30.5 crank with 28.5 cylinder/piston

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cody1

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Hey does any one know if a 30.5 crank with a 28.5 piston/cylinder work. I bought a 30.5 kit from oniel brothers, no more then two tanks the cylinder cracked about half way aroud the cylinder:mad:. call to see if they could replace it, but they said cy said it was my fault why it cracked. So would that work. Thanks in advance
 
yes they are the same head its the crank that will be a +2 stroker crank taking it from 28.5 to 30.5cc so no reason they shouldn't work and it shouldn'tof broke the head unless there was allready a stress crack in it
 
cody said:
Hey does any one know if a 30.5 crank with a 28.5 piston/cylinder work. I bought a 30.5 kit from oniel brothers, no more then two tanks the cylinder cracked about half way aroud the cylinder:mad:. call to see if they could replace it, but they said cy said it was my fault why it cracked. So would that work. Thanks in advance
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go with mmr kit ...they rock..
 
The OBR head kit is likely modified for the +2mm stroke. The combustion chamber is cut to allow for the extra stroke. To run a non modified cylinder with a +2mm stroke you will need to add a .040 base gasket as well as a stock base gasket. If you put a stock 28mm stroke crank in the 30.5 case you could run it without stacking gaskets.


Hope this helps out.
 
That's funny. I have two ONB 30.5 heads sitting on my shelf that my buddy busted all to hell. They cracked at the base about a 1/4 of the way around the cylinder around the rear most head bolt. This is the third ONB 30.5 head crack that I've seen or heard about. I have a good feeling that the amount of power a high compression 30.5 ONB puts out is not viable on a 2 bolt head. ONB makes GREAT engines, don't get me wrong. I would just roll with the 4 bolt if running that beast of a 30.5 engine they make.


Another really good engine to look at is Underdog's Wild Child line of engines. I have some video that I took of a Wild Child 28.5 vs a ONB full mod 30.5. Both engines were beasts but the WC would have been my pick because it was on par with the ONB but not even broken in. I've seen it run after break in and it's a beast.
 
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DemonRC said:
That's funny. I have two ONB 30.5 heads sitting on my shelf that my buddy busted all to hell. They cracked at the base about a 1/4 of the way around the cylinder around the rear most head bolt. This is the third ONB 30.5 head crack that I've seen or heard about. I have a good feeling that the amount of power a high compression 30.5 ONB puts out is not viable on a 2 bolt head. ONB makes GREAT engines, don't get me wrong. I would just roll with the 4 bolt if running that beast of a 30.5 engine they make.
Another really good engine to look at is Underdog's Wild Child line of engines. I have some video that I took of a Wild Child 28.5 vs a ONB full mod 30.5. Both engines were beasts but the WC would have been my pick because it was on par with the ONB but not even broken in. I've seen it run after break in and it's a beast.
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Thank you for the kind words on the 29.5WC. I would love to see some video of it running. I run with two other guys all the time and it seems none of us want to put a controler down for a camera.
 
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Underdog I like your modded engines one question you put a small oil hole in them?? I know its for oil to get to somewhere?? Im not 100% sure what its for and what it does? Can you talk about that mod?? Does it make the bearings lasts longeer?
 
Thanks guys, I guess since I already have I 28.5 cylinder ill just stack gaskets and go that way. Hopefully I don't crack that cylinder if so im just going to pull the stroked crank out and put in a stock crank.
 
chevy said:
Underdog I like your modded engines one question you put a small oil hole in them?? I know its for oil to get to somewhere?? Im not 100% sure what its for and what it does? Can you talk about that mod?? Does it make the bearings lasts longeer?
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On the piston down cycle the piston will increase the pressure in the crankcase which forces fuel and air up through the transfer ports. Correct me if I'm wrong but since our bearings are unshielded some of that fuel will flow through the bearing and up the hole. I'm sure it's not squirting like a stream. The point is there is now a small flow through the bearing.
 
DemonRC said:
On the piston down cycle the piston will increase the pressure in the crankcase which forces fuel and air up through the transfer ports. Correct me if I'm wrong but since our bearings are unshielded some of that fuel will flow through the bearing and up the hole. I'm sure it's not squirting like a stream. The point is there is now a small flow through the bearing.
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100% correct, the oil hole goes from the transfer port to between the seal and the clutch side bearing. this creates more flow of fuel and oil through the bearing making it last longer. I also use a higher quality bearing then stock for longer life. On my website in the Tech section is a few pictures of the oil hole mod.
 
cody said:
Thanks guys, I guess since I already have I 28.5 cylinder ill just stack gaskets and go that way. Hopefully I don't crack that cylinder if so im just going to pull the stroked crank out and put in a stock crank.
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You should check the squish in the engine before you run it. Pick up some electronics solder around .030 thick. Insert the solder in the spark plug hole, bent at a 90deg angle pointing at the coil. Insert it until it hits the cylinder wall. Make sure it is not stuck in the transfer port. Rotate the engine past top dead center to squish the solder. The solder should be no less then about .015. Optimal should be around .020 for offraod and .025 for oval give or take a few.


If you have any problems drop me an email and I will be glad to talk you through it.
 
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Underdog said:
You should check the squish in the engine before you run it. Pick up some electronics solder around .030 thick. Insert the solder in the spark plug hole, bent at a 90deg angle pointing at the coil. Insert it until it hits the cylinder wall. Make sure it is not stuck in the transfer port. Rotate the engine past top dead center to squish the solder. The solder should be no less then about .015. Optimal should be around .020 for offraod and .025 for oval give or take a few.
If you have any problems drop me an email and I will be glad to talk you through it.
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Will di thanks for the good info
 
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