[cforcht]

I bet! I've got the mill covered, however. Just need a bigger cnc lathe.

Selfish question: How far is the arrival of the new mill going to set you back as far as progress on your engines? I don't want to go into withdrawal.

It shouldn't affect the progress much at all. Im going to keep my old mill up and running until the new one is in place and running. I have decided I am moving all my equipment to the other end of my building. so the new mill will be the first to go there. I have more room on that end. this mill is very large. 14 feet from one end to the other. 10 feet front to back. 12 feet when you put the chip conveyors under it. where my machines are now cannot house that big of a machine along with whats already in there. When I put the first mill in there I never intended to have more than that mill. things change and so did the floor plan.

[FannBlade]

chip conveyors

I have one of those.......

[cforcht]

yay the blower belts arrived. very quickly too. I ordered them on Tuesday. excellent service for a custom belt.

[cforcht]

I have one of those.......

I have two of them. ones age 14 the other is age 16

[cforcht]

the gears for the starter drive showed up as well as the one way clutch bearing. I couldnt resist the urge to get them on the engine and see if it works. it does work. of course the engine isnt completely assembled but it does turn the crank over and lets the crank run without the gears turning with it.

[cforcht]

the carbide slugs for the crank balancing showed up today. I pressed in three of them to see if its going to work according to plan. I am happy to say it is. now just have to press in all the others.

[Ken_Shea]

Craig,

How did you calculate what weight was needed?

Ken

[cforcht]

that was done by a fellow member of this board who is by trade an engineer. its not a 100% balance. the closest I could get with the size of the crank is 76% which is far closer than no balancing at all. removing the excess material from the crank only got me to 51% or so. adding the tungsten weights got me to 76%. with that in mind imagine how out of balance it would be if I did nothing to the crank at all in terms of balancing.

[dynosor]

It is a beautiful thing, Craig!

How much interference between the weights and their holes?

[cforcht]

its about a .0005-.001 press fit.

[dbrija]

its about a .0005-.001 press fit.

Carbide slugs = Mallory metal?

[cforcht]

Carbide slugs = Mallory metal?

for the most part. I think mallory is a brand name. what Im using is tungsten carbide. its tungsten with 6% cobalt. there are only two metals heavier than tungsten they are platinum and iridium. both are considerably more expensive than tungsten. and they are just barely heavier than tungsten.

heres a comparison of specific gravity

Iridium = 22.16
Platinum = 21.51
Tungsten = 19.62
Gold, pure 24Kt = 19.29

[cforcht]

got the crank fully assembled and installed.

[FannBlade]

got the crank fully assembled and installed.

Your machine work is amazing.

Are the counter weights held strictly by interference fit?

Any chance they could come out due to expansion of dissimilar materials or do the slugs expand first since they are denser?

Any idea of what kind of crankcase temps you expect to see?

[cforcht]

Your machine work is amazing.

Are the counter weights held strictly by interference fit?

Any chance they could come out due to expansion of dissimilar materials or do the slugs expand first since they are denser?

Any idea of what kind of crankcase temps you expect to see?

thanks for the compliment. I try to do my best no matter what Im doing,

yes they are held by interference fit only. as for the other questions... I do not know with any certainty. Dynosaur might be able to answer them. I do know using tungsten is a common practice for balancing engines and it is installed in a similar fashion meaning no brazing or welding etc. only time will tell if its a viable plan or not. if not I guess its back to the drawing board.

[cforcht]

did some work on the timing gears. still have to do the cam gear. but wont do that until I get the cam made again.

[cforcht]

Fannblade,
I suppose if the press fit is not sufficient I could add a set screw for each weight as a mechanical means of retaining the weights in addition to the press fit.

[bluejets]

Craig,

How did you calculate what weight was needed?

Ken

Crankshaft balancing........

An old tutorial but still applicable.

Balancing Small Engines by ET Westbury: Page 2

[Ken_Shea]

Thanks bluejets.

[dynosor]

Are the counter weights held strictly by interference fit?

Any chance they could come out due to expansion of dissimilar materials or do the slugs expand first since they are denser?

Any idea of what kind of crankcase temps you expect to see?

According to this Wiki page: Thermal expansion - Wikipedia, the free encyclopedia the coefficient of thermal expansion for tungsten is 4.5 µm·m−1·K−1 and that for carbon steel is 10.8 µm·m−1·K−1.

Based on these coefficients and an assumed minimum interference fit of 0.0005" (12.7 um) between the .3125" diameter weights and their holes in the crank, the interference becomes a sliding fit when you raise the temperature of the assembly by 252 degrees Celsius. This implies that if the crankshaft temperature rises from 25 to 125 degrees Celsius, the weights will still have more than half the original interference.

Consider that while the combustion temperature will be several hundred degrees Celsius, the block temperature cannot exceed 100 degrees Celsius without boiling the coolant, unless the coolant is pressurized.

Further consider that oil temperatures much over 200 degrees Celsius are unlikely unless the engine is on its way towards seizure. The kicker is that the forces trying to expel the tungsten weights act perpendicular to the possible axis of removal.

The bottom line is that I don't foresee the need for any additional retention method for the weights because there is no real force trying to press them out of their seats, even at 10,000 RPM, unless the engine has a bad axial vibration. With the care and precision evident in all the components it is hard to imagine where such an axial vibration might come from, but if present it would be immediately evident on running the engine. A vibration capable of driving axial creep on the balancing weights would probably be damaging the bearings and other components, and if present should be investigated before it does any real damage.

Considering the above, I would think long and hard before devising any additional balancing weight retention method. I don’t see where and how one can add screws that would be useful, and in my opinion the risk of damaging, weakening or unbalancing the crank outweighs the potential benefit. The only additional retention methods I would consider are creeping Loctite and crimping the edge of the counterweight pockets.

I have my doubts about there being any room for Loctite to creep into, as there should not be any – if the finish on the weights or their holes was slightly rough parallel to the axis of assembly there may be striations that Loctite could wick into.

As with adding retention screws, crimping the weights in place has the potential to cause harm and if the weights are not positioned a little below the surface of the crank webs on both sides, there would be no material available to move laterally by means of crimping, dimpling or punching.

Apply creeping Loctite. If it creeps in then good; if not it didn’t need to…