OHV/OHC vs. Flatheads.... AND THE WINNER IS......!

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Originally Posted By: lexus114
Originally Posted By: Maritime Storm
Originally Posted By: lexus114
Originally Posted By: ViragoBry
Who'll be the first to produce a mower with 4-valves, DOHC and VVT? Might as well throw in throttle-by-wire and fuel injection. Variable vane turbo w/intercooler anyone? :)


And dont forget a Catalytic Converter!
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Actually they are mandated for 2011, we have some with cats in-stock at work. They started making last year. Here's a link.

http://www.canadiantire.ca/AST/browse/2/...2BLawnmower.jsp


Oh you`ve got to be friggin kidding me!! whats next,one on our rear ends??
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http://www.sciencedaily.com/releases/2001/05/010529234907.htm
 
Not only does it have a catalytic muffler, it's got secondary air injection. I have a feeling this muffler is no different in function than my Husqvarna 2-stroke string trimmer. One the catalytic inserts in the muffler don't work anymore, the unit still works fine, just pumps out untreated exhaust.
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Joel
 
Actually, I would bet that lawnmowers and other small engines probably contribute the majority of pollution. Bet you didn't know this, but running a brand new lawnmower for 1 hour is teh equivalent of driving a 1992 model year car for 800 miles. And then think about how much people neglect their mowers. Pollution. Cats on lawnmowers is a great idea. Just extend the pipe so there is room for one that won't clog.
 
Originally Posted By: rudolphna
Actually, I would bet that lawnmowers and other small engines probably contribute the majority of pollution. Bet you didn't know this, but running a brand new lawnmower for 1 hour is teh equivalent of driving a 1992 model year car for 800 miles. And then think about how much people neglect their mowers. Pollution. Cats on lawnmowers is a great idea. Just extend the pipe so there is room for one that won't clog.


While I couldn't pull any numbers out of my butt like you did, I agree in concept. Cat-free, neglected, engines with carbs produce way more pollutants than modern road vehicles. The only thing worse is cat-free, neglected two-stroke engines with carbs. Of course other than running rich the carbon footprint is probably the same, it's all the other stuff that cats and proper mixture control clean up that'll make the difference.

Depending on whether the cost was ludicrous, I'd consider retrofitting a cat to my GXV140 if it didn't look totally stupid. I like nature, trees, furry woodland creatures and my children as much as the next guy...
 
Maybe it's more a fault of Briggs then the flathead design, but I've had to reseat the valve seats in my 6.5HP Briggs "I/C" lawn mower engine twice. The Honda and Kawasaki OHV motors I've worked with are excellent, quieter and smoother running. OHV any day here.
 
Flatheads were supposed to be off the market this year, the EPA granted manufacturers a reprieve due to the economic crisis. Expect to see them off the market next year or real early 2011. 2-cycles are in the same boat. Not sure if adding a cat will get them past the 2011 emission packages or not. MTD went to these OHV engines exactly for that reason, they wanted some experince with them before they HAD to use them. The chinese clones they are using seem to hold up as well as the Briggs they are replacing judging by the come-backs we've had since they introduced them.
 
Originally Posted By: Maritime Storm
Flatheads were supposed to be off the market this year...


I thought so too, but they still seem to be going strong in the ~6hp and under crowd. Most engines over 6-7hp have gone the OHV route and rightfully so IMO.

Joel
 
I wish we had gotten the Briggs 875 series OHV instead of the 675 Flathead. Gas is expensive and it is NOT fuel efficient. Not to mention, It knocks now after only a year, because my parents refused to change the factory fill until halfway through this season. We have a big yard, I would guess it got close to 35 hours of use last season, and at least 15 this year. *shakes head*
 
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Originally Posted By: rudolphna
I wish we had gotten the Briggs 875 series OHV instead of the 675 Flathead. Gas is expensive and it is NOT fuel efficient. Not to mention, It knocks now after only a year, because my parents refused to change the factory fill until halfway through this season. We have a big yard, I would guess it got close to 35 hours of use last season, and at least 15 this year. *shakes head*


I wonder how long she`ll go knocking like that??
 
Not to revive an old thread, but here's a slightly different take on this discussion. I've got a 98 Craftsman LT1000 with a 15 HP briggs flathead & a 2002 Craftsman LT1000 with a 17 HP Briggs OHV.

In a practical sense, what's the real difference in these motors? Both are IC's and externally look the same except for the valve cover and the sparkplug placement on the OHV motor being different.

I just picked up the 17 afew weeks ago. Should I see any real difference in performance?
 
Originally Posted By: DaGr8Tim
... I've got a 98 Craftsman LT1000 with a 15 HP briggs flathead


That's unusual to have a single cyl flat-head that large. Is it a horizontally opposed twin by chance?

I know Briggs made a 15hp flat head horizontal shaft engine back in the day, but I have never seen one in vertical shaft format.

That's gotta be a loud, shaky beast if that's what it is! It will use more fuel than the OHV as well.

Joel
 
Tough call- my 1989 10hp Kohler Magnum is still in service. Makes lots of torque for a 10hp. It does drink the fuel down though!
 
Of course, a well developed flathead engine can run quite well, efficiently and cleanly and have a superior size/weight to power ratio.

Years ago, there was some experimentation with multi valve flat heads and crossflow flatheads. The improvements were significant.

I'm 100% certain that development of flathead engines would result in lawn mower engines that match the OHV versions, with fewer moving parts.
 
I think the OHVs inherently flow better because of the shape of the CC. I like the idea of a cross-flow flathead but you can't get around the fact that 1/2 or more of that valve's breathing space is fenced in.

I find the OHV's quieter, cleaner, more thrifty on fuel, though lacking in torque compared to FH. And I'd wager a FH will last longer statistically at least, due to fewer moving parts.

That said, once OHV became affordable, I never went back. I like the fuel efficiency and cleaner burn. Briggs made a good flathead. if they want, they can build a good OHV too.

I've had 2 honda OHV mowers, both good. a honda eu2000i with a GX series OHV, GREAT machine. and now a yami genset with OHV. I love the reduced fuel burn, especially in things like the gensets. Oh-- and a r-subaru OHV project I was working on. That and the yamaha, IMO slightly outflanked the honda, but that is purely subjective.

OHV for me only.
 
Originally Posted By: JTK
Originally Posted By: DaGr8Tim
... I've got a 98 Craftsman LT1000 with a 15 HP briggs flathead


That's unusual to have a single cyl flat-head that large. Is it a horizontally opposed twin by chance?

I know Briggs made a 15hp flat head horizontal shaft engine back in the day, but I have never seen one in vertical shaft format.

That's gotta be a loud, shaky beast if that's what it is! It will use more fuel than the OHV as well.

Joel


Here's the 15 HP Vertical. At the end I start up. Doesn't seem too rough to me.
http://www.youtube.com/watch?v=tOBx2YbeKZQ

Here's the 17 HP OHV Vertical running.
http://www.youtube.com/watch?v=RP2czpeB2-0

Both Briggs & Stratton's.
 
The engine in my Subaru Robin generator is OHC. I'm actually kinda impressed with its construction: cast-iron cylinder sleeve and a timing chain (instead of a belt). It's run under load for about 8.5 hours now and the gas gauge is just coming off full. Since I've had it for a year, I changed the oil recently and it looked almost new...no glitter. So far so good...
 
I did own a single-lung tecumseh--- like 16 or 18hp, years ago. came off of a craftsman rider from the 1970s I believe. That engine was a workhorse... and while it didn't vibrate too badly (dual counterbalances) it was still a bit scary to use... one heck of an impulse on combustion.

Cast Iron body and cylinder, AL head. OHV, pushrod. Roller bearings on both ends, vacuum-fired fuel pump. It threw a rod and shattered rod, piston, and cracked the head under its previous owner. I pad $20 for it, replaced rod and piston, the head crack was not huge... and ran it for a couple of years until the coil died.

The flywheel on that thing was a monster. I MUCH prefer OPE engines in that size to be twins.
 
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