Combat Valve Springs

As my dad and I approach our next task (assembling the head) we are faced with another uncertainty. He seems to remember hearing that combat valve springs are different than regular 750's due to the wild cam. And it doesnt surprise me either because of the wilder cam. I did a quick search but didnt find anything. Im sure you guys know the right answer, are combat valve springs different than regular valve springs?

Thanks,
Matt

1. springs are the same as regular commando
2. no heat insulation washer on intake. (one of the causes of short spring life in combats)
3. some of the spring seats were defective and did not seat properly in the head.
it's documented in the INOA tech digest w/drawings

Thanks,
Ive never heard of problems with the washer. Its a good thing to know though.

Matt

dynodave said:

1. springs are the same as regular commando
2. no heat insulation washer on intake. (one of the causes of short spring life in combats)
3. some of the spring seats were defective and did not seat properly in the head.
it's documented in the INOA tech digest w/drawings

Click to expand...

Heat washer was used from the factory on intake, not on exhaust springs. My combat has 50K miles. Never had a problem with springs. The only potential issue is coil bound condition. It's close, but doesn't happen. Then again maybe my valves have sunk a bit and would improve that condition.

The only proper way to be sure using the right valve springs is to measure their pressure at rest (mounted in the head, aim for 80 - 100 ft.lb) and at full cam lift (aim for 180 - 200 ft.lb.) Too much pressure can distroy your cam and followers, too little pressure can cause floating valves at high revs. I have used springs from various manufacturers and their pressure can differ a lot. SHIM YOUR HEAD :!:

nortonspeed said:

The only proper way to be sure using the right valve springs is to measure their pressure at rest (mounted in the head, aim for 80 - 100 ft.lb) and at full cam lift (aim for 180 - 200 ft.lb.) Too much pressure can distroy your cam and followers, too little pressure can cause floating valves at high revs. I have used springs from various manufacturers and their pressure can differ a lot. SHIM YOUR HEAD :!:

Click to expand...

i agree 200%
i shim mine to get 90 to 100 kg at full lift and go for 2mm before coilbound

illf8ed said:

dynodave said:

1. springs are the same as regular commando
2. no heat insulation washer on intake. (one of the causes of short spring life in combats)
3. some of the spring seats were defective and did not seat properly in the head.
it's documented in the INOA tech digest w/drawings

Click to expand...

Heat washer was used from the factory on intake, not on exhaust springs. My combat has 50K miles. Never had a problem with springs. The only potential issue is coil bound condition. It's close, but doesn't happen. Then again maybe my valves have sunk a bit and would improve that condition.

Click to expand...

Dave
Please review the factory parts book pub 063402 :
"group2
plate #10 NM23392 valve spring insulator (2 only on combat at exhaust position) Qty 4

The defective spring seats are well documented in the INOA tech digest. I happen to be the one who discovered (or bothered to tell the public) about the incorrectly formed spring seats NMT2072. My combat did have problems and only by fully examining every components form and function was I able to discover what had obviously fooled even experts. All this work was done well over a decade ago so I would have to refer to my detailed drawings and notes to fully refresh myself.
Any one who has done custom assembly and measurements of these heads/valve train will also have detected the bad spring seats (if present).
These defective spring seats only become apparent with combats or hot rod camed engines once the insulation washers are removed.
I even bought new genuine spring seats and received the defective style. So I ended up selecting correctly shaped used ones to properly assemble my head

Thanks for the dedicated detailed examination discovery David. Your close inspection of machining and crack detection reset my level of what's possible to observe by human's at least an order of magnitude beyond what I thought possible.

The 1st few days with my 1st Combat [pre-Peel] in '99 almost killed me as I worked up my throttle use in Mt highway conditions, began a pass of a semi which should of been no issue until about half way along the truck the strong acceleration just turned into horrific misfires/engine noise until I up shifted to 3rd and got around before oncoming got me. Somewhere in upper 6000 rpm my Combat really came on cam and felt like another piston kicked in but too soon after it felt like it dropped a piston. Six months later took apart just to renew normal wear items and learn Combat mechanics, one side of head was found to have swallowed a thumbnail size piece of carb slide that pecker-ed the whole chamber and piston and chipped-bent lip of exhaust valve. Don't know if slide beating bent stem to lower its spring/rpm tolerance of just innate w/o any damage straining in guides. The avatar photo was taken 3 days later, so didn't hurt performance short of valve float I could tell. Its possible the old points ign had floated too - to misfire horrible till backed off rpm.

6+ yr later with Dreer K/W valve kit installed there was no valve float above 11,000 rpm, though rest of the engine couldn't take it. This same head just opened up to accept 920 pistons by Ken Canaga and no other repair is to be used on new Peel. It had 7000 miles on it, 2000 after the over rev event but not power after 5000 so had to start over again from the crank up. I think rev limiter is a good idea now as well as trained reflex to tag kill button if throttle stuck and not just snap throttle closed. A flattened RH exhaust lobe was found on the 2S cam, which I think messed with Boyer timing to over advance by 5000.

How does one measure the pressure on the springs? This has got to be a bit of trick with it in the head. I tried to C-clamp a bathroom scale on there but couldn't read the dial.

Russ

How does one measure the pressure on the springs?

Click to expand...

Typically you would have a valve spring tester. There are many varieties. The ones designed to work with the valve spring mounted on the head probably will not work. There are simple gauges you place on top of the spring and use a drill press or arbor press to compress the spring to a given height. More elaborate versions have the gauge mounted in a dedicated arbor-type press.

You can compress the spring to the desired seat pressure and then measure the compressed length. Then install that spring adding shims to achieve the length determined in the tester. Be sure that if your spec was for full lift, you have the cam on the proper lobe face.
http://static.speedwaymotors.com/pdf/913-81103.pdf

Similarly closed seat pressure is measured by mounting the valve with the intended shims and retainer in the head, then measure the length with the valve full closed with a snap gauge. Transfer this measurement to the spring height on the tester and read the closed seat pressure on the spring tester at that spring length.

dynodave said:

illf8ed said:

dynodave said:

1. springs are the same as regular commando
2. no heat insulation washer on intake. (one of the causes of short spring life in combats)
3. some of the spring seats were defective and did not seat properly in the head.
it's documented in the INOA tech digest w/drawings

Click to expand...

Heat washer was used from the factory on intake, not on exhaust springs. My combat has 50K miles. Never had a problem with springs. The only potential issue is coil bound condition. It's close, but doesn't happen. Then again maybe my valves have sunk a bit and would improve that condition.

Click to expand...

Dave
Please review the factory parts book pub 063402 :
"group2
plate #10 NM23392 valve spring insulator (2 only on combat at exhaust position) Qty 4

The defective spring seats are well documented in the INOA tech digest. I happen to be the one who discovered (or bothered to tell the public) about the incorrectly formed spring seats NMT2072. My combat did have problems and only by fully examining every components form and function was I able to discover what had obviously fooled even experts. All this work was done well over a decade ago so I would have to refer to my detailed drawings and notes to fully refresh myself.
Any one who has done custom assembly and measurements of these heads/valve train will also have detected the bad spring seats (if present).
These defective spring seats only become apparent with combats or hot rod camed engines once the insulation washers are removed.
I even bought new genuine spring seats and received the defective style. So I ended up selecting correctly shaped used ones to properly assemble my head

Click to expand...

Hi Dave

Your saying defective valve seats were an issue, not the heat insulators. My response was related to eliminating use of the insulator.

rvich said:

How does one measure the pressure on the springs? This has got to be a bit of trick with it in the head. I tried to C-clamp a bathroom scale on there but couldn't read the dial.

Russ

Click to expand...

So I guess I can use the bathroom scale after all! Just place it on the drill press table and compress the spring to the predetermined length!
Thanks for the reply
Russ

rvich said:

rvich said:

How does one measure the pressure on the springs? This has got to be a bit of trick with it in the head. I tried to C-clamp a bathroom scale on there but couldn't read the dial.

Russ

Click to expand...

Click to expand...

So I guess I can use the bathroom scale after all! Just place it on the drill press table and compress the spring to the predetermined length!
Thanks for the reply
Russ[/quote

absolutely , but you might find that you need a few bat hroomscales , as they do not like the pressure . a plank of wood is a good thing to save the scale .
I use one under my press
will post pic later

Hi Dave

Your saying defective valve seats were an issue, not the heat insulators. My response was related to eliminating use of the insulator.[/quote]



1 Yes the insulators were eliminated on the intake NOT the exhaust as you claimed....or did I read it wrong?
2 the reason they were eliminated, is the spring comes close to coil bind.
3 Yes there is a potential problem with spring seats that affects any norton head when the insulator is eliminated is that removing the insulator does NOT give the extra .063" because the bad shape hangs up and prevent the seat from dropping to the bottom of the pocket....

I'm sitting in the garage right now staring at a table full of head parts. I only have 2 insulating washers and to clarify, they only go on the exhaust valves?? Do they go underneath the springs and bottom retainer right against the casting? Or in-between the spring and the bottom retainer?

Thanks,
Matt

There were W & S valve spring sets , progressive rate , centerless ground wire , came with keepers , colletts seats and shims .included fitting instructions .
packet said " yamaha 550 & 750 twin , also fits Triumph and Norton " . which tells you a few things. The yams were the old
XS ? Four Valve suckers , so you got TWO sets , for $ 15 , 1980 .from ' Blue Wing Honda ' . :lol:

The std. Terrys springs arnt bad , but dont last forever . Drawn wire is evident in comparison .
I'd inadvertantly ran .016 clearance & set Combat Cam 5 Deg early.As I was informed it was a ' 3 S ' camshaft .
Later inspection showed it was definately two Ses , stanmped " S S " , though looked to be " 3 S "stamped across .

This combined with the W & S springs meant backing off as revs hit 7.000
Later with std cam and timing it really wound out , moreso regarding rpm
increase toward redline, so one kept ones eye in there .

If they are still available ( try Yamaha suppliers ? ) theyre a bargain at twice ( or 10 ) times the price.
very high grade components.
Obviously Comp Parts there from these Yamahas are interchangeable .( those horrible overweight brown things )
But WHY did they use stuff that size with Four Valve gear ! :| :mrgreen: :shock:

I have 4, one for each valve(for what it's worth) and they go against the casting underneath the retainer.