Help With Port Timing

[CHEVYTOWN13]

Say I want to drop the jug

Now things are falling into place...squish I've heard a lot about. But never knew what it meant. I'm guessing that is this situation. Now messing with compression + messing with the port duration...way cool man. Cams are awesome, but 2stroke ports are a sweet science...

 

[blsnelling]

It has always been my understanding that modders meaure when a port opens/closes in degrees and then calculates duration from there. No?

 

[parrisw]

Now things are falling into place...squish I've heard a lot about. But never knew what it meant. I'm guessing that is this situation. Now messing with compression + messing with the port duration...way cool man. Cams are awesome, but 2stroke ports are a sweet science...

Ya, cool stuff. Squish is the band around the outside of the cylinder to piston clearance. Drop the jug= more compression=more power/torque. Machine a popup piston=even more compression=even more power/torque. Oh the fun to be had. I need me a Lathe.

 

[CHEVYTOWN13]

This is getting insane!

Ya, cool stuff. Squish is the band around the outside of the cylinder to piston clearance. Drop the jug= more compression=more power/torque. Machine a popup piston=even more compression=even more power/torque. Oh the fun to be had. I need me a Lathe.

I'll experiment with Milwaukee's big router and see if I can find a CNC bit that will run on the machine's top RPM to machine down a piston. I'm going to make a jig to hold jug and use a machinist square to make sure everything is cool before I mess with that Homie's piston... Maybe have someone CNC a gasket made out of aluminum and take a few hundred/thousands? off. Playing around a little to make that 5100 a monster for a 50cc. Interestingly enough, the stock port on the 5100 looks stout. Super clean and super clean lines and edges. I'm thinking of keeping it like that less a polish and messing with different varialbes for the ultimate compression on the "Tazmanian Devil"

 

[CHEVYTOWN13]

Where are the different department professors at!?!

It has always been my understanding that modders meaure when a port opens/closes in degrees and then calculates duration from there. No?

I wouldn't be surprised if there are multiple mathematical formulas for the same end result.

 

[Metals406]

Did you degree the exhaust side? I'm still curious to see what duration you ended up with?

 

[CHEVYTOWN13]

Metals, I haven't. I'm still trying to learn my starting point. Great info going on right here for newbies.

Hopefully by the end of this week I'll have things figure out.

 

[troutfisher]

Me too. Measure the duration on the top side of the piston.

 

[CHEVYTOWN13]

Hope this helps fellas

It's grass roots style but maybe someone can figure it out. Here is a picture of how long it took fom BDC to complete closure of the exhaust port on the upstroke just past the ring. Would it be the same for the downstroke where it matters in this case, letting the spent gasses escape?

Disregard the red tag underneath. I started at 0º and it seems like it traveled 66º to closure

http://web.mac.com/bluemetal/Blue_Metal_Studio/CAD.html#10

 

[CHEVYTOWN13]

Me too. Measure the duration on the top side of the piston.

Ooooops. Top side? Did I do it backwards?

 

[troutfisher]

Ooooops. Top side? Did I do it backwards?

I'm just making a bad joke, telling you not to measure your freeport time 66* means you have 132* of exhaust duration. That seems low, but I haven't messed with Dolmar's much. Maybe one of the dolmar guys will chime in here. I think you've got a bad measurement, especially if you've been grinding on it.

 

[CHEVYTOWN13]

No worries homeslice

Yeah, I thought that number was low too. I did not count the free port. Just the time it took from BDC to the closing the top of the port, with the piston ring well below the top of the port.

Dang, I went to HOG HEAVEN on the job...or did I change it at all? I must have.

The very top of the port was not worked on. Only the sides and hogged away at the bottom.

school of hard knocks fo shooooooore!

 

[Erick]

Man this is getting brutal to read :censored: Chevy your waaaaaay over thinking this.

I could probably pitch in a little more info if I didn't think you were gonna call me Darth somebody or one of the Stormpoopers or Professor Homeslice or something.

Man... just take out the spark plug look into the cylinder and raise the piston up to the top of the cylinder. Stick a pencil or some thing in the plug hole and rotate the crank in small increments until the pencil stops going up and down "Zero" the wheel there..... this will be CLOSE. to fine tune and get true TDC just follow either one of the methods from TW or 4paws from above. If the piston stops at 89° one way and 91° the other then your wheel is off by 1°... move it.

When you've found TDC rotate the crankshaft through it's cycle look at when the top edge of the piston passes the top edge of the ports and record the numbers on the wheel and tell us what they are.

All of this a bit academic at this point because of the HUGE free port you have at TDC but it's best to learn something from your mistakes.

Like I said getting an education isn't cheap.... it looks like this lesson cost you the price of a new jug.





Porting with a router

 

[CHEVYTOWN13]

No worries homeslice, it's all good. A jug here a jug there...

I don't mind learning. Isn't that what's it's all about?

Nice trick though.

 

[Metals406]

Like I said getting an education isn't cheap.... it looks like this lesson cost you the price of a new jug.





Porting with a router

Why a new jug? The saw idles, and cuts fine?

 

[troutfisher]

Man... just take out the spark plug look into the cylinder and raise the piston up to the top of the cylinder. Stick a pencil or some thing in the plug hole and rotate the crank in small increments until the pencil stops going up and down "Zero" the wheel there..... this will be CLOSE. to fine tune and get true TDC just follow either one of the methods from TW or 4paws from above. If the piston stops at 89° one way and 91° the other then your wheel is off by 1°... move it.

When you've found TDC rotate the crankshaft through it's cycle look at when the top edge of the piston passes the top edge of the ports and record the numbers on the wheel and tell us what they are.

All of this a bit academic at this point because of the HUGE free port you have at TDC but it's best to learn something from your mistakes.

Porting with a router

Yup, finding TDC works. And getting within a degree or two is close enough for now. What ever way makes sense for you.

 

[troutfisher]

Why a new jug? The saw idles, and cuts fine?

Because when he starts dropping the jug to adjust squish the problem is going to get worse. Might be OK, but might not.

 

[Metals406]

Because when he starts dropping the jug to adjust squish the problem is going to get worse. Might be OK, but might not.

I'm not sure he intends to shave the jug (or remove the gasket)? I think he wants to understand the timing thing a little more is all.

As it is, the saw runs fine, and cuts a little stronger than stock... What he did is supposed to be a big no-no, but yet the saw still lives. Fluke? That's what he's trying to figure out I think?

Once he can get some timing numbers written down... He could still widen the port if he wanted... It's not close to the edge of the piston at all.

At this point, the jug is far from destroyed.

 

[troutfisher]

I'm not sure he intends to shave the jug (or remove the gasket)? I think he wants to understand the timing thing a little more is all.

As it is, the saw runs fine, and cuts a little stronger than stock... What he did is supposed to be a big no-no, but yet the saw still lives. Fluke? That's what he's trying to figure out I think?

Once he can get some timing numbers written down... He could still widen the port if he wanted... It's not close to the edge of the piston at all.

At this point, the jug is far from destroyed.

true, if he quits now it's still useable. Might as well learn to use a degree wheel with it, the next one will go better I'm sure.

 

[CHEVYTOWN13]

I'm not sure he intends to shave the jug (or remove the gasket)? I think he wants to understand the timing thing a little more is all.

As it is, the saw runs fine, and cuts a little stronger than stock... What he did is supposed to be a big no-no, but yet the saw still lives. Fluke? That's what he's trying to figure out I think?

Once he can get some timing numbers written down... He could still widen the port if he wanted... It's not close to the edge of the piston at all.

At this point, the jug is far from destroyed.

THE DOCTOR HAS SPOKEN...

Metals406 is correct as far as the saw cutting better than stock. So I don't see what the problem is? I guess you hometowns just want to spread your knowledge around and more power to you! and better for me. Learning tricks.

It's just a saw for cutting back brush. I wouldn't be cutting a log that size(in the video) with the 510. I'd bust out Storm Trooper #6401...or let the Taz take care of it. I could care less if the jug is done, but the 510 still drinking beer from it

Don't worry, it runs fine. Cuts better.

Besides, a jug with me is like pennies...when I don't want to carry it anymore, I toss it in the basket in favor of another one...and another idea possibly?




PS... I never said anything about the squish other than saying NOW I understand what everyone was referring too when they mentioned squish...

I hate going to forums and posts are as blunt as a blunt...it's boring cuz no one has no color to their comments...