Cheap Rubber Motor Mounts

greasy tom · Apr 30, 2010

I ran across these
rubber motor mounts and ordered a few. They are 1/4" X 20 threads; male on one side, female on the other. I removed the motor mount studs from the engine case and re threaded the holes with a 1/4" X 20 tap (no drilling required). The male studs on the rubber mounts will then thread in the newly tapped holes nicely. I bought a length of 1/4" X 20 "all thread" and made new studs which screw into the female side of the installed rubber mounts. Next, slide the aluminum motor mount block over the new studs and mount to the seat tube in the usual manner. My first attempt utilized both front and rear mounts but resulted in too much engine movement. I wound up attaching the front mount in a normal manner on the down tube (using old inner tube rubber around the tube, and used the new rubber mounts on the rear (seat tube). The result is less vibration but not as vibration free as I had hoped. Also, the chain will rub very slightly on the left rubber mount for a few miles until it "wears in". This mod works fairly well, is cheap and easy to install, and looks like it was made for it. tools needed: 1/4 X 20 tap, and hacksaw (for cutting all-thread). Also, a couple nylon insert locking 1/4" X 20 nuts will be needed.

2door · Apr 30, 2010

Forget it. The engines should be mounted solidly to the frame. In addition those rubber isolators you are thinking of using are for light duty applications such as fans and such. They will not stand up to the vibrations produced by a 2 cycle gas engine. Rubber mounting these engines has never proved to be successful and the thicker the rubber the more problems you'll make for yourself. Do what works; mount the engine the way it was designed to be mounted. These are not Harleys or Hondas. Forget the rubber mounts.
Tom

greasy tom · Apr 30, 2010

Thanks for the good advice 2door. I am aware that these are not intended to be used under these conditions but so far, on my "test bed" bike, they are working nicely. In addition to your comments, I am also concerned about their ability to stand up to gas & oil contact but the sample I have soaking in a bowl in a gas/oil mix show no signs of degradation after 10 days.....time will tell. When installed on the bike, I can only move (with effort) the engine side to side about 1/8 inch but multiply that times 4000 times a minute........
As far as "mounting the engine the way it was designed to be mounted" I have found a lot of room for improvement in that area as well. I replace most of the Chinese mounting hardware with upgraded materials.
Tom

Venice Motor Bikes · Apr 30, 2010

I concur with 2door!

civlized · Apr 30, 2010

I have to agree with the "room for improvement" statement, greasy tom. I have never owned a 2 stroke engine, so I can't say much for them. But I made a anti-vibration mount for my 4 stroke that worked GREAT! The problem, I think, that 2door is addressing may be that most of the rubber mounts weren't built or installed properly and ended with not so favorable results. I think if it is done properly, it does nothing but improve the ride and display some creative flare. I rarely purchase anything and don't modify it in some way, so I'm all for making stuff better. You can make these things ride a lot smoother with some trial and error. I guess the problem for some is that the error part could result in death!

Oh yeah, if the design and intention thing is why you shouldn't modify the mount (to the naysayer's), why install an engine on a bicycle that wasn't designed for it?

2door · Apr 30, 2010

To elaborate a little on "vibration isolation" here is what you have to consider: The source of the vibrations you feel are produced by a single cylinder, 2 stroke engine coupled with manufacturing tolerances that leave a little to be desired. The engines are going to vibrate no matter how they are mounted. When they are isolated from the frame by rubber or some other resilient material the vibrations will be transfered to the mounting hardware (engine case and fasteners) and this is where you'll begin to see failures. If the engine is mounted solid to the frame the vibrations are transfered into the bike and, yes, you'll feel them, but they will be absorbed to a degree and that will lessen the possibilities of fastener/mount failures we've all read about. Unless the engine (crankshaft, piston, connecting rod) are properly balanced, not a job for an amateur, you can expect vibrations and even with these parts in sync, it is still a single cylinder engine and WILL, produce vibrations (actually harmonic pulsations) that will be felt when the engine is running and amplified by higher rpm. Not just my opinion, guys. That being said, yes, you can rubber mount the engine and possibly make for a smoother ride and lessen the 'buzzing' you feel in your butt and hands but the vibrations are still there and will show up in other ways that will cause you more problems than a tingly backside.
Tom

azbill · Apr 30, 2010

I agree with Tom,,,
in my experience, rubber just makes the inherant 2stroke vibration worse causing mounting stud failure

the vibes the rider feel might be lessened but at the cost of the stud having the to take it

Maxvision · Apr 30, 2010

I've found that I got more vibration from a poorly aligned rear sprocket than the motor itself.

greasy tom · Apr 30, 2010

Rats! blown off the saddle on my first post. OK, OK. You all have convinced this newb that rubber mounts are not good. Everything you have pointed out makes perfect sense, especially when I find things like a cracked chain guard after a few miles of riding...what's cracking next?
I will be removing the isolators and replacing them with a 1 piece, 3/4 inch wood spacer. Perhaps the isolators would be better used under my butt! Like CIVLIZED, I always have to tweak or modify in some way to try to make things run better or faster, i.e.; custom exhaust which utilized 1/2" EMT (electrical conduit). It is easy to shape with a conduit bender and with the stock muffler welded on the end, sounds and looks fairly cool. Didn't do squat for more power but has generated many complements.
BTW, my "builds" so far include 3 Crannys, 2 mountain bikes (Rat bikes) and one very clean & shiny Kingston 3 speed cruiser. Next build will be a Schwinn beach cruiser from Sears (on sale now for $149.95).

civlized · Apr 30, 2010

I'm still pro isolation. The only good way, that I know of, is to not mount rubber using only the studs. The studs should be mounted solid into some kind of bracket of sorts and new bolts from a bracket to the frame with some isolation material in between. Part of the problem with stud failure is that most have just stuck some rubber in between the frame and the engine using the same studs. This gives the studs the ability to move and causes a lot of problems, but like I said, I don't know the two strokes. I do know that I had great success with the mount that I made for my 4 stroke.

http://motorbicycling.com/f37/anti-...123.html?highlight=anti+vvvvvvibration+mounts

This is what I made, if you feel impelled, maybe it could help you come up with something.

civlized · Apr 30, 2010

Max hit on something too. There is a lot of vibration that comes from sprockets, tensioners, tires and wheels, etc. You can't get it all, but it can be improved. That chain guard would have cracked anyway(your rubber mounts should have nothing to do with it) and yes, something else could be cracking. Keep an eye out, but don't give up.

AaronF · Apr 30, 2010

You may want to check Manics custom fitted motor mounts out @ $43.00 shipped its a great deal.I've had them installed for about a week now with the rubber isolators that fit into the machined grooves no problems here. If I may,here is a picture of his new designed mounts.

happycheapskate · Apr 30, 2010

I am running a grubee 48 on a beach bike. I had huge vibration problems (numb but and wrists, mirror falling off. I found that using a spring powered tensioner (mounted on the gear case by the downtube, on top of the chain), took a LOT of vibration out.

Next was a suspension seatpost (one of the $20 ones, works good enough). This helped some. The best mod was a better spark plug and running 32:1 and a good KMC chain instad of the factory chain.

Now I can ride it for about 1.5 hours before I've had enough of it. If I get the 38t sprocket, I bet it will be even more tolerable.

PS my grubee chain guard broke at 100 miles, the metal is too soft (broke at little bracket that mounts on engine. If someone made a plastic one and used a rubber washer back there, it would probably hold up.

I just make sure my shoes are tight and my pants leg is taped or use a toe strap.

2door · Apr 30, 2010

AaronF said:
You may want to check Manics custom fitted motor mounts out @ $43.00 shipped its a great deal.I've had them installed for about a week now with the rubber isolators that fit into the machined grooves no problems here. If I may,here is a picture of his new designed mounts.

I believe if you check with Jim he'll tell you that he doesn't use rubber in his mounts but a very hard polyurethane material. He has done a lot of experimentation and found that rubber didn't work.
Tom

happycheapskate · Apr 30, 2010

Thats a good idea. Polyurethane: think skateboard wheels. They take tons of vibration and pounding but don't split.

civlized · Apr 30, 2010

2door said:
I believe if you check with Jim he'll tell you that he doesn't use rubber in his mounts but a very hard polyurethane material. He has done a lot of experimentation and found that rubber didn't work.
Tom

Yet it is a resilient material that absorbs energy, not a direct engine bolted up to the frame. Jim, have you been chastized for your engine mount or do they sell and people like them? Cause any bikes to fall apart yet? Any spontaneous exploding engines to report from using your mounts?

BarelyAWake · Apr 30, 2010

>.<

As you stated previously - it's a different game with mounts designed to isolate the engine, but I'm pretty sure there'd be problems even with Jim's mount & hardware should ya just wrap the frame a coupla times w/some old inner tube.

Trying to compare rubber to polyurethane is seriously reaching, even just for a jab.

Cabinfever1977 · Apr 30, 2010

You can buy Polyurethane for mounting at many auto parts stores.

civlized · Apr 30, 2010

civlized said:
Yet it is a resilient material that absorbs energy, not a direct engine bolted up to the frame.

BarelyAWake said:
>.<
Trying to compare rubber to polyurethane is seriously reaching, even just for a jab.

Just so we are clear, I wasn't comparing rubber and polyurethane. I was comparing polyurethane and a rigid (as designed in the original kit) mount, if your statement was directed towards me. No jabs, just sayin'. We're all friends here

PS: What does this mean? >.< I'm not much into the whole texting and chatting lingo.

Creative Engineering · May 1, 2010

The engine mounts that I produce utilize Neoprene rubber as a liner for the frame clamps. This liner was not designed into the product for the benefit of eliminating the vibration that the rider experiences. The metal part of the frame clamp is larger in diamter, .030", than the frame. The Neoprene is recessed in a machined groove so that it is trapped in the clamp. The Neoprene is a .015-.020" crush against the frame tube which makes for a very rigid engine installation.

Considering the inconsistencies, in diameter, of bent tubing...I did not want to make the clamps a metal-on-metal union. This would have created stess "hot spots" that could lead to frame cracking.

As far as the frame clamps are concerned; they work the same as the Ridley design, which has been proven. I created the link set-up, (and provided a field for frame tube sizes), in order to make my mounts fit many different frame sizes and styles. Although for sale, the Ridley mounts were made for internal use on thier own motorbikes. They fit the Felt frame only.

The current offering is shown in the photo, (post #12), provided by AaronF.

The original pan type design shown on my website, (post #17), is no longer available for a number of reasons. I made quite a few of them and 80% worked great. A few of the pans cracked at a bend. In addition the original design just wasn't universal enough for mass production.

The new design will work with a wide variety of frames just by altering the length of the forward link.

Jim

Cheap Rubber Motor Mounts

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