Beginners

I am trying to open out the ports of a cast iron BSA Bantam barrel to get a little more omph and the elbow grease/file method is proving very slow.

Could anyone suggest a suitable ‘cutter’ to use in my B & D drill to speed things up, ie material and type.

Jimmie,

You really need a high speed grinder, not a general purpose drill.

Have a search online for Die Grinders.

MichaelG.

[learned to ride on my 125 D1 Bantam]

Thanks Michael

Had been told about die grinders but found the cost was prohibited for a one off job even with a second hand one. The exercise is probably more a way of passing the time than getting the job done asap. Why oh why does being an OAP = more time on one's hands and less energy in them!

Jimmie

Hi Jimmie
How about a rotary file in your Black & Decker
Nobby ( another AOP)

Hi JimmieS

Black & Decker Powerfile. Every home should have one.

regards

Jim (another OAP)

Hi Jimmie,
If you have a compressor you could try an air powered die grinder similar to this one. From time to time Aldi and Lidl have them on offer for about £10.00 but I do not think they are supplied with any grinding wheels.

Les.

A dremel will do the same job as a die grinder if a little slower.

J

Jimmie, for years I used to port and polish 2 stroke cylinders (Lambretta LD's & LI's) with a Black and Decker drill, flexible shaft and rotary carborundum grinding wheels, you should be able to pick up cheapo packs of grinding wheels at general hardware stores, car boots or eBay etc,

I later graduated to using proper steel die grinder cutters when porting and polishing everything from Mini (A-Series) heads to F5000 Chevrolets (Chev 283's), did quite a few Stag alloy heads too!
I had to hand high speed electric and air die grinders for those honking great chewing jobs though, but the cutters work just as well in hand drills if a bit slower and scruffier, you just have to watch for them vibrating out of the chuck if you get a bit too ambitious about the metal you're chewing out!

You will probably need a flexible shaft with a smallish chuck to get the cutters deep enough into the ports though, seem to remember the Bantam has deep exhaust and transfer ports!

The Clarke Rotary tool kit comes with a small die grinder thing a bit like a Dremel but a lot cheaper, and also has a flexible shaft in the box plus small versions of the grinding wheels!
You're likely to burn out either a Dremel or a Clarke size grinder on that job if there's a lot to do, but if you let it cool down for a while between shortish bouts, you may get away with it!

For polishing ports after chewing them out, I used 6" lengths of steel rod (1/4" - 5/16" dia) with a deep sawcut across the end, slip some emery tape into the slot and wind a good length of it around the rod, (remembering which way the chuck revolves) it wears off as it polishes, or you can just rip a bit off the end as it dulls!

By eck, takes me right back to me good old days does this!

PS. wear a mask when grinding ports out, it's incredibly unspeakably filthy work, latex gloves too (as long as not allergic to latex)  if you value clean finger nails and cuticles!!
And before someone mentions it, goggles too, those carborundum bits and metal shards hurt like hell, and the eye clinic medic's get a bit peeved if you make too many visits!

Edited By RJW on 22/01/2013 16:32:55

Jimmie,

An excellent book that you might track down is:

The High-Speed Two-Stroke Petrol Engine ... by Philip H. Smith

First published 1965, but none the worse for that !!

Also, have a look at this, on YouTube

Have fun

MichaelG.

I used to do a lot of head work on Pinto & A series. Basically you can use a drill, but be aware that you will likely destroy the bearings as they arent designed for prolonged side pressure. I cant imagine a dremel bit lasting long enough. Flexi shaft is fine but only for light pressure. If you are using a die grinder be sure to use propper grinding bits - the cheap diy ones will literally explode in a die grinder! One piece od advice already covered which I can not emphasize strongly enough is never ever use this equipment without good goggles - not a shield or specs but goggles. I too have lost count of the number of times I had to go to hospital in searing agony! And if your in the northwest uk you are welcome to borrow my Bosch die grinder! But I want it back afterwards

Many thanks indeed for to everyone for their kind first hand advice, especially the health and safety issues. Sadly, Francis and Fizzy, I can’t take up your offers as I live across the ‘wet bit’ in Ireland.

As my wife also uses the garage for ‘more important things’ ie tumble drier etc, any grinding will have to be done in the garden. Who said that there was no such flower as a black rose?

Jimmie

Hi Jimmie - I used to port out, pack cranks and crankcased, of bantam engines for competiyion work (Road racing and Grass track). I found the best way was with small grinding stones and burrs on a high speed flexable shaft driven of the end of the bench grinder.

An alternative to porting out was to seal off the induction ports and make up a crankcase fitting with a reed valve (A lot of the modern 2 strokes have induction reeds and can usually be picked up from bike brokers.

If you want to go the whole hog in tuning then look arround for a George Todd head - They can still be found on the web.

Hope this helps

Hi Jimmie,

I can remember doing the same job years ago. I had no power tools at the time and have well rounded off knuckles ever since!

The other lads have covered the most of the "tips". I have used carbide burrs with good success on similar jobs. The 1/4 shank ones take a lot of punishment and a pointed oval shaped one will do all the shaping you need on the Bantam.

If you are within reach of the NW of this green isle you are welcome to PM me and I may be able to offer some help.

John

Jimmies,

I have a number of suitable mounted points and carbide burrs which I can supply to you if you want them. If so, please PM me with contact details.

Trevor.

I had a BSA bantam a many years ago and copied an Austrailian's ( Hogan ?) tuning details that were publishished in the "MotorCycle" in the late 50s or early 60s .I carefully filed out the ports to the larger sizes specified ( may have made them a little larger thinking that the larger the better) but found the larger port sizes killed the air flow velocity and the power output was much reduced. So don't go overboard on the port sizes !

Hi Mike

Thanks for the advice. A friend who raced a 50cc in the 60's did the same thing. He said the power output was flat - flat dead.

Jim

Porting the bantam was very popular in the 60/70's - Both the inlet and transfer ports had to be enlarged and polished - one of the main problems was that the ports were enlarged in the piston bore in a vertical (up and down) situation - this altered the timing and usually resulted in power loss.

It was always better to open the ports around the the bore so as not to alter the timing - !! unless you have design knowledge of 2 stroke timing ??

Also if the fuel induction and transfer is altered the consideration should be made to the exaust system - as it is not practical to alter the exaust port/flange then it was normal to fit a performance designed exaust pipe and box - this for some reason had a restricted flow cone at the end ??? -It worked

Two-stroke tuning is/was a black art, more akin to writing a symphony than engineering. A chap I worked with was a Bantam racer ,he had one that could do over a 100mph in IOM trim. Thats the point really, any tuning will alter the power output, and the rev. range it is produced at. IOM trim or Scot Trial ? There some good books out there. Two hints:- put a bit of tin opposite the port ,stops hitting the bore by accident. If you are broke rotary files can be made from old round files, even chainsaw files.

Thanks HomeUse and Gordon. Other folk's experience is certainly the best way to learn quickly. I am continually surprised, amazed and delighted that so many kind folk are willing to give advice on this site.

Came across this site. www.bsabantamracing,com - a lot (too much!) info on my 'simple' aim.

Jim