Are they supposed to be painted black? Flat or gloss if so.

Hi Mike..Assuming you are talking about an M20 (iron head) they were painted black...

The few new ones I have had through my hands over the years were painted in a satin black finish...

Whether that was universal throughout the long production run of the M Series machines I can't confirm...

Interestingly, just today I unpacked a NOS Triumph TRW cylinder from its original packing crate and protective wrapping and was surprised to find it only had an extremely light coat of black cylinder plate, certainly insufficient to give it any meaningful protection when in service...Ian

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

Ian, yes thank you! I just picked up some engine matte/satin black paint at the car parts store, just need to take a steel brush and clean everything a bit before I paint it.

email (option): mike.kaczorowski@gmail.com

What about alloy heads? I've just had mine hydro-blasted and wondered what to do to a) give it a protective finish to hopefully keep it looking sparkly and b) is there a finish that will also improve heat dissipation?

G'day Nigel,
I wouldn't do anything to the surface of your hydro blasted head. I had my M21's alloy head hydro blasted some years ago and it remains bright and easy to clean.

email (option): spacemonkeym@gmail.com

Nice bike Matty...Ian

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

Thanks for that Matt. It's all the excuse I need to leave it as it is! I'll pop out to the workshop and take a picture of the head to see how it compares to yours...

Here's a couple of pictures of my head. It was a right mess (broken and missing fins etc) when I got it but I had all the basic repair work done and then handed it over to Basil and Stewart at Headworks. I gave them all the relevant measurements, explained what I had in mind for the engine and this is what came back - beautiful!

Hi
very nice work & nice bike also
Hussein

email (option): sl_hussein@yahoo.com

Hello Nigel,

The bike (And head) are very nice.

I have few questions..

Is the bike 500cc?
When you filled up the head's chamber, did you leave the original dept
On the remaining, unfilled part?

Do you know what is the comp ratio now,
And did it really change the bike performance significantly?

Thanks,
Noam.

I experimented with my own bike, filling in the head to produce a compression ratio of 8.5-1 more or less....

I then ran the bike over a few miles locally, at normal speeds and revs, which included a reasonably steep test hill...

As expected when the engine warmed up 'pre ignition' or 'pinking' occurred...

I removed the head and machined a little material from the combustion chamber to slightly drop the ratio...same result..

I continued progressively dropping the ratio and testing over the same piece of road until pinking was no longer present unless the engine was really 'slogging' under load...

Final measurement of the compression ratio produced a figure of just over 7.2-1...

All testing was carried out using UK spec. lead free 'pump' petrol, without altering the timing settings or plug grade and over a distance that allowed the engine to reach normal running temperature..

It should also be born in mind that substantial alterations to the head and squish area that are not carefully considered can reduce gas flow and cost power as well as raising compression ratio in an effort to gain some!...Ian

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

I'm quite impressed with Hydroblast and the finish they achieve, the process also hid or blended in repairs to fins that I had made.

And Thanks Ian.

email (option): spacemonkeym@gmail.com

Firstly, sadly the completed bike is not mine - it's Matt's and I'm dead jealous!

The engine I'm fitting to my bike is a 626cc. Standard M20 stroke but with the cylinder bored to take a Holden 202 piston that is 92mm, so it's much closer to being 'square'

I had the head hydro-blasted by Phil Pilgrim at Union Jack Motorcycles but Basil and Stewart did the combustion chamber and all the tidying up. I aimed for a 7-1 comp ratio to start with because as Ian says, there's going to be some trial and error in the set-up and I can always back it off a bit if needs be.

The barrel has been ported, has a bigger inlet valve and it has lumpy cams too but these may well have to be softened off as Doug Fraser originally built the engine for road racing.

Thanks !

Noam.

email (option): noam10@gmail.com

Hi Nigel...Could you keep us posted about progress, set up and performance...I'm interested to hear how you get on and I'm sure others will be as well....

You may find the cams a bit superfluous if you haven't lightened the crank..but time will tell...Ian

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

Will do Ian. I've been keeping a diary and taking lots of photos as I'm hoping to write a feature for a magazine. If nothing else it will appear in the BSA MOA magazine!

I think you may be right about the cams, they are Gold Star road race at the moment as the engine was originally destined for an historic sidecar outfit (hence the crank wasn't lightened). However I've got Scrambles cams to try and plenty of cranks to play with if it isn't too successful.