Valve Clearance help?

staticmoves · May 10, 2012

Bike is 72 750 ( decombatted )

The engine has been bored 1 over and 9:1 pistons installed ( barrles done and pistons purchased by previous owner ), and I will double check but I believe the cam has an "S" stapped on it.
When checking valve clearances before first start up, should I be adjusting to what I would assume be standard spec? or Combat?
I noticed in the manual that there is a difference in the clearance specs for the two engine types.

Thanks in advance. :?:

staticmoves · May 10, 2012

Re: Valvle Clearances?

I am going to add another question here as well.
What are the differences between the standard and combat engine besides compression and HP?

Norton-Villier · May 10, 2012

Re: Valvle Clearances?

1 would be the timed breather

Phil

bill · May 10, 2012

Re: Valvle Clearances?

a change in camshaft with more lift and duration, higher compression by milling the head, enlarged intake ports ( some times a lousy job) , larger intake manifolds and 32 MM carbs V 30MM on NON combat.

staticmoves said:
I am going to add another question here as well.
What are the differences between the standard and combat engine besides compression and HP?

bill · May 10, 2012

Re: Valvle Clearances?

the timed breather was dropped on ALL engines in 72

Norton-Villier said:
1 would be the timed brether

Phil

staticmoves · May 10, 2012

Re: Valvle Clearances?

bill said:
the timed breather was dropped on ALL engines in 72

Norton-Villier said:

1 would be the timed brether

Phil

Click to expand...

I have a CNW reed type on the way after reading many posts on its ability to aliviate most oil leaking and gasket damage. ( I will be installing as they have an adaptor plate that will bolt on directly to the 72 crankcase, and as an added bonus, maybe I wont have to unbolt my engine to install the gearbox.

Hobot · May 11, 2012

Re: Valvle Clearances help?

A De-Combat-ed Combat must have its CR lowered if using the S cam instead of the SS/2S cam or tends to detonate. If standard cam as seems to be then it lash is set .006" intake and .008" exhaust, cold of course. Several ways to lower Combat to 9-ish CR, most involve base plate and maybe thicker head gasket, though pistons height also lowers w/o the plate. What matters in how the CR is lowered is that plate/gasket way messes with the push rod length on where the rockers bare on the valve stems. Combat push rods were not shortened when Norton milled .040" off CHO head so might improve the geometry and lower CR by just .040" Steel base plate. The INOA tech manual has chart of the combo's of various gasket and plates and resultsant static CR. Your pistons are the mystery component to measure for resultant CR on assembly. Personally I like the real deal Combat 10 CR 2S cam and run just fine on many occasions of 87 octane with and w/o ethanol, but keep in mind what's in the tank for how hard I press the throttle for zoom ups, but short of throttle snaps in 4th on steep climbs with cargo, its a non issue to cruise any speed I dare. A fully de-Combat will not use the CHO hi compression head as its big ports stifle response w/o the extra breathing velocity of higher compression + 2 S cam. If going the lower power-response route it may be more pleasant to bump the final gear ratio up 20t or 21T as real Combat don't really wake up on cam till over 6000 rpm.

ILLF8ED · May 11, 2012

Re: Valvle Clearances help?

Combat cam has a .390 intake lift while the standard Commando cam has .330. Exhaust lift is pretty much the same... only slightly more on the combat. Hobot is correct about needing compression lowering if a standard cam is used in high compression combat engine to prevent engine detonation (pinging)....my recent discovery and resolution with Norris RX camshaft for my combat. Valve clearance should be set to camshaft specification. Typically more lift requires more clearance. For the Norris RX I set to 0.012" for all four, however Norris recommends 0.020".

staticmoves · May 11, 2012

Re: Valvle Clearances help?

hobot said:
A De-Combat-ed Combat must have its CR lowered if using the S cam instead of the SS/2S cam or tends to detonate. If standard cam as seems to be then it lash is set .006" intake and .008" exhaust, cold of course. Several ways to lower Combat to 9-ish CR, most involve base plate and maybe thicker head gasket, though pistons height also lowers w/o the plate. What matters in how the CR is lowered is that plate/gasket way messes with the push rod length on where the rockers bare on the valve stems. Combat push rods were not shortened when Norton milled .040" off CHO head so might improve the geometry and lower CR by just .040" Steel base plate. The INOA tech manual has chart of the combo's of various gasket and plates and resultsant static CR. Your pistons are the mystery component to measure for resultant CR on assembly. Personally I like the real deal Combat 10 CR 2S cam and run just fine on many occasions of 87 octane with and w/o ethanol, but keep in mind what's in the tank for how hard I press the throttle for zoom ups, but short of throttle snaps in 4th on steep climbs with cargo, its a non issue to cruise any speed I dare. A fully de-Combat will not use the CHO hi compression head as its big ports stifle response w/o the extra breathing velocity of higher compression + 2 S cam. If going the lower power-response route it may be more pleasant to bump the final gear ratio up 20t or 21T as real Combat don't really wake up on cam till over 6000 rpm.

Ok so I just checked the paper work from original owner,he wrote me a blurb when he sold me the boxes of parts.
" Head, commando with "C" stamp " and the "C" is there.
" has " SS" cam "
" New pistons are 9:1 "
" cylinder head honed to one size over "
So it is not the "S" cam, it is the " SS " cam.
So this being said, would I set the valve lash to combat specs?
And this would be my first time setting valve lash, any advice or known issues when making these adjustments on commandos?
Thanks in advance 8)

RennieK · May 11, 2012

Use combat specs as you have a combat head that gives you the 10/1 compression. Pistons were the same in both engines. SS cam calls for .008 and .010 clearance. Nothing much to it with pistons a tdc your feeler gage should just nip so you can feel some resistance. You will need to retorque the head and reset the valve clearances after you run it in the 1st time. The 750 combat is a sweet engine, you're going to like it.

staticmoves · May 12, 2012

Was there really a day before the dawn of the online forum? :lol:

A one to two year project would have taken a lifetime, or you would really have to of confided in the advice of your neighbour, who's own project was at least smoking or making sparks, so at that rate he was decades ahead of your basket case. :shock:
At witch point you would have to sit and listen to 3 hours of terrible beta and lots of B.S just to find out what kind of plugs he's running, and the gap ( if his plugs had any electrode left to gap? )

And the worst part about that whole scenario, is that two hours into the conversation on plugs and gap, you would be drinking the same piss warm beer you started with because you were to cheap to bring over a small cooler with a few beers each ( as you delicately extract the much needed information ) because you spent your beer money on a gap gauge the your hoping to use with the info you are currently extracting.

What I am trying to say is good Job everybody, and thank you.

P.S keep it coming. 8)

Matt Spencer · May 12, 2012

A privledged individual . The Combats the only real Commando . 8) :lol:

.

concours · May 13, 2012

staticmoves said:
Was there really a day before the dawn of the online forum? :lol:

A one to two year project would have taken a lifetime, or you would really have to of confided in the advice of your neighbour, who's own project was at least smoking or making sparks, so at that rate he was decades ahead of your basket case. :shock:
At witch point you would have to sit and listen to 3 hours of terrible beta and lots of B.S just to find out what kind of plugs he's running, and the gap ( if his plugs had any electrode left to gap? )

And the worst part about that whole scenario, is that two hours into the conversation on plugs and gap, you would be drinking the same piss warm beer you started with because you were to cheap to bring over a small cooler with a few beers each ( as you delicately extract the much needed information ) because you spent your beer money on a gap gauge the your hoping to use with the info you are currently extracting.

What I am trying to say is good Job everybody, and thank you.

P.S keep it coming. 8)

We actually had to talk to people then. The guy at the bike shop, for one. Folklore was passed along. I remember SOME incomplete information, but nothing like the misinformation that flows on the web. More accountable, I suppose, because you'd see that person again.

Valve Clearance help?

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