JD built engine help

[yakson]

so i have a buddy who has had a bike built by JD or just the motor, anyhow he burned a hole through a piston last year. being not very mechanically inclined i decided to help him get back in the sand.

 

so far the cylinders have extensive drag porting, the jetting was set to 55/175 and reed cages had some work done too... its all polished from top to bottom. i guess what im getting at is what should he run for fuel? pump gas caused the detonation. and maybe if anyone knows of these motors built by JD and could maybe help me get a better understanding of what he has here.

[Jereme6655]

The requirement of race fuel is not what causes a hole to be melted through pistons. Deto will look like a bunch of smash marks on the tops of the piston face. Melted piston will have obvious signs of a trench being formed right through the middle of the piston.

 

Deto is caused by lack of octane in fuel. Basically when you squeeze something so hard it will generate heat and after a certain amount of compression the heat is actually hot enough to cause combustion. So the fuel mixture will fire off while the piston is still on the way up.....thus leaving the small dings in the face of the piston.

 

A melted piston is caused by a lean fuel mixture. When 2stroke motors are run lean they lack lubrication.....causing the cylinders to destroyed by the piston moving without enough lubrication. Running them lean can either by poor jetting or lack of oil in the mix or the hidden danger....an air leak. When the crankcase loses its air tight seal it begins sucking air in and causes the motor to run lean. Basically if you don't have a good air tight motor your going to melt piston after piston.

 

Usualy higher octane fuel such as race gas is more commonly needed around 150-160 psi. So do a compression test. This is the easier/more inaccurate way of testing octane requirements. The other way involves measuring the internals of your motor.

 

We also use homemade tools called leakdown testers to check for leaks. There is a sticky posted on here showing how to build them....

[Starwriter]

If this is JD's old drag motor. It was built by the Havoc Racing crew. Maybe get a hold of Mr.Bling or Mrs.Toyboxx and let them know the details of the motor. They might beable to help you if you can't get ahold of JD. There is 3 of them out there. Which one you got, I dont know.

Different JD. I'm sure the OP is talking about JD Racing out of Hillsborro. They built very fast Banshee motors in the 90's. They're long gone now. I wonder what Chad is up to these days. This thread tells a bit about them.

 

http://bansheehq.com/forums/index.php?showtopic=134055&st=0

 

To the OP, the only way you're gonna know what he's got is to start measuring stuff.

[shanYE west]

Different JD. I'm sure the OP is talking about JD Racing out of Hillsborro. They built very fast Banshee motors in the 90's. They're long gone now. I wonder what Chad is up to these days. This thread tells a bit about them.

 

http://bansheehq.com...pic=134055&st=0

 

To the OP, the only way you're gonna know what he's got is to start measuring stuff.

 

I think your right.

[yakson]

Different JD. I'm sure the OP is talking about JD Racing out of Hillsborro. They built very fast Banshee motors in the 90's. They're long gone now. I wonder what Chad is up to these days. This thread tells a bit about them.

 

http://bansheehq.com...pic=134055&st=0

 

To the OP, the only way you're gonna know what he's got is to start measuring stuff.

 

 

 

 

 

Yeah we have been going through everything to check it out. Took it all down to pieces to clean the case out an see whats up in the bottom end. Yeah the bike was bought outside of cali. The motor runs strong an fast as hell before this happened. I have been looking an had a hard time finding any info on the previous builder. Figured this would be a really good place to start.

 

Thanks for the info and help, its greatly appreciated.

[yakson]

The requirement of race fuel is not what causes a hole to be melted through pistons. Deto will look like a bunch of smash marks on the tops of the piston face. Melted piston will have obvious signs of a trench being formed right through the middle of the piston.

 

Deto is caused by lack of octane in fuel. Basically when you squeeze something so hard it will generate heat and after a certain amount of compression the heat is actually hot enough to cause combustion. So the fuel mixture will fire off while the piston is still on the way up.....thus leaving the small dings in the face of the piston.

 

A melted piston is caused by a lean fuel mixture. When 2stroke motors are run lean they lack lubrication.....causing the cylinders to destroyed by the piston moving without enough lubrication. Running them lean can either by poor jetting or lack of oil in the mix or the hidden danger....an air leak. When the crankcase loses its air tight seal it begins sucking air in and causes the motor to run lean. Basically if you don't have a good air tight motor your going to melt piston after piston.

 

Usualy higher octane fuel such as race gas is more commonly needed around 150-160 psi. So do a compression test. This is the easier/more inaccurate way of testing octane requirements. The other way involves measuring the internals of your motor.

 

We also use homemade tools called leakdown testers to check for leaks. There is a sticky posted on here showing how to build them....

 

 

 

 

This was extremely helpful. I was not too sure that just fuel would have a part in this. As soon as the engine gets back in to the bike gonna go ahead an compression test it an go from there.

 

Thanks for the info!