[Agusta74]

I got my wheels back which was good all trued and tight! I have an appointment on Monday with an engineering shop to skim the rear drum brake before I can mount the new tyres etc.

The project is evolving to suit new information...

Today I raised the engine up twice, it's now sitting 250mm (9.8 inches) off the table/ground at full suspension extension. So when the front suspension compresses to is lower limit the vertical engine ground clearance will be 130mm (5 inches). The crankcase also clears the 45 degree lean angle test at full compression. So I am getting closer to the right engine position. I might still have to move the engine back a little more to make sure I can clear the front header pipe on full compression.... maybe half an inch.

Changes to the original plan..... I was always going to fit two front heads. And I WAS going to have both headers on the RHS of the bike. Which can be done.... but it can not be done well. Simply put, the rear header coming out the right side would have a funky angle that would just look wrong. It was going to be a two into one.
New plan.... front header to the right. The rear forward facing header to the left... with "two into two" high pipes. Look up "Ducati Imola pipes" if you want to get the idea. And now the front intake will exit to the right along with the rear inlet which was always going to the right.
The main idea for the two front heads was to get the headers on the right so I will have to think hard about that idea now....

The next challenge is the chain line. The measurement from the rim center to the inner face of existing Yamaha rear sprocket mount is 70mm..... the measurement from the inner end of the out put shaft is 110 from the motors center line. So I have 40mm (1.5 inches) to work out to get the correct chain line..... I can either move the engine 40mm to the left, or make a new mount for the sprocket on it's carrier that comes out another 40mm (with bearings inside) or a combination of both. With the big primary case it already looks like the engine is too far left! So making a presson and bolt on extension for the sprocket carrier might be the go...... ?

 

[Agusta74]

hummmmmmm.... maybe I CAN make the two right side headers work with a combination of a bolt on extension to the exhaust port or ports to get a better angle and having the angle of the header itself more out and around the engine... not trying to keep it in tight.... like these Vincents....

 

[Agusta74]

So today I revisited the header pipe "situation".... I sat and looked and drank tea. Then looked about for something I could use to create the rough shapes and curves of the exhaust headers.... after some considerable rustling and disturbing an errant rodent, I found an old bicycle tyre that was PERFECT!! So I cut that up and mucked about with them for a while and put a level out to show the path of the muffler. The end result is I CAN make it work and work well. So we are back to plan "A" with the RHS headers and a two into one with low pipes and muffler tapering up.

Some of the key design considerations for these headers are these.....

The front header must follow and respect the angle of the forks.
The rear header must start and stop at the same place (vertically).
The rear header pipe must intersect the centre line of the timing cover.
The header pipes must have a flowing organic curved line.
The muffler must be at 90 degrees to the rear shock.
I really must try to not be so bloody pedantic.

 

[Agusta74]

Then I turned my attention to the rest of the frame and swinging arm.... finally cut the top tube shorter (still too long as I as still working it out!)
And I set up a line to see what angle the swinging arm would be, and set the first rear tube in rough place..... 27 degrees to match the fork angle... of course....
I cut the 6 longer rear tubes roughly to length, plus the swinging arm flat sided oval, which will be doubled up as in the picture.

Then I spend a lot of time looking at the chain line and how the perfect frame member position has a chain running exactly though the center of it!!!
I am deciding if the chain line will run inside or outside the frame member that comes down from the rear of the main tube.,,, pros and cons... and I have spent a while working out how wide the swinging arm has to be to keep the chain line right and how they all work together.
More tea needed for SURE over that one.....

 

[Agusta74]

Ok, chain line, swinging arm width and motor position I think I might have nutted out today..... with the help of a mate who dropped in for a catch up (Hello Alien!!)

The frame INSIDE the chain line would leave the frame too narrow. The upside down V as looking from the back of the bike at the two tubes that come down from the rear of the main tube to the swing arm pivot would be to narrow a V to have much strength..... and it just looks "wrong".

The frame OUTSIDE the chain line is better, BUT the tubes end up very wide where they meet the swinging arm.
I think the end solution IS to have the frame outside the chain line, BUT move the engine 15mm (0.6 of an inch) to the left....

The 15mm move of the motor to the left will have these benefits...

1. 30mm narrower frame (15 each side at swinging arm pivot point).
2. Narrower swinging arm by 30mm.
3. Only a 25mm extension needed on the sprocket carrier (as opposed to 40mm).
4. Swinging arm more in line with the frame above for shock mounts top and bottom.
5. More room to tuck the exhaust in close on the left.

The down sides are these...

1. Less cornering clearance on the left. (could be got back by either moving engine up or machining metal off the left side of the case)
2. Big blob of a primary will stick out even further!

So at this stage I think that's going to be the way ahead.

The engineer in me does not want to use either a bent tube or a cut away tube to clear the chain.....

First picture is the tubes INSIDE the chain.. too narrow.
The second picture is a position of the tube if the motor is moved 15mm left. (there is a just visible pen line on the tube where it would be cut off.)

 

[Agusta74]

Ooooooh shinny new things!!!!! I like shinny things!!!

 

[Agusta74]

I did a new frame drawing today.... the main forces are between point A and point B and from C. The engine has three points of contact with the frame.

The front head which will have a full 4 inch wide mount that I will make to pick up 5 of the forward cap screw holes in the rocker cover (two of which are also picking up the minimal extra bracing in the casting for the factory mount). SO that will really help with the motor not "swinging" below the frame.

The rear head (which will of course be a front head) I will use the factory mount as on the rear of the head there is not really enough room to make a good strong mount.... and the factory one will be good there.

Then the 6 10mm bolts in the back of the engine, the top four for the factory frame mount and I guess the bottom two were for suspension? The top four will have a plate bolted to them that will have the swinging arm pivots welded to them.... taking that force straight into the motor. I am hoping that I can pic up the bottom two also maybe with extensions of the two tubes that come from the rear shock top down to and past the swinging arm pivot.

I will also try and keep the swinging arm sides as straight as I can to avoid weak areas. Fully straight if I can....

 

[Agusta74]

I am having brain issues working out suspension sag and frame building positions, angles and how long to let the tea brew.... braining is HARD!

The front fork will have 135mm of travel at 27 degrees so that makes 120mm of VERTICAL travel.....

The rear suspension has 70mm of travel also at 27 degree inclination with gives me 62mm of vertical wheel travel....

So if I assume a third of the suspension travel is used when the person sits on the bike..... thats 40mm front and 20mm rear.... !!

So do I have to build the frame main tube level, BUT with a 20mm spacer UNDER the rear tyre to compensate for the different amounts of movement front and rear when the weight comes on???? Oh my brain hurts!

 

[rossmick62]

So does mine now

Thanks

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