Have I shortened my lawn tractor life?

[circus]

Re: 30 yo, 18hp, B&S opposed twin.
Just got a tachometer. Raised rpm from little over 3000 rpm to little over 3500rpm. Very pleased with the results but have I shortened the engine's life?

 

[RedMF40]

Re: 30 yo, 18hp, B&S opposed twin.
Just got a tachometer. Raised rpm from little over 3000 rpm to little over 3500rpm. Very pleased with the results but have I shortened the engine's life?

I don't understand this post. Are you saying that installing a tach somehow increased your engine's RPM?

 

[MM-TX]

Pretty sure he means he got a tac to check rpm then upped it to 3500 rpm. My answer to the question would be probably. My take is old machines last longer going slower not faster.

 

[Nordic]

If you are not working your tractor unreasonably hard and not overheating the engine while having clean, good quality oil in it, I don't think the increased RPM will do any significant harm. It's likely in good condition now, after 30 years, even if you were to reduce the life span by 10% it's going to serve you well for time to come. I used to have a gravel truck with a big Detroit diesel. From the time of purchase until I sold it, more than 10 years later, the governed RPM was at more than 10% higher than spec. I worked the truck very hard, often 'pedal to the metal'. It handled the increased RPM no problem.

 

[Russ from MN]

3500 shouldn't hurt it, like others have said. 3600 used to be the standard for lawn mowers, but as blade length increased, they lowered the rpm to reduce tip speed. Is it really opposed, or a v-twin? We have a 12 year old JD Z-turn with a 20 hp V-twin Briggs, seems to be a great engine.

 

[timcasbolt]

Re: 30 yo, 18hp, B&S opposed twin.
Just got a tachometer. Raised rpm from little over 3000 rpm to little over 3500rpm. Very pleased with the results but have I shortened the engine's life?

These engines are designed to provide maximum efficiency at 3600 rpm. When you're under full load, that's the speed they should be running at.

 

[circus]

Pretty sure he means he got a tac to check rpm then upped it to 3500 rpm.

Correct. Even when sharp the mower blades often didn't cut it. Going over the same grass twice got old.
3540 rpm is OK, great, now only worry is keeping the mice nests out.

 

[BarnyardEngineering]

The answer to your original question is, "Yes, but probably not appreciably."

 

[Duner Wi]

When new what was factory suggested RPM? That's what I would go by if you are concerned. If factory says 3500 you are golden.

 

[buickanddeere]

All all designed to operate 3600rpm on generators

 

[T.R.K.]

I am against the grain on this one. Briggs probably designed it to turn 3600 rpm all day long. And they actually run cooler if the fan turns faster.

That said, being 30 years old, and I bet you don't know the number of hours on it, I have seen two or three of those twins die in the last few years. What happens is the plastic oil slinger gear wears out and no longer is turned by the camshaft gear. (The gear teeth never fully meshed and only about a 1/8" triangular area actually contacts the cam gear) When the plastic gear wears out, then the engine seizes. If you ever have to remove the sump for any reason, replace the oil slinger/governor assembly.

 

[Dober_paw]

I have a 1994 MTD lawn tractor with this engine setup exactly as per your picture. It’s B&S model 422707 and my notes in manual say 3600 max.. FWIW I have recently added an inline fuel tap next to the inline filter next to dip stick. Reason - if like me you routinely <fill - mow - park near empty> you will mask a leaky 32 yr old fuel pump/carb. On the one occasion that you refuel before parking the fuel level is now above the leak and gravity will drain gas thru pump/carb/cylinders and fill the sump. Next time you start you will have lots of smoke and run rough/stall - yikes! the poor old, normally reliable, girl is very sick. Belt & suspenders - I refurb’d carb/pump and added tap. Changed oil - there was an extra quart in there! I guess that is why you should always check oil before starting - you may "know" your engine is not burning oil - but it might be gaining!

 

[circus]

as blade length increased, they lowered the rpm to reduce tip speed.

Didn't factor the blade tip speed. Multiple pulleys was another confounder so I measured the rpm of a blade spindle pulley. There are three blades, each 16" diameter. Spindle running at 3800rpm X 16"/12 X 3.1416 = 15,917fpm. ANSI B71.1 limit is 18,000fpm for push mowers. I'm OK.

PS I stopped looking for something that worked better so, in a way, raising rpm lengthened my weed mowers life.

 

[buickanddeere]

Didn't factor the blade tip speed. Multiple pulleys was another confounder so I measured the rpm of a blade spindle pulley. There are three blades, each 16" diameter. Spindle running at 3800rpm X 16"/12 X 3.1416 = 15,917fpm. ANSI B71.1 limit is 18,000fpm for push mowers. I'm OK.

PS I stopped looking for something that worked better so, in a way, raising rpm lengthened my lawn mowers life.

180mph for your mower . Legal limit is 204mph .

 

[Tony in Bama]

And they actually run cooler if the fan turns faster.


There's your correct answer...