917 180 degree V 12

[steamer]

We'll call it two guys talking feasibility.......  8-).....and yes, the roots are getting deeper

Dave

[steamer]

something like this?

http://image.slidesharecdn.com/couplings-121226211146-phpapp02/95/couplings-8-638.jpg?cb=1356556550

Dave

[crueby]

We'll call it two guys talking feasibility.......  8-).....and yes, the roots are getting deeper

Dave

Fascinating conversation to be following, even if I need to google some of the terms flying back and forth. Never heard of hirth coupling, for one. Hope you guys actually build one/some of these engines, as long as you post pictures!!   

[Vixen]

Yes, it's like two bevel gears made with a 90 degree Vee cutter. Easier to make than the manufactures let on.

Key on the separate gear wheel supported by the adjacent big end bearings, as in your sketch.

Mike

[steamer]

We'll call it two guys talking feasibility.......  8-).....and yes, the roots are getting deeper

Dave

Fascinating conversation to be following, even if I need to google some of the terms flying back and forth. Never heard of hirth coupling, for one. Hope you guys actually build one/some of these engines, as long as you post pictures!!   

crueby....right now its more two guys having a pint....but you never know!....Mike has "Eatin this dirt" already...so it's good to bounce ideas around.   That way I can all my OWN mistakes.....8-)

Dave

[steamer]

Yes, it's like two bevel gears made with a 90 degree Vee cutter. Easier to make than the manufactures let on.

Key on the separate gear wheel supported by the adjacent big end bearings, as in your sketch.

Mike

OK you sold me!   Two 3 throws seem a lot easier than 1 six throw!

Next pint is on me!!!

 

Dave

[Vixen]

Nice one Thanks
Mike

[Vixen]

I would be inclined to look at the camshaft gear train next. Ideally, you should try to use standard involute cutters or gear hobs rather than be forced into making some odd ball size. This may influence the final scale.
Mike

[steamer]

YES!   Hence starting at the crank and working out...that will drive the internals...and the scale...

Riddle me this?     the gear drive is slightly asymmetric......how come?

I suspect it was to get the cam box up to the same level as the engine block for ground clearance.....the 917 looks big....but it's not!....

Dave

[steamer]

Of do you think it has more to do with the difference in size between the exhaust and intake valves?

Dave

[Vixen]

If I told you the answer to that riddle, I would then have to shoot you; it's that secret.

Actually I am not sure. Even if the exhaust cam box were identical to the Inlet it would still be above the level of the lower crankcase seam split. Besides, the snake pit of exhaust pipes are even lower than the crankcase.

Could the asymmetry be there to prevent resonance in the drive train and between the two camshafts, each camshaft runs 'half a tooth' out from each other? Just thinkin.

Mike

[Vixen]

Don't think they would design the whole cam box asymmetrically because of different lengths of the valves. Porsche could afford to buy/make valves to fit. I guess the asymmetry has much more subtle roots than that.
Mike

[steamer]

No so much length of the valve, but valve head diameter....you need to lay it over to get those two HUGE valves in there....and have some meat in between them to put in a Titanium seat and have a head gasket land......I think THAT is the reason....

By the way ....the 0.3 scale engine has a intake valve of 0.625" and an exhaust valve of 0.50
With a cylinder bore of 1"


Dave

[Vixen]

You sure you are right, I think you have nailed it.
I just noticed the angle of the inlet is much steeper (nearer to the vertical) than the exhaust, in order to accommodate the oversize inlet valve head. The two cam box positions merely reflect the different valve angles. Porsche really had to work hard using different valve angles to get such large valves into the head. Just as well they settled for two valves per cylinder when most race engines, on this side of the Ocean, usually have four valves per cylinder.

Mike
 

[steamer]

The big gear in the opening graphic for this thread works out to 2" in Outside diameter.    That could be a 64 tooth 32 DP gear which would be robust!....with a 40 tooth crank gear.   going to a 28 tooth gear, then two idlers, and then to a another 35 on the cam shaft

So that is 64/40 x 35/28 =2/1

1/8 scale 2 HP 4x4 Remote control buggy runs 32 DP gears open at 25000 RPM....so clean and oiled, should be fine for demonstration runs