[FannBlade]

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…

Thank You for the well thought out explanation.
I was pretty sure cforcht had given it some thought, I personally wasn't sure of the metal properties he was using this helps alot.

I too was thinking loctite but wasn't sure it would hold under heat and oil and like you said his machining finish is so smooth would probably just shove it out.

Looking forward to the ring fixture.
Now take some NyQuil and hit the sack and stop thinking about those NEW machine purchases.

[cforcht]

Thank You for the well thought out explanation.
I was pretty sure cforcht had given it some thought, I personally wasn't sure of the metal properties he was using this helps alot.

I too was thinking loctite but wasn't sure it would hold under heat and oil and like you said his machining finish is so smooth would probably just shove it out.

Looking forward to the ring fixture.
Now take some NyQuil and hit the sack and stop thinking about those NEW machine purchases.

Loctite is a great product however it does have limits. the one thing to keep in mind when you decide to use loctite on something is whether it will see heat and how much. enough heat will make ANY variety of loctite de-bond. so take care when using it in an engine. it is not a replacement for loose tolerances. at least in an engine.

as for the nyquil. my wife dosed me up with some stuff she had in the cabinet and man it knocked me down right now. I was pretty much out of it for about 12 hours.

[Prawnhead]

:wee:

[FannBlade]

How's things coming along?
I need a pic fix!

[cforcht]

How's things coming along?
I need a pic fix!

sorry man I got nothin right now. been busy with work etc. too many irons and not enough fire to go round. I havent abandoned the project just been uber busy. been working on the shop too, prepping for the machine arrival which has included building walls, pouring concrete etc.

[FannBlade]

Awesome to hear about the shop expansion. I hope to send you a little project in 3-4 weeks.

[cforcht]

Awesome to hear about the shop expansion. I hope to send you a little project in 3-4 weeks.

An update on the shop progress.....
heres a pic of where my equipment is going. still need to do some work yet but its getting closer. the new to me mill will be here on Nov 1st. where I am standing taking this picture will be a wall to enclose the "shop" area. the walls are already built but wont be put in place until the mill is moved in.




heres a pic of the new office space in progress. a little larger than my current office thankfully.

[dynosor]

heres a pic of where my equipment is going...

Looks like you could build full size cars in there.

[cforcht]

Looks like you could build full size cars in there.

actually, from where I took the picture there are 3 cars behind me. (BMW, Honda and an Opel) what you see is half of the length of this section of my building. the width of the room in the pic is 1/3 the depth of the building. moving everything to this end of the building gives me the ability to expand later on without having to move the equipment again. I just wish the ceiling height was a little higher though.

[FannBlade]

Hey been out of the loop for awhile...hows the build coming along?

Get the shop done?

[cforcht]

well, the build has been put on hold due to setting up the "new" shop. I had a lull in the work load over the holidays which I took advantage of and moved the rest of the machinery along with all the other stuff to the new shop. still situating things here and there but for the most part its done. glad I did it when I did. because after the holidays my customers dumped a bunch of work on me. heres some pics of it.










the new office area. yay its much bigger than the old one.

[FannBlade]

WOW! Nice layout. I bet that took some time to get done.

[AMCjeepCJ]

Nice looking shop. I just moved ten pieces of manual equipment and a kneemill CNC to my garage. Hoping to build a new shop behind my house and move my entire company to my residence by fall and since our CNC lathes and VMC's are roughly identical in size it's nice too see how much space I actually need.

That engine is awesome! I'm researching a small engine I could build from scratch and put in a custom 3/4 scale scratch built motorcycle for puttering around bike shows and showing off my products. A V8 would be crazy in a teeny bike and sound incredible!

Looking forward to seeing it finished, about how much power would you expect out of one of these at a reasonable RPM, not just maxed out?

(Looked all over for something to click on so I could get emailed updates on this thread but posting is the only way I know to do it, if anyone knows what to click on PM me the instructions~)

[cforcht]

AMC somewhere there is a place to subscribe to threads, Ive seen it but cant find it now. as for shop space. figure out what you think you need and then double it. no matter how big it is. its never enough. had my service guy here over the weekend. Hes a friend of mine. He was here customizing my mill to suit my particular desires. he installed a new pendant control with loads of features I didnt have before. then he had to re-write the ladder diagram in the machine to use the features. there are other things to be added later. (ran outta time) one is the 4th axis. which I need to get the servo installed on my indexer to make it a full 4th axis instead of just an indexer. hes already made the machine ready for the 4th in most respects.

[cforcht]

I have made a little progress. not anything really amounting to much other than buttoning up some of the small things. I got the intake and exhaust ports done in the heads as well as the ports in the intake. engraved the valve covers with the heartbeat logo. got the heads fully assembled aside from the rockers. thats about it for now.

[AMCjeepCJ]

Good point and I basically will be doubling what I need but I'm building the shop in two stages, the first stage is double what I'm currently packed into in a portion of my 6,000 foot building now. Once that is up and running it saves me 35 minutes driving each way into work and I can take my time for the BIG addition that will also have an upstairs apartment for my inlaws and other guests. Fortunately their end won't be above my machine shop, just above the warehouse area and NON loud equipment that I don't use a lot~

My parts can run up to 8 hours per setup so my limiting factor is driving time since no one wants to drive an hour and ten minutes to do a 45 minute setup and then babysit the machine all day. At least at home I can watch it via a camera on my iPhone and just zip out and change a cutter if needed. Plus since my kids are little it lets us play on our property a whole lot more!

Do you have a rough idea of the horsepower your little engine will produce at a realistic engine RPM where it should actually last quite awhile? What CNC lathe do you have? Is that a wire EDM against the wall? Lucky!

[cforcht]

power estimate is unknown. there are so many factors it would easier to throw darts in the dark. My lathe is a Mori Seiki SL-15 with live tooling. yes that is a wire edm Mitsubishi DWC-200H. in fact just got it fixed this weekend when the service guy came. he had another EDM machine he was going to scrap so I bought the entire control from it, for pennies on the dollar. mine had a bad com board from a lightning strike we had. Of course I didnt know what was wrong with it other than it was probably a bad board. Mitsubishi wanted me to "register" my machine for $1500.00 before they would even talk to me for tech support. needless to say it will be the first and last Mits machine I ever buy. going to stick with Fanuc from here on out.

[dynosor]

power estimate is unknown.

Ponder this estimate:

IC engines are just air pumps. The more air an engine can pump the more fuel it can burn and the more power it can produce - the air fuel mixture matters only a little in this equation, driving probably not more than a 10% peak power difference because the operating mixture range is pretty narrow, from flaming out either too lean to too rich. Chiefly, a rich mixture is used wide open because it runs cooler, allowing more ignition advance to produce more torque and power. With a turbo or supercharged engine this cooling effect may allow more additional power than 10% because it allows more boost.

As such, if we take Craig's model engine and assume the displacement is 95 CC (from memory) we can ballpark the power by looking at full size V8s. The 5 and 6.2 liter Ford F150 truck V8s are rated at 360 and 411 hp respectively at 5500 RPM.

If Craig's engine is running on the same fuel at the same compression ratio (thermal efficiency), the same valve timing and proportional porting and resultant gas flow (volumetric efficiency) and the same proportional friction (mechanical efficiency), then you can simply scale the peak power according to displacement at a given RPM:

Based on these generous assumptions, engines with 90, 95 or 100 CC displacements should produce 6.2, 6.6, or 6.9 hp at 5500 RPM. At 8000 RPM this would scale to 9.1, 9.6 or 10.1 hp. [The reason I bracket the displacement is because I don't know if 95 CC is correct for Craig's engine and I don't feel like searching for that post right now ]

In practice, model engines can rev much higher than full size engines due to their shorter stroke length and as such, may produce more peak power per CC. Then again, achieving low friction and equal volumetric efficiency is not trivial for the home builder. Now, at least one of Craig's engines is supercharged, so it may even be possible to exceed the above figures on the right fuel, otherwise you may need to de-rate them to somewhere in the range of 50 to 75% of the numbers given above...

Hope this rambling serves as fuel for thought.

[cforcht]

Dyno,
not surprised you jumped in here. glad to hear from you. one thing to note. the big reason small engines can rev higher is less reciprocating mass than its larger counterparts. the bigger ones tend to dis-assemble themselves at high RPM's unless special care is given to balancing. your recollection is correct, it is 95cc and both are supercharged. port and valve size are probably a little bigger in relation to the full size engines. so volumetric efficiency should be the same if not better. compression ratio is the same. if not a smidge higher. although I may need to cut the pistons for valve clearance. more power can be had if you were to overdrive the blower more. but there are hazards to that like blowing the supercharger or heads off the engine. or breaking the rotating assy of the engine. but that typically doesnt happen unless you really wind it up.

[cforcht]

heres a couple pics
lower end assembled on both engines now.




valve covers engraved with heartbeat logo





lifter bushings have been installed. you can see the head porting and the top side of the heads with the valves in.