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AcFordHawk

OHV engines

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AcFordHawk
Curious about the OHV engines. Brother-in-law got a Craftsmen cheap (hejust wants the tires) and wondered about the difference in design vs the in block valves. Supposed to make more power or be more reliable? Dont know the make just glanced at it last weekend and will look closer next time there.

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JP
Well, Can't be all bad... Most every 'performance' engine has them. I think it's power. Instead of the cam pushing the valve spring, a lever is used (rocker). I would also think it would lend itself to allowing the valve train to be 'flexible' & moved to where ever. Good question! Am I close?? LOL

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HubbardRA
Overhead valve engines have the potential to make more power than a flathead in the same size. It has to do with the combustion chamber design and fuel flow in and out of the head. Flathead engines are very limited since the fuel charge and the exhaust gases have to flow up thru the engine block, across the block and then back down into the cylinder. This requires that the head have enough volume of a specific shape for this to happen effectively. In the overhead valve design the fuel mixture and the exhaust gases flow straight into the head from the top. The volume needed for the cross-flow in the flathead is thus eliminated. The combustion chamber can be smaller (higher compression) and the combustion chamber can be designed to meet the performance needs (like wedge or hemi heads in cars). This flexibility of head designs falls right into the desires of EPA to control emissions from garden tractors and other power equipement. I have heard that it was pressure from EPA that caused most engine manufacturers to drop the old flathead designs and go almost exclusively to overhead valve engines in their current lines. I would question the statement about reliability. From what I have seen, none of the overhead valve designs are likely to last the 40+ years that most of the flathead designs have been around. In fact, some of them are lucky to last more that two or three years. We now live in a throw-away society, and it looks like most of the newer engines are also designed to be throw away units. The average suburban homeowner thinks nothing of buying a new riding lawn mower every 5 or 6 years. Same for the construction companies, since in that time the equipment is so used and abused that it needs replacing anyway.

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PatRarick
The overhead valve design allows for a higher compression ratio than the L-head engine. That translates to more power from the same cubic inch of engine displacement, with better fuel economy and lower emissions. I know the OHV engines run a lot cleaner. I did my first engine conversion on a B-210 by installing a 16 horse Briggs V-twin Vanguard. That was 13 years and 750 hours ago. I change oil every 50 hours. At that time, the oil is a little dark, but still transparent. I've changed the spark plugs only once in all that time. I've since converted a 7018, and an HB-112 to 16 horse briggs V-twins, as well as installing 18 horse V-twins in my 914 and 917. Very little difference in the fuel economy between the 16 and 18 horse V-twins, and the fuel usage per hour is very close to the same as the 12 horse cast iron singles. The only drawback I've noticed is that the V-twin engines don't have the torque of the cast iron singles. As a result, they'll pull down faster and lose power quicker. As to reliability, I've been very well satisfied with the engines in all of my conversions, as have my customer's whom I've done conversions for. My V-twins start easier in the winter, but seem to take longer to warm up than the cast iron singles. Longevity would be my biggest concern, but I'm impressed so far. Only time will tell. Pat

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MrSteele
While I was looking for parts for an old cast iron engine, I talked to a shop in a nearby city that supposedly is one of the larger Briggs dealers around. The parts man's conversation started with "your engine is obsolete, let us sell you a new one" During the conversation, I asked what I would have to replace a 10 HP Briggs cast iron engine with in later model to get the same performance of the older. His rule of thumb for the same performance is double the horsepower in the later model engines. I'll keep the old cast as long as I can!

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Al
Hi, Keep in mind that the OHV engines run much cooler than the L heads. None of the L heads can run 10w30 oil because there is an inverted triangle of heat in top of the cylinder next to the exhaust valve. It runs so hot in this area that can't be adequately cooled the multi-grade oil breaks down here and the engine uses oil. Straight 30 can handle this hi heat and not break down. The OHVs move this heat out the exhaust in a direct line and the cylinders can be cooled effectively all the way around. This lowers the crankcase oil temps and increases the life of the engine. There is a fleet of Kohler Command engines in an oil field in Texas that are running the "pump jacks". These engines run on natural gas which is a very clean fuel and does not "dirty" the engines up. This was in a Kohler dealer news bulletin several months ago. The maintenance guys come once a week and change the oil, oil filters, air cleaners and restart the engines and come back a week later and repeat the sequence. These engines run 24/7 week in and week out and each has over 50,000 hours on them. If they used oil, they would be blown when the maintenance guys came back. Also remember that they run on extremely clean fuel. I know of a Briggs Vanguard 12.5 we sold in the early 90s that has over 4000 hours on it and still going. We have also seen them that didn't go that far, but with good maintenance these new generation engine will run a long time, and they usually start almost instantly. Al Eden

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AcFordHawk
Got the tractor and looked up the PN 917.254241 on the Sears website, should be a Tecumseh with PN 143.386162. The engine in the tractor is 143.376012 SN 71560 so I am guessing it is a Tecumseh.

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gregc
It is a Tecumseh. The 143 is a Sears prefix for Tecumseh. Here's a parts list for that engine should you want one: http://www.outdoordistributors.com/pdf/Tecumseh/CRAFTSMAN-MODEL-143.376012-PARTS-LIST.pdf

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