Rotax 277 piston port to reed valve conversion

[Desertduler]

Here is my Rotax 277 on my kart that I am going to convert from piston port induction to reed valve induction.I will be posting here in this section the process that I am taking to do this conversion and my end results.Here one can see one of the reed cages that I am going to experiment with and I have others of the same configuration and I will be cutting windows in pistons in order to get the 180 degrees of intake that I need and this modification will give my engine the low end power that it lacks in being a piston port induction and the power band will be wider and will be more useful with one gear ratio that I am using.

 

[Doc Sprocket]

Your work continues to amaze me. I'll stay tuned.

 

[rmm727]

Same here. This is an area I have little knowledge in and look forward to what you post up.

 

[itsid]

Thanks Bret..
I'm definitely going to follow this.

Good luck (as if you need it )

'sid

 

[machinist@large]

I know just enough to know just how little I know about what you're planning to do...... I've done a lot of hydraulic cylinder work, but I.C. ?????

Brett, here's where I have to bow in respect in advance...... Pat.

 

[Desertduler]

Can we really get 180 degrees of intake duration by reed valving an engine?
The answer is yes sometimes,how can that be? We will look into how and why.
And thank you for the kind words gentlemen!

 

[Poboy kartman]

 

[Desertduler]

Here I am milling the windows in my 277's piston,I will finish dressing the windows and the rest of the piston.Here is a shot down the intake port showing the widows in the port.

 

[Poboy kartman]

Now....one question.....seeing that 2 strokes are basically high revving engines...and you are removing material from the piston......have you given any thought to balance.....and how to calculate counterweight material removal????? Or do you think this is a non-issue? ???

 

[Desertduler]

Now....one question.....seeing that 2 strokes are basically high revving engines...and you are removing material from the piston......have you given any thought to balance.....and how to calculate counterweight material removal????? Or do you think this is a non-issue? ???

It might just shift the harmonics to a slightly different RPM.This is not my first reed valve conversion and the ones that I have done have all turned out great.Sometimes a lighter piston depending on the counterweight balance the engine winds up with less vibration.I will let you know for sure.If indeed it winds up being an issue I can split the case and balance the crank as needed.Check this info out.
http://juicemotoparts.com/crankbalancing

 

[Poboy kartman]

That's pretty cool.....and I learned something......thanks! !!!!

 

[Desertduler]

That's pretty cool.....and I learned something......thanks! !!!!

Most certainly my friend! I hope you are working on some songs to post so I can try to learn some of those riffs you do!

 

[Poboy kartman]

Well....first I want to get a set of strings that aren't 20 years old.....then make sure my axe is sound.....it used to stay in tune for weeks....going out in minutes is embarrassing.....but I will.....with close-ups....of the fingerboard that is....not my face......

 

[Desertduler]

Well....first I want to get a set of strings that aren't 20 years old.....then make sure my axe is sound.....it used to stay in tune for weeks....going out in minutes is embarrassing.....but I will.....with close-ups....of the fingerboard that is....not my face......

Do you want me to send ya some new strings? I have a ten pack of D'Adarrio XL110's!

 

[itsid]

Here I am milling the windows in my 277's piston....

And with that post I think there should be a message to your viewers:

"Please Kids, DO NOT TRY THIS AT HOME!
All stunts are performed by or under the supervision of professionals. No animals where killed during...."

I know you can do it Bret, but I might have a name in mind that could come to the conclusion he should do that to his "whatever" engine as well (likely a four stroke)..
on the garage floor with a handheld powerdrill ....

Oh wait.. I just remember your signature...
hehe
that should do for most parts

'sid

PS forgive me I'm a nerd... I'm really excited about this.... ODD!

 

[Poboy kartman]

I know you can do it Bret, but I might have a name in mind that could come to the conclusion he should do that to his "whatever" engine as well (likely a four stroke)..
on the garage floor with a handheld powerdrill ....

ODD!

What???? You're a mind reader now......???? Joke's on you....I don't have a garage.....I was going to use the kitchen......

 

[Desertduler]

So lets take a look at the original intake port timing.The intake cycle begins when the piston is moving upwards towards T.D.C. and the volume of the crankcase is expanding,the piston skirt just starts to come to the edge of the bottom of the intake port at 82 degrees B.T.D.C.,the engine starts to draw air fuel mixture as the port is opening and the air fuel mixture will continue to be drawn into the expanding volume of the crankcase until T.D.C.,then the piston changes direction and starts heading towards B.D.C. and this is where the piston port engine loses some of the air fuel mixture that was just drawn in the crankcase because as the piston is moving downwards the volume of the crankcase is getting smaller and the air fuel mixture will escape back out of the intake port and out through the carburetor until the bottom of the piston skirt closes the intake port and traps the remaining charge,the lower the RPM of the engine the more effect of this reversion of the intake charge occurs and this is what makes a piston port engine have a narrow power band because as the engine PRM increases there is less time for the air fuel mixture to escape and this is where the reed valve comes into play by being a sort of one way check valve to contain the air fuel mixture in the crankcase and then in turn having more of the air fuel mixture trapped in the crankcase and compressed by the downwards movement of the piston until the transfer ports open and the charge enters the cylinder during the scavaging cycle.

 

[Desertduler]

This casting seam should be removed and the piston needs some cleaning up and smoothing in this area in order for the air fuel mixture to move past here during the scavenging cycle smoothly.This is the location of the piston at B.D.C.,also notice the edge of the bottom of the cast iron cylinder I have blended it here in this location in order to help direct the air fuel mixture with less restriction,these modifications enhance performance that costs nothing but a little work and time.

 

[Desertduler]

Here is a picture of the bottom of the cylinder and the piston is at its location at B.D.C.
Notice how the top of the windows in the piston are opened in the intake port and at this time all of the ports shown including the exhaust port are open,they are connected to each other by the cylinder porting,it is at this time during the correct RPM that the expansion chamber will pull extra air fuel mixture past the reed valves into the crankcase and pull the incoming charge up into the cylinder without the aid of the piston movement at this location thus kind of supercharging the engine and then the piston moves upwards and part of the charge that escapes out of the exhaust port is forced back into the cylinder by the returning pressure wave that the shape and size of the sections of the tuned pipe make.At this time the engine will indeed have a intake duration of 180 degrees.This effect cannot happen with a piston port engine during this time because the intake port is closed off by the piston.

 

[itsid]

Thank you.. finally I understand where you got the 180° from,
I was rocking back and forth because I couldn't get past the "both ports opened" stage...
completely forgot about the exhaust pipe....
well sometimes you indeed have to have the bigger pic to see the details

'sid