60cc 2 Stroke Gas Crankshaft Design and Materials

[PatrickM]

Hello Folks,

I'm an RC airplane guy who has a mini machine shop and have always
toyed with the idea of creating my own gas engines for RC use in my
airplanes.

I'm getting ready to start my first project, here's what I've got going
on at this point:

I've got a 2 stroke engine, basically everything I need except the
crankshaft and crankcase. So I need to design and build them myself.

Now, before a bunch of people go nuts about this, please let me explain
what's going on here.

I'm doing this on purpose! I'm doing it for the learning experience and for
the enjoyment of doing it myself. That's all! Just for the fun of it!

So what I've got is a 60cc gas engine that needs a crankshaft and a
crankcase. The crankcase is the easy part, and I've pretty much got that
all designed. In fact, I've got the crankshaft designed for the most part,
but what I need to know is:

1) What type of steel should I be using for the crankshaft?
Will run up to about 12,000 RPM max, shooting for 8500-9500
actual in use RPM.

2) Do I need to heat treat the crankshaft after turning at some point?

3) What's the proper way (for the home builder/designer) to balance a
crankshaft?

4) I will be machining the crankcase out of 6061 aluminum.

5) and any other info I am over-looking!

Once I have all of this worked out and have a reliable running engine, then
the fun part starts! Then I take the other 60cc cylinder/piston/rod I have
and combined them to make a twin cylinder engine!

Anyway, if this is the wrong forum for this, please let me know what forum
I should be in.

I look forward to any and all help the experienced engine builders out
there might want to share with me.

I will post pictures once the project gets under way.

Thanks,
Patrick

 

[canadianhorsepower]

1) What type of steel should I be using for the crankshaft?
Will run up to about 12,000 RPM max, shooting for 8500-9500
actual in use RPM.

do you have bore and stroke from original manufacturer?
were did that cylinder came from "chain saw weed eater ??"

[quote3) What's the proper way (for the home builder/designer) to balance a
crankshaft?
][/quote]

I have an article somewhere you can use I'll try to find it

Once I have all of this worked out and have a reliable running engine, then
the fun part starts! Then I take the other 60cc cylinder/piston/rod I have
and combined them to make a twin cylinder engine

I don't know what your machining experience is but personally I would do the twin right from the beginning. fabricating a single crank or a double is almost the same. But the research for seal, bearing, and everything else might require you start from the beginning again

good luck

 

[PatrickM]

Hi Luc,

do you have bore and stroke from original manufacturer?
were did that cylinder came from "chain saw weed eater ??"

Bore is: 45mm, stroke is: 37mm

Yes, they're originally chainsaw engines.

I have an article somewhere you can use I'll try to find it

That would be great, I would appreciate that.

I don't know what your machining experience is but personally I would do the twin right from the beginning. fabricating a single crank or a double is almost the same. But the research for seal, bearing, and everything else might require you start from the beginning again

Actually, I have 4 of these engines. I'm going to use two of them as they
are (as singles), and then will figure out how to combine two of them to
make a twin engine a little later on for a giant scale Pitts I have.

Just thought it would be easier doing the single cylinders now and getting
them out of the way and flying and getting the experience.

Thanks,
Patrick

 

[canadianhorsepower]

Bore is: 45mm, stroke is: 37mm

Yes, they're originally chainsaw engines

what brand? or model?

Actually, I have 4 of these engines. I'm going to use two of them as they
are (as singles), and then will figure out how to combine two of them to
make a twin engine a little later on for a giant scale Pitts I have.

Just thought it would be easier doing the single cylinders now and getting
them out of the way and flying and getting the experience.

having 4 of them make your life easier in one way. You already have measurement, and bolt pattern for your crankcase and crankshaft to work with. At this stage I would suggest you to simply use the crank that you have now on the clutch side leaving enough space for the bearing having a closed case on this side would be one less seal to worry about.
The other side simply machine them to fit your desire
I can tell you by experience that they are stiff as hell and would suggest you use a grinder for the first part of the machining
or if you have a 30 ton press and want to build a jig you can un press it

On this forum their is an excellent ignition system circuit you
could use to replace the original one.
59 cc sound a bit awkward for a good performer chainsaw motor

I'm actually in the process of retrofitting a partner r420 motor in my
RC Baja truck with nitrous and 2 boost bottle:fan:

 

[PatrickM]

what brand? or model?



having 4 of them make your life easier in one way. You already have measurement, and bolt pattern for your crankcase and crankshaft to work with. At this stage I would suggest you to simply use the crank that you have now on the clutch side leaving enough space for the bearing having a closed case on this side would be one less seal to worry about.
The other side simply machine them to fit your desire
I can tell you by experience that they are stiff as hell and would suggest you use a grinder for the first part of the machining
or if you have a 30 ton press and want to build a jig you can un press it

On this forum their is an excellent ignition system circuit you
could use to replace the original one.
59 cc sound a bit awkward for a good performer chainsaw motor

I'm actually in the process of retrofitting a partner r420 motor in my
RC Baja truck with nitrous and 2 boost bottle:fan:

Well, thank god in RC airplanes we don't have to worry about clutches!
Put a prop right on end of a crankshaft and go flying.

I guess the experience I was looking for was to create my own
crankshafts, and learn from the experience. If I go using the cranks that's
already there, I'll lose out on that experience. Just wondering what is the
best metal to use to create crankshafts from? 1018, 12L14, 4130, 4140,
stainless?

One day I want to build a 7 or 9 cylinder radial engine, and would like the
experience on these other engines to learn from.

As for the engines themselves, they are actually classified as 58cc
engines, and they're cheap Chinese jobs to learn and burn with. Once I
know what I'm doing and have it down to at least rough science, then
I will start converting all of my Sachs Dolmar engines I have on hand. But
I'm not going to go screwing up a bunch of high quality, very expensive,
German engines as a learning process.

Thanks for the help.

Patrick

 

[canadianhorsepower]

As for the engines themselves, they are actually classified as 58cc
engines, and they're cheap Chinese jobs to learn and burn with. Once I
know what I'm doing and have it down to at least rough science

Hey Patrick
I have enough experience with 2 stroke chainsaw
motor to have a world title at Boonville 24 years ago.
All I can say at this time I prefer to retract from this forum
just in case I would be badly stated And you would crash your plane
and here is why

cylinder porting, scavenging, and tuning including comp ratio and primary compression and more will produce an EXCELLENT ENGINE

on a chain saw if you don't have enough power torque or whatever you want to call it you will accommodate your technique with it

on a RC airplane not enough power is the best way to have memory of
all the work you did.

I would strongly advise you to try to get that motor assembly your planning to use and get it to whip a blade at 8500 rpm
you might re-think your project

 

[Lakc]

Well, thank god in RC airplanes we don't have to worry about clutches!
Put a prop right on end of a crankshaft and go flying.

Dont go all too crazy trying to make the crankshaft light, that clutch is part of the flywheel effect, which props are not very good at. Mass=inertia=ability to idle, start, and run at a reasonable rpm.

I guess the experience I was looking for was to create my own
crankshafts, and learn from the experience. If I go using the cranks that's
already there, I'll lose out on that experience. Just wondering what is the
best metal to use to create crankshafts from? 1018, 12L14, 4130, 4140,
stainless?

If you have your choice, try 1144, aka stress-proof. The 41 series makes great crankshafts but if you dont have a way to normalize, or stress relive them, they will move on their own as you remove metal from the bar.

 

[PatrickM]

Hey Patrick
I have enough experience with 2 stroke chainsaw
motor to have a world title at Boonville 24 years ago.
All I can say at this time I prefer to retract from this forum
just in case I would be badly stated And you would crash your plane
and here is why

cylinder porting, scavenging, and tuning including comp ratio and primary compression and more will produce an EXCELLENT ENGINE

on a chain saw if you don't have enough power torque or whatever you want to call it you will accommodate your technique with it

on a RC airplane not enough power is the best way to have memory of
all the work you did.

I would strongly advise you to try to get that motor assembly your planning to use and get it to whip a blade at 8500 rpm
you might re-think your project

Hmmm, not sure what you're saying here. But, I've been flying RC planes
for well over 30 years, and have converted many, many (more than I can
remember) chainsaw engines for RC aircraft use, and have yet to ever
have a problem.

The only reason I come to this forum is to learn about actually creating
the working parts myself, and I thought that's what this forum was all
about!

So, if there is anyone here at the forum who can name the proper steel
for turning out crankshafts, I would appreciate it.

Thanks,
Patrick

 

[Lakc]

I think you missed a post there Patrick.

 

[PatrickM]

Dont go all too crazy trying to make the crankshaft light, that clutch is part of the flywheel effect, which props are not very good at. Mass=inertia=ability to idle, start, and run at a reasonable rpm.


If you have your choice, try 1144, aka stress-proof. The 41 series makes great crankshafts but if you dont have a way to normalize, or stress relive them, they will move on their own as you remove metal from the bar.

OK great! 1144 I can work with!

As for the clutch and flywheel, we in the RC aircraft hobby do away
with those all the time, have for many years now, and have never had a
problem. We also understand that once the engine is started, everyone
stays behind the prop and not in front of it.

Believe me, we've been doing this for years, and if you do a search in
that hobby, you will find tens of thousands of converted chainsaw
engines running all day long and twice on Sunday with only a prop
attached to the crankshaft end and spinning that wood at 8500+ RPM.
Some guys will even run tuned pipes and twist them puppies over 12,000!

There was a company years ago called A&M and they converted Sachs
chainsaw engines for RC aircraft use. They are the only company I ever
heard of having any problems with braking crankshafts, and that's
because that had a design flaw in their own crankshafts. Their cranks
would brake on impact on a ground strike but I never heard of anyone
getting hurt from such things.

Yes there has been guys who screw around and get themselves hurt,
but it's not because of any fault of the engines.

Anyway, I've been doing this for years, I take every precaution, and I
totally understand there are dangers involved. But I like to think that
I have enough respect for that danger that it speaks to me never being
hurt in those 30 years I've been doing this.

Anyway, thanks for the info, I appreciate it.

 

[PatrickM]

strange enough your asking for our opinion
and we are all wrong

don't ask our input build your stuff and show us how it's done:hDe:

Sorry, but I'm not understanding you.

I asked what was the proper steel to turn crankshafts from. You chose
not to tell me for some strange reason. Now I'm the bad guy? I don't get
it.

Whatever, I joined the wrong forum I guess.

Later.

 

[mu38&Bg#]

I'd machine the crank and webs from 4xxx prehard and design it to be pressed together using some type of purchased hardened ground pins for crank pins. Press fits still need tight tolerance and good surface finish. If you decide to make the pins verify the hardness required of the needle bearing journal, 53-57HRc rings a bell. Guys have simply welded two cranks together for opposed twins. A one piece crank for a twin doesn't allow using the existing rods.

 

[Lawijt]

Why you don't build a turbine...And then you build a turboprop. Sounds much better than a petrol engine.

 

[canadianhorsepower]

Sorry, but I'm not understanding you.

I asked what was the proper steel to turn crankshafts from. You chose
not to tell me for some strange reason. Now I'm the bad guy? I don't get
it.

Whatever, I joined the wrong forum I guess.

Later.

I will try to make more sense. all I was trying to do is give MY WAY of doing it. I was asking a lot of question so I could give the best possible answer to your question. I didn't feel comfortable giving a suggestion. Dieselpilot gave you an answer, 4xxxx. Those X means variable and let you decide of the final digit. I don't doubt your knowledge and experience and sure you will succeed
this link could be useful
http://www.mckinnonmetals.com/products.cfm

 

[mu38&Bg#]

http://www.popularhotrodding.com/tech/0710phr_crankshaft_tech/viewall.html

Keep in mind how you'll get the rods onto the crank and the fact that you'll be running needle bearings on the crank journals. The above link is only a reference for the strength of materials used in cranks. Automotive engines have caps on the rods and hydrodynamic bearings. That fourstroke boxer design will be of limited help.

Building it once would be great but even the big guys get it wrong sometimes. [ame]http://www.youtube.com/watch?v=vHHdhbAJxT8[/ame]

Here is some inspiration.

[ame]http://www.youtube.com/watch?v=YF4Mofe6ltY[/ame]

 

[lohring]

A lot of good information on a racing 15 cc engine is available on Jim Allen's gallery. (requires log in) The stresses on your larger but lower speed and power engine probably would be similar. The overhung crankshaft design used in smaller model engines is easier to build than the more common two sided variety. It will work in large engines if you make things heavy enough. Do you have a roller bearing connecting rod big end? If so a reamer blank comes hardened and ready to be cut to length and pressed into the crank web for the crank pin. You need to find a size that fits the needle bearing and that could be a problem. Jim uses S-7 heat treated for the rest of the crankshaft, but any heat treated steel like 4340 would work. The crank pin is the critical part. A full circle crank web is easy to make. Just drill a series of holes and plug the top (crank pin side) ones with aluminum and the bottom ones with tungsten. The pictures below will give you some idea of where to start. Note the sealing bushing in the second picture. This is carefully shimmed to length to set the correct bearing play when the thrust washer or flywheel is tightened on its split collar.

Lohring Miller

 

[///]

Whatever, I joined the wrong forum I guess.

Later.

I think the helpful posts are too late guys, sounds very much like Patrick is out of here.
Luc's winning personality at work again.

 

[canadianhorsepower]

I think the helpful posts are too late guys, sounds very much like Patrick is out of here.
Luc's winning personality at work again.

Instead of blasting me off, do me a favor and read post 14
I'm trying to do my best here you can also read this
cheers

http://www.homemodelenginemachinist.com/f16/apology-21067/