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Gear Preload


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The preload specs are 100 to 130 inch lbs for the nose gear and 240 to 280 inch lbs for the mains.  Mine has always been adjusted to the high end of these ranges but I am wondering if this is really a good idea since the bunges appear almost totally compressed and it takes a very strong push to put the gear down.  It may be causing extra wear. Not sure if reducing it some will increase the chance of collapse. I wonder what others experiences and thoughts might be?  

Edited by Gary0747
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The manual gear Models only have bunges on the main gear not the nose gear.  My concern is the springs on the main gear may be so compressed that there is little if any gap between the coils in the spring when the preload is close to the upper limit.    There is a spec for the permissible compression of the nose gear bunges on the automatic gear models but no spec that I can find for compression of the bunges on the main gear. 

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On my E if the gear was rigged according to the maintenance manual thr J-bar would stop about 5/8" short of engaging the "gear down" block (under panel) making it very difficult to lock the gear down. With all 4 retract links removed from the J-bar it would engage the down lock block with ease, looking at the system and the way it works the front retract links are shortened to increase the preload of the nose wheel and with no bungees on those retract links the very solid feel is the "over center" link on the nose wheel bottoming out meaning that the J-bar has to flex the remaining way to get it to engage. By the book after setting the 4 retract links to "zero" you shorten the front links 2 turns and lengthen to rears 2 1/2 turns and check the preloads which on mine fell into the specified range, we turned the front links out 1/2 turn and shortened the rears a 1/2 turn (at the same time), this allows the J-bar to rotate closer to the lock block. We did this process untill the J-bar felt correct then checked the preloads, mains were in range but on the low side the nose was below the minimum so the front links were turned back in 1/2 turn and all preloads checked again at this point all were now in spec and no more binding at the very end of J-bar travel when locking the gear down. If memory serves it ended up being 1/2 turn in on the nose and 1 turn out on the mains from "Zero Preload". It can be done by one person but 1 running the J-bar and 1 making the adjustments sure makes process go faster. 

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My preloads have not been touched in the 25 years That I have owned the airplane. They all reman within the specification range but have creeped up some. Is it best to rerig per the manual after a long period like this or just leave it alone?  The only weak point on the manual gear models is that there is no way to check if the proper balance in loading is being maintained between the two actuating rods that attach to the nose gear.   The auto gear models can measure the bunge compression in both rods and verify balanced tension. The manual gear has no bunges and this can not be verified with out rerigging starting with zero preload. 

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If your nose rods have been kept well lubed and movable you can sometimes get a ball park figure of load balance by rotating the rods around the ball joints with the gear down. If one shows lots of resistance and one moves very easy the balance is wrong. They should both show about the same amount of rotational resistance. This is just a ball park check. I have one slightly tighter than the other but not much. 

You also might find, as as I did, that after 20+ years enough wear was showing on the bolts throughout the system that they could use replacing. I replaced all of mine 2 years ago. 

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1 hour ago, cliffy said:

If your nose rods have been kept well lubed and movable you can sometimes get a ball park figure of load balance by rotating the rods around the ball joints with the gear down. If one shows lots of resistance and one moves very easy the balance is wrong. They should both show about the same amount of rotational resistance. This is just a ball park check. I have one slightly tighter than the other but not much. 

You also might find, as as I did, that after 20+ years enough wear was showing on the bolts throughout the system that they could use replacing. I replaced all of mine 2 years ago. 

+1. I replaced not only my bolts but the bushings, as well.  Most of mine were worn so bad I had to get oversized bushings from LASAR (PMAed replacements).  

Also excellent advice about the dual nose gear pushrods.

I would be reluctant to change anything, BTW, unless you have a specific reason.  IIRC, Paul Steen had absolutely ZERO problems with his manual gear M20C, but after he sold it the next owner's new shop wanted to adjust his gear preloads and shortly thereafter the gear collapsed.  It is now one of the nicest scrapped M20Cs out there that will probably never fly again.

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