Yamaha RD400 Engine Mount Dampers

[Milan]

So earlier this year I had a post on the RD400 engine mounts.

My existing ones on the purchased bike were worn out & bike was vibrating

So my post explained how you could replace the mounts without removing the engine.
Just had to un-chain.

Well the new mounts I got from Sumo Rubber.
They sure seemed overly hard & thin when I saw them.

I put them on & it did reduce the vibration
But still have some.

So I went on a search for other ways to dampen the motor.
I acquired some rubber bushings, which I believe are for springs.
I also got some brass spacers.

The bushings have the proper 1" O.D. and the bushings press fit in to give the proper I.D. for the bolt.

So, I am going to try this.
I have 2 sets of rubber, one harder than the other; I will try the softer one first.

The only problem I can see is the brass sleeves working their way out, or in, along the bolt when riding.
So The front have the spacers sleeves, just need to make sure they are snug to the brass sleeve.
Other places I will cut a piece of CPVC to the proper length to hold them in place.

One other thing.
I need to figure out how to trim the rubber flange to give me the proper width for install.
I believe I measured 1/8" needed

M

[Striker1423]

The three main types of plastic used in injection molding parts are as follows. Polypropylene, Acetal, and Nylon. With the addition of elastomers to polypropylene you get TPE. Thermoplastic Elastomer.

New rubber parts are overly hard and less flexible because of the type of thermoplastic overseas factories are using. Typically rubber molding of this nature is done with a low-concentrate poly with a higher elastomer content (plastic with rubber mixed to allow flexibility) TPE or even TPE-o. The cheaper versions of TPE that make up a lot of the overseas parts are a higher concentration of polypropylene and less elastomer. Hence they flex less.

This results in significantly harder rubberized parts that do not possess the strength and elasticity of more expensive elastomer products. Crumbly and/or easily broken parts mean under or over-melted plastics outside of the range recommended for molded TPE. OR a higher concentrate of plastic with less elastomer that leads to part structural rigidity loss (Broken and imperfect molecule bonding).

Contaminated injection molding machines can cause problems across plastic types as well. Some plastics melt at lower temps... Say, 250F versus 600F. If a 600F chip of plastic is still in the machine when you're melting a lower temp plastic and it escapes through the injector nozzle and into the mold, the result can cause an unbonded void inside the over melted part. This creates strength issues.

As well as how overheating metal causes crystallization and weakness of metal parts, the same principal applies if say an Acetal part is burned. The part not only is weakened, but acetal gives off the distinct gut-wrenching formaldehyde that's enough to make your eyes burn and induce coughing fits. Ask me how I know.

[Milan]

The stock motor mounts, or replacement ones, have considerably less rubber than the bushings do.
Annular-wise.
The stock metal sleeve I.D. is even oversized for the 10mm (?) bolt that goes thru it.
Which is what takes away from the rubber area.

The parts in the picture were also about 75% cheaper that the replacement stock mounts.

Must just be the old way of designing them back then.

Sumo's ( or whoever makes them ) quality control over the rubber content probably is non existent, as for what they are

[Milan]

Don't think the rubber on the mounts is a plastic.
More of a Thermoset, as it does not re-melt; only burns.
Could be extruded, but more likely molded onto the metal sleeve.

But the same principal applies as to the % content which affects the hardness & flexibility

M

[rd400canuck]

quick question now that I see this thread... my rubber dampers came out easily and go in easily. Does that mean they are gone?

[Milan]

My old ones cam out with just a Pinky push.
Very worn down

The new ones were snug, but not so much that a hammer was needed.

[IR8D8R]

The original bushings were most likely vulcanized butyl rubber like tires. They are cured in a steam press. Bonds the rubber to metal parts at the same time it cures them.

IR8D8R

[Milan]

I will second that.

Had some old mounts and had to scrape off the rubber with a knife.

I wanted to see if the bushings I had would just fit over them.

They are larger in diameter, so bushings did not fit.

M