Gear Driven Valve Train?

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

Plakton51

New Member
Joined
Jun 24, 2022
Messages
3
Reaction score
0
Location
Central Pennsylvania
Is a gear driven valve train possible to replicate in model form? The engine in question is a Ford GAA 1/5 scale tank engine. It's a 60° V8 DOHC with a bore of 1" and a Stroke of 1.2". The reason I ask is before I get too involved in the designing and drafting of the gears and shafts, I would like to know if those gears would get enough torque to open the valves or will it get too much torque and shear off the gear teeth (Pictures for reference)?
Accessory-drive-gear-train-cams-included-FIXED-flattened-1600x1441.png

Thanks in advance.
 

lee webster

Well-Known Member
Joined
Oct 4, 2019
Messages
151
Reaction score
52
Location
cornwall uk
I can't help with your enquiry. Perhaps you can answer mine. It looks as though shaft F slides within shaft H. Is this to allow adjustment of the camshaft timing?
Good luck with the build.
Lee
 

Jasonb

Project of the Month Winner!!!
Project of the Month Winner
Joined
Mar 30, 2008
Messages
3,159
Reaction score
820
Location
Surrey, UK
Certainly quite a few small 4-stroke model engines that use skew gears to get the axis of the cam shaft 90deg to the crankshaft. Without knowing the size of the rest of the engine it's hard to say what size gears would result from your 1" bore engine
 

Plakton51

New Member
Joined
Jun 24, 2022
Messages
3
Reaction score
0
Location
Central Pennsylvania
I can't help with your enquiry. Perhaps you can answer mine. It looks as though shaft F slides within shaft H. Is this to allow adjustment of the camshaft timing?
Good luck with the build.
Lee
Yes, shaft H and F are splined together to help with valve timing. Shaft F would be pulled up through the housing out of the splines, and then the camshafts adjusted. You have a good eye.
 

lee webster

Well-Known Member
Joined
Oct 4, 2019
Messages
151
Reaction score
52
Location
cornwall uk
There has been some amazing machinery made for war. I wonder if that system was used elsewhere?
My late father was a tank driver after the war. He was stationed in Germany in the early 50s where he met his future wife, my mother, a Welsh girl visiting her brother, my dads commanding officer. My dad was also loaned to the American military, and they loaned us some of their tank crew.
 

Drawfiler

Well-Known Member
Joined
Apr 7, 2020
Messages
62
Reaction score
18
Location
Uk
IMHO Helicals or skew gears will work the valves as it’s been done often before in model sizes. I would be worried about the other gears, particularly J and T which appear to be spiral bevels or helical bevels, these are very hard to make well on home kit, Q has internal splines and appears to be integral with the crank (it’s hard to tell) and could pose some broaching problems in scale sizes sizes, you could also have trouble with the telescopic shafts H and F, remember you don’t want any backlash
 

Plakton51

New Member
Joined
Jun 24, 2022
Messages
3
Reaction score
0
Location
Central Pennsylvania
Certainly quite a few small 4-stroke model engines that use skew gears to get the axis of the cam shaft 90deg to the crankshaft. Without knowing the size of the rest of the engine it's hard to say what size gears would result from your 1" bore engine
I did some quick math and a simple drawing and concluded that gears A, Q, J, and T are all around .5". As for the worm gear and gear P they came out to around .33". These aren't completely drawn out and constrained measurements so they maybe off by a little.
 

gbritnell

Project of the Month Winner!!!
Project of the Month Winner
Joined
Jul 16, 2007
Messages
2,857
Reaction score
826
All the gears could be made but my concern would be the worm. With the steep pitch it looks like it has 2 leads which is easy enough to do but most lathes probably won't cut that pitch.
gbritnell
 

Jasonb

Project of the Month Winner!!!
Project of the Month Winner
Joined
Mar 30, 2008
Messages
3,159
Reaction score
820
Location
Surrey, UK
You should still be able to do it by playing about with the gear train and driving the leadscrew by hand rather than driving the spindle. Just make sure the tool has plenty of clearance.

This is mine geared for 32mm pitch that is 0.8tpi (zero point eight)

 

Asm109

Well-Known Member
Joined
Nov 2, 2018
Messages
54
Reaction score
24
Location
Poway, CA
you could also have trouble with the telescopic shafts H and F, remember you don’t want any backlash
Any backlash is not on the menu. If the shafts slide, they have clearance, therfore backlash.
Now we are arguing about the magnitude of the lash. Since the engine turns in one direction, I don't think lash is an issue at all. When the follower goes over the nose of a cam lobe the valve spring tries to force the camshaft ahead. In a single cylinder this might be an issue. With 8 cylinders at least one lobe is going to be compressing a spring at all times.
 

Drawfiler

Well-Known Member
Joined
Apr 7, 2020
Messages
62
Reaction score
18
Location
Uk
I take your point about backlash so it should be OK. The worms would be better milled rather than screwcut, with a 135 to rack cutter,,it all depends on the kit you have.
 

Latest posts

Top