540 short jug info.

Aircraft powered airboat discussion.
Southern Airboat Member
Posts: 13
Joined: Wed Jan 02, 2019 5:46 pm

540 short jug info.

Postby Kmr320 » Sun Feb 10, 2019 2:26 pm

Here goes. Went look at a supposed 540 260 yesterday. And as usual the owner wasn’t even close. Lol. “I just ran it” lol. So I know it’s a 540 case and sump and hopefully crank. It’s got angle valve 480 cylinders on it and the owner said he had to get a piston cut down once after a jug replacement. So my question is would it be a 540 crank,480,320 rods and a milled piston or is a 480 crank possibly in there? Also if a person like myself didn’t want a hot running high compression engine like this why couldn’t you get some low compression pistons made and get back to normal? Also this motor does not have spacers. Thanks y’all ideas/info is appreciated

Southern Airboat Member
Posts: 51
Joined: Wed Jan 21, 2009 2:45 pm

Re: 540 short jug info.

Postby woodlineO540 » Sun Feb 10, 2019 8:58 pm

More than likely it’s a short Jug engine it’s a 540 crank 480 rods and cylinders. the Pistons are back cut to clear the crank on account of that short rod. You can Machine the Pistons probably as low as 9 to 1 compression that is ballpark

Gary S
Site Supporter - I
Site Supporter - I
Posts: 1534
Joined: Wed Mar 03, 2010 3:30 pm
Location: Redlands

Re: 540 short jug info.

Postby Gary S » Mon Feb 11, 2019 6:49 am


Southern Airboat Member
Posts: 40
Joined: Thu May 22, 2008 8:12 pm

Re: 540 short jug info.

Postby BobBrack » Wed Feb 13, 2019 1:16 pm

The theory behind this setup is the piston goes down farther in the cylinder. Thus bringing more air into the cylinder. It also rises higher in the cylinder. Thus making higher compression. I have even seen them with the 540 rods installed. The rods have to be machined in order to turn the rod bolts around. I personally think this combination started because it's easier to find and a lot cheaper to find 320 rods and 480 cylinders. Most people buy 6 540 rods. Have space plates made to go under the cylinders. Get longer push rods and tubes. Put it all back together with correct pistons and run it like you stole it.

Return to “Aircraft Power Only”

Who is online

Users browsing this forum: Blownaway540 and 26 guests