Need help

[TimD]

Fast way to loose performance = Dremel. If you must skirt the piston, the area under the exhaust port is not the place to do it!

I agree with Anders - a colder plug is like putting a band- aid on a severed limb until the piston is replaced.

 

[Don Ferrette]

Fast way to loose performance = Dremel.

85892[/snapback]

​

I would have to say FASTEST way to lose performance = Dremel.

I have seen more motors slain with a Dremel than one would care to imagine.

I know this is not what jasonspeedy wants to hear but ...... the truth is out here.

 

[EatMyShortsRacing]

yes it wont go as well.... but it will go further faster than what he has got now.... If it is performing well enough to take the plug out it should have enough grunt to play with and at least go around for more than a lap....

If he wants to play with it this weekend for instance he wont get a P/L in time but he can get an MC 9!!!

 

[TimD]

What would the timings be if he raised the sleeve 0.070"? :lol: :lol:

Hey Don,

I have 2 Dremels in my shop - just imagine the performance I could remove! :lol: :lol: :lol: :lol:

Tim.

 

[EatMyShortsRacing]

I will see your 2 Dremels (one with right angle head) and raise you an Ozito!!!

 

[AndyBrown]

The P/L is fine......I know it's "not supposed to work" But the .070" is not hurting performance at all.

It is just starving for fuel. He has the "In-line needle", not the third channel, so he's good there.

The only problem is the full bore (.470") stinger on the AB 67 pipe (black). He's trying to run in cool weather (good air), so he needs more stinger restriction to deliver more fuel.

Big fuel lines will help, but the stinger is the Big issue here. Nothing else.

Get a .410" or .430" bushing in there Jason, then tell us how it runs.

And yes, use the Mc#9 if you have some, otherwise the #59 will do for now.

 

[Don Ferrette]

The P/L is fine......I know it's "not supposed to work" But the .070" is not hurting performance at all. 

85912[/snapback]

​

HUH??? :blink: :blink: :blink: :blink:

 

[EatMyShortsRacing]

The P/L is fine......I know it's "not supposed to work" But the .070" is not hurting performance at all. 

85912[/snapback]

​

HUH??? :blink: :blink: :blink: :blink:

85925[/snapback]

​

yessiree MACS do have a bit of enigma about them.... sometimes you just have to take what you learned on any other engine and throw it out the window. Prolly due to (in part) the massive intake sizes which means you are more reliant on fuel pumping (tank pressure) than normal... smaller carbs will draw fuel more efficiently but I guess limit the maximum HP...

I still cant get used to the fact my 67s wont ring out on the bank at full throttle but does the business when on the water!!!

*still reckon the 60% nitro and MC59 is not helping....Needs to be a MC9 although the stinger sleeve will give increased fuel pressure*

I am going home now to measure my MAC 67s and see just how much they open....

How many degrees on the txfers and exhaust did we say 0.070" was? (apart from way too many!!!)

 

[Glenn 787]

[How do you anneal the K&S brass tube and why?

85761[/snapback]

​

heat it up red and let it cool then you can bend it

85772[/snapback]

​

Bent like butter......I'll have to make note of this in my one page notebook on metallurgy

 

[jasonspeedy]

I don't understand why the "area under the exhaust port is not the way to do it."

If your piston bumps the crank, and the crank weght or lobe is directly under the exhaust port, how else do you make the clearance? I assume the crank is balanced, so I figured balanced crank - metal=unbalanced crank.

By the way, the plugs were MC-9's, not 59.

Also, I didn't cut the sleeve, I was just taking enough from the piston to smooth the speed bump.

Just a side note...I never intended to give any indication that I have a problem with CMD, or their products. Andy & John have always bent over backwards to help me out. I've bought a truckload of stuff from them, and everything has always been of the utmost quality. The only problem with any of it was this motor, and I think we've made an accurate prognosis of "operator error!"

I can't count the times that I've been to their office and they've stopped what they were doing to work on my motors and props...WITHOUT CHARGING ME A SINGLE PENNY!!!!!

Trust me when I say these guys are busy people, so I appreciate the help.

Also, thanks to eveyone else who contributed to my problem, it's been a valuable learning experience.

Jason

 

[EatMyShortsRacing]

Hey no one here is knocking CMD

Just trying to offer solutions based on the info available

I have had nothing but great service from them too

 

[EatMyShortsRacing]

Although the 0.070" is an interesting question.... but they obviously do work. I had always been told that a little sub piston would not hurt the motor but I never had an actual figure (in thou or degrees) that was the 'acceptable limit'.

I do know that 5mm doesnt work!!!!

 

[AndyBrown]

LOL Don.... yea I know it don't make common sense, but the piston sub port won't hurt the MAC................speed secrect............it helps! shush! Don't tell anyone....well come to think of it they won't believe it so it don't matter.

One thing that seems strange...the piston should not have hit the crank.....Hmmmm!

 

[jasonspeedy]

Well...it wasn't slamming into it or anything..wait a minute...I'm from georgia...it wern't slappin' 'ginst it er nuthin...it wuz jest a small tap...

Hey Andy, the crank had a faint mark where the skirt appeared to have been tapping. I talked to someone about it, and they advised that I remove just enough of the skirt to alleviate the potential for a problem. So I didnt remove the entire skirt, only about 90 degrees centered over the crank. It may not have ever been an issue, but I didn't know, so I fired up the dremel. I'll stinger the pipe down and see what happens.

I've got this new modification program I do with my dremel. Here's what I do...when you're wife is pissed because your love of model boating is taking a toll on the family, she sends me the motor, I turn on the dremel, and HER problems are solved...he he he...

 

[John Knight]

LOL Don.... yea I know it don't make common sense, but the piston sub port won't hurt the MAC................speed secrect............it helps!  shush!  Don't tell anyone....well come to think of it they won't believe it so it don't matter.
One thing that seems strange...the piston should not have hit the crank.....Hmmmm!

85983[/snapback]

​

All right guys,

For those that do not understand what a sub piston port is or looks like, please explain it, why it can work, how far to go and post a photo to see. Now that the cat is out of the bag.

 

[Eric Canto]

I've got this new modification program I do with my dremel. Here's what I do...when you're wife is pissed because your love of model boating is taking a toll on the family, she sends me the motor, I turn on the dremel, and HER problems are solved...he he he...

Jason, you must be the comedic star of Georgia. For those of you who have never had the pleasure of meeting Jason, he is one funny dude. Jason is one of those guys that has quick wit in many situations. I can't wait 'til Jason starts attending races, it is sure to be fun. Hey Jason, don't forget why the St. Johns river flows North.

 

[Don Ferrette]

LOL Don.... yea I know it don't make common sense, but the piston sub port won't hurt the MAC................speed secrect............it helps!  shush!  Don't tell anyone....well come to think of it they won't believe it so it don't matter.
One thing that seems strange...the piston should not have hit the crank.....Hmmmm!

85983[/snapback]

​

I've seen many a motor's performance go south by poorly skirted pistons that created sub port induction, alot less than .070" too. Then again the MAC is a cat of different stripes as I have learned.

The piston touching the crank is odd as well, now I'm wondering about the big bearing, too much play?? Bad bearings would also explain ALOT of the poor running issues. :blink:

 

[TimD]

All right guys,
For those that do not understand what a sub piston port is or looks like, please explain it, why it can work, how far to go and post a photo to see.  Now that the cat is out of the bag.

Basically it means the exhaust port is not sealed shut by the piston at TDC. If you look into the exhaust port while the piston is at TDC, if you can see inside the sleeve thru a gap under the piston - thats a sub-piston port. So fresh inlet charge is coming in from the drum / disk (being open at this time) and is either short circuiting the combustion chamber going into the pipe, and / or the exhaust pulse can come in under the piston from the pipe.

Tim.

I wonder why the MAC 45 runs the bottom of the exhaust port higher than the rest? Seems to be the opposite to this arrangement..... Andy, what am I missing?

 

[EatMyShortsRacing]

LOL Don.... yea I know it don't make common sense, but the piston sub port won't hurt the MAC................speed secrect............it helps!  shush!  Don't tell anyone....well come to think of it they won't believe it so it don't matter.
One thing that seems strange...the piston should not have hit the crank.....Hmmmm!

85983[/snapback]

​

All right guys,

For those that do not understand what a sub piston port is or looks like, please explain it, why it can work, how far to go and post a photo to see. Now that the cat is out of the bag.

86003[/snapback]

​

Basically it is when the bottom skirt of the piston goes above the bottom of the exhaust port at TDC. This opens the crankcase to the exhaust. The issues are the bigger that opening is the more crankcase pressure you will lose.

 

[EatMyShortsRacing]

I wonder why the MAC 45 runs the bottom of the exhaust port higher than the rest? Seems to be the opposite to this arrangement..... What am I missing?

86019[/snapback]

​

My guess for part of the function is if you have cleared most of the exhaust gas before the piston makes BDC then you would be more interested in retaining the incoming charge in the cylinder. The bottom lip would prevent some of the charge just going out the exhaust port.

Another interesting theory is it is possible at since area of the exhaust port is somehow linked into the tuned pipe calculations maybe there is some sort of resonance for that area port????? (stab in the dark)