brain fart

[DannyWeimer]

my neighbor bought over a boat with a k&b 45 i was taking the motor apart and clean it out and saw the motor was mod but what i saw was . When the piston hits tdc the ext was open at the bottom of the piston . i look over all my ops and other k&b 7.5 motors and this does not happen to any of then. i am thinking this motor will not run am i wright .

 

[Daniel's Racing]

my neighbor bought over a boat with a k&b 45 i was taking the motor apart and clean it out and saw the motor was mod but what i saw was . When the piston hits tdc the ext was open at the bottom of the piston . i look over all my ops and other k&b 7.5 motors and this does not happen to any of then. i am thinking this motor will not run am i wright .

It is called freeporting when a engine has a gap under piston at TDC. A little bit you can get awy with and some engines were actually intentionally designed to have some thinking the exhaust could somehow supercharge the crankcase with a little pressure. Most modified engine builders for the most part try to avoid this.

Many times when building a stroker engine and using a stock piston some freeporting is unavoidable.

I would think that if it were caused by the floor of the port being lowered it might have been by mistake on the engine porters part. There is usually not much to be gained as the

piston is most likely not going that low at BDC to allow any increase in exhaust duration. Then again I would say you would have to run it as nothing is ever set in stone when it comes to porting a two stroke engine. There are so many variables that need to come together as a whole to create the most power.

Daniel

 

[El Zorro]

my neighbor bought over a boat with a k&b 45 i was taking the motor apart and clean it out and saw the motor was mod but what i saw was . When the piston hits tdc the ext was open at the bottom of the piston . i look over all my ops and other k&b 7.5 motors and this does not happen to any of then. i am thinking this motor will not run am i wright .

It is called freeporting when a engine has a gap under piston at TDC. A little bit you can get awy with and some engines were actually intentionally designed to have some thinking the exhaust could somehow supercharge the crankcase with a little pressure. Most modified engine builders for the most part try to avoid this.

Many times when building a stroker engine and using a stock piston some freeporting is unavoidable.

I would think that if it were caused by the floor of the port being lowered it might have been by mistake on the engine porters part. There is usually not much to be gained as the

piston is most likely not going that low at BDC to allow any increase in exhaust duration. Then again I would say you would have to run it as nothing is ever set in stone when it comes to porting a two stroke engine. There are so many variables that need to come together as a whole to create the most power.

Daniel

Daniel is right on with his post. I did some controline racing and Free Flight airplane engines with the free porting but I would not recommend doing it with a piped engine. Exhaust timing on an unpiped engine works well up to about 160-165 degrees ( with a little freeporting ) on some engines, but you're turning a lot of RPM's to get your power.

Dick Tyndall

 

[Don Brown]

my neighbor bought over a boat with a k&b 45 i was taking the motor apart and clean it out and saw the motor was mod but what i saw was . When the piston hits tdc the ext was open at the bottom of the piston . i look over all my ops and other k&b 7.5 motors and this does not happen to any of then. i am thinking this motor will not run am i wright .

It is called freeporting when a engine has a gap under piston at TDC. A little bit you can get awy with and some engines were actually intentionally designed to have some thinking the exhaust could somehow supercharge the crankcase with a little pressure. Most modified engine builders for the most part try to avoid this.

Many times when building a stroker engine and using a stock piston some freeporting is unavoidable.

I would think that if it were caused by the floor of the port being lowered it might have been by mistake on the engine porters part. There is usually not much to be gained as the

piston is most likely not going that low at BDC to allow any increase in exhaust duration. Then again I would say you would have to run it as nothing is ever set in stone when it comes to porting a two stroke engine. There are so many variables that need to come together as a whole to create the most power.

Daniel

Daniel is right on with his post. I did some controline racing and Free Flight airplane engines with the free porting but I would not recommend doing it with a piped engine. Exhaust timing on an unpiped engine works well up to about 160-165 degrees ( with a little freeporting ) on some engines, but you're turning a lot of RPM's to get your power.

Dick Tyndall

A basic mod to old K & B motors was to remove the skirt from the bottom of the piston on the intake side. Then if the piston is installed backwards this could cause the exhaust port to be slightly open at TDC.

DonB

 

[DannyWeimer]

thank you for your answer u saved me from pulling my hair out

 

[moparbarn]

thank you for your answer u saved me from pulling my hair out

what hair?

 

[DannyWeimer]

hat what up up i here u i only got a little bald

 

[DannyWeimer]

same motor k&b 45 mod what is a good pipe length the pipe is a mac 45 muffled i also have the head clearance set at 14

ho does this sound what prop