HS50 Build

Rupp 72

Active Member
#1
I'm restoring an original HS50 for my Rupp SS-5. Similar to the HS-40 I built I'm going to hop this one up a bit, maybe even more so than my last build. I plan to eventually fully restore my Rupp SS-5 so this engine is going to be the start of that. I rebuilding this engine for one of my classes in college so it works out that I can still work on the hobby while in college. Here is what i have so far.

The start.





Disassembled and sandblasted.



Some of the internal components going in this engine...

 

cfh

Well-Known Member
#2
Are the springs a stronger pound rating? if so do you have a part number?
on the piston is that just a standard Tecumseh piston?
thanks!
 

Rupp 72

Active Member
#4
Are the springs a stronger pound rating? if so do you have a part number?
on the piston is that just a standard Tecumseh piston?
thanks!
The springs and retainers I am using are for a briggs and stratton animal engine. I used them on my last build when Brian (Delray) and I were looking into different spring options compared to the super weak tecumseh springs. The ones I purchased are from comp cams and are their high load animal springs (GP970).

The piston is a NOS .020 over OEM tecumseh piston. So the engine bore should go from 2.8125" to 2.8325." I'm planning to send this block out to be not only bored but nickle silicon plated again as well to ensure longevity on the cylinder wall.
 

delray

Well-Known Member
#5
The springs and retainers I am using are for a briggs and stratton animal engine. I used them on my last build when Brian (Delray) and I were looking into different spring options compared to the super weak tecumseh springs. The ones I purchased are from comp cams and are their high load animal springs (GP970).

The piston is a NOS .020 over OEM tecumseh piston. So the engine bore should go from 2.8125" to 2.8325." I'm planning to send this block out to be not only bored but nickle silicon plated again as well to ensure longevity on the cylinder wall.
nate, makesure them retainers fit correct. the last set I had on my engine had to much off set and end up using the dyno retainers/keepers...:thumbsup:
 

cfh

Well-Known Member
#6
The springs and retainers I am using are for a briggs and stratton animal engine. I used them on my last build when Brian (Delray) and I were looking into different spring options compared to the super weak tecumseh springs. The ones I purchased are from comp cams and are their high load animal springs (GP970).

The piston is a NOS .020 over OEM tecumseh piston. So the engine bore should go from 2.8125" to 2.8325." I'm planning to send this block out to be not only bored but nickle silicon plated again as well to ensure longevity on the cylinder wall.
Thank you!
on the piston, do you have a part number for the .020 over HS50 piston? i mean are these readily available?
 

Rupp 72

Active Member
#7
Thank you!
on the piston, do you have a part number for the .020 over HS50 piston? i mean are these readily available?
34537 is the standard piston part number, but then you need to find one designated as .020 over. As far as I know it's the same part number for both pistons but will have the .020 designation on the top. I don't think it's all too common but i haven't looked to hard lately either.
 

cfh

Well-Known Member
#8
34537 is the standard piston part number, but then you need to find one designated as .020 over. As far as I know it's the same part number for both pistons but will have the .020 designation on the top. I don't think it's all too common but i haven't looked to hard lately either.
did a quick ebay search and this came up:
Tecumseh HS50-67124D Engine
Part(s) included:
Piston Assembly .020" OS Part 33564B or part 34537
Connecting Rod Part 32875

It seemed reasonable but it was also a used piston/rod. NOS versions were expensive!
 
#10
Getting back to the topic of your engine, will you be installing a compression release? Or has Delray sworn you to secrecy? :laugh: I know of two guys now who have removed the Dyno cam because the kick back on the start was more than they wanted to deal with.

I am familiar with the nikasil plating in two strokes. What kind of longevity are you expecting here? Cost versus value?

I'm another guy doing one of these builds, based on the information that you and Delray shared. I don't know why people keep asking for the part numbers, as all of those parts are posted numerous times here, recently. :shrug:

I had to turn down the Briggs spring perches a bit for the Animal springs.

Looking like a cool build and happy to see you can incorporate it with school, and thanks for sharing it here. :thumbsup:
 

Rupp 72

Active Member
#11
Getting back to the topic of your engine, will you be installing a compression release? Or has Delray sworn you to secrecy? :laugh: I know of two guys now who have removed the Dyno cam because the kick back on the start was more than they wanted to deal with.

I am familiar with the nikasil plating in two strokes. What kind of longevity are you expecting here? Cost versus value?

I'm another guy doing one of these builds, based on the information that you and Delray shared. I don't know why people keep asking for the part numbers, as all of those parts are posted numerous times here, recently. :shrug:

I had to turn down the Briggs spring perches a bit for the Animal springs.

Looking like a cool build and happy to see you can incorporate it with school, and thanks for sharing it here. :thumbsup:
I plan to add a compression release. I have access to a few mills and measuring devices here at school so i plan to cope the design Tecumseh used an incorporate it into the dyno cam. Very similar to how Brian did his.

In terms of having the cylinder plated, it is certainly an added expense and it's hard to indefinitely say it is or isn't worth it. I personally think if I'm going to try and hot rod this engine it's a good idea to have a more robust and durable cylinder wall. This engine is going into my SS-5 that I want to be daily rider so i want it to last without having to worry about rebuilding it again or taking it easy on the bike. I hope to put some miles on it once its all done, should be a great Windber bike!:laugh: So is it totally worth it, I'm not positive but I figure since i already have the engine apart I might as well do it up right.

And the briggs retainers are interesting and certainly something to keep an eye on because they worked perfectly for me on my last engine but not for brian. So we will see I guess.
 
#12
Thanks for your response. Hey, if you ever have extra time on your hands, my rheumatoid arthritis says it'll pay you to machine my cam. I have both HS40 and OHH50 cams' with their associated springs and levers standing by for donor purposes. :thumbsup: Looking forward to following along with your build.
 

Rupp 72

Active Member
#13
So I did some machining lately. The Dyno Camshaft I am using is one that I've had for awhile and didn't really have a use for. It was the 356OHV cam. Well it was far too big to fit in my L-head so i thought what the heck, rather than buy a new one maybe I can grind this cam so the lobes aren't as high. It worked really well. The original lift when measuring how far the valve is actually travelling in comparison to the top of the head stock was about .245 and now with the machined dyno cam in specs out to .3125 with a longer duration as well. I then took a page out of Brian's book and machined a compression release into the dyno cam as well. To get the cam to fit without interfering with the crankshaft I had to mill off a little material from the counterweight.

Video of grinding the cam
[video]https://www.facebook.com/124490871581353/videos/2593736593971607/?t=3[/video]











 
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delray

Well-Known Member
#14
it will be interesting see how that cam will run nate. are you going to run that though your hardness class program. will your teacher let you do the machining so it's a full roller bearing motor.:rolleyes:
 

Rupp 72

Active Member
#15
it will be interesting see how that cam will run nate. are you going to run that though your hardness class program. will your teacher let you do the machining so it's a full roller bearing motor.:rolleyes:
I havn't hardness tested this cam yet however I did hardness test the stock tecumseh cam and it was only about 6 Rockwell C. I have no clue if the cam will work well but there is only one way to find out:laugh: I could make it a full bearing engine however I'm not sure if I am going to, i may just leave the flywheel side a bushing.
 

delray

Well-Known Member
#16
also see you open the area where the compression arm swings out more. that's going to totally change how the lifter rides on the tip of the compression lever. i'm guessing it will be swing to far open, more on the back side of the lever where it is round and it will try to push the compression arm lever down and out and at a angle towards the pto cover and maybe brake. it has to sit in the flat spot when fully open.


also where the cam bushing area will need to be welded up. this will help hold the arm in it's correct place.:thumbsup:
 
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delray

Well-Known Member
#17
I havn't hardness tested this cam yet however I did hardness test the stock tecumseh cam and it was only about 6 Rockwell C. I have no clue if the cam will work well but there is only one way to find out:laugh: I could make it a full bearing engine however I'm not sure if I am going to, i may just leave the flywheel side a bushing.
I know you can get a 20 pound animal spring to fit. with a 312 lift your going to need something more. I believe ole4 found a 26 pound spring that will fit without coil bind. if I remember right it was a clone spring. but it was shorter then a normal standard clone spring.
maybe he can chem in on this?
without doing the research I think it might be the clone spring with the white strip.

that part number is DCS-CL1 from dyno cams.
 

Rupp 72

Active Member
#18
When you say 26lbs spring. Where are you measuringthat? At installed height are at the fully compressed hieght like the valve is completely open?

Here are the springs I have at the moment that I am planning on installing. Think they'll work?

#GP971 Stock Class Valve Springs
Made from Chrome Silicon Spring Steel Wire
Valve Spring Specs.:

Spring Rate: 196.0 lbs./Inch
Installed Load: 17 lbs. @ .825"
Open Load: 66.0 lbs. @ .570"
Coil Bind: 0.471
Outside Diameter: 0.83"
 

delray

Well-Known Member
#19
here is what you got when the spring is installed with retainer and keepers with the valve close.
Installed Load: 17 lbs. @ .825"

17 pound not going to be enough. the valve could float on you.

even the 26 pound could float if rev high enough. but the chances on that happening would be very unlikely. I know the bike your putting it on and the gearing too and it won't see above 7000 rpm's unless you got a quarter mile or more to run the bike out hard.

if that cam works. the dyno cam with the .356 lift was rated at 9500
rpm's with less lift now I would say 8000+.
 

delray

Well-Known Member
#20
another problem that you could have with the 26 pound springs is coil bind. just depends on how the 26# springs are rated when installed. with you having a .312 lift your really beyond 26 # spring. in reality you would need a 36 pound dual springs and if I am correct on this a spring like that would have a .950 spring height when installed and a flathead hs-motor only has about .800 height spring clearance and there is very little you can machine out or none in a hs-motor to increase the spring height. can you run a .300+ lift in a hs-motor still? maybe in a round about way. I would take a set of new briggs ss narrow stem valves at $14 pc(good thing here is they will flow little more air) cut them down to length and size and then cut a new groove in the stem for the locks/keepers with a .150 off set that should give you the correct spring height. that's if everything I mentioned earlier is correct. the stock length at the tip of the valve to the lock is about .250 so .150 off set would give you about .100 of material to hold the locks in place. lot of if's still. I would be measuring things first before jumping the gun.
 
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