Radial Engine Design - Cam rings/timing, etc.

[Dave Downs]

I've been fascinated by the internal combustion engine since I took the head off my Grandfather's Briggs & Stratton lawn mower engine to watch the valves go up and down when I turned the flywheel. I was 9 at the time and Gandpa was not amused.

Since then I've rebuilt many Inline and V-type auto engines, but never had the chance to get inside a radial.

I'm most interested in the valve train, specifically the cam ring (gear?) and how it is timed to the crankshaft. I do remember reading years ago that the ratio of cam ring rotation vs. the cranshaft was somewhere in the neighborhood of 1:6(?), but varied depending on wether it rotated in the same direction of the crankshaft or in the opposite direction.

Can anyone point me to some reference material, preferably on-line. I've 'googled' radial engine(s) several times but never found details on cams.

[Robbie Stuart]

Try this site. http://www.enginehistory.org/ There is a ton of information there. There is also a book "Powerplants For Aerospace Vehicles" from the Northrop Institute Of Technology thats very good. Good Luck.
Robbie

[Matt Gunsch]

how it attached depends on the engine, single row vs double.

Here is a cut away engine, you can see the cams in the engine.
http://commons.wikimedia.org/wiki/File: ... tten_2.jpg

and this is from the B-29 thread, page 9

[Vessbot]

"Aircraft Powerplants" by Michale Kroes and Thomas Wild has a few pages on radial engine valve trains.

As you said, the cam plate can rotate in the same direction or opposite to the crank, and the ratio varies with the arrangement.

The general formula is cam-plate RPM = crank RPM / (no. of lobes x 2)

The x 2 is there since it takes 2 revs of the crank to complete a cycle.

So, for a 9 cylinder engine, for either the intake or exhaust system, you can have a 4 lobe cam plate running at 1/8 crank RPM in the opposite direction, or a 5 lobe cam plate running at 1/10 crank RPM in the same direction.

It's pretty hard to describe without the diagrams, and I don't have a scanner unfortunately.

[Canso42]

Contact Graham White at Redbaron301@earthlink.net (tell him I sent ya.) He's written a couple of tech books on a/c engines, at least one of them on radials. He has a Merlin and a PW R2800 both on test run stands that he occiasionally cranks up and runs just for the heck of it. He's also the head honcho of Antique Engine Historic Society. Drop him a line about getting a copy of his round engine book. It's said to be pretty entertaining reading as well as a good reference work.

Doug Ratchford, 'Canso42'

[SPANNERmkV]

Matt,
That can't be a happy B29 engine...

Doug,,, Howzit Floatin'? !

I'd forgotten how much neat stuff resides on Graham White's page.

[engguy]

The whole gearing/timing thing has to do with the number of cam lobes and the number of cylinders in the row.
(I made a chart here but it didn't work sorry)


If the cam has external gear teeth it turns with crank
If the teeth are internal like an R2800 and R4360 it is Opp crank rotation.

And actually the timing of events will be determined by the actual size and configuration of the lobe and its placement.

Here see it work.
Except it is 4 rows with 7 banks, they said the wrong thing.

http://www.youtube.com/watch?v=qpmOb46b ... =1&index=1

[The Inspector]

Snapped off rocker tip? sure screwed up the cam plate!

[Matt Gunsch]

Snapped off rocker tip? sure screwed up the cam plate!

I guess you have not been following this thread
http://warbirdinformationexchange.org/p ... =dave+fifi

the info is on this page
http://warbirdinformationexchange.org/p ... &start=120

[Dave Downs]

Thanks to all for the replies!

[Jase]

Have a look at www.nomeking.com Ralph has done an animation of an R-2800 that should help you visualize the inner workings.