Briggs RPM question

[Craftsman GT]

I just repowered my 1948 Simplicity Model D with a 5.5hp Briggs I/C 134202. I only have a sickle bar and run the engine at 1/4 throttle just above idle. Is this gonna hurt the engine? Thanks

[madmantrapper]

I don't think it will hurt the engine but I can't believe it develops enough power at that low an RPM.

[RJRacing]

yes, it will hurt the engine, needs to run full throttle for proper cooling

[bgsengine]

I just repowered my 1948 Simplicity Model D with a 5.5hp Briggs I/C 134202. I only have a sickle bar and run the engine at 1/4 throttle just above idle. Is this gonna hurt the engine? Thanks

Yes - you're gonna end up overheating - Flywheel fan is the only thing providing engine cooling and loading it at just 1/4 throttle you will not generate sufficient cooling for the engine.

Also running at part throttle, you'll have more frequent spark plug fouling, use more fuel (amazingly enough!), and if it has a charging system, it can also run the battery dead since you won't be developing enough to fully charge the battery.. also you'll have lubrication issues since it is a splash lubricated engine, running at slower speeds you won't be splashing enough oil to places where it should be going..

And the above advice is all based on ONE assumption that we all have to make - the assumption that the engine's governed top no load speed is properly set. (if it isn't you got worse problems)

[bluemower]

there is a picture of an identical machine with the same engine conversion on anther site. Quite an antique. this link has a picture: http://www.simplicityva.com/page-12.html

Most of the 134202 engines are adjusted to idle around 1700 rpm. Usually full power is set to 3300 - 3600 rpm. So---- 1/4 throttle is probably around 2200 - 2300 rpm. This equipment was originally equipped with a 2 hp cast iron Briggs. The replacement engine will not be worked very hard, so I doubt if you will experience overheating. I suspect you may experience carbon fouling and carbon build up in the combustion chamber. You may also need to remove the blower shroud occasionally to clean cooling fins and dirt residue from the breather / oil fill areas.

My opinion is based on supporting ranchers who use identical engines to fill their pasture stock tanks. The ranchers usually fill the fuel tank every day and leave the engines running until they run out of fuel. Rpm is set at fast idle. The last time I sold to a rancher, the engine lasted about 3 1/2 years before the owner ordered a new engine. This translates into about 1800 - 2000 hours of use.

[bgsengine]

Rpm is set at fast idle.

Technically that is top no load.. AKA High Idle.

However I have seen similar engines that will , eventually, experience premature failure from overheating (burned valves, hot spots on the cylinder, heavy carbon build up, etc) when they are not run to top no load at least some of the time - I'm gonna have to throw together a couple junked mowers and invest a little gas to do a comparison side by side.. when running at less than top no load for extended periods, the ambient temperature is going to be a huge factor in engine cooling - Much like starting up an air cooled motorcycle and leaving it running without moving - how long you think it would run at quarter throttle with little to no air flow?

But as a rule of thumb, the simple and most correct answer to the original question will be "yes" - if you have more information such as the load being applied, the amount of work the engine actually must do, the ambient operating temperature, and maintenance habits, you can then weight that answer out with a "might be just fine for 20 years" to "Thar She Blows, less than a week" - it'll be heavily dependent on the application and how much supplementary cooling the engine may get besides the flywheel fan - Engines are designed and spec'd to run at a specific RPM and that will also include the shrouding and ducting, the application environment, etc.

Engines built to run at extended idle or low RPM may have different or additional tin duct work to more precisely direct the reduced air flow for better cooling.. - again it really is heavily dependent on the application.

[Craftsman GT]

Other stuff I've read from some other sites said not to run above 1/2 throttle with the sickle bar. I'm usually Rotella 5W40 oil if that helps

[bobodu]

Had one of those with a CLINTON !!!

[Craftsman GT]

The Clinton on this one wasn't original. Supposed to have a Briggs model N on it. The Clinton runs, but needs a carb rebuild so I decided to upgrade to this 5.5 Briggs

[Skywatcher]

Hi GT and Others

Whether I'll clear things up or just add fuel to the fire, I don't know but I'll chip in anyway. A sickle bar mower takes very little power as opposed to a rotary mower. For example, a 20 horsepower tractor can run a 16 foot sickle bar swather through 3 foot tall grass no sweat however, put a 6 foot gyro mower behind the same tractor and you'd better take it easy through the taller grass or you'll bog the tractor down. I had a customer with a 36" Jari sickle bar mower that kept shaking itself to pieces. I finally set the top governed speed down to 2,500 and the machine has run fine ever since, that was 12 years ago.

I agree that the cooling air velocity is not there at lower RPM, neither is it on a motorcycle when you're riding through town where the speed limit is 30 mph (50 kmh). At the same time though, you're never at more than ¼ throttle so you're not putting the HP through the engine. The time you need cooling air velocity is when you're at ¾ throttle or higher doing 70 mph (110 kmh) or more down the highway. In closing, I would say go with the engine you have, use good quality fuel and keep an eye on the condition of the spark plug. The SAE-5w40 may tend to burn through the engine a little faster than would SAE-15w40 of SAE-30 oil. Myself I use SAE-30 in all B&S engines as the oil has no viscosity enhancing polymers that are prone to breaking down at the higher operating temperatures of air cooled engines. Anyhow, best of luck with your project and be sure to give us an update in 5 years or so. All the best,

Sky