View Full Version : grinder crankshaft

06-19-2005, 07:20 AM
where can find a mini grinder machine to build small crankhaft for OS engine?

because i need longer crankshaft for my model helicopter...


06-19-2005, 09:09 AM
It would be easier to buy a new one from OS.

And then get some lessons. http://bbs.homeshopmachinist.net//biggrin.gif


06-19-2005, 12:06 PM
original one is 6mm shorter!
meaning i need one longer then original,

any idea?


06-19-2005, 02:54 PM
Should be able to make one in a lathe, turn and then polish the journals.

06-19-2005, 03:07 PM
Making small crankshafts by a homeshop machinist is a common project. It is done in a standard metal lathe equiped with 4 jaw independent chuck. Using the independent jaws (that is each jaw is tightened seperately) one can with care acchive extreme accuracy in ofsetting the shaft to machine the throw. Then if he has a tool post grinder ( most people don't ) the final few thousands or tenths of thou is ground off for perfect tolerance. Lacking a motorized toolpost grinder to do the finishing ( some use dremel type tools or die grinders clamped in the tool post for this) the final finish can be acchived by lapping or honing.

J Tiers
06-19-2005, 08:42 PM
Even if you DO have a TPG, it can be a problem, depending on the diameter of the grinder wheel. Might not reach in.

The wheel housing often must be removed to get in there also, which might be a safety issue, especially reaching in with a thin wheel next to the throws.

06-20-2005, 09:20 AM
"Making small crankshafts by a homeshop machinist is a common project."
ok, i will start for this project with my Sherline lathe, and which steel is good enough for that 2.1p 50 class engine?

and is it difficult to balance weight?


i'm a newbie

06-20-2005, 10:08 AM
The crankshafts for these engines are highly stressed. These are real "working" engines as opposed to a model engine that merely has to just run.

If you have taken your engine apart you will see that the crank in that thing is very nicely machined or ground to very close tolerances and although you can't see it, heat treated. Kinda sophisticated work for the average HSM. But not impossible.

Another point that you have brought up is the balancing. A single cylinder engine is not "perfectly" balanced. You will notice a counterwieght on it. I'm not sure of the exact number but they are generally brought to 80% of balance. This is to counteract the magnified weight of the piston and rod comeing down on the power stroke. You will need a fixture for the crank to rotate in and a degree wheel, etc.

As for the steel to use I would not know exactly, some kind of heat treatable tool steel I would think.

Have you exhausted all your other options? Such as an extension of some kind? Or is there an optional set of mounts that would put your engine in a differant place?

Actually if where mine I would look for another engine, one that manufacturer has recommended to fit.

One other note. I have seen some of these engines with a replaceable stud screwed into the end of the crank. If yours does, you could easily get a longer one or make one on your Sherline.

The bottom line is, if you want to try it, go for it. It would make an interesting project, and your Sherline would be a good machine to do it on. Good luck.

I apologize for my smart remark earlier. I put the words "model helicopter" and "crankshaft" together and assummed the usuall.


06-20-2005, 08:48 PM
THe new HSM came today with an article by George Genevro called "Build the Crusader .60"
In the material list, the crankshaft is listed as "steel UNS G10180" . But the article is part one, and building the crankshaft is in part two. There have been other model airplane engine articles, maybe one of those would give you some ideas on what is needed. Try an article search.

06-20-2005, 10:25 PM
thanks everybody,
i know that is not a easy job for newbie, and i know that easy way is just buy a new motor...

but i know here many people can make engine and any metal work...

http://us.f1.yahoofs.com/groups/g_1257299/CRANKSHAFT1.jpg?bcbM4tCB7R79KCOE" width="648" height="460">

anyway, i really want to use my engine for that heli.


06-20-2005, 10:27 PM
sorry, post again

[This message has been edited by ACME (edited 06-20-2005).]