Author Topic: 1/4 Scale Cosworth DFV Engine  (Read 3291 times)

Offline gerritv

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Re: 1/4 Scale Cosworth DFV Engine
« Reply #60 on: July 29, 2020, 06:09:40 PM »
Ferrari 308 method:
Single helical gear on crank driving 2 cam drive gears with pulleys. Good for repeated 7500 rpm from my experience :-)
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Offline steamer

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Re: 1/4 Scale Cosworth DFV Engine
« Reply #61 on: July 29, 2020, 06:36:21 PM »
Or...even just a single reduction gear off the crank to a single timing belt pulley driving two belts, with a larger diameter so more tooth engagement....but if you have 6 teeth engaged at 180....you're probably fine....just looks small.

Dave
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Offline JonC

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Re: 1/4 Scale Cosworth DFV Engine
« Reply #62 on: July 29, 2020, 08:27:19 PM »
Hi Steamer, I agree it doesn't give much engagement but working back from the cam pulley size restriction it's the biggest I can get on the crank.

The bouland engine below is 1/3rd scale and looks like its using a 12.7mm single belt driving both cam shafts from a similar small crank pulley.

Jon

Mike and Jon,   What size is the crank shaft pulley?.....

Dave, it's 3/8" diameter and cam pulley 3/4" diameter

Jon
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Offline JonC

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Re: 1/4 Scale Cosworth DFV Engine
« Reply #63 on: July 29, 2020, 08:31:13 PM »
My usual starting point for actual designs (when I am not winging it) is: https://sdp-si.com/D820/PDFS/Technical-Section.pdf

6 teeth seems to be minimum wrap. Belts that are wider than diameter of pulley give tracking issues. Short belts also give tracking issues. Roundinsh profiles have less cogging action and don't tend to ride up the pulley as much. But their profiles are generally proprietary although the sdp-si manual conveniently gives the related patent numbers for further educaation. They can apparently be approximated using ball nose end mills and cnc. :-)

One suggestion might be to gear drive from crank to the large central pulley, then single belt from there around al the cams. Outside idlers are preferred over ones riding on teeth.

Gerrit,

Some useful info, thanks. I think having two belts running next to each other may cause problems if they don't track perfectly and there's no room for a central flange to separate them.

A take off from an intermediate off the crank sounds like a plan.

Jon
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Offline JonC

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Re: 1/4 Scale Cosworth DFV Engine
« Reply #64 on: July 29, 2020, 08:48:27 PM »
Hmm, problem.
I need to keep the top centre pulley running at half crank speed. It drives the auxiliary pullies for the water and oil pumps as well as the distributor.

Lucky old Mr Duckworth didn't have this problem before the invention of toothed belts.
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Offline steamer

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Re: 1/4 Scale Cosworth DFV Engine
« Reply #65 on: July 29, 2020, 08:49:56 PM »
Hmm, problem.
I need to keep the top centre pulley running at half crank speed. It drives the auxiliary pullies for the water and oil pumps as well as the distributor.

Lucky old Mr Duckworth didn't have this problem before the invention of toothed belts.

You could gear drive off the crank to the intermediate pulley and drive everything else with belts from there....

That's what I was getting at ....

Dave
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Offline JonC

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Re: 1/4 Scale Cosworth DFV Engine
« Reply #66 on: July 29, 2020, 08:56:59 PM »
Got it. I'll have a play with some layouts.

Thanks Dave  :ThumbsUp:
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Online Vixen

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Re: 1/4 Scale Cosworth DFV Engine
« Reply #67 on: July 29, 2020, 09:34:49 PM »
Quote

 I think having two belts running next to each other may cause problems if they don't track perfectly and there's no room for a central flange to separate them.
Jon

Would you have enough room to fit two plain toothed pulleys ( i.e. without end flanges) onto the crankshaft with a thin 10 thou (0.25mm) washer between them to act as a combined flange, to stop the two belts rubbing and fighting each other?

Mike
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Offline JonC

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Re: 1/4 Scale Cosworth DFV Engine
« Reply #68 on: July 30, 2020, 07:52:36 PM »
Mike, yes that would work or maybe just slice them to bits  :Lol:

I cant do anything in the way of an intermediate arrangement off the crank and then another off to the cams as this inevitably creates a third step in the train.

I've ordered some standard pullies 9.55mm Diameter and 19.1mm diameter and will mock up the arrangement to see what sort of load it can take.
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Online Vixen

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Re: 1/4 Scale Cosworth DFV Engine
« Reply #69 on: July 30, 2020, 11:18:15 PM »
Quote
Mike, yes that would work or maybe just slice them to bits  :Lol:


Ummm!!! a Cosworth powered bacon slicer    Interesting idea   :facepalm:

Mike
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