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Motor Mount ShimsTREX DECKING

knuckle47

knuckle47

Advanced Contributor
"I was hesitant about replacin

"I was hesitant about replacing the wilted plywood with new plywood that can settle and wilt again shortly and a call to Silverton claims they use starboard these days for shimming. I need to build my stern mounts up 2 1/2 inches. Yep! they have a bunch o' plywood under them. I can't get hold of any sizeable amount of starboard today so I bought a piece of TREX decking.

It is water proof, high density and although a mix of plastic and wood, it is suitable for wet locations and it does not crush.

I have until Tuesday morning to replace the TREX that is when we are lifting the engine back into the hull. It sure machines nicely with wood working tools and it certainly seems like it will outlive any plywood.

Anyone know why it is NOT a good idea to use this stuff?"
 
"Al:

You have GOT TO STOP a

"Al:

You have GOT TO STOP asking all these questions that make me out to be a bad guy....

I don't know who told you it won't crush. Its compression properties are NOT much different than the standard softwoods that go into a piece of plywood (625 vs ~500 psi). The other thing is that a mount's shim is a dynamic environment, NOT like a deck where most of the load is static. The last item is that the mount has a relatively small surface area so all the applied load is pretty concentrated.

I'd look for some plate or box tubing myself; preferrably out of some metal compatible w/ the angles...just my two cents, from an electrical guy."
 
"Mark... If the bad guy has th

"Mark... If the bad guy has the right answers , too bad !
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On the other hand I did smack the heck out of it with a hammer and the wood makes a dent, this does not.

Dave, Is there a place that routinely sells Delrin that I might have here locally? My shims are about 3" x 12 " long and need to be stacked up to 2 1/2" and 1 1/4" I can't work with metal that is so hard to cut and trim with my tools since I am not equipped for it so I am hoping that an EASY solution is at hand by Tomorrow Morning at 9AM... Is there a Delrin 'R Us place in NJ?"
 
Al I use a angle bracket throu

Al I use a angle bracket through bolted through the stringer. It's been there for 30 years without problems.
 
"Almost all machine shops work

"Almost all machine shops work with delrin. As stable a plastic as you will find. Harder and denser than polyethylene (starboard). But, i think HDPE is all you need for a spacer. Cheaper too. You can cut HDPE nicely with a skill saw and a carbide tip blade."
 
Al go to your 99 cent store an

Al go to your 99 cent store an check out the white plastic looking cutting boards. Most are made from delrin or HDPE. I bought a store cutting board from this material and used it for a backing underneath each seacock on my boat. No more rot from plywood backed valves.
 
"Small pieces of trex can spli

"Small pieces of trex can split, thats a downside. if you use it, pre-drill slightly larger than your bolt, there is a small amout of expansion and contraction that takes place, same as starboard."
 
"EJ, I am using new angle iro

"EJ, I am using new angle iron brackets BUT I am using the original mounting bolts as they are NOT removeable without some major time consuming work. Since the original brackets worked fine with the newer engines all I really needed to do was to replace the erroded iron mounts.

The newer engines were shimmed with 2" of plywood which over the years looks like junk, mushy and not supportive at all. The TREX stuff is a composite of wood and plastic. I just took a 20oz framing hammer, a 8lb maul and pounded the crap out of a small piece. It seems ok and survived better than any plywood stack.

My bolts are 1/2" and I have 9/16" holes so they are a bit larger. We were thinking about the cutting boards but I am not sure about the quality of the plastic used at the .99 store. I have a few here from fishing that are cracked and yellowed so they may not be a reasonable grade of high density material.

I realize aluminum or steel is strong but if the plywood lasted this long, should'nt a piece of this stuff. I LOVE ALL OF THESE COMMENTS and suggestions and I am really looking to compromise on the side of longevity without that 101% knock out job !"
 
"Al:

The hammer smack is eq

"Al:

The hammer smack is equivalent to one piston firing....try a jack hammer with the stroke turned down low.

Excellent suggestions - DELRIN or HDPE. Both are at least 10X better in the comression area. As far as finding it locally, there's always a thomasnet search."
 
"Al, high density polyethylene

"Al, high density polyethylene (HDPE) is a very good choice (cheap, dense, and impervious). Delrin (acetyl) is very good but more costly and harder to find. Lexan is also a good choice. I do not like TREX because it contains wood fibers and is alot flimsier than say, AZEK decking, (celluar PVC)."
 
"UPDATE: This topic, out of a

"UPDATE: This topic, out of all the things I have learned about boating and mechanical STUFF, THIS FREAKIN SHIM thing has made me the most crazy. Naturally, it is not a 1938 Trumpy...its a Silverton. I don't expect it to last forever but I am sure another 15 years is within its potential so I am trying to get it right.

I could not get the HDPE in time and no matter what I tried, it was not gonna happen in the next 18 hours when I have the appointment to drop the block back in. The SLIGHTEST probability of having to go thru this thing again because of something silly happening to an unknown product just does not make any sense.

The original plywood lasted 25 years .. SO Back to plywood it is ! The Dr. Rot stuff I used to treat exposed wood in the past has been an outstanding material and the new plywood will surely outlast this set of engines... DONE.. Problem Solved.

What made me change my mind? Despite my admiration of some VERY respected folks right here on ME.com, my friend with the exact same boat 3 serial numbers away is also a structural guy, architect, engineer person. I asked him to read thru these posts and give me an opinion. He said, What happens if the material gives way at a point where the engine tips to one side, cocks the shaft and the prop slams into the rudder or breaks thru the hull? ALL because the material was not a proper use? Then a few web sites talk about Trex and ExxonMobil being sued for mis-representing the product and the class actions suits....blah blah blah

HOLY COW? Imagine that ? In a way, while a bit of a stretch, what would have happened had the drive damper not been contained by the bell housing (which was destroyed)? Would it have looked like the scene in CON AIR where the airplane propeller broke loose and sliced thru the plane and had sliced thru my hull?

I absolutley THANK YOU ALL for playing the devils advocate in the challenge to re-consider the use of the plastic. Jeff, you had suggested that the plywood was a good service use here and after all of this...I am using the plywood.

Here's hoping it all goes together smoothly!"
 
"Hey, when do we get to analyz

"Hey, when do we get to analyze the drive dampener, and how to make a better one?
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And also, the plywood will absorb more high freq vibrational energy than delrin. Just keep the dry rot out."
 
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