M20E Main tire tube size and stem

[takair]

I know this has been discussed in years past, but can’t find the details right now.  Had a right main go down on landing today.  Closed runway, but luckily the FBO had a dolly and jack handy.  Anyway, every time I do the mains, I can never seem to find the right tube.  I always end up with the straight valve that is then preloaded by the bearing cover.  I think that is what caused my flat today...

So, I’ve read the threads on whose tube to buy, but it seems that the bent stems are rare.  The available choices seem to be:

Goodyear G15/6.00-6, Butyl, with TR67A,B 90 degree stem.....or

AeroClassic 6/600-70, with TR-87, 70 degree stem

At this point, I just want to get it right.  Anybody know what the optimal tube/stem combination for our old wheels?  I’ve yet to get it right on the mains.  What’s the difference between the 90 degree and 70 degree?  Only in the past few years did I get it right on the nose.

Thanks for any help.

 

[Yetti]

Generally underinflation and the tube rotates in the wheel.  Pump up the old tube and see where it is leaking.    Straight valves on the mains.   90 degree on the front.

[takair]

17 minutes ago, Yetti said:

Generally underinflation and the tube rotates in the wheel.  Pump up the old tube and see where it is leaking.    Straight valves on the mains.   90 degree on the front.

It’s not taking any air.  Seems like it failed at the stem.  Haven’t pulled anything apart yet, but want to get parts on order.  Someone here posted a video about changing the tire and had an angle valve, which is what I think is intended for this vintage wheel....but they don’t mention the part number.

[Yetti]

failed at the stem is under inflation.  tube rotates in wheel and rips stem.  Check your other side and make sure the stem is straight.

[RLCarter]

Walked into my hangar Friday afternoon and noticed the Mooney wasn’t sitting right, went around the Cessna just to see the right main was flat. Aircraft is down for annual for the past month, hadn’t moved. Valve stem was pulled out of the tube, same issue as OP, stem is in a bind as it comes out of the wheel, you have to bend it even more to add air or check pressure..... PITA

[Immelman]

The straight stem on the mains also seems wrong to me. The last couple flats I've had have been the stem getting torqued and failing where the stem meets the tube. And the tires were not underinflated!!

I am very interested in what you figure out takair.

Edited December 14, 2020 by Immelman

[carusoam]

Let’s see where @M20Doc is on the tube stem challenge..?

Best regards,

-a-

[takair]

48 minutes ago, Yetti said:

failed at the stem is under inflation.  tube rotates in wheel and rips stem.  Check your other side and make sure the stem is straight.

Both getting replaced 

[Bob E]

It's a small design flaw in early Mooneys that straight-stem main tubes in WILL eventually fail because the stem is pushed slightly off to one side, placing a constant stress on the rubber, leading to failure at some point. This is true for properly installed and properly inflated tubes, even if you remove the valve stem cap and even if you remove the bearing cover.  (See photo.)  In the years I've owned my '65 C, I had three such failures (all on landings). I finally bought bent-stem tubes.  They cost twice as much, but that has solved the problem once and for all.  The manufacturer spec sheet and the Aircraft Spruce listing for tube are in the photos below.

There are, however, a couple of CB solutions I tried in the past that did work; no failures but I decided they weren't really kosher:

1.   I found bent-rim snowmobile tubes of the same exact size at a fraction of the price and installed them.  The problem was that they rendered my aircraft non-airworthy.  Turned out that non-aviation tubes are MUCH thinner than aviation tubes and aren't designed for the sudden rotation when the tire makes contact with the runway.  Bad idea, but they worked for more than two years until my A&P noticed.

2.  A truly effective CB solution is to wrap a bunch of twine around the base of the valve stem before installing the tube.  The idea is to use the twine as a spacer, preventing the valve stem from fully protruding out of the hole.  All you need is about 1/4" reduction in valve stem height.  It actually does work.

But I figured, this is one of those situations where, "if you can afford the aircraft, you can afford decent tubes."  Especially since proper-spec bent-stem tubes will last for many years. 

 

 

[takair]

Thanks @Bob E!!  This is the confirmation I was looking for.  Surprisingly hard to find details on this subject.  They also have a 70degree version.  Any pictures of your 90 degree install?  Would 70 degree provide benefit?  

[RobertGary1]

I don’t know what you all are on about. I’ve had same tubes as long as 12 years jn my Mooney and never had an issue in over 20 years.  Are you installing them off alignment?

Edited December 14, 2020 by RobertGary1

[Bob E]

I don't have any photos handy regarding the 90-degree bent-stem, but it's exactly what you would expect (basically looks like the nose wheel stem).  Never heard of a 70-degree stem; that's pretty unusual, but 70 degrees should work nicely.

[Bob E]

RobertGary:   As far as I can tell, there's no way to install 600-6 straight tubes in my '65 C main rims without the stem being pushed off to one side.  My A&P agrees (although he seemed to think it wasn't that big of a deal when he installed a set of straight-stem tubes earlier).  Your aircraft is 11 years newer than mine.  Maybe the rim design was improved for the F?? 

[takair]

4 minutes ago, Bob E said:

I don't have any photos handy regarding the 90-degree bent-stem, but it's exactly what you would expect (basically looks like the nose wheel stem).  Never heard of a 70-degree stem; that's pretty unusual, but 70 degrees should work nicely.

TR-87 is the 70 degree.   https://www.aircraftspruce.com/catalog/lgpages/aero_06-03303.php
 

I’m thinking I will go with your suggestion.

[Bob E]

Very astute, takair.  Had I known about the 70 degree version I could have bought quite a few more pizzas.

[takair]

2 minutes ago, Bob E said:

Very astute, takair.  Had I known about the 70 degree version I could have bought quite a few more pizzas.

Hmmm.  I like pizza and we have really good pizza here in CT.  Do you recall if the 90 degree gives you enough clearance for checking pressure or adding air?  I know n the nose it is a little tight.  I wonder if the 70 degree might give more clearance to the rim while not getting near the bearing cap?

[Bob E]

Can't speak to the difference between 90 and 70, but unlike the nose wheel, the mains with bent stems have plenty of space. Checking air pressure and adding air is much easier.  (With the straight stems, doing those things required bending the stem to the side even more.)

[RLCarter]

I’ll check in the morning but one of the problems is the stem is centered on the tube and the hole it exits on the wheel is off-center, either the 90° or 70° will make it easier to check/add air but where the stem meets the tube will still be in a bind and eventually fail

[Hank]

10 minutes ago, takair said:

Hmmm.  I like pizza and we have really good pizza here in CT. 

Mmmmmm . . . Clam Casino pizza in CT!

Not sure what tubes are in my C, but I got them from Spruce when I bought tires. You can always call them and ask. I've replaced my mains once and nose tire / tube three times (the joy of no taxiway:  backtaxi to the end then turn around for takeoff, or stop on rollout and turn around to back taxi for the single entrance). Never had a flat . . . .

[Bob E]

23 minutes ago, RLCarter said:

I’ll check in the morning but one of the problems is the stem is centered on the tube and the hole it exits on the wheel is off-center, either the 90° or 70° will make it easier to check/add air but where the stem meets the tube will still be in a bind and eventually fail

The stem is centered on the nose wheel but not on the mains.  (See photos)   Although I don't have any straight-stem spares, as I recall the straight-stem tubes for the mains are also off-center to the same extent.

[47U]

These did not work out well in my ‘63 C.  New tires and tubes, but the tubes only lasted a few flights.  As least it went flat in the hangar, not on the runway.  The other main was still holding air, but upon disassembly, that stem was separating at the base, just like the other side.  Neither main tire were under inflated.  I don’t remember what make tube was previously installed, but they were straight-stem and were fine until the tires wore out.  I just picked the wrong manufacturer.  

I replaced both main tubes with 90 degree stems.  It took a little finesse to get the stem through the hole, but once it’s in, no issues.  The stems are quite long, so if you have a hub cap it will interfere.  

As an added safety measure, I always remove the valve core from the stem before loosening the axle nut.  Don’t want QA to give me a DSV.  

 

[carusoam]

OK...

You inspired me to do some reading... 

When spec-ing the tire tube... we get options...

1) Rubber type... butyl is the one that holds the air forever... (nearly)

2) Valve stem... often 0 or 90° same name, just confusing... 70° is a slight offset... good for not bumping into the hub.

3) Valve stem material... as Bob posted the bent metal stem...

4) TR seems to be the valve stem spec... but no chart to say what all the options can be...

5) There is also a bunch of valves themselves to consider, but I didn’t find those details...

Often the word valve and valve stem get blended together... when one is inside of the other...

I used https://shop.desser.com/ecomm-collections/aero-classic-3470/e/collection/

Bbest regards,

-a-

[Bob E]

Definitely on board with the 70 degree stem.  Much less expensive and maybe even easier to service than the 90 degree.  Hey takair, when you get the tubes, please post some photos of them before and after the install !

[carusoam]

I suppose this may be in the 300 page POH somewhere...?

Put it on Monday’s reading assignment.

Best regards,

-a-

[RLCarter]

12 minutes ago, 47U said:

These did not work out well in my ‘63 C.  New tires and tubes, but the tubes only lasted a few flights.  As least it went flat in the hangar, not on the runway.  The other main was still holding air, but upon disassembly, that stem was separating at the base, just like the other side.  Neither main tire were under inflated.  I don’t remember what make tube was previously installed, but they were straight-stem and were fine until the tires wore out.  I just picked the wrong manufacturer.  

I replaced both main tubes with 90 degree stems.  It took a little finesse to get the stem through the hole, but once it’s in, no issues.  The stems are quite long, so if you have a hub cap it will interfere.  

As an added safety measure, I always remove the valve stem before loosening the axle nut.  Don’t want QA to give me a DSV.  

 

If I didn’t know better I would think you had been in my hangar a took a picture of my tube...... going with the 70°, will be replacing both main gear tubes