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We just automatically replace them at our 1500 hour inspections (used to be 1000 hour extended by TC). I think they compress with old age. I have seen some aircraft that we bought actually misting the small rubber at the bottom or missing a puck completely.

I believe my pucks were most influenced by age and a lifetime of being compressed. The stack of old pucks was shorter and less "elastic." The height does not change as you compress then down to the same height but older pucks simply won't give you the same degree of cushioning.

I have seen two different puck colors . . . wonder if they changed the composition somewhere along the line.

From a larger perspective, I like the puck design, even though it seems a bit clunky. The NW shock on my PA28-201T is prone to blowing seals and the shaft wears more on the fore side due to the angle. It has occasionally been known to stick in its compressed state on takeoff and then thrill you with a loud thunk at 500 AGL. The first time it happened, I made an "urgent" RTF to investigate the possibility that something important had departed the aircraft.

So, I finished making a compression jig. I think it came out OK. Some pictures below:

Steve wrote:So, I finished making a compression jig. I think it came out OK. Some pictures below:

Wow. Very nice. How much would I have to pay you to make me a set? )

I finally bought replacement pucks. On the DA20's, in particular the DA20-A1, we use just 5 larger pucks and 1 smaller one. The DA20-A1 AMM doesn't list anything about a custom tool to compress the new pucks (elastomers). I just checked Diamonds website and can't find anything about a custom jig for DA20's. Am I missing something? Thanks for any help. -John

The SB jig will work on the DA-20 or the DA-40. Only difference might be in the end fitting. I remember a little more cutting out of the one end piece of the jig so it would fit around a couple of nuts at the end of the puck stack for my DA-20. See picture to my earlier post - it was intuitively obvious that I did not want to compress the stack by putting force on the top of those two nuts. I just used a jig saw with a metal saw blade to cut two indents into the jig’s end plate so it would fit around the nuts.

Rubber becomes harder over time, thus causing more stress to the nose gear assembly when landing. In an ideal world you would always grease your landings and land on the mains, but we don't live in an ideal world.

Over a period of several years, the rubber pucks also compress, lowering the nose, reducing the propeller clearance, and slightly changing the angle of attack in the initial takeoff roll.

I the rubber pucks replaced on my airplane last year and although it did not change a whole lot in the way the airplane flies, I felt that for an 18 year old airframe it was time to do it.

Pascal,
Concur with the age assessment - they get hard and inelastic over time - IMO, not really based on the number of hours flown or number of landings executed, good or bad. The AMM recommends replacing the rubber components every 1000 hours - which is probably correct if the aircraft if flown 200/yr making it around five years. I don't believe DA20-C1 AMM Chapter 32-20 has any "criteria-based" inspection or replacement recommendations - I replaced mine in 2015 and I'm already near the 1000 hours flown in three years. I will inspect them at this annual but I'm not inclined to swap them out simply based on tach time flown. Anyone have a historical reference based on calendar time vs tach time?

Thanks for the info. I will use the DA40 SB for reference. I didn't want to end up taking the NLG off and then finding out I either didn't need the jig or to have a drastically different design than the DA40's.

For me, the DA20-A1 has an SB (DA20-32-04 Rev 1) about propeller clearance. This is what triggered the replacement for me. If the propeller clearance is less than 9.8" then pucks need replacing. The SB doesn't mention building a jig and it claims a mere 2 hours of time to remove the NLG, degrease, etc, and remove and install the pucks.