+20 year old donuts (1966 M20E)

[carusoam]

As far as the quirkiness of part numbers for the really old Mooneys goes...

There was a different donut used early on...

The stack height was the same, but the donut count was five in place of four...

The manufacturer was Firestone, not Lord...

The two different donuts also had a different dimension that required a different steel tube to be used...

Somewhere along the way... the Firestones became unavailable, and most Mooneys changed them out over time... following the route of proper parts interchangeability... common to all M20s...

It would be great to have two suppliers for commonly replaced parts.  It would be really great if a new part was better quality and lower Cost at the same time...

There is plenty of room for improvement... Rubber technology has evolved over the last few decades...

PP thoughts only, not a polymer chemist...

Best regards,

-a-

[Gert]

14 hours ago, Andy95W said:

I, too, would like to know this, but admit the product looks pretty good.

My concerns:

-I don't know what FAA-OPP is supposed to signify as any sort of legal pronouncement.  Perhaps the lettering is supposed to make the owner/inspector feel like it is more legal than it actually is.

-The rules for an owner produced part is that it is supposed to be constructed out of the same material as the original. This is why the new Johnson gear lock blocks went through such a rigmarole trying to determine the exact alloy of the originals.  But Gert, above, states outright that these new discs are more robust/more stable/longer lifespan than Lord discs.  How does that make them the same material as the original?

-The lettering on the discs does not include the C, but on the website it does.  Seems like a small of an oversight, but if something as easy as that was missed, it makes me begin to question more aspects of product.

I like the idea and the look of these discs, I'm just not going to be the first to install them.  Or the second, for that matter.  But in 10 years, who knows?

I have seen this and it is not a slip or omission and refer you to all other manufacturers detail. You will note that the lettering on all alternative products are inclusive of the M20 models as per my discs and non have it printed on the disc, however Aircraft Spruce also states that the disc will fit a Model C. I have checked this with them and they have confirmed. I have written to Lasar and await their response as well. The Mooney specifications seems to be the same, however I stand to be corrected - if you have information on this, please share.

Best Regards

Gert

[Andy95W]

Gert-  I completely understand, and as I said, I like the look of the product.  I was simply expressing my concerns.  As an A&P/IA, I'm skeptical of anything that isn't specifically FAA-PMA or TSO approved, but I'm very open to a good quality OPP- such as yours appears to be.  But as with any other OPP provided by a manufacturer, I simply don't wish to be first.  I'd rather hear some reviews from others before installing them myself.  My discs will be due in about 10 years and I hope you're still manufacturing them then.

[Gert]

Hi Andy

I am offering to provide a set  for free to whoever want to test the units. I have been manufacturing units for Beechcraft type aircraft for a while now and have only had successful feedback. I am confident this will be no different. The accelerated wear tests conducted included 10 000 compression cycles in minimum and maximum temperatures under constant UV radiation. The units are unloaded and checked for elasticity every 2000 cycles. It is measured against original size and how long it takes to de-compress as well as final shape and size after a two hour rest period. There are allowable tolerances and compression measurements on the original drawings and the shockdiscs stay well within these at all stages of the tests. I plan to also install a set on a South African Mooney and conduct operational tests. I will let you know the results. 

The manufacturing process is not by means of molten rubber squeezed into a mold via multi-ports as some other manufacturers do. The problem with such processes are that the rubber discs form seams where the material cools down before amalgamating and could split under load - and also did( Specifically AECI Discs). The manufacturers then published a complicated procedure whereby the discs had to be "baked" overnight in a oven powered by a 100W incadescent lamp and then installed. I use a compression molding- and curing process that molds the rubber disc as a one-piece item with no seams etc. The natural rubber and polybutylene mix has been extensively researched and provides the right shoring degree as per the original specifications as well as superior compressibility and elasticity.

Best Regards

Gert

[philiplane]

FWIW- on some aftermarket items, you aren't getting a bargain. I've bought some aftermarket Beechcraft shock discs from AECI in Florida. 

They begin cracking in about 4-5 years. 

[cliffy]

3 hours ago, philiplane said:

FWIW- on some aftermarket items, you aren't getting a bargain. I've bought some aftermarket Beechcraft shock discs from AECI in Florida. 

They begin cracking in about 4-5 years. 

See Gert's above post

[hoot777]

Just finished doing five Mooneys. C thru G .  Spruce was best price on disk. Got tools from Lasar. Both were great to do business with. Soak all your bolts thoroughly a day before you start and remove the cover plate above the collar so you can get plenty of PB blaster on the collar. We had one that took a day and a half of soaking before it came loose.  

[201guy]

Here's the difference in height  from the age of shrinkage over the years.

Note the bulging edges from sitting under compression.

 

[cliffy]

Rubber also hardens with age

[carusoam]

Often, you get UV cracking to go with that too... the above donuts look pretty fresh, even though they have been squeezed...

Rubber relaxes over time... essentially, it flows very slowly.... the donuts get shorter, as they spread out radially....

Rubber hardness, and changes to hardness over time.... hmmm... wonder if @Gert has explanations for that... expect that some form of solvent is escaping over time...

PP thoughts only, not a rubber band man...

Best regards,

-a-

[hoot777]

Just helped replace disk on five aircraft. Rented tools from Lasar. Disk from Spruce.  Both great to work with.  My steering is noticeably smoother. My disk were made in 1967. It was time.  PB blaster the ever loving $#@*&& out of the gear bolts and especially the collar holding the strut the disk are on a day before you jack aircraft up . 

[Skydancer2992]

On 6/10/2020 at 9:33 AM, hoot777 said:

Just helped replace disk on five aircraft. Rented tools from Lasar. Disk from Spruce.  Both great to work with.  My steering is noticeably smoother. My disk were made in 1967. It was time.  PB blaster the ever loving $#@*&& out of the gear bolts and especially the collar holding the strut the disk are on a day before you jack aircraft up . 

Did you check the bushings. Did any require replacement?

[hoot777]

We did not put a micrometer on any but inspected and greased thoroughly.  I assume your talking the horizontal bushings on the gear structure  call me 8934636043 if I need to clarify

 

 

thanks

 

fly safely

 

[RobertGary1]

It’s an old mechanics trick when a boat payment is coming up to suggest changing donuts. Like others have said Mooney has a procedure to measure them. If they pass they’re good. Everything else is princess and the pea as far as I’m concerned. 
 

-Robert 

[cliffy]

On short bodies they may harden before squashing out

[brndiar]

I was under my 77 C, took these pictures. 

It is possible (on the basis of code) to say the year of production?

Thanks, 

M

 

 

Edited July 11, 2020 by brndiar

[carusoam]

Cold flow vs surface cracking...

Weight and warmth vs age and hardening....

newer donuts vs. older donuts...

 

 

Year date codes are a pretty good method of telling how old they are...

Use some caution... as @Hank found out...  right side up matters...  69 not 96...  

Best regards,

-a-

[Hank]

2 hours ago, carusoam said:

Year date codes are a pretty good method of telling how old they are...

Use some caution... as @Hank found out...  right side up matters...  69 not 96...  

You're right!

How do you remember all of this??? I replaced my "69 not 96" pucks in Dec 2012 . . . .

[Andy95W]

8 hours ago, brndiar said:

I was under my 77 C, took these pictures. 

It is possible (on the basis of code) to say the year of production?

Thanks, 

M

 

It looks to me like they are from January 1977 (1 77) so they're original!

[brndiar]

Not so bad,  younger than me!!!!  

[carusoam]

23 hours ago, Hank said:

You're right!

How do you remember all of this??? I replaced my "69 not 96" pucks in Dec 2012 . . . .

As soon as I can figure out how this memory thing works/doesn’t work...

I’ll share it with the world! 
 

Looks like many memories go in place.... getting them back out is a separate process...

Some days you can’t remember something... the next day it comes to mind....

Usually remembering something comes five minutes after you needed it.... Stress gets in the way of memory recall too...

PP thoughts only, not a cognitive scientist...

Best regards,

-a-

[RLCarter]

1 hour ago, carusoam said:

As soon as I can figure out how this memory thing works/doesn’t work...

my memory is excellent, its my filing system that is messed up 

[Will.iam]

Reviving this subject. Did anybody test these on their plane yet? $60 per donut including shipping sure beats $130. Mine were replaced in 2007 so I’m over due. 

[Gert]

Hi

We have submitted two sets to two different members that are also  AMO’s and they have been tested with good results. The only comment was that my rubbers were approx 2mm thinner than the originals. I have had the moldchanged to accomodate that and we are running tests on the new sets. I expect production to start within a month.

best regards

Gert

[Will.iam]

I’ll be looking to change mine at my annual in Aug 2021. Last time they were replaced was 2007.  Hopefully you will have a set ready by then.