Timing Question

JBSracing · Mar 24, 2005

This is basically a timing question, apologies if it has been answered elsewhere. Can any body tell me the angular displacement of the Woodruff keys on the drive side and magneto side of the 650 Husaberg crank? In case thatÃ¢â‚¬â„¢s not very clear what I want to know is how many degrees rotation it takes to go from a reference point ,say the pin centre at TDC to each of the keys being at TDC.

Thanks

Ben
JBSracing

LINEAWEAVER · Mar 24, 2005

Hi Ben,
I have never bothered to index the keyway, however, I have on many occasion omitted the index key rotating the flywheel on the taper in order to accommodate a different rotor and / or timing figure. For a small (ie skunk Works) production run of crankshafts one could simply omit the keyway.

Not much help this time, sorry.

Best Regards,
Dale

JBSracing · Mar 24, 2005

Ah well, thanks anyway Dale. If you haven't indexed a crank then probably few ever have. I could omit the key on the Magneto side of the crank, but obviously I will have to include it on the drive side. When I stripped the engine a few months ago now I found, much to my consternation that the drive side key is about 5 degrees in advance of the pin at TDC. If only it had been in line then I could have clocked up and machined it easily.

Is every bodys drive key advanced like this? I don't just have a bum crank do I?

The 750cc kits are tantalisingly close to being finished, I hate the fiddly little bits like this. They seem so trivial but take so long and are actually very important to get right.

I will clock up and index both sides on my rotary table, I'll post the results here for reference when I have them.

Thanks,

Regards

Ben

LINEAWEAVER · Mar 24, 2005

Hi Ben,
The drive side keyway is indeed advanced though exactly how much I honestly cannot say.

A word to the wise:
The drive pinion spur gear is primarily secured by its key.
Unfortunately when heavy loads are applied to said gear it has a tendency to fracture through the keyway. I highly recommend a good shot peening of said area and insurance that the drive nut does in fact bottom against the gear as opposed to that of the crankshaft.

Best Regards,
Dale

JBSracing · Mar 24, 2005

Point well taken Dale. I don't have the experience with Husabergs that you do so I couldn't say that the key had a tendency to break out in this engine. But in other engines that I have experience with I know this happens, so I was a bit surprised when I stripped it to find a key on the drive shaft of a modern motor.

The KX 500 motor had a woodruff key on the drive side form the 1983 air cooled motor to the 1986, in 1987 they went over to splines.

What I was thinking of doing on the drive side was to cut a parallel key in the shaft, and machine the key partly into the bearing journal and installing a long key. This has 2 benefits, 1) parallel keys have a higher shear and fatigue load than woodruff for the same size, 2) the bit of the key that protrudes into the bearing journal acts as a shear pin as well as the key functioning normally at the bottom. It would still fit the stock drive gear.

Any thoughts on that idea?

Ben

LINEAWEAVER · Mar 24, 2005

JBSracing said:
Any thoughts on that idea?
Ben

Hi Ben,
The broached keyway in the gear is the weak link. The sharp corners (ie lack of a root fillet) is largely responsible hence the suggested shot peening of said area.

I personally prefer the taper drive pinion gears of the earlier model Husaberg. Perhaps such is an option for your custom crankshafts?

Best Regards,
Dale

BD · Mar 24, 2005

keyway bottoms

JBSracing, your machining detail in the bottom of the key is critical per Dales reference to fillets, (absent in the broached key on the gear). If you do not want to modify a key cutter in order to leave a fillet, then definately get it bead blasted to peen those bottom corners well. Unfortunately, it requires some very fine peening to get into a sharp corner, so the modified key cutter is the best option to minimize the stress raiser. Regards, BD

LINEAWEAVER · Mar 24, 2005

Hi BD,
I take it you received the exploded pinion gear?

Dale

JBSracing · Mar 25, 2005

Hi Dale

I probably should have read your post a bit better, I didn't quite realise that the gear was the first to fail out of the gear and shaft. It seems strange to broach a gear with sharp corners, you would think that they would radius the broach simply to prolong tool life let alone the component.

Anyway I will be running the engine in the next week, we will see what happens. If needed I can produce a gear with a root fillet, I have gear cutting equipment. I am hoping it will be OK as is.

I think there might be a way to calculate the timing at least on the drive side, using the numbers of teeth on the gears, and the fact that the 1 dot and 2 dots on the drive and counter-balancer shaft line up at TDC, and possibly some other dimensions. I need to put it in CAD, you might get the figure by construction/calculation.

Many thanks for all the advice.

Regards

Ben

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