people wouldn't need them anyway. You would have to take it as an article of faith that the action of the valve doesn't correspond exactly to the cam lobe. Valve trains flex and all the components want to sail on you. It can't be helped but at least you can get all the cylinders doing the same thing so the output between cylinders is equalized. It really only matters to people who race with engines at or near redline who need the HP and reliability. Valve spring measuring devices measure pressure at different heights to set up the shimming.
There's a good book Four Stroke Performance Tuning by A. Graham Bell. (Yes, his first name is Alexander) That spends more time on valve springs than most. But there's a lot of engine building books out there that explain it. Redine's are defined by valve trains so racing forces builders to push them to the edge.

P.S. This Youtube video is good at show valve spring measuring.

http://www.youtube.com/watch?v=3Hyw3fantpk

Click to expand...

Yep that all make sense to me and as good an explanation that i can get... Thanks for that..

If you shimmed them down so the valve spring was closed , youd get maximum pressure . And not a lot else working .

Its usual to shim a Commando to Full Lift plus 40 thou. That means AT full Lift , theres still 40 thou / 1 mm , travle available to the Valve .

The heat insulators prolong El Cheapo valve spring life . As theyre commpressable , some frown at their use . Or leave them off , so set clearances are maintained .
A race or Hot motor , being pulled down more frequently , the springs are checked , and if theyve gone soft or shifted length , Scraped . As going quick is the object .
not saveing pennies .

Im a SOC so give me some grace.. Why would you use washers and shims ......... Is this not just to get "seat Pressure" as you say, or increase the tension on "weak" springs..... Why not go buy new/rated springs and chuck the patchup remedey.. Or am i missing something.... Also how does the DIY bloke measure "seat pressure"???[/quote]

Hi

Several people above have answered much of the question so I will just add some clarification from my experience.

-Firstly not all valve springs are created equal. You can buy springs with different pressure ratings - ie racing springs take more pressure to compress per inch than normal springs.

-The higher rated springs are basically to control the valves in racing applications with high non standard rpm, larger valves, higher lift and longer duration cams.

- heads are not machined exactly the same. Some will have deeper valve pockets, some may have deeper machining from the valve spring side.

- more unusually some valves or the machining for the valve collets can be different.

All this means that in order to get the correct clearance from coil bind and sufficient pressure to control the valves at full lift, valve opening and closing it is necessary to control the pressure of the valve springs by shiming them.

On many machines this is simply done done by measuring the valve installed height. This is not so easy on a Norton twin.

Shims come in steps of about 10 thou. The thick ones in your photo are probably 100 thou (2.5 mm which is pretty thick) . From memory I think the insulating washers are about 1to 1.5 mm ?? - 40 to 60 thou.

Now comes the question. How hard do you want to make this?

For a street bike with a standard cam, standard valves , standard springs, standard non messed about head etc you could just assemble the parts and ride.

The more you have a non standard bike the more you need to do.

On my race bike I do the following.

Have the valve spring measured on a spring compressor. You will need to go to a race tuning engine shop to do this. Record the spring length per psi accros the full range of spring compression. Especially carefully measure the pressure just before coil bind. A standard Norton spring is about 180 psi just before coil bind. Some racing springs go over 250.

Make a graph of the results. Lenght versus pressure.

Now assemble the head and fit it to the bike. Make sure you cam lube and oil the cams etc because even turning the engine over by hand can gall the cam surface.

Now mount a dial guage directly over each valve so you can measure the valve compression.

Then set the valve at maximum cam lift and lever the spring down to mesure how far you are from coil bind. In my opinion you should be about 60 to 80 thou off coil bind as a miniumum. There is no harm in having more provided you have the required spring pressure. See the next step.

Take this lenght and measure off your graph what the current pressure on the valve is at full lift.
On a street bike 160 lb should be enough. On a race bike maybe 215. Dont use more than you need unless you have a perverse pleasure in wearing out your cam and followers.

Do this for each valve and carefully record the valve pressure and distance for coil bind.

Using the graph you now know how many thou of shims to take out or add in order to get your desired valve spring pressure and clearance from coil bind.

Like I said a lot more work than just assembling the motor. But this is what you should do if you have a race or tuned street bike.The consequences of coil bind are a torn up cam and valve train. This is the sort of tuning that lets bikes finish and hopefully win races.