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Building a Javron Cub

I think if you can engineer a Rotec radial and sell 'em you ought to be able to reverse engineer a Warner and build them again. To me it's about the coolest radial engine going for a small airplane. Those new radials don't sound like a radial. For many years I shared a hangar with Harold Newman and propped his 145 on his Monocoupe. That was a treat for me.
Had to take the Warner heads to the machine shop for a little tweeking so went back to the Cub for a day or two.
I really liked the thread on removing the triangle shaped left side window so I jumped in with both feet. Here is a before shot (well, actually I had started cutting on the bottom channel as you can see)........


And after cutting the post and bottom channel out, (I placed a piece of channel on the bottom part to see what it would look like)..............


I will get some of the appropriate stock from Jay, weld it in, (lest folks think I know more than I do and that they could never build a Cub because they do not know how to weld....I will have someone else do the welding) touch up the paint and have a cool mod that I did not know about before.

MMR came by and I put him to work cutting plexiglass.........


Mark has been a great friend and really helpful. Very meticulous.

More in a moment

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Weight Savings

I do not have firm data on all of these items but I thought I would share a few things I have done to help keep the weight down on this build. Many of these are in relation to my last Smithcub project.

Fuselage - I am fairly sure that my current 105 pd fuselage is lighter than my last one but unfortunately I do not have a weight from my last one so I can't quantify this one. It is a narrow body and much effort was placed on watching the weight. My guess is a min of 10 pds lighter and it may be more.

P-mags - 6pds lighter than my last Bendix mags (3 pounds lighter than Slicks)
Titanium Firewall - 2 pounds
Ztron Master Relay - .5 pounds
Alternator - at least 3 pounds but not really sure. Using B&C 8 amp. No belt, no mounting brackets and lighter Alt itself 2.5 Vs 5
Flywheel - 3.75 pds
Spinner - 1.8 pds (will use skullcap Vs full size unit)
Boot cowl - 2pds - factory = .020, used .032 last time, used 2024-T3 .020 this time (Calculated not weighed)
Main cowl - 3 to 5 pds?? see above,.... last kit was .032. I will go back towards factory and/or some CF
Sub Boot cowl - 1.5 pds - I will not use the metal behind the boot cowl. The fabric will go up to the boot cowl.
Built in thrustline - 1pd? not sure here, I will also not have a swing out mount. Together it may equal 1.5 pds
Firewall Blanket - 3 pds Last build I used a "Koolmat Heat Barrier" blanket from Spruce # 09-24730. It was nice but HEAVY. This
time "Thermo Guard FR" Spruce # 08-01029. Much better.
Engine itself + 10 pds depends on your starting value. As best I can tell my 0-360 weighs very close to my last 0-320 but I'll say I
added 10 pounds. If you do not pay attention here it can cost you a bunch. I am close to 20 pounds lighter than
many other 0-360 models and may very well be close to0-320 weights
Drilled brake rotors - .5 pds
Long Step - 1.5 pds Javron step Vs Atlee Dodge unit
Bungees Vs die springs - 2.5 pds
Interior - 5pds. Using more CF this time and less fabric covering.
Avionics - I think I may be able to get 4 or 5 pounds out of the panel
Wings - 20pds (may be more, unfortunately I have no wing weight from last kit) lighter ribs and going to 18 gal tanks Vs 24 on
last one.
ELT - 1.5 pds
Tail Feathers - 6 pds (known weighed value)
Trim system - .5 (no indicator this time, will use the painted mark AKA Cub Crafters)
Half Skylight - 1.5 pds ( known weighed value)
Landing lights - 2 to 3 pds I will be using LED lights mounted in the nosebowl, eliminates the heavy wing mount assembly, wires,
plexiglass cover, etc.

Hope this helps

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Bill you need to change you avatar and log-in name to Nutplate :up
Thats 85lbs. Would you have a picture of jays step?

Here is a step we had machined for the Warbug Cub. It also has a threaded end for a shovel head. Has the same lugs in the gear like Bill's. I don't know how much it weighs but it is light. On the other side is an axe that doubles as a step to check fuel. Also went with the swing up left window but the drawback to that is you either have no air or a bunch of air. I think I would go back to the stock sliding window on the next one. Don


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Slowly going back together. Possible test run tomorrow. Been getting a lot of help from my friends, Jim and Tom. BIG THANK YOU guys.



She started on the first flip today. No matter how many engines you build it still feels great to hear it run for the first time. Hopefully the rest of the break-in will go well and I can get back to working on the Cub once again. Again, many Thanks to Jim for all his help.




Jim sitting in cockpit.
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Bill, yaHOOO! on the Warner/Hatz startup. Thanks for sharing the great news. And I'm remiss in not saying thanks sooner for your gracious hospitality and tour last weekend--very impressive stuff all around your hangar/shop, and I especially appreciate you posting updates on this forum.

By chance, I ran into J.D. at the fuel pumps, who knew of your Hatz, since he's building one; I think we'll be at the same breakfast run tomorrow.

Keep up the positive good news.

Thanks. cubscout
Way to go guys, that Hatz looks and sounds terrific. Another project done! I see you are utilizing your time off in a great way. Can't wait to fly in it again.

Good Job Bill and Jim. I know a place you can land in Oklahoma if you and Jim need a break-in trip this summer. :smile: Awesome Plane. Greg
Love the sound of the radial!
I am just lurking watching your build and enjoying the pictures---Keep it up Bill ------thanks----tom
Thanks for all the support guys. Unfortunately on the second run, I found a cyl that was leaking around the cyl to head joint. Turns out there were two very small cracks at the head stud bases that allowed these studs to loosen out. That head will be very difficult to fix so I am scrambling to get another head together and installed. The good news is all the rest of it seems most excellent.
Still hoping to get it to NH.

Thanks for all the support guys. Unfortunately on the second run, I found a cyl that was leaking around the cyl to head joint. Turns out there were two very small cracks at the head stud bases that allowed these studs to loosen out. That head will be very difficult to fix so I am scrambling to get another head together and installed. The good news is all the rest of it seems most excellent.
Still hoping to get it to NH.


Can I get a ride on Wed night :lol:

Glen - Yes. You are officially on the list.

Many Cudos to Brian and the guys at Poplar Grove Airmotive. I took a head to the shop at 0810 Friday morning and in one day they cleaned it, checked it for cracks, powder coated it, did all the valves, seats, guides, etc and got it back to me at 1530. That is WAY cool. Great job guys!!

MMR and I put it back together today (while Jim worked on the Cub) and I got in a test hop this afternoon. Ran great. No problems that we could see. I will try to get some break-in time on it in the next few days and, if all goes well, it will be at NH.

I've heard nothing but good things about Poplar Grove Airmotive. If I ever find a suitable 90 horse PA18 to buy (soon, I hope!), I'll be sending it over there if it ever needs engine work (never, I hope!)
Hatz - I have about 2.5 hours running it hard to get the rings to seat and so far so good. I will try to do some more this weekend.

Jim was working on my seat while MMR and I were working on the Hatz. So here is a little detail on the seats. I ordered the Confor (temper Foam) from www.seatfoam.com in the soft and firm pads. This results in a comfortable seat that is not "too" heavy. Standard foam will work but only for a little over an hour then you will get a sore rump. Each layer is about 1 inch thick so I put the soft foam on top and the firm on the bottom for a 2 inch thick seat bottom. I use the lighter standard foam for the seat backs and that seems to work fine. I'll try to provide a little more data on all this when the seats are actually sewn up.

I like the simple clean look so I do not have a pocket on the back of the front seat. I place a piece of the Honeycomb composite material inside the sewn cushion and then screw it to the seat frame. To do that I use nut plates turned inwards so that there is as little protrusion into the seat as possible. These nutplates are riveted to the seat back and bottom with aluminum reinforcements. It all looks like this.......


Seat back being held on with 4 screws and nutplates.


Note the screw into the back.


Seat bottom.


Close up of the nut plate inverted and the reinforcement plate. Screws will be sized at the end so they do not protrude above the nut plate.


In this photo you can see the screw and both reinforcement plates. The composite board will be inside the seat upholstry so that all you will see when it is done are the 4 screw heads. Very clean and tight. There may also be a photo or two on the last thread "Building a Smithcub" (Jim does great work, Thank you)

More to follow

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JL - Yes. It was built by Dr Mehlin Smith. I have been fortunate to fly it from the beginning and now own it. Mehlin Passed away suddenly and unexpectedly last Oct. He was a good friend and is/will be missed.

Thanks Lou

Fuel lines. Here are some photos of my fuel lines. These are roughed in and will be secured to prevent chaffing, but it will give you some idea of routing. Note the right rear line may actually show slightly under the fabric on the outside at the wing to fuselage junction. I will have a fabric headliner and this will be the least noticeable positioning. I used the fuel valve part #6749 from Aircraft Spruce. I drilled out an additional port so I can have a "both" position. This is well detailed in the Backcountry Builders Manual. These are 3/8 lines. Note that all the lines run downhill all the way. I do not like having ANY fuel line going uphill. Also note there is only one connector (other than at the valve). Each connector is a potential leak point and also a possible flow restrictor. The fewer connections you can have the better off you will be. You may have to re-make the lines several times to get them all bent properly so you can do it without a bunch of splices.


This is the fuel valve with connection hardware. Total weight is 8.51oz. There are more sophisticated fuel valves that cost 250 to 450 dollars. This one works just fine and cost 25 dollars. It is quite common in the RV community and has few complaints. Your choice.


I like to use this fuel lube. It is also a sealant. You can see where I have smeared some on the threads of the connector. Keep it out of the line and use it on all your fuel connections and you will probably not have any leaks. Works great.


Note that no line runs uphill and also that three of the four lines have no joints. Thy go straight into the valve. The right rear is a really long line and it is two piece with one connector as you will see in a following photo.



This shows the top of the right front line. You want all your tops to be as low as possible once above the structure in the wing root area. You can also see the top of the left front line in the background.


More right front routing.


End of right front routing. Also note the bottom of the left front routing. The top part of the left front line just runs up the channel like the right front.


This may not be the best photo, but I like to run the left rear line right in the gap between the window channel and the back vertical post. I epoxy it in place and after paint it is almost invisible except to a cub guy who knows what to look for.


This is the front of the right rear line. Note it is outside the structure. This would not be necessary if you are going to use a metal headliner. I am doing it because of my intention to use a fabric headliner.


More of the right rear line.


This routing is again dictated by my headliner choice. There will be a slight bulge in the headliner fabric just behind the window for a few inches where it transitions down behind the interior panel. Best I could come up with given the circumstances.

Total weight of all the lines with AN hardware is 23.55 oz and with the valve, the total fuel line system weighs 32.06oz. Cub Crafters is using a nylon type of fuel tubing. There may be some weight savings there.

Folks - this is just my way (and certainly not the only way, or even probably the best way). Your circumstances may dictate a different set of lines, valves, routing etc. But I hope this helps someone.

Thats almost just like the CC headerless system. They put rubber line splices in the long runs to mitigate cracks.
Well, at the three hour point for the new Hatz motor, with everything running great, I did a thorough check to include timing the mags, checking all valve clearances, changing oil, checking cylinder base nut torques, compression check..............oh boy, found a low one.....found a crack at the spark plug hole. So, I will be at NH but not in the Hatz. I can fix it but not in the time frame I have left before the show. Looking forward to seeing all my fellow SC.org friends there. Back to the Cub.


After a little diversion fooling with the Hatz I did have a little time to fool with the Cub seats a little more and I said I would provide more info so here it is.


This is a picture of the tan colored foam that is readily available from craft stores, upholstery shops, etc. It is available in different densities and thicknesses. I used 1/2 inch firm on the bottom and 1 inch thick medium density on both the seat backs and the seat bottoms of my last Cub. Unfortunately the seat bottoms became uncomfortable after about 1.5 hours. The backs were just fine. This foam material is about 1/2 the weight of the good tempurfoam/Confor foam. The front seat bottom tan foam, firm, weighs 4.84oz. The 1 inch med density foam weighs 5.91oz so the total foam for the front seat bottom weighs 10.75oz. The good Confor foam is 1 inch thick and I used a layer of firm and a layer of soft. So the thickness is 2" thick Vs the Tan foam that would be 1.5 inches thick. The Green color is the firm density and it weighs 11.88oz and the pink, soft, weighs 11.0oz for a total foam weight here of 22.88oz so as you can see the Tan stuff is just about 1/2 the weight of the good foam. Bottom line. Use the good stuff for the bottom but the lighter Tan stuff will work just fine for the seat back and it will save you some weight. Since the back seat is about twice the size of the front seat your total weight savings would be close to 2 pounds by not using the good (but heavy) foam for the seat back. Further you could also use the three density good foam to build a seat like Oregon aero and it would be three inches thick. I don't think it is necessary as, after I remade my seats using just the two layers, firm and soft, I thought my seats were very comfortable even to the point of a thirteen hour (in the air) day.


This is a picture of the confor foam. The green color is the firm and the pink is the soft. They do make a medium density as well if you wanted to do a three ply seat.


This is a picture of how things go together. The honeycomb base goes in the seat cover, then the dense foam, and then the soft foam on top. Again this would be for the seat backs. For the bottoms you would use the better foam. Also note that we put zippers in the seat covers so that they could be taken apart for cleaning. These zippers were on the left (throttle) side of the seat so they could not be seen.


Here it is all zipped up together

The seat bottom is then screwed on like this...................


Makes for a very clean, crisp, seat job.


This is what the back seat will look like starting out. When I did my last one (and I'm doing on this one) I made the rear seat back like the front seat, with the board inside the seat cover. However for the rear seat bottom, I left the board out of the cover. I placed a couple of snaps on a finger tab so that the cushion could be snapped down onto the seat bottom board. This allowed me to easily remove that cushion and use it around camp as a cushion, pillow, or whatever I needed it for. Since it did not have a board zipped inside it was soft and pliable. Not a really big deal but it does allow you to get more uses out of that cushion. There are ways to do that for all your seat cushions if you want but the installation may not look as sharp. It's all a trade off.


This is a picture of the rear seat bottom snap installation/technique. The snap is just folded under the cushion and snapped down. It does not hold it down really tight but you don't need for this one to be rigidly tight. This just keeps the wind from lifting it up when flying with the door and window open.

I purchased my seat fabric from Active Foam Products, 6210 W. Douglas Ave, Milwaukee, WI 53218 414-462-9220
I used #661420 Marathon Grey Heather Fabric on the seats and also side panels.
The black vinyl is #525322 Sierra-Soft 9562 Black
The piping is #525622 Grand Prix:9456 Carmine

I hope this makes sense and is usable info for folks thinking about how to do your seats.

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Looking at the composite board you are using for the seat and baggage floors. There is a nice easy and light way to finish the edges . This will also seal the edges from any liquids soaking in , like water or fuel .
You can undercut the core only from the edge about 1/4 inch deep . Leave the outer layers of glass . Mix up some resin with micro ballons , fill in the edge . When cured , just lightly sand the edges to finish.
You can also do this to reinforce holes cut inside the board, such as lightening holes , and to reinforce drilled holes where you will put bolts thru . This will keep the board from crushing as you tighten the bolts. We use flox with the resin in these areas , it has more structural strength .
You can make a simple steel tool to scrape out the core material or a small grinding wheel on an air dremmel .
We do this all the time on composite aircraft.
What do you think about the 1.6 lbs composite
tailwheel spring that just got approved on the Husky?
What do you think about the 1.6 lbs composite
tailwheel spring that just got approved on the Husky?

Sounds fascinating to me. However, most cubs I've ever met need more weight on the tail...at least when they're empty. They may not break those AKBW ring bolts either.
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