Determining Valve Clearance Settings

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highdesert

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Jun 17, 2009
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Stock Commandos except for the Combat: .06 inlet .08 exhaust

Combat Motor: .08 inlet .10 exhaust

Why the difference? Presume it is because in the Combat the higher compressions and higher lift cam makes for more heat causing the valve stems to expand more?

How is the exact clearance determine? Mathematical formula or just measuring the clearances so they are nothing when the motor is real hot?

I have put in a Megacycle 5600 cam, compression on 850 remains stock. What would be the ideal valve clearance settings for inlet and exhaust?

Guessing somewhere in the middle of stock and combat, or the same as combat settings?
 
Different opening and closing ramp configurations not compression ratio, megacycle 560?, what ever mega cycle say it is ment to have.
 
Nothing in the package from Megacycle said anything about what they recommend to set valves at.

Lift seems quite close to combats, so guessed and went with .08 and .10.

But even when motor is hot and idling, I can hear the clicking. Is my crude assumption correct to set them tighter therefore? Should not hear any clicking when motor fully warm?
 
I have had a couple of people comment on how noisy my valves are. Usually while standing around listening to the bike idle. Can't say that I have stood next to very many running Commandos in recent years but it sounds normal to me for a bike with solid lifters, etc.
Traditional wisdom is that you are better off a little loose than too tight, but I have to admit that I have adjusted more than one tappet (usually on slower reving motors) by feel when the engine was hot by adjusting out all slack and backing it off a tiny bit. Old marine diesels are great for this kind of approach, don't know that I would recommend it on your Commando, but you could use it as a comparison for the amount of noise you are hearing. I would be curious as to how the more learned in the group feel about his kind of adjustment on these motors.

Russ
 
cold or warm , you need some clearrance for lubrification, in addition that's the only way to ensure valve are fully closed .
Valves are like Kids : it's when you can not hear them that trouble happend.
 
Somebody showed me when you use feeler gauges to check tappet clearance that you can be misled by a long shot if there is a dent or a groove in the top of the valve. If you can move the rocker more that what seems to be what you're getting told by the feelers then this might be going on. If there's dent then the effective clearance is what the feeler says plus the depth of the dent. It's possible to use a dial indicator lined up over the adjuster to get a more accurate measurement. I've been told you can go by the pitch of the threads on the adjuster, but I've never done it.
 
On new Peel, I'll start with megacycles clearance then adjust as any shade tree when hot for quietest operations just backed off enough to matter.
To compensate for the wear depression, IRRC adjuster thread are 28 tpi, but could be 26 tpi, anywho can either calculate or measure how much a turn moves screw and go by that no feelers needed.
 
Ludwig,

If valve lash doesn't have to do with expansion, then what is the theory behind it all? I ask because I have had noisy clatter and have tried to rein it in, with some success, although I admit I'm not sure what I should be looking for or how quiet it should be. Come to think of it, benchmarking standard Commando performace is somewhat of an unknown to me, because I don't have the history of comparison that many of you on this board have. I have to go by comparing changes made on my own bike, not on others I'm familiar with, or have had in the past, because this is my one and only Commando. I look at the condition of my valves and they look pretty fair. I assume the published measurements are appropriate and that's what I do. If I suspect wear, or concave wear, on the valve, then I'll replace it. What should I be adjusting to compensate for, if not the slop of heated components?

Thanks,

Eric
 
Ok I'm don't need any more expense lesions so will have to study up on push rod vs hydraulic lifter valve adjusting and thermal conditions vs valve timing effect and destruction. Too tight bends breaks things, too loose beat same things up. How is gap needed actually determined if not by trial and error?
 
Hobot, good question and mine also, how is the proper clearance determined?

Guessing, but would you not have to get the motor good and hot and then pull the valve covers off and measure the clearance? That way, all heat expansion it is in full effect, so any
clearance at all would be solely to allow some oil to get between the two parts? How much clearance to figure for oil? Just a stupid guess but about 2 thou?
 
Highdesert, I was expecting to learn that from yoose guys, ugh. We are missing something in our data banks, to understand why various cam profiles need differing clearances, way more than oil gap I'd think. Measure hot gap same way as cold, count the turns of adjuster per TPI. Likely as effective and safer that feeler.
 
hobot said:
Highdesert, I was expecting to learn that from yoose guys, ugh. We are missing something in our data banks, to understand why various cam profiles need differing clearances, way more than oil gap I'd think. Measure hot gap same way as cold, count the turns of adjuster per TPI. Likely as effective and safer that feeler.
Click to expand...

Some cam manufacturers will give a hot and/or cold clearance. My hunch is they're really trying to get is a certain amount of dwell of the valves against the seat to keep them from burning up. They then give a cold clearance based on the desired hot clearance.

-Eric
 
highdesert said:
Hobot, good question and mine also, how is the proper clearance determined?

Guessing, but would you not have to get the motor good and hot and then pull the valve covers off and measure the clearance? That way, all heat expansion it is in full effect, so any
clearance at all would be solely to allow some oil to get between the two parts? How much clearance to figure for oil? Just a stupid guess but about 2 thou?
Click to expand...

What if Ludwig's example is right. Loose-tight-loose, with increasing temp. What if the difference between mid-temp tight and high-temp loose is more than 2 thou? If you have set the clearance at 2 thou when good and hot then the valves won't be seating at the mid temp tight condition. I'd just go with the spec's, and make sure you're not misled by cratered valve tips, loose rockers and spindles, and way off valve geometry. The manufacturers don't pull these spec's out of thin air, I hope.
 
Seat contact time sorta makes sense, but why would a cam profile change how long a valve needs seating cooling. Until I understand full story, yes manufacturer's gap is what i'll stick with. Still would be neat if some excess clearance could be dialed out if we knew what the full story was on Norton solid push rods needs.
 
Rocker screw form is .010" per quarter turn. That takes care of the dint in the valve head.

750 Combat clearances are greater due to the shallower head. And technically, the pushrods should be .030"shorter than stock.

Mick
 
So going on your guys theory, all commando cams would have the same clearance
 
Slowly getting data to comprehend why to set lash to listed specs.

You can keep the fancy electro valve train for your cages, I'm holding out for roller hydraulic lifters. Until I fab up a planetary crank/rod gizmo, extra rpm valve train is just wrong for whiplashing the ends of the crankshaft.
 
fireballjrd said:
cold or warm , you need some clearrance for lubrification, in addition that's the only way to ensure valve are fully closed .
Valves are like Kids : it's when you can not hear them that trouble happend.
Click to expand...

Ditto that.

A loose valve is a happy valve.

Clatter is a good thing.
 
Im guessing that your average (or even hot) comando isnt radical enough to tighten up the valves by tuliping the valve stems at least
 
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