1/4 Scale Cosworth DFV Engine

[JonC]

A few update photos. I still have to get round to producing the waxes for the block and have been doing a lot of the other bits. Five speed Hewland FG400, suspension and printed a tyre master that I'm going to mould in rubber like the CV boots I've already done.

[gerritv]

Wow, with a different background these would look like photos of the real thing.

[mikemill]

Jon
This is very impressive work, are you using original drawings or the real thing for reference. Do you still intend to make castings available to buy?

Mike

[Vixen]

Jon,

It's unbelievable how frail those suspension arms look against the massive tyres. Pleased to see you back on the forum.

Mike

[JonC]

Hello again chaps, yes now that COVID is slightly less a part of my life I have a little more time to post.

Gerrit, thanks for that, I do try to be as near as possible to the real thing in all aspects.

Mike, It's a bit of everything - some known dimensions but very few to be honest, some super imposing a 3D drawing over a picture and some that make sense because of the known dimensions. Word got around and I was invited over to Hewland Classic Gearboxes for a look around which was a great help. The suspension etc is from the Tamiya 1/12 Tyrrell 003 model.

Mike, nice to be back in touch again. Yes it all looks fragile to the wheel doesn't it. I actually had to check the wheel dimensions myself to make sure it was correct but it is, although they seemed to run bigger tyre sizes in the mid 70's compared to earlier and this is the larger. I think when the rest of the suspension is on with wing supports etc it will look more in proportion.

[JonC]

Jon
This is very impressive work, are you using original drawings or the real thing for reference. Do you still intend to make castings available to buy?

Mike

Sorry Mike, missed the bit about casting. Yes absolutely, I have the moulds made for the block and the wax etc to try them out with. Just need the time to set it up give it a go.

Jon

[JonC]

Hi all,

Knowing the huge amount of knowledge out there, I wonder if I could ask for some feedback on another version of the DFV I'm working on. As you will see it's a belt driven version that still stays true to the engines appearance but massively simplifies the gear train of the original. Again it's 1/4 scale and uses 6mm wide x 2.5mm pitch dual belts allowing for the cylinder stagger that has been increased from 0.2" to 0.236". Crank pulley would be 0.375" diameter and Cam pullies 0.75" diameter.

This is just an initial layout drawing so any thoughts about whether this looks viable would be appreciated.

I have looked at the Bouland engine which seems to work ok based on the same principal but doesn't replicate the main DFV features very well in my view.

[steamer]

Angle of wrap and number of teeth engaged at the crank is pretty small.   

[JonC]

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

[Vixen]

Dave (Steamer)

The crankshaft pulley is the small one at the very bottom with nearly 180* of wrap.

Jon,

Instead of using two narrow belts to overcome the cylinder stagger, why not use one wider belt and overcome the cylinder stagger by increasing the length of the cam shafts on one side, by the amount of the cylinder stagger. That's what Mercedes Benz did on the W165 to bring their cam shaft drive all onto the same plane.

Mike

[JonC]

Hi Mike,

I thought about that. Bouland must be doing it as he's running one belt only. it would mean a complete redesign of the front cover to bring everything level but that's doable. I just wanted to keep everything as true to the real thing as possible and came up with this layout.
Do we think it would work? If Bouland is using a 12.7 belt to drive four cams then would 6mm work on just two?

Jon

[steamer]

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?.....

[Vixen]

Hello Jon,

In principle two narrow belts should do the same work as one wider one. Have a look at different belt manufacturers, some offer better strength and some offer greater flexibility/
.
Mike

[gerritv]

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.

[steamer]

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.

Yeah I was heading in that direction......