U Bolt replacement

Big Ed

Big Ed

N50247 - '79 Super D
Joined
Jul 20, 2020
Messages
1,938
Location
Tampa, FL
Looked under my Super D today and I have the old style U bolts. Will probably upgrade to the flat bar hardware. Is there anything to it other than removing the old and installing the new?

ACA says the kit is about $600. The bars and bolts are Aircraft Spruce for ~$160 each. Two of those, plus the two thru bolts, seems cheaper at AS. What am I missing?
 
you may have to trim your boot cowl a bit to make room for the bars. other than that it is as straightforward as it seems. keep the u-bolts, they are good for keeping the frame on its gear while you paint and do fabric.
 
I replaced mine on my 92 Decathlon years ago. Had to trim the wrap around just a little with a dremel tool. Easy to change. One of mine broke after a landing and was taxi back to the hangar. Sound of a loud noticeable pop. Was glad the weight of the aircraft was on the gear.
 
Following up on this. Log shows no evidence of u bolts ever having been replaced, so AFAIK those are the original bolts from 1978, with 1700 hours on them. Really worried about the bolts failing and gear collapsing under me.

Looking closely at the aircraft, it looks to me like the right gear is "sprung". Measuring from the top of the gear to the floor, the right gear sits about 1/2" lower than the left. Negative camber (top of tire leaning towards aircraft) is 2.5 degrees on the right wheel. Service manual says replace if more than 5 degrees. I called ACA and they said that was not unusual, and not a big deal. I also had Greg Koontz's old mechanic give the gear and bolt a close look, and he said it looked OK to him. But it still worries me, and it appears to be causing abnormal tire wear.

PXL_20210115_181058546 (1).jpg

I'm trying to decide among 3 options:
  1. Replace bolts only.
  2. Reconditioned steel gear.
  3. Upgrade to aluminum gear.
The bolts cost about $600. Reconditioned steel gear costs $800. Aluminum gear kit costs $7500. Bolt dimensions for steel and aluminum are different.

I really like the idea of the aluminum gear upgrade. However, I don't know if it makes much sense to do it now. I hope to recover the fuselage in the next few years, so seems like it would be easier to do the tube and fabric mod then.

Thoughts? Votes?
 
If you were close by you could check out my old steel legs, which may be better than yours.

I would get the bar style replacements for the U bolts, but get the ones with AN hardware to save bucks. Then put the saved $200 toward the aluminum gear mod. You can use the bars for either gear. The U bolts cannot possibly be 125,000 psi steel? Can you just buy the bars? Does Rainbow Ron have any?

The fabric mod is not all that big a deal, for the aluminum gear. Takes longer to re-route the hydraulics.
 
Univair shows the bar alone as U1-9805A - $195 each. AN bolts and nuts are probably an additional $25. I believe the AN bolts are way stronger than the original U bolts.
I used the higher strength NAS bolts at $30 some odd each. I think those are necessary on the inner bolts, but I bet the regular bolts are more than adequate outboard.
Opinion.
 
ACA told me the bars are same for steel and aluminum gear, but the bolts are different. Perhaps the best approach is to replace the hardware right now, and make the decision on gear later. Sounds like I would only waste about $200 on the bolts.

I am selling my boat, which should net $15K of airplane money. I have an annual in May. If my wood spar looks good, and no signs of problems with the engine, maybe I'll splurge on the gear upgrade.
 
What about just putting in new u bolts for now? I mean, the old ones only lasted 1700 hours...
Should buy you piece of mind until you do a recover in a few years.
You could do an EC inspection at the same time if you wanted to.

Chris
 
Are the U bolts even available? And if they are, I bet they are just as expensive as the bars.
Again, for the steel gear legs you do not really need the expensive bolts. The airplanes were delivered with AN-7s on the inside. The conversion requires the expensive bolts - a good idea, but again, these things survived a long time with 125,000 psi hardware.
 
I think I'm going to get the bar bolts now. Not that expensive, and the consequences of failure are ugly. Once I sell my boat and get a good annual under my belt, I'll make decisions on a long term upgrade plan. If everything else looks good, aluminum gear will be first on the list.
 
1977 Decathlon. That's all I know, except they seemed to be slightly less splayed out than yours. I was not uncomfortable flying them. Tell me what to measure.

I work slowly, so it took me almost a month to change over. Used the same bars. Tried to adapt all the speed fairings, but did not succeed. The actual conversion was trivial. Flex line routing was surprising - a potential air trap. I just copied a new Decathlon for that.
 
I've got a sprung left gear leg, trade you one for one!!! JK. I would, and do go with the bar, but I feel that AN bolts are sufficient for it. I do use a NAS bolt for the inboard. But we do mostly off-airport work here. when I go to floats, I use AN all around.

I too am thinking about reconditioned legs.

I'd like to do the aluminum, but man! I just wish it was half the cost
 
Bob Turner said:
1977 Decathlon. That's all I know, except they seemed to be slightly less splayed out than yours. I was not uncomfortable flying them. Tell me what to measure.
Click to expand...

I'd say yours are almost certainly the same length as mine. I don't know the particulars, but AFAIK in the late 90's and early 00's ACA produced a steel gear that was 1 inch longer than the original, and which also came with the 150# max gross increase.
 
Got from ACA. Jacking fixtures were 50 bucks each.

Spent about 10 hours today removing the old thru bolts, which were seized tightly in the gear legs. Could not come up with a good way to get leverage to pry them out.
 
Big Ed said:
Got from ACA. Jacking fixtures were 50 bucks each.

Spent about 10 hours today removing the old thru bolts, which were seized tightly in the gear legs. Could not come up with a good way to get leverage to pry them out.
Click to expand...

Ed, are you planning to use standard hardware store bottle jacks or do you have something more elaborate in mind? I had a bottle jack roll out of position on me, luckily before I had the wheel off. Improving how the plane was anchored fixed it but I had a pretty good scare!

Was there any trouble getting the inboard hardware free of the frame?
 
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