Cam Gear Loading on Crank

[Fingers]

Been Thinking. Always a dangerous thing when I start thinking.

1. How much torque does it take to make the cam gear slip on the cam shaft?
2. We know the cam gear slips on the cam shaft because of all the damage to the alignment pins on stock cams. Even at stock power levels.
3. The cam gears are helical
4. Helical gears generate thrust on the shafts that drive them.
5. How much thrust?
6. Can we figure out how much axial thrust is being applied to the Crank?
7. Knowing how much force it takes to move the cam gear, what is causing all that force. Valve train resistance or rattle from the crank.
8. Lastly, are these additional forces enough to fatigue the crank?

 

[duratothemax]

Interesting thoughts Jon! Ill add one to it...

Does the 2-piece cam gear on the LBZ+ have any effect on the above questions?

 

[Fingers]

Still creaming the pin on the 2 piece cams IIRC.

It is interesting that the Duramax crank gears have the opposite helix as the Ford or Cummins.

 

[02ilduramax]

Subd

 

[MarkBroviak]

Enough load to rip the teeth off the crank gear under big power when loaded down really hard...:thumb: That one didn't break the crank or hurt the main bearings, weird isn't it. We blamed it on a bad heat treat of the gear but who knows?

 

[Fingers]

To determine the break away force, we need to first know the clamping force on the gear without the pin/key.

The bolt is a M16x1.5 torqued to 173 ftlbs.

Looking this up in a table gives about 20,000 lb clamping force. OK​

Now we need to know the effective diameter of the clamped area.

Total clamped area is 1.57" diameter with 1.1" diameter hole taken out of the middle (measured and rounded)

Effective diameter of the clamped area is about 1.355"​

The resistance to moving the clamped part is between .5 (dry) and .25 (oiled) of the clamping force for steel on steel.

In this case that gives us between 5,000 lbs and 10,000 lbs of force resisting at 1.355" diameter or .6775" radius.

The pitch diameter of the cam gear is about 7" or 3.5" radius.

So. at the cam teeth, we are seeing in excess of 1,000 lbs (oiled) and probably more than 2,000 lbs (dry) of force.

Our poor 5mm pin is only able to hold back about 1400 lbs of force at most on it's own. So at 1.1" diameter, it only adds another 220lbs or so at the cam gear teeth.

A 10mm long key gives us at least 9000 lbs at 1.1 diameter or an additional ~1500 lbs of resistance at the cam teeth. Essentially doubling the holding capacity of the cam-gear connection.

I know of no-one that has sheared a keyed cam, so we can safely say the forces are less than about 3500 lbs at the cam gear teeth.

 

[LBZ]

.........

I know of no-one that has sheared a keyed cam, so we can safely say the forces are less than about 3500 lbs at the cam gear teeth.

Brad Makinen just did in his Willy's motor at Texas World Finals.
He is running a bunch of extra pumps and whatnot off his gear train though so not sure if that had an effect or not.

 

[Fingers]

That's interesting to know. Extra loads on the gear train shouldn't matter to the key since it is only controlling the load from the Cam. Now if the cam bearing crashed and caused the shaft to lock up, that's another thing.

Makes you wonder what the heck is going on with the cam loads.

 

[x MadMAX DIESEL]

My cam pin is a 1/4 woodruff key filed to fit. So i will have to get to see if its bending any. 2 seasons of pulling on it. With lots of shock load on it from driveline breaking

 

[MarkBroviak]

I've not seen any issues with the cam gears on keyed cams at all, just the one crank gear that ripped the teeth off it.

 

[bcdeutsch731]

Here is my crank that I beat the hell out of for 2 years in a stock motor then built the motor and beat the hell out of it for another 2 years. Last winter I took my truck to Florida and did some testing with it. I ran 12 passes in Florida all faster then a 9.49. Engine was running great so I dropped the oil pan to put my other adapter on so I could run the 400 trans and that is when I found the teeth in the pan. I had no idea the teeth were ripped off because the engine was running so good.

 

[Fingers]

Thanks for the pictures. :thumb:

 

[juddski88]

Anyone know of anyone else using Straight cut gears other than Watson?

 

[MarkBroviak]

X2, thanks Brett! I couldn't find them in my collection, lol!

 

[x MadMAX DIESEL]

So your thinking that cam is pulling on the crank to much?

 

[Fingers]

I am not sure if it is a symptom or a contributor.

The actual push-pull on the cam gear and thus the crank is about 200 lbs. I will need to put a crank on the press to see what the deflection is under axial load.

 

[Chevy1925]

just thought of this but what about the added load of the water pump and CP3 connected to the cam gear?

 

[Fingers]

Those are loads that would not contribute to the shearing of the cam pin, but are loads on the cam gear itself. So they would be in addition.

 

[rickaveryjr]

This is pretty interesting. Typically straight gears are weaker than helical simply due to the fact that there is less contact area for the same size gear. They are also much louder than helical gears at higher speeds. The problem with helical gears is the axial force (thrust) when loaded. There is also a force trying to separate the gears at that point. Could the uneven loading/unloading from the cam have something to do with resonation at a certain frequency? I don't know. Maybe that was a thought for the CRANKS thread

 

[Fingers]

This is pretty interesting. Typically straight gears are weaker than helical simply due to the fact that there is less contact area for the same size gear. They are also much louder than helical gears at higher speeds. The problem with helical gears is the axial force (thrust) when loaded. There is also a force trying to separate the gears at that point. Could the uneven loading/unloading from the cam have something to do with resonation at a certain frequency? I don't know. Maybe that was a thought for the CRANKS thread

Actually, spur are stronger. Especially stub spur. Helical only have a small portion of the gear faces in contact at any given moment. Helical are quieter however because the gradual engagement along the gear face.

The axial thrust from the helical depends on the angle of the helix. In the case of the cam gear, it is about 10% of the loading on the gear teeth.

I think the loading on the cam gear is a clue to the axial loads being applied to the crank. Whereas the crank can easily handle 50,000 lbs of radial force from the connecting rods and the resultant torque. The failure and fatigue point from axial loads is much smaller.