Race preparation - does and donts...

[Luders]

To save weight, as I also suggested upgrading the radiator, this is a must.

so you top of your rad every time before you go out ?

For the benefit of members who have never seen a race bike, we remove the expansion tanks, upgrade the radiators and replace with a small expansion bottle, mounted to the side of the radiator as pictured.

[Luders]

Back to the cases, I have stripped this bottom end right down, to do the required flowing work.

Starting with the top half and looking down the inlets where your reed valves are usually located, you will notice a step of sharp material on either side, where the crank journals are normally located.

What we want to achieve, is a smooth passage for the air/fuel mixture to pass through and up the transfer ports of the barrels.

[Luders]

I've flowed the left side of the left inlet only so you can see the difference between the two sides.



Here's what it looks like from the inside



If you have any questions, just ask.

[banditbob]

Hi Ben is the crank in good nick and what are the barrels and pistons like? thanks for under taking this job i know you were starting a new project, If you require funds just ask I saw you found some kips off martin cheers bob.

[Luders]

I've not stripped your engine yet Bob, these cases will be cleaned up and used to replace your cracked ones.

[JanBros]

For the benefit of members who have never seen a race bike, we remove the expansion tanks, upgrade the radiators and replace with a small expansion bottle, mounted to the side of the radiator as pictured.

aah, ok

(should have mentioned in your first aswer )

[KFOR]

Hi Ben, what compound are you using...J.B Weld or the putty ?
and how much prep work do you do to get it to adhere to he case well ?

Kev

[Luders]

Hi Ben, what compound are you using...J.B Weld or the putty ?
and how much prep work do you do to get it to adhere to he case well ?

Kev

I've not started on that yet, but in answer to your question, both.

I use a product called J-B Stik, which is J-B Weld's epoxy putty.

Search J-B Stik on eBay for full product details and specifications.

[Luders]

I have ground down the excess material from the left hand side and photographed it alongside the right side, which has not been touched.

As you can see from the inside of the crankscase, I have just smoothed all the shap edges off.



Here you can see the material I have removed from either side, allowing for a smooth flow of air/fuel, through the crankscase and up into the transfer ports of the barrel.

[Luders]

Once you have flowed the areas as pictured previously, you are best off filling with an epoxy metal filler (J-B Weld) where the I have photographed.

Score the areas before applying the metal filler.

It is applied and shaped to follow the tops of the crank webs.





I just dress the surface off with a file to make sure it's flat and even.

These modifications complete the work required to the top half of the cases and you are ready to move onto the bottom half next.

[Luders]

Where the oil holes are, these areas are best filled.

Once again, prepare the surface by cleaning and scoring.
I cut a plastic straw to length, split and insert it through the holes and then fill.

before


Once the metal filler has gone off, you can remove the straws. I find it best to redrill the holes because, when you are working the metal filler in and around the area, it tends to put them off slightly, plus it looks neater.
I also smooth off the areas with the dremel to get a nicer finish.

after


Once you have done this, your cases are flowed and ready to be re-assembled.
I recommend getting some three bond to seal them.

[Peter4180]

Quite a difference - very clear to see in the last picture.
Any ideas or even measurements showing the improvement in performance?
Peter

[Luders]

I believe in bhp terms you're looking at around 4-5 bhp gain on these mods with barrel matching.
To quote MJ

Stock motor = 50hp
+
Flow the cases and set the squish = 56hp
+
35mm carbs = 58hp
+
a bit of porting = 62hp
+
Lomas pipes = 62hp but 5more hp mid range (seen 64 but 62 probably closer to the mark)

forgot
+
TZ pistons for reliability and reprofile the head to suit.

That is dyno pro horsepower - easy and reliable.

On 28mm carbs 135 jets with airbox
On 35mm carbs 155 main jets with airbox
jet sizes up or down a size depending on the weather.

[Luders]

Whilst you have the barrels off, place a base gasket over the barrel and look at your transfer ports.

You can remove any visible material protruding beyond the gasket.

I've taken this picture comparing barrels before and after removing the excess material.



HTH

[Mikkel]

Peter...

Did you ever go racing?

Ill just send you a PM

Mikkel
Copenhagen