Shimmin' a liner?

[Propjockey]

I was going over a K&B 7.5 OB powerhead that I had laying around and noticed that at TDC I can see the bottom edge of the piston skirt through the exhaust port. The gap is very small, but you can tell it's there. I haven't run the engine, so I don't know how this will affect it, but I'm pretty sure it ain't supposed to be like that.

Do I need to shim the liner?

 

[htbboats]

What you are seeing is called sub induction. I"ve seen motors with it run just fine but really I would think that it should not be there. I'd run it before doing anything and see how it does. Rod "G" would be the one to talk to about this for the best information.

Mark Hopper

 

[Propjockey]

Thanks Mark. Anybody know anything about sub-induction? Pros......cons? Rod G?

 

[elafleur]

you must consider if you shim the liner ,all of the ports will be raised . this elevated port timing may cause worse effects than the piston skirt opening the floor of the exhaust port .

 

[htbboats]

I did not have his address the other day. You can contact Rod Geraghty at [email protected]

Mark Hopper HTB BOATS

 

[Chris Wood]

HEY PROP..

WHAT ERNIE IS TALKING ABOUT IS EXACTLY RIGHT.. YOU CAN GET AWAY WITH IT TO A POINT.. BUT IF YOU GO TO MUCH THE MOTOR WON'T RUN... AS FOR HOW MUCH IS TO MUCH I HAVE NO IDEA... I DO KNOW IF YOU RAISE THE SLEEVE LOOK CLOSELY AT THE BOOST AND TRANSFER TIMING.. TO MUCH AND YOU LOOSE ALL YOUR BOTTOM END POWER OUT OF THE MOTOR..

FOUND THAT ONE OUT THE HARD WAY LOL

CHRIS ;D