HS50 Build

BingCrosby

BingCrosby

Member
#1
#1
Yessir... a Tecumseh build montage.

My grandfather's (may he rest in peace) mini bike had an HS40 on it, and after being gifted a near-new GX160 the well-worn Tec motor was shoved to the side.

I was planning on restoring the pitted, ancient engine when another post was talking about built HS50's, so I bought an HS50 block and piston and am preparing an ultimate build:
-racing cam
-bigger valve springs (possibly B&S Animal valve springs?)
-billet rod
-animal carburetor
-new intake
-straight pipe (EDIT: I might try to open up an H35 muffler, since it's much less restrictive than the stock muffler)
-governor removal
-racing spark plug
-possible fuel pump
-HS40 head on HS50 block for compression
-port and polish job on exhaust & intake

Are OHH50/60 racing parts interchangeable with HS40/50's? I hopefully want to get OHH60 parts for the cam, rod, and spark plug.
Pictures to come.
 
ole4

ole4

#2
#2
Use 6282 arc rod. If you want a compression release cam get a stock HS40 or 50 mechanical release cam and get isky to weld and grind you a cam. He makes a tec grind similar to the black mamba Jr but on a 108 LSA. I built one like this with a Chikuni and home made straight stepped pipe.
 

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markus

markus

Well-Known Member
#3
#3
Just an FYI, the HS40 and HS50 head were exactly the same part number/part. Not sure about that whole H35 muffler flowing better either H35 and even the HS40 exhausts were actually chocked down to better match the port size, they had to up size the HS50 exhausts due to a larger opening.
 
delray

delray

Well-Known Member
#4
#4
markus said:
Just an FYI, the HS40 and HS50 head were exactly the same part number/part. Not sure about that whole H35 muffler flowing better either H35 and even the HS40 exhausts were actually chocked down to better match the port size, they had to up size the HS50 exhausts due to a larger opening.
Click to expand...
markus are sure on this? I got a picture here with a HS-40 gasket on top a HS-50 head. two are different.

 
delray

delray

Well-Known Member
#5
#5
BingCrosby said:
Yessir... a Tecumseh build montage.

My grandfather's (may he rest in peace) mini bike had an HS40 on it, and after being gifted a near-new GX160 the well-worn Tec motor was shoved to the side.

I was planning on restoring the pitted, ancient engine when another post was talking about built HS50's, so I bought an HS50 block and piston and am preparing an ultimate build:
-racing cam
-bigger valve springs (possibly B&S Animal valve springs?)
-billet rod
-animal carburetor
-new intake
-straight pipe (EDIT: I might try to open up an H35 muffler, since it's much less restrictive than the stock muffler)
-governor removal
-racing spark plug
-possible fuel pump
-HS40 head on HS50 block for compression
-port and polish job on exhaust & intake

Are OHH50/60 racing parts interchangeable with HS40/50's? I hopefully want to get OHH60 parts for the cam, rod, and spark plug.
Pictures to come.
Click to expand...
here you go BingCrosby
couple part numbers and ideals to help you on you build.....

https://www.oldminibikes.com/forum/index.php?threads/hs-40-build.161335/
 
markus

markus

Well-Known Member
#6
#6
Only for the first year and half of engine production (1968-mid 1969) did they use the small head/small bolt pattern, which indecently is the same as the H25-35 head and bolt pattern. They upsized mid year 1969 and phased the small bolt pattern small head by end of 3rd quarter that year from what I have seen. Production of the HS50 began in 1972, and it used the same head as the current, common HS40 and remained that way till the end.

delray said:
markus are sure on this? I got a picture here with a HS-40 gasket on top a HS-50 head. two are different.
Click to expand...
 
markus

markus

Well-Known Member
#8
#8
Yea I was surprised you used that small bolt pattern block for all that work you put into it, I think one reason they ditched it was a heat issue. I figured you knew all that since you posted in the thread I started about the early blocks.
 
BingCrosby

BingCrosby

Member
#12
#12
The block has the mounting points for the magneto on the inside of the flywheel, I'll try to check tomorrow to see the original magneto. The original HS40 was a 1970 model.
 
markus

markus

Well-Known Member
#13
#13
BingCrosby said:
The block has the mounting points for the magneto on the inside of the flywheel, I'll try to check tomorrow to see the original magneto. The original HS40 was a 1970 model.
Click to expand...
Are your plans to use parts from the original HS40 on the HS50 block? I just noticed you did not mention a crankshaft pertaining to the HS50 heres another FYI that you should also know about the HS series cranks:

https://oldminibikes.com/forum/index.php?threads/hs-engines-crankshaft-differences.160796/

the HS50 needed more counterwieght to go along with the big piston. Using 1970 HS40 external bolt on parts will be fine to use with exception of the exhaust and stock intake, If you plan to run it with a tank in front and its plastic you may want to add the heat deflector that bolted under the tank mount that started to become standard in the 1970's since it sounds like you want it run hard, it will also run hotter.

On that note, I would really be curious what the original engine looked like if possible(tank style, model number, and rough time of year it was built) for reference if its off that Aggie you have in tat avatar....It would be great reference for me and others on this board. thank you!
 
delray

delray

Well-Known Member
#14
#14
markus said:
it sounds like you want it run hard, it will also run hotter.
Click to expand...
not necessarily true running hotter. that can be misleading when on a minibike. good example of something that would run hot would be a stationary engine on a generator or even a sump pump in 80-90 temperatures running wide open. now the engine is relying on the cooling fins to help move air around the engine and all that air around the stationary engine also becomes hot,creating more problems. minibike for the most part is always moving and getting cooler fresh air then a stationary engine would get.
 
BingCrosby

BingCrosby

Member
#15
#15
markus said:
Are your plans to use parts from the original HS40 on the HS50 block? I just noticed you did not mention a crankshaft pertaining to the HS50 heres another FYI that you should also know about the HS series cranks:

https://oldminibikes.com/forum/index.php?threads/hs-engines-crankshaft-differences.160796/

the HS50 needed more counterwieght to go along with the big piston. Using 1970 HS40 external bolt on parts will be fine to use with exception of the exhaust and stock intake, If you plan to run it with a tank in front and its plastic you may want to add the heat deflector that bolted under the tank mount that started to become standard in the 1970's since it sounds like you want it run hard, it will also run hotter.

On that note, I would really be curious what the original engine looked like if possible(tank style, model number, and rough time of year it was built) for reference if its off that Aggie you have in tat avatar....It would be great reference for me and others on this board. thank you!
Click to expand...
1) Thank you for the rod info, will go grab one soon.
2) The fuel tank is steel, but the HS40 came with a heat shield so it will stay that way.
3) I believe it is a 1969 model, it had no decals when I got it although when I got it it had been sitting outside since the late 70's without a spark plug. The headbolts are of the newer, wider style (compared to the H35 style used pre-1968. It's white.

The model number plate on the pull starter says:

HS40-55225B
SERIAL 9269 03119
 
markus

markus

Well-Known Member
#16
#16
BingCrosby said:
1) Thank you for the rod info, will go grab one soon.
2) The fuel tank is steel, but the HS40 came with a heat shield so it will stay that way.
3) I believe it is a 1969 model, it had no decals when I got it although when I got it it had been sitting outside since the late 70's without a spark plug. The headbolts are of the newer, wider style (compared to the H35 style used pre-1968. It's white.

The model number plate on the pull starter says:

HS40-55225B
SERIAL 9269 03119
Click to expand...

thanks for the engine info, I will check out the specs and scribble it down into my Mini bike engine list! Yes, its a mid 1969 built.

That deflector I was talking about was something to help keep the hot air off the Plastic tanks so they don't warp or melt for the most part. Its been a rarity, but I have picked up engines/tanks in the past that had some damage right there from heat, your steel tank should not be an issue. The HS50 does seem to run a little warmer if you modify it with the smaller HS40 flywheel and shrouding over using what they originally came with.

thanks again for posting up those numbers
 
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