Need oil cap ideas...

[NoShopSkills]

Helping a buddy with his Peitenpol... (a model "A" Ford engine powered home built aircraft). He built the sheet metal cowl around the oil filler tube. The cap just rides below a rolled lip in the cowling. The tube has a 1.5" I.D. and a simple turned aluminum plug cap that is retained by a long cotter pin running through holes in the tube. The problem is the tube is too short and dosn't stick out of the cowl far enough. Now that the cowl is built, he realizes there's no way to access and remove the cotter pin... We cant really extend or make a new tube, because it will interfere with the straight exhaust pipe that is just above the filler port and all of the other work is now done.

He's asked me about putting in a threaded aluminum bushing and then turning down and threading the existing aluminum oil cap, Making it a screw on and off affair. Particularly, the existing cap has some nice engraving that says "Oil 5 Quarts" and he'd like to retain that and orient it so that when screwed down tight it's upright.

I'm worried about cap retention and/or bumming up the threads so I told him I'd try some new turnings first to see how well he likes them and how good we can make a fit. To stay within the 1.5" I.D. however, I'm thinking the new cap will be small and the oil service hole even smaller, maybe too narrow.

There must be a better way to cap a tube?

 

[David S]

I am helping a friend build his Sonic experimental aircraft and he is using an aircraft version of a VW engine. His oil filler plug is simple a plug with two large O-rings that gets pressed into the filler port.

David

 

[GK1918]

my problem is seeing this without a pic I know A Fords we rebuild them so whats the problem pipe too tall, so cut it and use the expandable
plug that detroit diesels have. The origionl pipe will come out, so just make up another one. ?

 

[NoShopSkills]

GK, the motor has been completely reworked for an aircraft application and aside from the block and head still looking like a model A, nothing else is stock. The engine builder built a straight oil fill tube that stops about 3" under the short straight pipe chromed exhaust tube that only sticks out about 4" from the side of the block.



A very tight sheet metal cowl has been built around the engine for purposes of aerodynamics both top and bottom, but the above photo only shows the bottom cowl in place... The oil tube and plug style cap are in the lower right hand corner of the cowl. A hole in the top cowling, with a rolled lip leaves access to the oil fill port without a latch door. The dressed cap compliments the period aircraft appearance.

Here's a prototype/extra cap I turned out of a cast ingot. I cut two O-ring reliefs into the plug as suggested by David S. I'll try his idea before I commit to cutting O-ring grooves in the real nice cap.



I'll try the compression fit tomorrow after I scrounge some 1.5" O-rings. I like this idea better than the cotter pin! It's a low pressure application, but since it's on an aircraft engine, I'd like to see more positive retention. I didn't get to be an old gray pilot by leaving things like oil caps to chance...

I had the idea of two opposed spring latches milled into the cap that catch a ring that I'd weld onto the tube... What do you guys think of something like that?

 

[David S]

I see a lot of clecos, so I guess she is not quite ready to fly. That plug that you made looks very similar to the VW one with the exception that his is red anodized. I would have thought that a more positive retention would be required, but they seem to thing it is fine.

David

 

[FanMan]

Instead of the cotter pin, use a wire in a tube (push-pull cable) so you pull it from somewhere else. It could be a cheap cable like a lawnmower throttle, solid wire in an outer coil, and wouldn't have to be long. Or you could just add a small flap door in the cowling to access the oil fill, like Cessna does.

 

[NoShopSkills]

Fan man... your post just baffles me... I have no idea what you are talking about. If he wanted a door over the oil tube we'd have built a door there. He wants the cowl open in places, because the cowling is unique to the style and timeframe of the aircraft's vintage heritage. My question isn't really about the cowl anyhow, it's about designing a system that retains a plug in a tube that may be under pressure.

Now that I've talked a little more with him about the motor, I was reminded about the splashers that bolt to the bottom of the connecting rod caps. They vigorously atomize the oil on each rotation through the oil pan. With that knowledge, I am now thinking that O-rings might not be enough to retain the cap unless there is a provision for crank case ventilation/pressure equalization.

 

[dickr]

Not being an airplane guy or engine rebuilder I'm gonna show my ignorance. Does the oil tube bolt on or can you remove it then silver solder (unless it's aluminum) a thread around the outside and a threaded cap for it. Well I tried. Hope you find a simple solution.
dickr

 

[NoShopSkills]

Hey dicker...

The oil tube is both aluminum and it bolts to the bottom of the block at about a 25 degree angle. Here's a photo of the block with the simple tube removed while I've been working on the dimensions for the prototype plug, which by the way fits perfectly now!



Here's the part all done. We also agreed on a way to vent the tube with a mesh two way reliever tapped into the side of the tube. It will both keep pressure from blowing the cap off and should prevent atomized oil from slathering all over the inside of the cowl. Now if the owner likes it, I'll commit to cutting slots in the real nice cap that the engine builder made up with the engraving on it... Thanks for everyone's input!!!!!!!

 

[FanMan]

Fan man... your post just baffles me... I have no idea what you are talking about. If he wanted a door over the oil tube we'd have built a door there. He wants the cowl open in places, because the cowling is unique to the style and timeframe of the aircraft's vintage heritage. My question isn't really about the cowl anyhow, it's about designing a system that retains a plug in a tube that may be under pressure.

Oh... re the door, I got the impression from the photo that the oil cap was inside the upper cowling, in which case a small door (they're about 6" square on some Cessnas) would give access.

As for the wire in the tube, if I understand you correctly you're sticking a cotter pin into a cross drilled hole in the filler tube and cap to hold it in, right? So instead of the cotter pin, a longer piece of flexible wire in a sleeve (just like a throttle cable); one end is a pin sticking into the filler tube to hold the cap when it's extended. You pull the other end (where there's a conveniently located handle) and it pulls the pin out of the filler tube.

The crankcase on those engines is usually just vented to atmosphere (perhaps with a puke jar), isn't it? So there should be no pressure inside the crankcase to push the plug out, though you still want to secure it against vibration.