Engine mount spacer & rubber isolation. '69 Rupp Roadtser

[robgmn]

And, the project gets closer to completion, due in good part to the help and info from members of this forum.

My son and I are down to the point of mounting the Predator 212 as a retrofit for the original H50 on this bike.
Based on the mock-up, we have to raise the front of the motor by 10mm and the rear by 35mm.

I was originally thinking of getting some aluminum block and milling it to a rough wedge shape, then drilling the holes.
While unable to sleep at 3AM, I started thinking about vibration isolation.

Any opinions on me just using rubber/poly sway bar link bushings (cut down) for the front spacers and some aluminum block PLUS some cut-down bushings for the rear spacers in order to dampen vibration a little?
My only concern would be making sure the engine couldn't "walk" in the mounting slots, but I'm sure I could figure a way to lock it in place.

 

[control4userguy]

Plenty of subject matter on this forum regarding "isolation". My opinion is, do not do it. Others have indicated that Harbor Freight engines may not be built to tight tolerances resulting in excess vibration. I run a H50 in one of my bikes and it is smooth as properly aged whiskey.

 

[robgmn]

That makes sense.
Maybe we'll get to find out about the H50 once we get it restored (budget restrictions keep this makeover as basic as possible, hence the Predator engine).

??

 

[stargazer7467]

i just have a piece of mudflap under my engine

 

[stargazer7467]

 

[Charles S]

Actually, I think your aluminum block/wedge idea would be great, especially if you don't bolt through. Aluminum tends to absorb vibration; the thicker, the better. If you were to drill and tap your wedge (thread inserts optional) top and bottom (different locations, obviously), bolt engine to wedge, bolt frame to wedge from bottom, you would have a rigid mount (beneficial to your chain's health), and I believe it would reduce vibration transmitted to the frame.

 

[neo71665]

Actually, I think your aluminum block/wedge idea would be great, especially if you don't bolt through. Aluminum tends to absorb vibration; the thicker, the better. If you were to drill and tap your wedge (thread inserts optional) top and bottom (different locations, obviously), bolt engine to wedge, bolt frame to wedge from bottom, you would have a rigid mount (beneficial to your chain's health), and I believe it would reduce vibration transmitted to the frame.

I know that looks good on paper but I can tell you replacing the rubber body mount bushings on a car with aluminum ones will jar your teeth loose.

 

[Charles S]

I know that looks good on paper but I can tell you replacing the rubber body mount bushings on a car with aluminum ones will jar your teeth loose.

Not the same thing.

 

[creia]

Rubber isolators do not work. This topic has been discussed many times before. Do a search and you can read up.
Michael

 

[jim85541]

My Suzuki Gt 750 water buffalo was rubber mounted. But in an odd way. Engine bolts went into the oversized holes with o rings on the bolts to make up the slack. The engine would shake in the mounts but was one of the smoothest bikes I had. I ride a BMW now and I still think it was almost as smooth as the Beemer. Wonder if something similar could be used in this case? A little creative drilling with some over sized, counter sunk holes with a few o rings in the holes?

 

[robgmn]

Believe it or not, I sliced up some hockey pucks into wedge shapes, drilled them out, and mounted the engine on them.
It works fine.

After the first hour of riding, I checked them and they're snug and secure.
Ten hours in and no change.

 

[Charles S]

Cool. If they ever should loosen, try Nyloc nuts.

 

[KB2ROCKET]

It can be done the trick is to not use through bolts from the engine to the frame
.
In industry machines are mounted using isolators just do a search " vibration isolation mount " I'm sure you will get some good ideas. In a minibike there is a very fine line between vibration control and to much movement

 

[KB2ROCKET]

I have always wanted to design an effective vibration isolator for small engines I am currently working a project that will use a gx390 with the balance shaft removed remember these engines are supposed to be used as mostly steady state operation and those shafts really only work at one rpm point and they rob power but let me get back to the point if I make an isolator that actually works I will share it with everyone