lightened Primary

got2dv8

I am considering lightening my primary gear. There is a CNC water-jet place locally. I am assuming balancing won't be an issue since they (their cuts) are extremely accurate. Anybody have a lightened primary?

Robert

griff851

Going hard core. As Steve mentioned in an earlier post, are you machining out the guts of the selector drum? You might as well now.

Griff

got2dv8

griff851 wroteGoing hard core. As Steve mentioned in an earlier post, are you machining out the guts of the selector drum? You might as well now. Griff

Is that a joke? I have a drum sitting in my closet o' parts and it's already hollow...😳 .

Robert

Mr.R

No Robert it's not a joke.
Unfortunately I haven't got a picure but, the drum has three slots that the selector forks slide around, between these slots is a lot of metal, it's this metal that you pepper full of holes to lighten the drum.
I got the idea years ago when I saw pictures of the bevel 900TTF1 NCR Ducati's internals, at the time I was working as a Ducati mechanic/race engine builder.
I had a spare selector drum kicking around, so I painted it with engineers blue and then marked out where to put the holes without weakening the drum too much and the shop got it spark eroded or drilled I can't remember which.

When I club raced self tuned Triumph T150 Trident's back in the 70's I went over to drilling lots of holes in (and slimming them down) the standard steel timing gears after a set of alloy gears shed their teeth.
So I wasn't a stranger to lighening engine internals.

About a year or so back I had the use of a spark eroder FOC and lightened a couple of primary gears, one for my 851/916 and another with the later ratio for my 984 project motor, so while I was at it I 'attacked' a spare 916 drum for the 984 motor.
I downloaded and printed pic's of lightened primary gears from the V Two and Kamna Racing websites to then decide how many holes to put into my gears and where to put them.
I wanted them lighter but didn't want them flying apart, the further out towards the outer edge of the gears you put the holes, the greater the effect they will have when the motors spinning up/slowing down.
But too many holes/not enough meat left to take the strain could result in a very large and expensive BANG!
I was also going to lighten the 851/888 oilpump drive gear, but the 749/999 oilpump I've got already have has a seriously lightened oilpump drive gear as standard.
As a 'rule of thumb' I have anything over a 2" diameter rebalanced after lightening them.
If anythings causing vibration it's sapping power/causing stress inside the motor, both of which you need to avoid when tuning/prep'ing a motor for high performance.

Many many, years ago now (back when I was a teenager in the early 70's)when I started on this never ending learning curve, my parents bought me copies of Phil Irving's Tuning for Speed and Black Smoke for Xmas one year, although these books were 1st published in the 50's the lessons held inside them still hold true today...
IMHO They're well worth a look/read if you can find them anywhere.
Thinking and methods may have changed over the years, but the basic science still remains the same if you want to make a bike/engine go faster/run smoother.

Steve R...I've NEVER denied being a complete ANORAK!

hauge

I had mine water cuted.

Cheers
Thomas

got2dv8

Mr.R wroteSteve R...I've NEVER denied being a complete ANORAK!

I had to look that one up! I am using the corse primary as well as the pantah primary as models. The Pantah has holes in conjuntion with the mounting holes, where as the corse has them slightly offset.

Yes, I see the big heavy chunk of metal in the drum.. but I think I'll leave that alone. How does one go about getting lightened gears balanced?

hauge wroteI had mine water cuted. Cheers Thomas

See, that's what I thought the factory should have done as far as offsetting the holes with the mounting points for more strength... of course I could be wrong as this piece is rotating.. then maybe the forces coming from the center shift???

Robert

here is the Corse and the Pantah

Mr.R

Robert,
I use a company that specialises in 'Dynamic Balancing' here in the UK.
If you get the new holes opposite each other it shouldn't throw the balance out by that much, then the balancing co' only need to grind a small amount off to get it back into balance.

Steve R

hauge

I have a set of primary gears for a 749R wich looks as Roberts.
How ever the the 749 R has a conical(?) fitting on the crank, not a key(?) and strait shaft. (could somebody help me out with the right terms please).

Water cutting is pretty straight forward. However I guess a balancing is good. I could not use my watercuted primary because the sealing surface was not covered when they did the job so grinding material made som marks in it.

Cheers
Thomas

griff851

hauge wroteI have a set of primary gears for a 749R wich looks as Roberts. How ever the the 749 R has a conical(?) fitting on the crank, not a key(?) and strait shaft. (could somebody help me out with the right terms please).

Morse taper.(As used on the lathes, mills, for holding in large drill bits.)
I assumed all crank primary's have them in conjunction with the key. Is this not correct? The taper provides more surface area to help the gear grab the shaft, and works like a wedge at the same time, as there is a shit of torque load going on there.

Griff

Mr.R

Griff,
Later Corse and 999 onwards cranks mount the primary gear on splines.

Steve R

griff851

Thanks Steve. Testarettas onwards basically then.

Griff

hauge

Mr.R wroteGriff, Later Corse and 999 onwards cranks mount the primary gear on splines. Steve R

Ofcuorse!
I meant the other way around. The standard desmoq. has the morse tapper and the 749R the splines....
Sorry

Cheers
Thomas