Still want to argue about rubber mounting?

2door · Jul 1, 2014

Hockey pucks aren't made of rubber and rubber squished down to .005" is doing nothing but protecting the paint. 'What we're talking about is thick rubber or resilient material between the engine mounts saddles and the frame and then using the stock engine mounts and fasteners to hold the engine in place.

You can defend rubber mounts all you want but the fact is using the method I described above will cause eventual failure of the fasteners or the frame.

You CAN'T eliminate the vibrations produced by a single cylinder, especially a 2 stroke engine. You can either live with them, or go electric. Trying to isolate them to the engine is futile.

Tom

scotto- · Jul 2, 2014

I wonder why so much of all this said vibration is transmitted and felt by your hands holding onto rubber grips? Would you feel as much with solid grips?

Theon · Jul 2, 2014

Weighting your bar ends is suppose to help.

scotto- · Jul 2, 2014

2door said:
Hockey pucks aren't made of rubber and rubber squished down to .005" is doing nothing but protecting the paint. 'What we're talking about is thick rubber or resilient material between the engine mounts saddles and the frame and then using the stock engine mounts and fasteners to hold the engine in place.

You can defend rubber mounts all you want but the fact is using the method I described above will cause eventual failure of the fasteners or the frame.

You CAN'T eliminate the vibrations produced by a single cylinder, especially a 2 stroke engine. You can either live with them, or go electric. Trying to isolate them to the engine is futile.

Tom

Huh??? Hockey pucks aren't made of rubber? Really?

Every hockey puck I've ever encountered was made of thick, black, hard rubber....by Goodyear?

Goat Herder · Jul 2, 2014

So with the hockey puck the front of the motor is always flexing and moving around. That sounds destructive on solid rear mounts???

curtisfox · Jul 2, 2014

Prolly get flack but I don't think it weather you use rubber or not it useing a muffler clamp for a motor mount. Anytime you use that kind of mount it's going to pinch. When I first seen the china engines I had to laugh, they pinch tail pipes what will they do to frames.

As a kid I had a Monark twin it had a split tube type clamp about 2" long with about 1/8" rubber between them and the frame. Somewhere my son still has that mount( blew a rod )

So after all these years I am surprised they haven't changed the mounts,just my opinion.......Curt

wret · Jul 2, 2014

So, if I'm getting this right, the issue is not the choice of specific materials its the PARTIAL isolation of vibration which results in focusing the forces on a smaller area; the mounting bolt rather than the entire mating surface?

curtisfox · Jul 2, 2014

In my opinion yes. Others have use CB Antana clamps as showen hockey pucks. Just plane old conduit clamps would be better if they fit. The engine itself has a wider pocket for the tube to fit ( or is suppose to ) Scotto, Pat ,and some others have used round clamps the there mounts that bolt to plates for there bigger builds............Curt

biknut · Jul 2, 2014

Goat Herder said:
So with the hockey puck the front of the motor is always flexing and moving around. That sounds destructive on solid rear mounts???

It's not just a hockey puck. There's also an automotive muffler clamp hidden inside the hockey puck. The rear mount has a thickness of inner tube wrapped the down tube. It's all clamped together so tight there's very little movement if you try to move it by hand. You could call it solid mounted, but there's just enough movement to absorb about 50% of the vibration.

The mistake most people make when trying to rubber mount their motor is in having too much movement.

Motorcycle manufacturers used to successfully rubber mount their engines all the time. New Sportster's are referred as rubber mounts, because their motors are rubber mounted.

Of course they spend thousands figuring out how to have the right amount of resonance so the rubber mount doesn't destroy itself. It's not that easy to do, and that's why it's better for most people to solid mount their china girls.

The Atomic BB, and Stunner have the same Flying Horse 80 motors purchased at the same time. Stunner is totally solid mounted with fancy billet mounts front and rear, while the Atomic BB is rubber mounted. The Atomic BB has noticeably less vibration than Stunner.

2door · Jul 2, 2014

This augument will never go away. There are two schools of thought and they are diametrically opposed. Those who have successfully soft mounted their engines are the ones who understand the dynamics of what is happening when the engine runs, where the vibes are concentrated and how to keep the stress off of the mounts and fasteners.

All too often the new, inexperienced builder will arbitrarily wrap a chunk of thick rubbery material around the frame, clamp the engine to it and then come here asking how to remove broken studs from the engine case.

This is where I feel telling a new builder that it is okay to rubber mount is a disservice that we should give close attention to before suggesting it. It goes without saying that there are more successful builds with solid mounted engines that there are where resilient material was used.

If you have soft mounted and had success, good for you. It goes to display your mechanical understanding of how to do it correctly. But don't advocate to a new builder to try it unless and until he knows what the results can be if not done right.

Tom

scotto- · Jul 2, 2014

2door said:
This augument will never go away. There are two schools of thought and they are diametrically opposed. Those who have successfully soft mounted their engines are the ones who understand the dynamics of what is happening when the engine runs, where the vibes are concentrated and how to keep the stress off of the mounts and fasteners.

All too often the new, inexperienced builder will arbitrarily wrap a chunk of thick rubbery material around the frame, clamp the engine to it and then come here asking how to remove broken studs from the engine case.

This is where I feel telling a new builder that it is okay to rubber mount is a disservice that we should give close attention to before suggesting it. It goes without saying that there are more successful builds with solid mounted engines that there are where resilient material was used.

If you have soft mounted and had success, good for you. It goes to display your mechanical understanding of how to do it correctly. But don't advocate to a new builder to try it unless and until he knows what the results can be if not done right.

Tom

Well said

curtisfox · Jul 2, 2014

Yes so very true , it's just if they had a nice flat strap clamp inmy way of thinking this all wouldn't be nessesary. It's so easy to get the U clamps crocked.............Curt

biknut · Jul 2, 2014

I have a friend I won't name, who's here on the forum, and lives in the Dallas area. For his first build he bought some very sturdy automotive engine mounts for the front and rear mounts. He mounted the hard rubber engine mounts to his motor, and frame like a genius. It looked, and felt like it was going to work really well.

Then he started the engine, and the whole thing shook, and vibrated so bad it was immediately obvious that wasn't going to work. What a shame too, because he really did a great job putting it all together.

maniac57 · Jul 2, 2014

I meant to stir the pot with this inflammatory post. I also meant to scare noobs thinking about a innertube wrapped frame into rethinking this long-since settled argument.
I see far too much mis-information from vocal know-it-all newcomers giving bad advice.
The builders I see above all have the experience to do things others should not attempt, and this statement is NOT meant to hack on the few who know.
But you simply HAVE to admit, most builders coming here for info are ripe for poor ideas.
Boost bottle anyone? Electric turbo kit?
My original statement stands:
For 99.999% of motorized bicycles, rubber is a BAD IDEA.

greaser_monkey_87 · Jul 2, 2014

When I built my first bike, my down tube was wider than my front engine mount. I bolted a seat post to the engine, and the seat post I clamped to the frame. The seat post was actually smaller than the engine mount, so I cut a piece off an old garden hose, the type threaded with nylon, and used it to shim the front engine mount for the seat post. I didn't know this forum existed at the time, and I didn't know that sbp sold an adapter plate either. I didn't even know sbp existed at the time. I'm not saying rubber works for mounting to the frame, but it did work for my creative engineered mount. Of course it wasn't the proper way to mount an engine, but it did work and I never had any problems with it. The motor did not sway or vibrate badly.

Goat Herder · Jul 2, 2014

I hear you Manic . Could not agree more. CNC style milled clamps or welded in mounts. Then rubber tubing as a minute buffer smashed in done ''presentably'' . Think nice broad clamps. I am not to impressed my self or my skill to even wanna make a anorexic one lol.

''With good steel not cheep flat stock would be best''. can do the trick but I found in the long run where stuff will crack. Use good alloy and get it back in return.

I got to work on bowling machines that when the wrong fastener came loose it was more drama. I seen the steel brake, crack clean though on Japanese steel alloy. Racks where the sweeper was guaranteed to fracture!

Worse yet the turret cages on down would shake apart Could find fasteners on the floor . Mandatory to do a shake down on every part and clean it up again after that. Got to clean up after enough from the lazy gent that was there. I did not want his job and well the guy had no retirement. Besides I was just passing through.

turboragtop · Jul 6, 2014

There's just a massive, big bad ol' world out there of wave theory, harmonics, natural frequency and vibration damping that most of us have never seriously studied and don't understand. Every engine architecture will produce different harmonics and thus require a different approach to damping those vibrations. For example, a 90 degree V8 is inherently balanced, but a 90 degree V6 is not, and requires a balance shaft. But a 60 degree V6 does have that inherent balance, so no balance shaft needed. Harley has a great body of knowledge about V-twins, and their unique damping requirements, etc.
However, none of the above applies to single cylinder two-stroke motors!
Best to stick with what the experienced guys are doing rather than trying to R&D something in your garage that is too complex to understand with the tools most of us have at our disposal.

2door · Jul 6, 2014

Well said, Turbo and welcome to the forum. You're absolutely correct in that a single cylinder 2 stroke engine is an animal apart from multi-cylinder 4 strokes and damping or eliminating the vibes produced is a task most have no skills for. This is why solid mounting is the lesser of evils.
Thanks for the input.

Tom

abracadabra · Sep 18, 2014

Ive got close to 1000 miles with rubber sandwiched between motor and frame. I used self tapping screws into the frame thru the mounting plates, & rubber.
I have a very smooth and quiet ride. Motor isnt hurting the frame. And it hasnt twisted sideways. I drive 10 miles each way to and from work on some bumpy roads.if it was gonna be a problem im sure id know by now

Kioshk · Sep 18, 2014

abracadabra said:
Ive got close to 1000 miles with rubber sandwiched between motor and frame. I used self tapping screws into the frame thru the mounting plates, & rubber.
I have a very smooth and quiet ride. Motor isnt hurting the frame. And it hasnt twisted sideways. I drive 10 miles each way to and from work on some bumpy roads.if it was gonna be a problem im sure id know by now

Just to reassert Tom's advice:

2door said:
If you have soft mounted and had success, good for you. It goes to display your mechanical understanding of how to do it correctly. But don't advocate to a new builder to try it unless and until he knows what the results can be if not done right.

Tom

Still want to argue about rubber mounting?

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