Hi all - While my M21 is apart I'd like to do some modifications to improve engine breathing to get a little more top speed. Firstly, I've seen some photos of modified heads, either manufactured (like the Ricardo one) or home welded. Does anyone know where I can get one of the professionally manufactured ones? Failing that, is there specific technical advice available (a pattern I guess) on how to do this? Secondly, I believe people have success with grinding and/polishing ports. Can anyone describe the best way to do that, again with technical specifics? Thanks a lot for your help. Cheers, Brett

Brett,

Read Ian Wright's piece "A Little Extra Power" in the technical section of the website, and read the recently-completed thread "Fitting Gold Star Cams" on this forum. The last entry was 2 October.

If you email me I'll send you other references.

Jeff Bandola USA

email (option): jjbandoo@aol.com

Hi Brett...There aren't any 'professionally' made heads that I am aware of, though some, such as Jeffs, look that way as they are very nicely done...

The alloy head is the easier one to work with and also will help the engine to run cooler...

Some mild work on the inlet port (and a bigger carb) would be beneficial along with some mods to improve compression ratio and breathing in the head..It's also worth considering a bigger inlet valve.

If you are thinking of alternative cams, or maybe even if your not, some lightening of the flywheels will be needed...

Enlargement of the engine capacity is also worth thinking about

After any work is completed the gearing can be raised somewhat to take advantage of the gains in power...

Sidevalve engines are not the best candidates for tuning so you need to think a bit about what you expect the finished result to be and how much work you might have to do to achieve it...Ian

email (option): ian@wright52.plus.com

Thanks guys. I'm not really looking to get this highly tuned, more just fix some of the basic (and easier) breathing design issues. I'd like to grind and polish the inlet port a bit and perhaps get a new carb, but no increasing bore size or replacing cams or pistons. I saw the Ricardo alloy head somewhere else and hoped it might be off the shelf, and another one called a K-type(?), but if they're not off the shelf I won't bother getting one made. I don't need more power through the range, I just want a bit more at the top end to save me getting run over on the freeways.

I also read somewhere that the distance of the inlet port from carb to valve makes a difference too, and increasing this distance can be helpful. I see the logic, but don't know if that's already been tested and found to be not worth the effort. So some info on how to go about the grind and polish, carb manifold distance, and perhaps carb suggestions would be really handy. Thanks a lot.

cheers
Brett

email (option): brettsyoung@yahoo.com

Hi Brett...On one of mine I opened out the inlet port to the B33 size (1 1/8") and fitted a matching 289 carburettor..I also reshaped the area under the valve head and shortened and tapered the top of the inlet guide to reduce the obstruction in the port...

Some mild reshaping of the top of the barrel between the valve and bore and a little reshaping inside the head, along with a head skim to increase compression ratio completed the job...

That was 'minimal tuning' really...You can't do any less and expect a change in performance...

Jeff Bandola will be able to give you some pointers on the head work...I would take up his offer of help if you haven't already....Ian

email (option): ian@wright52.plus.com

Thanks Ian and Jeff. Really useful and comprehensive advice - just what I was after. Of course like most people that like playing with engines I'm slowly getting hooked on getting this well- tuned. (It's a '54 M21 incidentally.)

I'm comfortable with porting and tuning a bigger carb, but not at all with welding the head and lightening the flywheel. I'm sure I could pay someone to do the head, but on the flywheel: is there a drilling pattern to avoid throwing it out of balance? And as I'm running an outfit should I lighten it at all?

I'm also warming to Jeff's idea of increasing the intake valve size, and perhaps fitting goldie cams as you've described elsewhere.

At the end of the day I just want to be able to cruise at 65mph safely. But knowing myself I suspect I'll go the whole hog.

Cheers and thanks again
Brett

email (option): brettsyoung@yahoo.com

When Ian made my M21 flywheels slightly lighter. He just machined about 1/4" from the outside circumference Ron

email (option): ronpier@talk21.com

I'm conflicted about this. Yes, I can see the benefit of lightening the flywheel as part of mods to improve power. On the other hand, I get a kick when someone says something like "holy smoke, I can count the strokes when it's idling!" Human tachometer.

email (option): jonny.rudge@verizon.net

It's really a question of percentages...A good slow tickover can still be achieved with a lightened crank...even a crank that has had quite a bit taken off it...

A standard set of flywheels weigh 28lb. which is a pretty substantial lump of metal.

Tuned B33 engines, which use the same flywheel forgings in later engines, will still tick over with far more material removed from them than I would normally take from a sidevalve set..Though not quite as slowly perhaps.

Removing material from the sides of the flywheels and leaving the outside diameter the same will also help to preserve flywheel effect...

I removed about 1/2" from the outside diameter of Ron's flywheels....Just a slight reduction in weight to aid initial 'pick up'.

This would be insufficient in a more tuned engine to allow it to 'rev out' at the top end..Ian

email (option): ian@wright52.plus.com

Great info everyone. So, I'm going to increase the inlet port and valve, fit a 289 carb, grind and polish the exhaust port, and maybe (if affordable) change the cams for touring goldies. The last questions (for now anyway) are is there a specific 289 I should use? And how do I lighten the flywheels to the extent needed? Just take weight off the sides? Is there a pattern for drilling about so I don't affect balance should I do that also? Also, does the 289 off the B33 match up without modifying the manifold? (As opposed to the port)

Thanks all for the useful and fascinating feedback

cheers Brett

email (option): brettsyoung@yahoo.com

The 289 will fit the mounting flange andstuds of the 276...You need to go for an 1 1/8" or 1 5/32" 289 and port to match the carb throat...You will have to experiment with jetting once the bike is running so the best bet is to set it up rich and then weaken it as required...

The crank is far more complicated unfortunately...The crank assembly will have to be stripped and each flywheel dealt with separately...

First you will have to check whether you have cast iron or steel flywheels..Steel flywheels have a part number beginning with a 6...E.G.66-636.

Cast iron flywheels have a number beginning with 7..e.g. 66-724..

Some cast iron flywheels have no number on them or a number that doesn't match the sequences shown above...

If you have cast iron flywheels this will limit the amount of material you can remove...This may not be an issue in your case as you are not going for extreme lightening...

If you machine material off the sides of the flywheels then remove the material equally from both sides of each wheel...I would remove approx. 1/8" (.125") from both sides of both flywheels for your purposes...

However, having done this you will have to have the crank/piston/rod assembly rebalanced...There is no way round this if you remove material from the flywheels...

This is a subject in itself and is really a job for a professional engine shop...Ian

email (option): ian@wright52.plus.com