Tecumseh HS40 HS50 connecting rod improvement thoughts

cfh

Well-Known Member
#1
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!





 
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#3
Even on my basically mild builds I use the arc rod. All my tec‘s are hs50’s and with the big bore heavier piston the arc rod is cheap insurance. I’m sure polishing the beam and peening can add durability but all my failures have been cap or bolt letting go, so failed in tension.
 

cfh

Well-Known Member
#4
So you’ve had the connecting rod bolts loosen up and the rod Cap come off? Couldn’t you hear that happen? That is, wouldn’t it make a terrible knocking noise as the bolts loosened? Personally I’ve never had that happen, nor seen it happen. Interesting...
 
#5
couldnt hear it but felt it when it blew thru the crankcase. It had a broken bolt in the carnage but too much damage to do any kind of post Morten. I’ve also seen it on a briggs I took governor off of. I will no longer rev them any higher than about 5K because of no billet flywheel.
 

cfh

Well-Known Member
#6
That’s kind of my opinion too. I don’t like more than 5000 RPM. I know some of the guys here are really pushing those hard seven or 8000 RPM. But that’s not me.

So you think the bolt broke versus loosened? They are hardened bolts. I’ve never seen that happen but I’ve only experienced a thing where the journal got so hot that it melted itself onto the crankshaft and then just disintegrated.

I think what happens is you get a lack of oil on the connecting rod journal and it’s Freezes. the motor is still spinning and it just rips the connecting rod apart
 
#7
I can’t say for sure and it was long ago but I don‘t remember if crank had aluminum on the rod journal or if I even looked at it.
 

markus

Well-Known Member
#8
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 thats funny some funny stuff!!! If oil "sniggles" its way down and around the bolt thread and then"ozzes" on the journal, that's not luck my friend, that's a loose rod cap :D Thanks for making my night, I needed a good laugh. If you think thats were/how the lubrication to the journal is picked up from on a stock rod, you should maybe just stick with the ARC rods....... as you need all the help you can get! ;)
 

cfh

Well-Known Member
#9
Came up with a different approach. Since on a stock Tecumseh rod there's already an oil hole that connects to the rod bolt, why not utilize it? on the top of the rod journal, drilled a 3/32" hole straight up and into the existing (stock) oil passage. You just need to aim the drill so it goes past the bolt threads, and into the existing hole. It's only about 1/4" drill depth to make that new hole connect to the existing oil passage hole.

As a test, before drilling the holes, tightened the rod cap bolts. Now blow into the existing rod oil hole. Do you feel any air movement? Frankly i feel next to *none*. Try it, very revealing to how little oil can get through that passage.

Now drill the hole, replace the rod cap and tighten the bolts. again, blow into the stock oil passage. Big difference! Pretty much night and day.

With this modification, a lot more oil can get to the journal on a stock Tecumseh rod. There are other passages for the oil to get to the journal too. But this really gives a pretty solid passage. Which is what the Arc rod guys were doing this too (it does seem like a good idea.)

I put this modified rod in an HS40 with a dynocam 245 cam clone. So it will spin more than normal rpm. I will report back after some time. Maybe it will be fine, maybe it won't, maybe we'll never know? it's hard to say because i can't do a double blind study to figure it out...



 
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delray

Well-Known Member
#10
I had good luck in the pass with just one test experiment with stock rods. the whole motor was a test to see how well it would hold up and perform
on a ohh motor. mild performance up grades where animal 16 pound springs,dyno retainers/keepers,stock steel cam, mid porting in the head,Tecumseh hot coil(advances the timing),new adjustable hs-40 carb with main and idle,mod air cleaner,header...etc....
I have found the rods that come in my ohh motors look to be casted much better then the old hs-40 rods.
here is a picture of it next to a hs-40 rod. notes how much more material is around it and the casting is much smoother too.
make the a story short I polish up the rod beam and installed it in this little 195cc ohh motor and that motor just ripps right up to 5000 rpm's all day. been a few years now and still running strong. I do run a 5w-30 oil with just little zinc added too.




I was really cheap like you cfh….lol and
took a stock air cleaner and cut the lid off and ran a outerwear pre filter.....:scooter:

 
#11
Delray: Very interesting setup all the way around for the OHH for sure, thanks!
CFH: Interesting thoughts, Got 2 or 3 stock HS50 cams, any way to get ya to grind some 245's?
Getting Bored over here!
let-me-mix-efc95e5351.jpg
 

cfh

Well-Known Member
#12
Del, it's not so much that i'm cheap... just i have like 40 Tecumseh motors! volume kills the wallet!!

on the polishing the rod shaft, that looks great. does it improve strength having it smooth? i like the air cleaner thing. that's a good idea!

since the Arc rod is basically an OHH5.5 rod, maybe i should be looking at those stock rods. the problem is, i have a bunch of extra HS40/HS50 rods sitting around, doing nothing (they were from motors where the Arc rod was installed.) Hence why i started getting all happy with the drill! i mean who would buy a bunch of used rods anyway? they were getting dusty... ha!

Florida on the cams... i'm really hesitant to do grinds for others....
 

delray

Well-Known Member
#13
I thought you would like the cheap part...lol I call that my poor mans K&N filter setup....hey it works good.
I also purchase a new ohh block off of ebay and then modified that one with a billet rod and gave my original to a friend that was rebuilding a stock vintage bearing hs-50 motor. he has the governor set a 4000+ and no problems yet.
 

cfh

Well-Known Member
#14
I will start looking for an OHH rod. Problem is, hope they’re a lot cheaper than $65 otherwise what’s the point? Ha!

That air filter thing is ingenious. That’s the sheet I’m talking about !
 

delray

Well-Known Member
#15
if I am correct some of the hs-50 rods maybe the same casting as the ohh rod....really smooth looking too. it's like they casted a bunch of rods like my ohh rod at one time certain way. if you look up replacement rods with a picture they don't look the same way or I should say finish on them like the one in the picture a posted.
 
#17
Hello ! I’m brand new to this awesome Forum. My name is Richard (RMCUSTOM) And I’m buying parts, etc to restore an Arctic-cat Climber. The same mini-bike that my dad bought me when I was 7. And what started my life-long interest/hobby & love of anything that creates internal-combustion & has wheels & is American made. So,
I recently joined oldminibikes.com to be “part-of” this kind of Community. To “Talk-shop” w/other like-minded guys & to give & receive advise & help on occasion. So, in my search of “Climber” parts, I have an opportunity from a kind gentleman (via oldminibikes.com) to purchase a Climber project that is a barn find. It is rusted to the hilt though. So much that just the engine, frame, swing arm, forks, and wheels are salvageable. But, the engine, which is the original HS40, has a broken rod. The Seller doesn’t know how it broke. He just said that he bought the Climber that way, and he removed the head & said the following: Quote. “The motor turns over but I think the rod is broke. I took the head off and the piston moves but not with the crank.” End quote.
So I’ll be discussing the engine w/this gentleman tonight. My main concern is the engine block. Is it cracked from the rod slamming into it !?? Now, I custom build Harleys & other machines. So I’m very well rounded in the mechanical world. And I know small engines as well. It’s just been a while & Im not specifically familiar w/the Tecumseh HS40 engines, yet. :)
So, by the sounds, you guys definitely know your stuff. Would you guys be willing & kind enough to help me figure out whether I should buy this Climber for its HS40 engine or not. This Climber was left outside, leaning up against the barn (Not on it!) it’s entire life ! Very sad. Actually here are pics. He wants $600 for it. Any help/advise would be extremely appreciated ! I’d like to just buy the engine from him. That’s what I’ll be asking him tonight when I call him. Thank you so very much for allowing me to budge in like I have. I hope I’m not violating any Forum rules or respect of any type. This is the ONLY forum I’m part of. So I don’t know the proper forum etiquette ! Thank again ! Looking forward to any responses.
Sincerely , Richard
 

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cfh

Well-Known Member
#18
to be honest, the climber doesn't look that bad. you can get NOS fenders. and you can get a seat. The gas tank looks OK, but if it's not, a lot of times it can be repaired. didn't see the torque converter side, so can't comment on that (though TC covers are available.) you can get new front shock springs (cheap). and you can rebuild the rear Sebec shocks too (with new springs.) the rest looks Ok. but the $600 price is pretty darn strong. i could not justify that price in my world. as for the motor, that's a crap shoot. you really don't know what's going on until you open it up.

when i bought my climber, it was off craigs list and it was $225. this was it as i got it...
http://www.pinrepair.com/minibikes/p/arcticcat_climber_mine0.jpg
with some work (and a different motor) this is where it ended up:
http://www.pinrepair.com/minibikes/p/arcticcat_climber_mine1.jpg
now if i put it up for sale, i'm not sure it would bring $600. just saying...

you should probably start a new thread about this stuff though....
 

delray

Well-Known Member
#20
to be honest, the climber doesn't look that bad. you can get NOS fenders. and you can get a seat. The gas tank looks OK, but if it's not, a lot of times it can be repaired. didn't see the torque converter side, so can't comment on that (though TC covers are available.) you can get new front shock springs (cheap). and you can rebuild the rear Sebec shocks too (with new springs.) the rest looks Ok. but the $600 price is pretty darn strong. i could not justify that price in my world. as for the motor, that's a crap shoot. you really don't know what's going on until you open it up.

when i bought my climber, it was off craigs list and it was $225. this was it as i got it...
http://www.pinrepair.com/minibikes/p/arcticcat_climber_mine0.jpg
with some work (and a different motor) this is where it ended up:
http://www.pinrepair.com/minibikes/p/arcticcat_climber_mine1.jpg
now if i put it up for sale, i'm not sure it would bring $600. just saying...

you should probably start a new thread about this stuff though....
i see you mention about my discovery on using animal springs and dyno retainers from a briggs flathead and modifying them to work with the single springs(animal) and using the newer compression release cams in your pinrepair right up and me not getting any credit for it....lol. there is one more retainer that might work and that would be the tecumseh motorsports parts. maybe on my next small block build i will look into this and if it works you can add it to you pin right up.
also in your right up i feel your little misleading on the 245 cam and it's power band(rpm range) you say it's only is good to 5000 rpm's?
i guarantee with my 245 in my hs-40 it pulls easy 7000 rpm's. if i am correct that cam was rated for 6500+ in a ohh-motor and 255 was 7000 and the 356 was 9500. here is also something you cam mention in your right up. dyno will grind other profiles. i know of one other member here pm and told me they had a 308 profile ground. just may try that out in a ohh motor some day.
running a 18 pound springs is not alot of spring pressure for a stock or even a 245 cam. when you start to get into the 20+ pounds and above you can start to wear on the cam if it's not harden correct. i just tore apart my hs-40 a while ago and did not see any damage at all on the cam lobes and that was using 18 pounds animal springs and we all know that engine went to hell and back more then once...lol..:scooter:

also looking back when you installed the newer compression release cam in a old hs block with the hs lifters you where getting about .030 higher lift. thats because the newer cams with the release have a different base circle then the older cams did and you where picking up the extra .030+/- height. not the reason why tecumseh was getting 5.5 horse power out of there engines. 5.5hp is more then likely coming from jetting,rpm settings...etc.....
if your going to have this info out there for everybody to see need to try to get some of this more accurate....;)
 
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