Broken Wings

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I needed a new connecting rod for a OS Max H-80 that I found on *bay and figured it may be of interesting for others to see how it was made.

I use a program called Mastercam to draw and make the necessary tool paths used to cut out the part.

The old rod was “reverse engineered” which is a buzz word for “knock-off”… I drew the model of the connecting rod and positioned it on the computer screen in the same orientation that I would be holding the part in the vice.

I picked out the necessary cutting tools required to cut it out and started to make the tool paths. You can see the path in the first picture.

In this case I used a;

3/8 flat endmill to face the top surface of the stock.
¼ inch bull mill with a .0625 corner radius to machine around the wrist pin and crank journal bosses.
1/8 center drill
Letter P .323 drill for the small end.
27/64 drill for the big end
¼ inch endmill to machine the periphery and circle mill the holes to final size.

You can see the result in the final rendering.

rainedave

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This is really awesome! Fantastic work!

Is there any chance you would make one for the old OS .60? or, other old engines?

David

Broken Wings

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There is a new rod on *bay for that engine, about $15 bucks

Broken Wings

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Here is a shot of the new rod vs the old one.

The early H-80's use a needle bearing on the big end of the connecting rod and a two ring piston. I found a late model piston and machined an extra piston ring groove.

LeeHop

John - how did you remove the part from the billet?
Just curious - Lee

Broken Wings

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I walked over to the band saw and lopped it off of the rest of the billet…smiles

Both of the journal surfaces or “Ends” are the same thickness on this rod so I just flipped it over on parallels and used a couple small set-up blocks to hold the rod in the vice. I used the same program and edited out the tools that I didn’t need to do the other side, drills, ¼” periphery cutter, etc.

I indicated the small hole and ran the program again, it machined the top surface and the narrow indention or center section of the rod. After the program ran I measured the thickness and adjusted the “Z” offset in the control so it would cut it at the thickness that I wanted. Mashed the button on the control and ran the same program again. Done…

If you look at the tool path you can see the same tool marks on the new rod. The guy that made the OS rod used a much larger cutter, probably made a hundred at a time.

I made this rod out of 7075 aluminum and used bearing bronze for the small end. I used Gage pins to measure everything and turned the bronze bushing on the lathe and pressed it in. The large end gets a new needle bearing.

I work as a tool maker in a R&D lab.

Broken Wings

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Yes, I could make them if you have the old one that I can copy.

jeffie8696

Great work. I myself needed a custom part to fix my old K& B sportster and ended up machining new nuts for the new head studs. I replaced the head bolts because one was stripped in the block. Easy project . used 1/4" drill rod tapped and slotted so I can tighten the new nuts with a screwdriver. Still having trouble keeping the stud in the block, there just wasn'e enough thread to keep it in there despite the red threadlocker then JB weld. I will be drilling the case for a cross pin, probably 2. That should hold it. Why all this trouble. A new case costs $38.00 plus shipping (outragous no doubt) and I achieved this for about $3.00 . [sm=lol.gif] And it is very satisfying.

Broken Wings

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What size was the tapped hole? I'll look for a roll tap for you. Sometimes they can be used to form a little more thread as they don't cut any material.

I agree, its very satisfying and a hobby itself. Just ask Flyboy Dave...Smiles

jeffie8696

Thank you for the offer but the tapped hole is no longer tapped by any stretch of the imaginination.
K&B used the 6-40 size which wa a challenge in itself. I did end up buying a die but I do not consider that into the price since I only paid 5 bucks for it on FeeBay and I still have it till it wears out or I sell it on FleaBay. My frind Mike is a master machininst and even has his own CNC mill in his garage at home (insert green with envy smiley here). Mike was a huge help getting the custom nuts made and he knocked them out on his lathe at home (insert next green envy smiley here) in a matter of minutes. But I did design them in my head so I will take credit for that one [sm=49_49.gif]. After being stripped out for about 80% of the lenth of the thread then studded t to bottom and the rest pulled out even with red locktite then JB Weld pulling out the remainder, well............. I have been considered it a challenge to do it on my own without the use of fancy equipment . All I have access to is my dads old drill press and I am going to make it work! [>:]. I think if I drill it offset just to catch about 1/32" of the side of the stud in 2 places far enough apart to not compromise the strength too much I will be OK. If I miss a little I can run a small diameter tap into the hole and screw a bolt in . We are talking real shade tree mechanics here. As a last resort there is always the Tig welder . If I can ever get my friend kevin home long enough. [sm=lol.gif] It's good to have friends.

Harry Lagman

Nice work BW - Very impressive!

Thanks for the post.

Broken Wings

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This is the front bearing support of the H-80. I modeled an “ear” on the front that will allow me to run a Hall sensor/trigger so I can fool around with spark ignition on this engine.

I guess what I’m trying to convey is that it’s not that difficult when you have the right software. Mastercam is expensive if you buy the full blown CADD/CAM package but they “Mastercam” will sometimes give the “design” package away for free at tool shows. There is also a student version that will let you do everything except post process a tool path. (Make NC Code for a machine tool)

However, if you have the Mastercam file of any of the parts that you want to make you can send them to machine shop that uses this software and they can open any Mastercam file and run the tool paths to make your parts.

If you’re interested in doing this sort of thing buy the best software that you can afford. It makes all the difference in the world in how your parts come out.

jeffie8696

How about some pistons? Actually I am thinking of a way to expand a slightly worn piston to restore compression. I wonder if hydraulic pressure could be used on the inside to expand it ?