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Antique Gas Engine Discussion

4hp Cushman Vibration

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Old 07-13-2005, 11:29:35 PM
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Bryan Brooks Bryan Brooks is offline
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Default 4hp Cushman Vibration

I went to look at a 4hp verticle Cushaman this evening that is for sale. It is a nice all original restoration on a cart. The price is right and I am ready to buy but for one question I need answered. When the engine runs it vibrates a lot at low speed. If you speed it up I believe it would jump around the block. All cushans I've seen are set up to run grist mills and are mounted to trailers which is more solid than a cart. Is the vibration normal for this engine?

Thanks, Bryan
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Old 07-14-2005, 12:26:33 AM
Dick Welty Dick Welty is offline
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Default Re: 4hp Cushman Vibration


The first Cushman Binder engine that I saw was bolted down to a piece of concrete because it jumped around.

I have one that I restored about 10 years ago and I have never run it . It is in my living room. I'm wondering if it will run smoothly or not.

When I had my engine open I noticed that the crankshaft weights seem to be bolted on at the factory. I believe if someone unbolted the weights and didn't put them back in balance that it would account for the engine bouncing around.

I have seen others run at shows and they seem to run ok.

Maybe one of the Cushman collectors can give a more definative answer to this question.
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Old 07-14-2005, 12:07:41 PM
Don C. Wiley Don C. Wiley is offline
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Default Re: 4hp Cushman Vibration


Most folks try to run them too fast. They are rated to run 800 rpm. The throttle will allow them to run in excess of 1000 rpm. I run mine, which is on a banjo cart, and it runs smooth at around 400 rpm. I had it belted to a table saw and it did a fine job. When I demonstrate it without a load I run it as slow as it will run smooth, that's about 100 rpm.

If yours has the brass Schebler carbutetor, you have to make sure the after market copper tube is adjusted to sit right at the notch at the bottom of the air intake. The needle valve is a little tricky to get adjusted just right. Be sure to back the speed control to allow it to run slow. You may need to leave it tightened up a little bit until you get every thing adjusted and then you can back it down until it runs as you like it to.

The intake manafold MUST be sealed tight or you're out of luck. Mine had a leaky gasket between the head and the manafold and it would not run slow at all. I worked at that thing for a week or better and after replacing the gasket and spark plug, it ran fine. Mine has a buzz coil ignition and I get a bright blue spark. I don't know what kind of ignition you have, but it needs to have a good spark to get it to run slow and smooth. Some had a rotary mag and some had an EK mag on them.

Good luck and if it weren't for the water needed to get it to pump, it would be one of my favorite engines to take to the show.

"DELCO DON" Southern Illinois
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Old 07-14-2005, 01:44:32 PM
Jim L. Brown Jim L. Brown is offline
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Default Re: 4hp Cushman Vibration

Bryan: I think all of the above replies are applicable. It may be a combination of factors, but I've found that the engine speed is the most critical - the slower the better. The crankshaft counter weights are also important, and you can usually tell by the spacing/clearance which one goes on which side. If not, be sure to mark them when/if you disassemble the engine. I've never had much trouble with mine (I've got them on cast iron generator bases, banjo carts, wood skid carts, etc.) but others have said they do have problems. I've even seen various kinds of weights added to the flywheel to get it "balanced" so as not to bounce around and I've seen them (and other engines) staked down at shows. Who knows what might have been done to an engine in its earlier years in terms of disassembly, rebuilds, etc. They are well built engines that run good if set up right. Jim
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