Advice on rotary burrs for cast iron use.

I intend to open the ports of a BSA Bantam cast iron cylinder for a parade racer. Have got a die grinder but would like, in addition to general advice guidance on stem diameter, length, head profile of suitable rotary burrs ? Also possible suppliers of half decent burrs.

Any and all advice would be appreciated. Should add that I have a spec for port size/shapes.

Jim

Just had a quick Google, feel better now - thanks for asking, and came across this which might help...

**LINK**

 

I only ever buy Garryson burs, they are very good! You can pick them up cheaper on ebay!

Only thing I can say is that you will need a round one.

Garryson burrs probably the best bit more expensive but worth it I think.

Good luck with the bantam!

Have a look at Headbytes porting on youtube , you will learn a lot about porting there - i did !

He gets his custom made but you can look at what he uses for the port , bowl and chamber and try to match them with commercially available burrs .

the ones i use the tip is sort of shaped like a rugby ball and slightly elongated football .

Ian

Over 50 years ago I attacked my 150cc Bantam broadly along the lines of Phil Irvings "Tuning for Speed", turned it from a 45mph telegram delivery bike into an 85mph Streak!! Best of luck!!

cheers

Bill

Just re-read the post-- I meant to say use a spherical burr. Bantam engines do tune well, ports + crankcase stuffing. Many years ago I worked with a bantam racer club man, he finished well in the IOM TT 125 Class with all BSA bike. The east Europeans did a good job after Bsa sold them off.

Tungsten carbide burrs cost a bit extra but last a lot longer than HSS

Paul.

Oops wasn't thinking about two stroke engines!

I don't know if you really want a burr for the transfer ports as they take a lot of metal off very quickly ,all the porting work i have done on my bikes i have only cleaned up the transfer ports and made sure the opening event of them is at the same time . I generally use a stone for the transfer ports as it is more controllable and you can dress them to the shape you need . Something resembling an egg shape is what i have used in the past for the transfers , the exhaust is a different matter for this i use a flame shape burr .

Length : as short as you can get away with , cut a length of round bar that fits in the collet and do a test run , you need it to reach in it to the ports without the die grinder fouling up , start out too long and trim to length this will give you the minimum length of burr you need to buy . I have also made an extension shaft for my die grinder , just a straight piece of roundbar that fits in the collet and hole in the end that the shaft of the stone fits neatly , some loctite holds it in and i put some heatshrink on the shaft so if it does contact the cylinder it doesn't do any damage .

Last time used one of those flexi shaft grinders that fits my dremel for the transfer ports as it is much smaller in diameter than a normal die grinder , if you look at some of the videos on the youtube channel i mentioed in my previous post you will see he uses a certain type of grinder not one of those chunky little units you buy from a harware store .

Two stroke performance tuning by A. Graham bell is worthy read , it opened my eyes a little as i had considered porting as the only power gaining modification there was , i never really paid any attention to the exhaust system , or crankcase size until i read that book !

Many thanks to those who offered advice especially Ian who would appear to ‘speak’ with practical experience including when things did not go according to expectations. All are very much appreciated.

Jim