Exhaust Cam valve gap - it reduces over miles ridden same as intake, not increases right?

Martin-Brighton-uk

Supercharged
Joined
May 7, 2014
Messages
330
Location
Faygate UK
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2011 Roadster in Red Haze; Honda Blackbird
I've seen posts in some threads on here that the exhaust cam clearances increase rather than decrease with miles ridden. Is that right? Yes the exhaust cam clearances are greater than the intake, but both valve wear in the same way don't they, snap closing each time? So the statement that intake valve gap reduces and exhaust valve clearances increase is not correct? Just wanted to double check as I am doing my clearances now and I aint a mechanic.

I understand that the wear of the shim itself could in theory balance out the wear on the valve head. As the valve head wears and the clearance gap to the cam lobe decreases, the shim is also wearing, so if the shim wore at the same rate as the valve head, the total clearance would be self correcting? :)
 

atomsplitter

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Nov 29, 2007
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Keller, TX
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2005 Rocket III
It's a matter of material hardness. What is harder, the valve, or the valve seat? Usually the valve is harder than the seat, so the seat wears causing shim clearance to cam to reduce. If the seat and the valve are of the same hardness then the shim will wear if it's not as hard as the cam lobe and the clearance opens.
 

TURBO200R4

stand up straight and grab the world by the a$$
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Jan 24, 2013
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6,117
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TUCSON AZ
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07 rocket III classic
when i got mine 6000 miles when cold it had some valves clicking when warm the clicking would go away.
at 50000 miles no clicking when cold (defiantly not to lose maybe to tight i do not know.)
 

Gregger

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Nov 2, 2013
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Timmins, Ontario
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2012 Rocket Roadster
There are two reasons for clearances to increase and decrease. Increased clearance can be due to wear taking place on the cam lobe, cam bearing and shim face as the lobe and shim rub against each other putting strain on the cam bearings. Decreased clearance can be due to the valve seat and valve face deforming due to the valve hammering into the seat moving the valve closer to the cam lobe. What I have found on the Rocket is that my exhaust valves tended to increase in clearance and my intakes tightened up. Don't know why? Maybe the exhaust valves are harder/more durable, or because they are smaller with less mass than the intakes producing less hammering on the seats, I don't know but it's what I've noticed on the Rocket.

When I worked on Detroit 60 series engines the valve clearances always tended to tighten up to the point that if you didn't get them checked you could end up with valves not closing resulting in burnt valves. I'd rather have valves with too much clearance than too little.
 

sonny

Living Legend
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Sep 24, 2015
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Henryetta Oklahoma
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rocket three x
Exhaust increases and intake tighten up. Don't care about If But And Why. Just know it as a fact of life period. Same would happen with the Bonneville a long time ago. I adjust my valves in accordance to this mystical admornality. Some seem to think as long as there is no noise in the valve train your good. Not so. A tight valve makes no noise until it is to late for a fix. I check my valves every 20,000 miles. I like to keep my valves within tolerance.
 

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