DIY CON RODS
 

Hey there you engine GURUS........

got a couple questions about making a nice rod.....on par with a Nelson, Jett or RPM rod. The application is .40 and under 2 strokes.

I understand the bushings are best made from leaded phosphor bronze.
B-544...[B2}....or 532, 534, 545

I've done some searching, even through the local Kaman bearing supplier and all I can find is wholesale, bulk type suppliers.

Anyone know who will sell me 2 foot worth of 3/8" round stock or maybe even tube?

Next question...the first rod I want to make has a .2185" crank pin and a .2035" wristpin. Where do I come up with the tooling to arrive at the final sized holes?

Finally, is the amount of crush of the bushing into the aluminum rod set by any standards to follow?

That's enough to chew on for now, I think. Thanks in advance.

RE: DIY CON RODS
 

CP,

For tooling (reamers), check out:
www.travers.com
www.use-enco.com
www.mscdirect.com
www.mcmaster-carr.com

They have decimal and metric hand reamers which should get you very close to your target. The above links will have some materials in stock, but there are many other small-quantity metal suppliers on the net. edit: I just checked McMaster - they have 3/8" diameter 544 bronze for about $12 a foot...

Yes, there is a magic number for "crush" or interference fits for bushings, but it escapes me at the moment. Maybe vicman or toad will catch this thread and chime in - lord knows they'll be much more knowledgeable than an amateur hack like me!:)

I highly recommend sitting down and reading Ron Chernich's Model Engineering and IC Engine Projects web site - especially his engine construction articles! You can find it here: www.modelenginenews.org

Anyhow, this should get ya started while others chime in...

RE: DIY CON RODS
 

http://www.mcmaster.com/#phosphor-bronze/=4zrfrz

RE: DIY CON RODS
 

Thanks you guys.........this is what I'd call "one stop shopping" for info!

RE: DIY CON RODS
 

Top secret info included in a pm[8D]

RE: DIY CON RODS
 

That just ain't right man.... ;)

RE: DIY CON RODS
 

I have a very good reason. ;)

RE: DIY CON RODS
 

Non top secret info is on the web.

http://www.go-cl.se/dye-rods.html

Rod bushings are usually honed to final size and crosshatch finish.

RE: DIY CON RODS
 

Don't use 2024. Pretty good link Greg. 7075 for the rod would be better.;)

RE: DIY CON RODS
 

CP...I might just have some 7075 bar stock kicking around here somewhere...
IIRC it was about 1.5" dia.

If you're interested, I will look around for it.

RE: DIY CON RODS
 

I have to assume you've looked up the strengths of both 2024 and 7075 at say 100°C and saw that 2024 is stronger;)

I can't find my source on that but did see that 7075 has a better fatigue strength at elevated temperatures. That would be good in a four stroke.

RE: DIY CON RODS
 

;)
I'm covered.

RE: DIY CON RODS
 

I would agree with Vicman, 100c is only 212F. At the temps the rod is likely to see, 7075 T651 has a higher tensil and would probably be a better choice, it's also a little harder than 2024. Just my opinion, I'm a novice on small engines, but not on aluminum.;)

Copper & Brass on 6th Ave in Seattle might be a good source for the bronze and aluminum you need.

RE: DIY CON RODS
 

Hone the bronze bushing can be a risk if used by untrained newbeginner. The grinding particles can be embedded in the bronze surface and make grinding contact with crankpin/wristpin...

The alternative are use the reamer or D-bit tool. Then running-in the engine will make fit adapted togheter.

The tolerance are not critical in the two stroke engine cause the bearing pressure in a direction are same place in whole time.

Aluminium are good to use until 15.000 rpm and above 15.000 use bearing bronze.

Do not use sintered bronze bearing who has oil inside to example used in electrical motor!
The bearing are not suitable for combustion engine as connecting rod bearing.

RE: DIY CON RODS
 

Out of curiosity have you tried both and observed any differences? The only real testing I've seen done was the stuff over at the international waters site. But he ended up with tool steel rod for what he was doing.

RE: DIY CON RODS
 

OK Ihave seen all aluminum alloys in the smaller engines rods that routinely turn up over 15,000. So a .15 size engine with a big togh all alloy rod would be a good choice in what material? And what about a .40 running upwards of 15,000? Hopefully it is moot since I have found out Ican buy inexpensive replacement rods for the Norvels that seem to have really weak rods.

RE: DIY CON RODS
 

Rpm range related to material are depending on bearing load. If the engine are a powerful hi reving engine, the aluminium con rod without bronze bearing will not last long time..

The engine used to run in moderate rpm and less load on bearing works well with con rod made of aluminium.

RE: DIY CON RODS
 

I've got all the bits and pieces lined up to make some rods now. What I have to work with is a lathe and a drill press with a cross slide vise.
I can also use a table saw as a dick sander .

Now, could someone please outline my order of operations.....a plan of attack?
I've never had to do any precision work before that had to have repeatable and predictable results, such as maintaining perfectly centered holes, working with home made bushings, etc.

This is the cast rod that I'll be duplicating.

RE: DIY CON RODS
 

I made the rod in the center for a OS H-80 engine. I use a program called Mastercam and a CNC milling machine to cut out the rod.

I used 7075 and bushed the small end with bronze. The large end uses a needle bearing.

With out a CNC machine it's going to be tough. :D

Here a link to the thread. http://www.rcuniverse.com/forum/m_72...tm.htm#7273524

RE: DIY CON RODS
 

What kind of bar stock are you using? Rectangle ? Round? It makes a difference in how you start.
If using round stock, the first thing you are going to have to do is mill a flat surface to drill the holes for the bushings and press them in. The lathe will not be much help unless you can clamp the part and use the cross feed like a milling machine with a mill bit chucked up in the lathe head.

If using rectangle stock, it's a little easier. Your first concern is centering and aligning the holes for the crank and wrist pin. Make sure your bar stock is square and has no twist, mark and drill the holes for a press fit for the bushings. Once the holes are complete, its just a matter of removing the matterial you don't need from the rod to get the shape and final dimensions you want. This would be easier with a vertical milling machine and small surface grinder. But if you're very carefull, you can do it with a drill press, milling bit, and a cross feed vise. The hardest part will be clamping your part at the angles you need and squaring the vise travel with the mill bit. Like I said earlier, I'm not a small engine expert, but I'm not a novice machinist either. Hope this helps.;)

RE: DIY CON RODS
 

Jerry, I'm using flat aluminum plate and I've got some bronze round stock.

I'd like a step by step out line of the key tasks involved. Not ever little detail, just the sequence of the key tasks.

RE: DIY CON RODS
 

Ok, so you're going to turn your own bushings out of the bronze round stock? Do you have a small boring bar or know how to make one? Or are you planning to just use a drill bit to get the I.D. in the bushings?

RE: DIY CON RODS
 

The way I machined the bushed end was to machine the inside diameter of the rod to the O.D. of the bushing. I turned down the bronze and pressed it into the rod then re-machined the hole to fit the wrist pin.
The overall "wall thickness" of the bronze will make it tough to press it in the rod without deforming it. You're better off pressing it in as a solid pin and machining out the hole to fit the wrist pin leaving a thin bushing behind.

Just my opinion...

RE: DIY CON RODS
 

One reason I asked how he plans to get the I.D. in the bushings is the dimensions he said he needed for the crank and wrist pin and the tools he has availible. If he has drill bits that will give him the correct I.D.s, then pressing them in as a solid piece and drilling the I.D. will be best. If not, then he will need to use the lathe to bore out the I.D., then turn the O.D. to match the hole he has drilled in the rod end, and use a brass or wood mandrel to help press the bushing into the rod without deforming it.

RE: DIY CON RODS
 

What kind of tools do you have available?