Can anyone confirm if the gear mesh gets tighter or looser when the engine gets hot?

I have a TC 103". I havefound it normal for a properly fit gear mesh (Backlash of .0005 - .001) to have a slight whine when cold and then go away when hot. The Harley Boys at the shop keep telling me that's impossible because as the gears get hot, they grow/expand which would cause the gear mesh to get tighter and the whine to get worse.That is true to an extent but what I believethey are over lookingis the engine growth. The aluminumcrankcase expands more than the steel gears which actually causes the mesh to get looser when very hot. That is why the slight whine, when cold, goes away when hot. Right? The distance between the crank 31T gear, and the cam 62T gear, grows causing the mesh to get losser. Right or wrong? Does anyone know for sure? Has anyone ever measured it? Thanks

 

You are correct and the Harley Boys are wrong (once again) The aluminum grows quicker and further that the steel gears which meant the gears grow APART from each other.....no need to measure anything...your ear will tell you that.

 

Thanks Doc I thought I was loosing my mind. I mean holy crap arn't these guys school trained?Maybe they're still thinking about how everything got tighter while it was chain-driven with the tensioner absorbing the change in distance but with gears, the backlash is going to increase. I just wish I knew how much it can grow to on a very hot engine. How much backlash would be considered too much on a cold engine? I'm thinking .002 is probably too much already by the time you add the engine growth of a hot engine? I know if it gets to be too much, it can actually sound like noisey lifters at lower RPM's. I don't think mine are that bad yetbut ALSO, at higher RPM's, I thinkthey can actually find a point (or small RPM range) where they will begin to resonate or chatter which I believe I am currently experiencing at about 82 - 85 mph when the engine is very hot. I can take it up to 90 and it goes away. Drop back down into the lower 80"s and holy crap it sounds like a swarm of locust around my head. I don't believe I'm hearing any other valvetrain noiselike they're trying to tell me it probably is. I hear all that and it sounds normal to me.I have just changed all that ie. cams, lifters,pushrods, flywheel asm. andheadsetc. (not because of this problem) and thischatter is still exactly the same as it was when I was running the old set-up.They re-used my old drive gearswith new keys but I wonder how muchbacklashI actually have?It's the only parts that didn't get changed other than my rocker asm's. which I guess I can't rule out either yet.This noiseis something else and ever since it started, I no longer get the slight whine when the engine is cold which makes me wonder. Oh well I'm probably babbling here. Sorry. I guess I just had to put it in writing? HAhahaaaaaa.....

 

I set my back lash at0.0 to .0005 in all the builds I do, I have several over and under size gears on stock just to assure a good fit. With this set up I get a slight whinewhen the engine is cold and with-in 90 seconds the whine is gone and the valve train remains quiet even at 230*. If you hear any noise in the gears while checking for the back lash, that noise will become violent with valve spring pressures added. .002 is way too muchto start with.

 

Thanks man. That's what I thought. That's what I needed to hear.