Two Stroke Mini Bike

[Desertduler]

I wish I could think like that.
All your stuff is so simple yet so Advanced from other parts most of us use.

Well like the saying goes (necessity is the mother of invention) I needed to come up with a way to start this engine (bump start) because I did away with the gigantic blower housing, cooling fan and recoil starter assembly in order to make this engine physically smaller and this was the easiest and most simplest way that I could come up with to start the engine, I have another way also but I have to do a little testing first to see if it works before I deem it effective, we will see as I have other test engines of this same type and if it works it will be like nothing you have ever seen maybe.

 

[Desertduler]

Bonanza 215 Mini Bike frame is on it's way to my front door.

 

[Desertduler]

Here are the crankcase halves with the worthless voids filled with JB Weld, the crankcase volume has been reduced quite a lot just by filling these useless areas.

 

[itsid]

Okay.. first.. you know what you're doing and I am NOT questioning that.

Just something I cannot wrap my head around:

Why would anyone overcomplicate a cast (or mold for that matter)
when the voids do not serve any purpose..
sure a "decorative intention"... but not INSIDE a crankcase, not inside a german crankcase for sure.
And while I see that the upper voids are there to ease tapping the threads for the studs..
The inner ring *shrugs*
I can't imagine it's purpose, I hope you do;
since if it had a purpose (and I'm nearly certain it had one)
it's now gone of course; and all I can do is hope it wasn't critical
[and wait for you to enlighten me... yet again ]

'sid

 

[Desertduler]

Okay.. first.. you know what you're doing and I am NOT questioning that.

Just something I cannot wrap my head around:

Why would anyone overcomplicate a cast (or mold for that matter)
when the voids do not serve any purpose..
sure a "decorative intention"... but not INSIDE a crankcase, not inside a german crankcase for sure.
And while I see that the upper voids are there to ease tapping the threads for the studs..
The inner ring *shrugs*
I can't imagine it's purpose, I hope you do;
since if it had a purpose (and I'm nearly certain it had one)
it's now gone of course; and all I can do is hope it wasn't critical
[and wait for you to enlighten me... yet again ]

'sid

This engine was designed to be a stationary industrial engine without a great deal of high performance in mind, the open areas around the cylinder base studs do serve a purpose as you say as they are open to the cylinder base studs and this would aid in the relief of metal chips during the drilling and threading in this location and that is all.
The magneto side main bearing is some what of a distance from the counterweight on this engine hence the deep webbing and space outwards supporting the magneto side bearing therefore shortening the overhang of the crankshaft which the flywheel is attached and that is why there is deep webbing in that location of the crank case halve which strengthens the bearing bore and that is all. These open voids increase the volume of the crankcase and they reduce the compression ratio in the crankcase, yes two stroke engines crankcase compression ratios do matter too low of crankcase compression can cause poor scavenging at certain RPM ranges and too high of a crankcase compression ratio can cause over spilling of the incoming charge out the exhaust port at certain RPM ranges, the old two stroke engines had low technology compared to modern day two strokes and every little bit that one can do to modify them in the right direction helps as this engine is from the late 60's, study two stoke engines and you will find out just how complicated these so called simple engines are and maybe you will be able to wrap your head around to what I am doing here as this is nothing new to two stroke engine tuning as there is a science behind this stuff I am not just doing it just because. Spend many hours messing with these things and they will teach you about how wrong you can be and what things really work and why. As far as engine preference goes if you pay attention to all of my engines I use on my builds and the motorcycles I race are either from Germany or Austria as European engines are my favorite for many reasons.
Do you still have a Rotax two stroke? if you do tear it down and look at every little detail that you may question and find out how and why and you might be amazed.

---------- Post added at 10:36 PM ---------- Previous post was at 10:08 PM ----------

And just as a brain teaser just for sh-ts and giggles if I want to simulate how this engine would have ran before I filled these voids after I have it running and tested then how could I test the original crankcase compression ratio without tearing it all back down and removing all of the JB Weld, how could I simulate the original crankcase volume and test run the engine? I have before just because many times.

 

[chancer]

Thanks for the explanation. Since I DO NOT know about 2 strokes. I did a little looking on line, and found mixed reviews about "increasing crank case pressure, Bottom line was just what you said. This is an older engine, the new ones they have already perfected. And I believe you have "piston port, not reed valves, which (reeds) would become a problem at high RPMs with excessive CC pressure.
You also mentioned the differences (pros and cons) at different RPMs. From what I learned in 20 minutes, It sounds like you do know exactly what you are doing.

 

[Desertduler]

Thanks for the explanation. Since I DO NOT know about 2 strokes. I did a little looking on line, and found mixed reviews about "increasing crank case pressure, Bottom line was just what you said. This is an older engine, the new ones they have already perfected. And I believe you have "piston port, not reed valves, which (reeds) would become a problem at high RPMs with excessive CC pressure.
You also mentioned the differences (pros and cons) at different RPMs. From what I learned in 20 minutes, It sounds like you do know exactly what you are doing.

You are right, this is a piston ported engine and too much crankcase compression ratio with reed valves and rotary valves can cause a number of problems including pumping losses at high RPM and over spilling of the intake charge. This is going to be a low RPM engine with put put power.

 

[chancer]

That makes sense, How fast do you really wanna go on a minibike, But the low end power wheelies.

 

[itsid]

The magneto side main bearing is some what of a distance from the counterweight on this engine hence the deep webbing and space outwards supporting the magneto side bearing therefore shortening the overhang of the crankshaft...

Ahhh, that's the info I was missing.. Now it makes sense.
Thanks buddy

I wasn't actually concerned about the compression ratio too much,
more about heat dissipation (or material expansion and stuff like that)
that as you put it was just less material and increased support ..
so yeah.

as for your brain teaser..
that maybe

knowing the amount of JB weld in place (which you likely do) that is

'sid

 

[Desertduler]

Ahhh, that's the info I was missing.. Now it makes sense.
Thanks buddy

I wasn't actually concerned about the compression ratio too much,
more about heat dissipation (or material expansion and stuff like that)
that as you put it was just less material and increased support ..
so yeah.

as for your brain teaser..
that maybe
View attachment 68187
knowing the amount of JB weld in place (which you likely do) that is

'sid

You are indeed smart! By adding a coiled length of impulse hose that has the same inside displacement as the material that was used to reduce the compression ratio in the crankcase one can simulate the crankcase compression ratio as it was, see that brain teaser made you use your brain and you figured it out, you got it!

 

[Desertduler]

The Bonanza 215 Mini Bike frame arrived today, I am real happy with the quality of the workmanship of this frame, I am going to have to mill the base of the engine crankcase base mounts down a little in order to get this engine inside the frame which I anticipated I might have to do which is an easy task on the mill. These pictures are just a rough idea to where I will mount the engine and I just may run the exhaust between the front frame down tubes and make an old school down pipe expansion chamber for this mini. I have different options which I will play with later as I am recovering from surgery.

 

[chancer]

Glad to see you here. Sounds like the surgery went Normal enough. Hope all continues well!

 

[Desertduler]

Glad to see you here. Sounds like the surgery went Normal enough. Hope all continues well!

Thanks! I have five holes in me where the Doctor repaired my Hiatal Hernia, he must of knew what he was doing because I feel good enough not to have to take any pain meds which I hate!

 

[landuse]

Thanks! I have five holes in me where the Doctor repaired my Hiatal Hernia, he must of knew what he was doing because I feel good enough not to have to take any pain meds which I hate!

I had a Hiatus hernia op about 10 years ago. The worst part was that i couldn't eat solid food for 2 weeks. I lost quite a lot of weight. Making smoothies out of every type of food gets a bit gross after a while

 

[Desertduler]

I had a Hiatus hernia op about 10 years ago. The worst part was that i couldn't eat solid food for 2 weeks. I lost quite a lot of weight. Making smoothies out of every type of food gets a bit gross after a while

I hear you, I am on a clear liquid diet for one more day and then I move on to creamed soups,yogurt,pudding,etc,then mushy foods or anything that I can pour, I have lost weight already and I know that I will lose more, I am not supposed to lift anything over 10 lbs for six weeks which is a bummer for me because I normally hit the gym 6 days a week.
I will get over this and resume it is just going to take time which will be forgotten in a while.

 

[landuse]

I hear you, I am on a clear liquid diet for one more day and then I move on to creamed soups,yogurt,pudding,etc,then mushy foods or anything that I can pour, I have lost weight already and I know that I will lose more, I am not supposed to lift anything over 10 lbs for six weeks which is a bummer for me because I normally hit the gym 6 days a week.
I will get over this and resume it is just going to take time which will be forgotten in a while.

Yup, it is soon forgotten. All i wanted was to eat a steak, and when i eventually did....it wasn't what i had made it all out to be .

I used one of those stick blenders to blend all my food. You can have a 3 course meal all in one cup

 

[Desertduler]

That looks horrible! Lol, just close your eyes and swallow huh?

 

[Desertduler]

I cut out the original engine mount (which I still will use after modifying it) and it will sit about the height of these nylon blocks that I have placed under the engine base mounts, I will not have to mill down the engine mount base on the crankcase like I thought I would. This is what a modified Sachs SA290 looks like in a Bonanza 215 frame.

 

[karl]

That is the most awesome thing ive seen in awhile.

 

[itsid]

one thing I know..
that thing should not see paint (clear coat yes.. color.. NOPE!).

Another thing I wonder..
have you thought about tilting the engine forward a bit?
I mean that'd look mean, wouldn't it?
Well maybe not till it's flush with the lower tubes, but maybe -what?- half way??

'sid