HS50 Camshaft help.

Sprocket86

Active Member
#1
I eliminated the compression release "bump" on the intake cam lob on my 1976 Tec HS50. I like the added compression but man it's a bear to turn over and I'm afraid of breaking the pull starter while I'm out on a ride, away from the house.

My question is, are the factory Tec camshafts for the HS50 engine the same?

Let's say for instance, would a 1970 mini bike specific HS50 have the same lift and duration as lets say a 1995 Tec HS50 snowblower engine? Something tells me they would have different lift and duration specs.

I'd like to replace my "modded" cam with a stock one so I don't blow apart my pullstart or rip my fingers out lol. I'm not sure the added compression pressure did anything besides making it very tough to turn over.

Thanks for your help guys and gals!
 

delray

Well-Known Member
#3
might be able to answer part of your question sprocket86. there is a differance between the old hs-50 and the newer flatheads that i have found. the newer flatheads that came with a release valve have about .010 more lobe on them. not saying that is better? just what i have seen and mic with my calipers. i do have couple engines without the release valve and they pull just find over. engines that i have modified (ohh-motors) with higher compresion and stiffer valves do pull harder. but not impossible to pull.
now this might be little off your subject,but the older flathead cams without valve release they seam to be made out of a better steel material. for example a honda/clone engine say they are a non-heat treated cams and to stiff of a spring will kill them.
i just pulled a hs-50 cam out of a 40+ year old motor and it still has the machine lines in the cam lobes. definitely made out of a better material...:thumbsup: going to put that in one of my ohh -motors this summer and also install a set of 1.3 rockers with 18# springs and see how well it holds up to...:thumbsup:
 
#4
just replace the cam with a stock cam like the one where you removed the decompressor.
that little 'bump' just lifts the valve at very low speeds only, like when pull starting, once
the engine spins up the bump is held away from the lifter by centrifugal force. there will
be no change in the 'running' compression.

:thumbsup:

phil
 
#5
just replace the cam with a stock cam like the one where you removed the decompressor.
that little 'bump' just lifts the valve at very low speeds only, like when pull starting, once
the engine spins up the bump is held away from the lifter by centrifugal force. there will
be no change in the 'running' compression.

:thumbsup:

phil
You may be mixing the types of compression releases.
Early had a perma-lump ground in the lobe, roughly opposite the main hump, and it stayed in place, always leaking some.
Swing-away ones came later, are used on a lot of newer engines.
 
#6
You may be mixing the types of compression releases.
Early had a perma-lump ground in the lobe, roughly opposite the main hump, and it stayed in place, always leaking some.
Swing-away ones came later, are used on a lot of newer engines.
hmmm. why would they cause a constant leak instead of simply lowering the
compression ratio? cant imagine the leaking valve would last too long doing that!

but, you're probably right. i need to stop breaking those pills in half
and take the whole thing.

:thumbsup:
 
#8
The bump was on the base circle of the exhaust and it opened the ex valve on the compression stroke for a instant, enough to bleed off pressure when you were pull starting it but very little bleedoff when running.
 
#10
With or without a compression release/bump a HS50 should not be THAT hard to "turn over". Must be something else going on...
Michael
 
#11
I just built a hs50 using the dyno cam with no compression release. It is next to impossible to pull over against the compression and I am sure it will damage the cover if I kept doing it. It starts just fine if I slowly pull it past TDC on the compression stroke then pull it and it cranks right up but if I forget it will yank the handle out of my hand. This is a lighted motor with a aluminum flywheel which also doesn't help. If I had to do it over I would have gotten a centrifugal cam and have isky weld and grind me another. My other HS50 with the isky cam with compression release starts just like a stocker.
 
#13
I also have the dyno cam in my HS 50 and it's just like OLE says . As long as you roll her over to the compression stroke you're good and she's starts right up . But if you just reach down and yank the it yanks back with aggression that will hurt you .
 

markus

Well-Known Member
#14
I just built a hs50 using the dyno cam with no compression release. It is next to impossible to pull over against the compression and I am sure it will damage the cover if I kept doing it. It starts just fine if I slowly pull it past TDC on the compression stroke then pull it and it cranks right up but if I forget it will yank the handle out of my hand. This is a lighted motor with a aluminum flywheel which also doesn't help. If I had to do it over I would have gotten a centrifugal cam and have isky weld and grind me another. My other HS50 with the isky cam with compression release starts just like a stocker.
Yea the HS50 will pull your arm of with no compression release! I modded the cam for one I built to sell, It was too much for general sale I felt so I popped it back open and stuck a stocker back in. HS40 is stiff but not as bad, I was hurting for 2 days on when i tried that HS50 out though :laugh: West bend/us power used a heavier duty recoil with 2 or 3 pawls that caught the cup instead of the one on a typical tec if you start getting recoil issues Ole.


Far as HS50 camshafts go, technically I think the only thing they used during entire production (for non PTO camshafts) was the 33158 which was shared with the HS40, it was "fixed" compression bump built into the lobe. As of now they use the OHH camshaft as a direct replacement, it is mechanical release....but it composite/plastic #37671. there was however a steel mech release cam for awhile #36620 which shows as still available, they suggest the composite as an alternative for that one too. Not sure why other than maybe the steel was very noisy in the OHV engines :shrug:. I am not sure if there is a timing or duration change compared to the fixed Comp release cams or not. I now they dropped the valve size down in the later HS engines but the cam still remained the same part number. I would like to try one just havent yet.
 

Sprocket86

Active Member
#15
You may be mixing the types of compression releases.
Early had a perma-lump ground in the lobe, roughly opposite the main hump, and it stayed in place, always leaking some.
Swing-away ones came later, are used on a lot of newer engines.
Yeah the early style with the small peak or rise on the inner base circle of the cam lobe profile is the type I have. I didn't know Tecumseh used the centrifugal mechanical compression release system:shrug:
 

Sprocket86

Active Member
#16
I just built a hs50 using the dyno cam with no compression release. It is next to impossible to pull over against the compression and I am sure it will damage the cover if I kept doing it. It starts just fine if I slowly pull it past TDC on the compression stroke then pull it and it cranks right up but if I forget it will yank the handle out of my hand. This is a lighted motor with a aluminum flywheel which also doesn't help. If I had to do it over I would have gotten a centrifugal cam and have isky weld and grind me another. My other HS50 with the isky cam with compression release starts just like a stocker.
You have explained the starting technique I have to perform on my Tec HS50 like pretty much exactly.:laugh:

Do you think that the added PSI build up in the cylinder is creating any more torque or HP? I know the clearance volume or compression ratio has remained unaltered here but I always have been curious or I wouldn't have gone through the time and effort to mod the camshaft.
 

Sprocket86

Active Member
#18
I also have the dyno cam in my HS 50 and it's just like OLE says . As long as you roll her over to the compression stroke you're good and she's starts right up . But if you just reach down and yank the it yanks back with aggression that will hurt you .
Unfortunately I learned this the slightly painful way lol when I first attempted to start my freshened up 76 HS50. I quickly learned the described technique.

I'd just like to be able to reach down and pull it over, especially if this cam mod isn't really making any more power.
 
#19
It is probably a fraction of an increase, better off with one with a compression release. Don't feel bad as a few of us here had the same idea only to find out how much compression a 6 to 1 HS50 has!!
 

Sprocket86

Active Member
#20
Yea the HS50 will pull your arm of with no compression release! I modded the cam for one I built to sell, It was too much for general sale I felt so I popped it back open and stuck a stocker back in. HS40 is stiff but not as bad, I was hurting for 2 days on when i tried that HS50 out though :laugh: West bend/us power used a heavier duty recoil with 2 or 3 pawls that caught the cup instead of the one on a typical tec if you start getting recoil issues Ole.


Far as HS50 camshafts go, technically I think the only thing they used during entire production (for non PTO camshafts) was the 33158 which was shared with the HS40, it was "fixed" compression bump built into the lobe. As of now they use the OHH camshaft as a direct replacement, it is mechanical release....but it composite/plastic #37671. there was however a steel mech release cam for awhile #36620 which shows as still available, they suggest the composite as an alternative for that one too. Not sure why other than maybe the steel was very noisy in the OHV engines :shrug:. I am not sure if there is a timing or duration change compared to the fixed Comp release cams or not. I now they dropped the valve size down in the later HS engines but the cam still remained the same part number. I would like to try one just havent yet.
Thanks for the informative write up Markus. I have another HS50 that has a thrashed bore and I plan on harvesting it's camshaft and other parts.

Hopefully the cam is in good shape and not worn from oil starvation. The bore seems to be worn due to dirt ingestion through the intake.
 
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