Allison V1710 as used on the P38 Lightning

[von Bek]

Here is a question that I think we may be able to find the answer to. The P38 had two Allison V1710 engines which rotated in opposite directions. How was the reversal of direction achieved?

There is a lot of BS out there on the net about changing the firing order, installing the crankshaft the other way round and inserting an additional idler pinion to drive the engine accessories. Anyone who knows anything at all about engines knows this can't be the whole story because there are obvious problems with valve timing and cam drives which are not explained by the claims.

These engines are still used by war-bird enthusiasts, pylon racers and tractor pullers etc. so I'm guessing there are guys out there who still mechanic on these on a regular basis and know how this contra-rotation worked.

Can anyone shed some light on this?

 

[Dev One]

Merlins on some Mosquitos did the same I believe, they had different mark numbers. I believe that they had another idler in the reduction gearbox.

Griffon props rotated in the opposite direction to most Merlins too, but I believe the crank rotated in the same direction on both, again due to an additional idler. Its possible a Google search will find the real answer.
Keith
Edit
Googling found this http://users.skynet.be/BAMRS/dh103/powerplant.htm - it shows the difference in the reduction gearbox.

This was for the DH103 Hornet, but it appears from this website that the Peregrine engine that was intended for the Westland Whirlwind was a reverse copy , i.e the whole engine was a mirror image. The design was never adopted though.

 

[n4gix]

According to this article, the engine itself was running "backwards" on the port side:

Another feature of the V-1710 design was the ability to turn the propeller either clockwise, or counter-clockwise, by simply assembling the engine with the crankshaft turned end-for-end, installing an idler gear in the drive train to the supercharger and accessories, and having a starter turning the proper direction. The ignition wiring and firing order were also arranged to accommodate the direction of rotation.

http://www.fact-index.com/a/al/allison_v_1710_engine.html

See also this complete "Allison Handbook for Operation and Maintenance..." from the manufacturer:
http://miravim.org/avimlibrary/Manu...gine, ALD-3-F2 3rd. Edition April 1, 1943.pdf

 

[von Bek]

Brilliant, thank you!

 

[Dev One]

Very Interesting....but maybe not so stupid ......to paraphrase Arte Johnson.....Obviously more than one way to kill a cat.
Keith

 

[Bomber_12th]

"ACE Allisons" http://www.aceallisons.com/, who is a leader in rebuilding/improving/overhauling Allison engines for warbirds, mentions that on the left-hand engines, the crank shaft still goes to the right, while the prop goes to the left due to the differences in the gear box.

Besides P-38's, the production F-82's, like the F-82 being restored to airworthy here in Minnesota, used left and right hand Allisons, though their left/right is opposite to the P-38's left/right - the left-turning prop/engine being on the right-side. Much rarer, the XP-82 being restored to airworthy in Florida, has left and right hand Merlins - the rare counter-rotating example being sourced from a garage in Mexico City of all places (how it got there, no one knows). Much harder to find for both projects, were the seemingly now non-existent left-turning props - both projects contracted together on a supply of new-build props from Germany.