HS50 tecumseh - change exhaust valve size?
- Thread starter cfh
- Start date
I have seen the OH195 advertised as anywhere form 5.5 HP to 7.5 HP. I have wondered what did
Tecumseh vary on the engine to vary the HP output. The camshaft? Some years ago I did look
up part numbers and seems that the 6 HP and 7.5 HP have the same camshaft. I suspect that all
of the engines were really 6.0 HP at 3,600 rpm.
Tecumseh vary on the engine to vary the HP output. The camshaft? Some years ago I did look
up part numbers and seems that the 6 HP and 7.5 HP have the same camshaft. I suspect that all
of the engines were really 6.0 HP at 3,600 rpm.
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Oldschoolcool , if you are talking about the same steel cam with the compression relief they use in a ohh motor? I would say yes for couple reasons. from the looks of the cams I have come across they have the same profile has the old points but little more lift (.037) and the base circle also little bigger. so it's not really just a bolt in and go. I believe I am only one that has installed a cam like this in a older points engine.
when I installed the newer cam I decided to take the material off the lifters instead of taking .037 off the tip of the valve to get the correct clearance. in my option I thought that was a lot to be taking off from the tip of the valve. not sure if I have the right answer why Tecumseh made this cam with more lift? maybe to make up for the smaller valves and by more lift it allowed more fuel and air in. creating more power or I should say trying to get the power back to the same level as the older motors? the other thing you need to be aware of is the little thrust washer that sits over the compression relief arm end and also sits on the end of the camshaft. on the ohh pto covers where the cam bushing is. that whole area is totally enclosed with just a small oil area. on a older covers there is a big opening on the bushing area for the oil to come in. that area needs to be welded up or the compression relief arm might just push the thrust washer into that area and cause some damage.
ps://ibb.co/iS49Gn]
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advantages I think you get with it, more lift= more air and fuel. compression relief, crank the timing up and not worry about kick back. at that point you got a header on too and a billet rod,porting and your going. I am running 16 pound animal springs so I don't get any valve foating and it pulls real good up to 4500+ . not bad for a stock motor with just couple mod's and aftermarket parts...……..:thumbsup:
when I installed the newer cam I decided to take the material off the lifters instead of taking .037 off the tip of the valve to get the correct clearance. in my option I thought that was a lot to be taking off from the tip of the valve. not sure if I have the right answer why Tecumseh made this cam with more lift? maybe to make up for the smaller valves and by more lift it allowed more fuel and air in. creating more power or I should say trying to get the power back to the same level as the older motors? the other thing you need to be aware of is the little thrust washer that sits over the compression relief arm end and also sits on the end of the camshaft. on the ohh pto covers where the cam bushing is. that whole area is totally enclosed with just a small oil area. on a older covers there is a big opening on the bushing area for the oil to come in. that area needs to be welded up or the compression relief arm might just push the thrust washer into that area and cause some damage.
ps://ibb.co/iS49Gn]
advantages I think you get with it, more lift= more air and fuel. compression relief, crank the timing up and not worry about kick back. at that point you got a header on too and a billet rod,porting and your going. I am running 16 pound animal springs so I don't get any valve foating and it pulls real good up to 4500+ . not bad for a stock motor with just couple mod's and aftermarket parts...……..:thumbsup:
As was stated earlier in the thread, the smaller exhaust valve reduces knocking (pre-detonation) by reducing heat in the combustion chamber. Since it glows cherry red, it can ignite the fuel in the combustion chamber before the spark plug does. In normal (cam and carburetor) configuration, a smaller exhaust valve is a good thing. When you increase flow through the engine, everything needs to breathe more, whether or not this is done with RPM, cam, or carb.
I suspect most of the playing around with parts was done from a logistics standpoint, more than an engineering one.
I suspect most of the playing around with parts was done from a logistics standpoint, more than an engineering one.
UPS dropped off a small valve SBH to me today....ZOINKS! first time having one of these small valves. I gotta say in pics that it looks small, but not THAT small (words you never want a woman to say to you :laugh
Intake side however seems to be opened up even more in the port though,
Oh and [MENTION=339]delray[/MENTION] , that BB sidecover on that other SBH is the long bolt version (think you asked about that somewhere). I just checked it against an early one since I pulled it out of the box to compare it to the other SBH.
I noticed too that neither of these have the upper centering retainers on the valve springs, was never a fan of Tecumseh removing them, will have to dig up some of those.
Intake side however seems to be opened up even more in the port though,
Oh and [MENTION=339]delray[/MENTION] , that BB sidecover on that other SBH is the long bolt version (think you asked about that somewhere). I just checked it against an early one since I pulled it out of the box to compare it to the other SBH.
I noticed too that neither of these have the upper centering retainers on the valve springs, was never a fan of Tecumseh removing them, will have to dig up some of those.
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Eeeek, no.
First, there's only 180 degrees of crank rotation in a "stroke". Roughly.
Second, piston movement is absolutely not the same, due to rod angles.
https://en.wikipedia.org/wiki/Piston_motion_equations
TorqSoft - Piston Position - Calculation Tool
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I was citing a "WAG" based on known parameters to explain a point I was making on total timing on another point made earlier stating 15-25 degrees BTDC. I was not annotating numbers for someone to glue on to their flywheels. There are spreadsheets for this and the formula for computing this is on the net. I did make an error on stroke, and should have multiplied my rough estimate by two giving that a 25 degree number.
I should have known to divide by 50%. I also should have known to type a disclaimer. Again.
I should have known to divide by 50%. I also should have known to type a disclaimer. Again.
Golly, I didn't intend it as chastising, judging, any of that nonsense. My point was merely that the zone from dead stop at TDC to full speed just before mid-stroke, the numbers aren't a linear correlation. It's math WAY beyond my "only passed Algebra, skipped mid-term and the rest of the semester, because my teacher was the wrestling coach" abilities. I love the calculation tools. I require the calculation tools.
Peace & Popsicles
Peace & Popsicles
Thank you for clarifying. It certainly seemed like you were talking down to me, on a day when I felt inundated with "google responses" from "internet experts." I do appreciate your expertise on this forum however.
Here is an .xls spreadsheet that handles the cosign of the stroke and will corelate crank angle with piston position BTDC. www.fastfromthepast.com/PDF/Static_Angle_Spreadsheet.xls
I'll keep it on hand, so I can compare it with the degree wheel on my next Tecumseh timing job. I've never had the wheel on when setting timing. It will be interesting to see if theoretical matches actual timing. I see your popsicle and raise you one banana dipped in chocolate pudding.
Here is an .xls spreadsheet that handles the cosign of the stroke and will corelate crank angle with piston position BTDC. www.fastfromthepast.com/PDF/Static_Angle_Spreadsheet.xls
I'll keep it on hand, so I can compare it with the degree wheel on my next Tecumseh timing job. I've never had the wheel on when setting timing. It will be interesting to see if theoretical matches actual timing. I see your popsicle and raise you one banana dipped in chocolate pudding.
Only about 2 years late for this reply, no I didn't run the HS-50 with the smaller exhaust valve I was looking for higher RPM's. I did build one earlier block HS-50 at the end of my Rupp projects had it iron sleeved, milled the head, Dyno cam, ARC rod, balanced, Dellorto carb, enlarged exhaust pipe... dialed the engine in I got the bike up to around 50 MPH didn't like the way it handled, my wife was not safe riding her Roadster2 with hand brakes so I started design work and building a foot brake then decided to get a motorcycle license bought a Honda Rebel we can both ride on. I will go over both bikes in a couple of years when my current car project is done and make them show again, still love riding the Rupp's I can't imagine ever selling them so many memories of riding when I was a Kid ) I have become a supporter of this site I have worked on small engines since I was 10 this is the best small engine resource ever you guy's get into some really fun projects!
Tony
) I have become a supporter of this site I have worked on small engines since I was 10 this is the best small engine resource ever you guy's get into some really fun projects!Tony