I have been modifying my HS40 and HS50 engines for a bit more power. The dynocam 245/255 cams are no longer available (unless special ordered and core sent), so I make my own version... I've demonstrated that with my custom cam grinder. But the one thing... the one part... the thing that BREAKS and breaks BAD is the connecting rod. Yes there is an Arc billet aluminum rod available for $65. That is a good solution. But it's money, not always available, and i have A LOT of engines. Is there another solution? Perhaps modify the stock cast aluminum rod? Well maybe...
Every blown connecting rod Tecumseh i have seen broke because of one thing... the journal that connects the rod to the crankshaft gets starved for oil due to excessive rpm. Basically the rod heats up (melts) at the journal and breaks. This ruins the rod (obviously) and probably the crank. And perhaps the case (hole in case) and the side cover (unless it's a ball bearing variety, but that's not the norm.)
Let's look at the stock Tecumseh connecting rod... There's but *one* journal oil feed hole. And it's a strange hole... it goes to one of the connecting rod bolts. Basically the oil gets in the hole, sniggles it way down and around the bolt threads, and ozzes on the journal (with some luck!) That seems like a roundabout way of feeding the journal some oil !!
Now let's look at the Arc billet connecting rod. It does not use the hole-to-bolt oil scenario. Instead there's *two* 1/8" holes that feed oil directly to the journal. What if we drill a hole through the stock Tecumseh connecting rod to the journal? This would feed oil directly to the journal, much like the Arc rod. The problem is, the rod is not that "meaty" to do this. There's but one spot I can see that would allow this. Unfortunately probably not a good idea to drill into the bottom (removable) part of the rod. It's just too skinny, not enough material. This sucks. Because then you could split the case, remove two bolts, drill a hole, and put it back. That would be easy... No piston removal! But personally I'm not comfortable with that approach because the material just seems minimal there.
Instead, after removing the piston and rod, a 3/32" hole can be drilled parallel to the "oil-to-the-screw" hole. But this hole goes right to the journal. None of this funky "through the bolt" stuff. Now is a single added 3/32" hole enough? Well probably not, but my bet is this... it sure will be helpful. Perhaps not good for 8000 rpm, but maybe Ok for 5000? But does it compromise the strength of the rod? That's the key question... Comment appreciated!
Every blown connecting rod Tecumseh i have seen broke because of one thing... the journal that connects the rod to the crankshaft gets starved for oil due to excessive rpm. Basically the rod heats up (melts) at the journal and breaks. This ruins the rod (obviously) and probably the crank. And perhaps the case (hole in case) and the side cover (unless it's a ball bearing variety, but that's not the norm.)
Let's look at the stock Tecumseh connecting rod... There's but *one* journal oil feed hole. And it's a strange hole... it goes to one of the connecting rod bolts. Basically the oil gets in the hole, sniggles it way down and around the bolt threads, and ozzes on the journal (with some luck!) That seems like a roundabout way of feeding the journal some oil !!
Now let's look at the Arc billet connecting rod. It does not use the hole-to-bolt oil scenario. Instead there's *two* 1/8" holes that feed oil directly to the journal. What if we drill a hole through the stock Tecumseh connecting rod to the journal? This would feed oil directly to the journal, much like the Arc rod. The problem is, the rod is not that "meaty" to do this. There's but one spot I can see that would allow this. Unfortunately probably not a good idea to drill into the bottom (removable) part of the rod. It's just too skinny, not enough material. This sucks. Because then you could split the case, remove two bolts, drill a hole, and put it back. That would be easy... No piston removal! But personally I'm not comfortable with that approach because the material just seems minimal there.
Instead, after removing the piston and rod, a 3/32" hole can be drilled parallel to the "oil-to-the-screw" hole. But this hole goes right to the journal. None of this funky "through the bolt" stuff. Now is a single added 3/32" hole enough? Well probably not, but my bet is this... it sure will be helpful. Perhaps not good for 8000 rpm, but maybe Ok for 5000? But does it compromise the strength of the rod? That's the key question... Comment appreciated!
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