Tecumseh HS40 question
- Thread starter Minibikephil
- Start date
Del Ray posted an hs40 build thread if I remember right
https://www.oldminibikes.com/forum/index.php?threads/hs-40-build.161335/
also this site has all kinds of info, I refer to it often
http://www.pinrepair.com/minibikes/tecumsehmb.htm
https://www.oldminibikes.com/forum/index.php?threads/hs-40-build.161335/
also this site has all kinds of info, I refer to it often
http://www.pinrepair.com/minibikes/tecumsehmb.htm
Not exactly the same thing, but maybe close enough-
I built a couple Hs50s, and did the usual stuff. Billet rod, oversized piston, aluminum flywheel, 255cam, valve springs, retainers, some light porting, 22mm Chikuni, straight pipe exhaust.
motor runs great pulls 6-7000 rpm no problem.
i know they are different motors. I have never built an Hs40 i know there are some differences, others here will know all of the details
I built a couple Hs50s, and did the usual stuff. Billet rod, oversized piston, aluminum flywheel, 255cam, valve springs, retainers, some light porting, 22mm Chikuni, straight pipe exhaust.
motor runs great pulls 6-7000 rpm no problem.
i know they are different motors. I have never built an Hs40 i know there are some differences, others here will know all of the details
I just did an HS40 with a modified cam and dellorto ua19 carb and alloy flywheel. i usually don't bother doing this to a HS40. the time and energy is better spent on an HS50. And in the end, my gut feelings were realized. that said if you are locked into an HS40. Just adding a slide carb will be the easiest/cheapest modification with the best results. other things will cost more and probably yield less (except being a cam, but that involves a lot of expense and you have to get a better rod).
There are a couple of us who have done those mods. There is no reason to sweat a flywheel on a Tecumseh. They are not the "grenades" you may have read about. True, a round slide Chinese carb will make it a little better. Here is a PZ16 carb added to an H30, where I modified the stock intake manifold to fit it. I also had to raise the fuel tank to feed the carb, even though it's hard to tell.
Here is a link to where I posted the parts I used in my first HS 40 hot rod build. Here are the parts I used:
Dyno 245 cam for the OHH engines.
ARC 6282 Billet Rod for the 5.5 OHH engines.
Dyno AN-001 18 LB valve springs for the Briggs Animal.
Briggs DCSH103 valve keepers for the Flathead.
Briggs DCSH102 lower valve spring retainers for the Flathead.
Note that some machining of the retainers is required to fit the spring. Easy job with a drill and a file. Also, note that the 245 am refers to the grind Dyno used for their OHH 5.5 Kart Engines, and those are NLA. I have Dyno grind my old cams to that specification, which actually equate to a .235 or so lift at the head, keeping a tad of lash in there. You can ask for a more radical cam, but you quickly run in to problems with pull starting using the Tecumseh shroud mounted recoil. (This is why the kart racing and drag racing crowd use electric starters)
What I did on my last cam was have Dyno machine it without burying the mechanical compression release spring holes, so I do have some compression release on start. This required the use of a shorter intake lifter, and all of the grinding opened up the lash. I simply sank the valves with a Nuway cutter to compensate. The alternative would have been to use a tappet end for the OHV's and then adjust lifter length. A weld does not work, as it needs a hardened surface.
Also, I port the hell out of the intake. Less out of the exhaust. (Torque)
If you're building a mini bike, you need to figure out how you are going to push fuel into the float bowl, and how efficient you want your intake to be. So that requires a tank mounted on top of the frame, or an intake manifold with a port to run a vacuum pulse to a fuel pump. I don't use these engines on mini cycles, so I end up engineering fuel pumps into manifolds, which due to the tight fit on an HS, requires some engineering of the exhaust as well.
I've probably made it sound more difficult than it is. That is because I don't have a life and have to try and impress people on the internet with my mad mechanical ability. (I have a pair of vice grips and an angle grinder, and do not make my own cams)
At the end of the day, it is not cost effective to build these, a stock Predator will eat it's lunch, and the average man on the street wont even know what you have. I have since sold the bike, but here is the video I made after restoring/modifying. I have another engine on the shelf looking for a bike, but I am involved with several other projects and too poor now.
I am more than happy to share information via Email, as I have curtailed most of my posting here.
Here is a link to where I posted the parts I used in my first HS 40 hot rod build. Here are the parts I used:
Dyno 245 cam for the OHH engines.
ARC 6282 Billet Rod for the 5.5 OHH engines.
Dyno AN-001 18 LB valve springs for the Briggs Animal.
Briggs DCSH103 valve keepers for the Flathead.
Briggs DCSH102 lower valve spring retainers for the Flathead.
Note that some machining of the retainers is required to fit the spring. Easy job with a drill and a file. Also, note that the 245 am refers to the grind Dyno used for their OHH 5.5 Kart Engines, and those are NLA. I have Dyno grind my old cams to that specification, which actually equate to a .235 or so lift at the head, keeping a tad of lash in there. You can ask for a more radical cam, but you quickly run in to problems with pull starting using the Tecumseh shroud mounted recoil. (This is why the kart racing and drag racing crowd use electric starters)
What I did on my last cam was have Dyno machine it without burying the mechanical compression release spring holes, so I do have some compression release on start. This required the use of a shorter intake lifter, and all of the grinding opened up the lash. I simply sank the valves with a Nuway cutter to compensate. The alternative would have been to use a tappet end for the OHV's and then adjust lifter length. A weld does not work, as it needs a hardened surface.
Also, I port the hell out of the intake. Less out of the exhaust. (Torque)
If you're building a mini bike, you need to figure out how you are going to push fuel into the float bowl, and how efficient you want your intake to be. So that requires a tank mounted on top of the frame, or an intake manifold with a port to run a vacuum pulse to a fuel pump. I don't use these engines on mini cycles, so I end up engineering fuel pumps into manifolds, which due to the tight fit on an HS, requires some engineering of the exhaust as well.
I've probably made it sound more difficult than it is. That is because I don't have a life and have to try and impress people on the internet with my mad mechanical ability. (I have a pair of vice grips and an angle grinder, and do not make my own cams)
At the end of the day, it is not cost effective to build these, a stock Predator will eat it's lunch, and the average man on the street wont even know what you have. I have since sold the bike, but here is the video I made after restoring/modifying. I have another engine on the shelf looking for a bike, but I am involved with several other projects and too poor now.
I am more than happy to share information via Email, as I have curtailed most of my posting here.
I would have to generally agree with Dave on those points. I think the slide carb is the best/easiest/cheapest mod. You don't have to tear your engine apart either to do it. Open exhaust is nice too. But yea a predator (even a stock one with the governor deleted) will kill an HS50 (unless you go nuts with the HS50.)
On the cam thing... i have many tecumseh bikes with no compression release and a 245/255 or my own custom cam. i don't find them hard to pull start. you just have to remember to get the motor in the right spot before you pull. I slowly pull the cord until i feel the compression stroke, and then go. Some people do it after the compression stroke. but if you forget it will remind you. So it's become habit to me.
if you do the cam, you do need a new billet rod. not because the rod makes the motor faster, it doesn't. it just protects it from throwing the rod. that's the problem with a cam, as it will allow an increase in rpm. but you have the cost of the cam ($100 or so) plus the rod ($65). Dynocam says you don't need to change the springs on a 245 dynocam. In fact they discourage that (they feel it will wear the dynocam lobes, because on that cam, the lobes are not hardened.) But if you're spinning above 5000 rpm you probably do need better springs. Personally i don't run super high RPM. but i do like the 245/255 cam as it gives faster acceleration and more rpm potential. i modify my own cams. not because it's fun, but because it's cheap. dynocams have to be special ordered and a core sent for tecumseh motors. so i just mod my own.
on the flywheel i think dave is right... it's not really an issue. you can use a cast iron flywheel. just make sure the magnets are secured well. The alloy flywheel is nice, and it will allow the motor to accelerate a bit faster. I haven't found this to be a big deal though. To be frank, the only reason i use an alloy tecumseh flywheel is so i can use a rounded blower housing, for that pre-1973 tecumseh look. i don't think spending $50 to $100 for an alloy flywheel is worth it, from a performance point of view.
personally i don't increase the size of the block's ports. that block area seems thin to me. it just seems like an easy way to ruin a motor, if you don't have experience doing it. also i would really need to see some 'before' and 'after' performance tests to believe that the risk is justified in doing that modification.
On the cam thing... i have many tecumseh bikes with no compression release and a 245/255 or my own custom cam. i don't find them hard to pull start. you just have to remember to get the motor in the right spot before you pull. I slowly pull the cord until i feel the compression stroke, and then go. Some people do it after the compression stroke. but if you forget it will remind you. So it's become habit to me.
if you do the cam, you do need a new billet rod. not because the rod makes the motor faster, it doesn't. it just protects it from throwing the rod. that's the problem with a cam, as it will allow an increase in rpm. but you have the cost of the cam ($100 or so) plus the rod ($65). Dynocam says you don't need to change the springs on a 245 dynocam. In fact they discourage that (they feel it will wear the dynocam lobes, because on that cam, the lobes are not hardened.) But if you're spinning above 5000 rpm you probably do need better springs. Personally i don't run super high RPM. but i do like the 245/255 cam as it gives faster acceleration and more rpm potential. i modify my own cams. not because it's fun, but because it's cheap. dynocams have to be special ordered and a core sent for tecumseh motors. so i just mod my own.
on the flywheel i think dave is right... it's not really an issue. you can use a cast iron flywheel. just make sure the magnets are secured well. The alloy flywheel is nice, and it will allow the motor to accelerate a bit faster. I haven't found this to be a big deal though. To be frank, the only reason i use an alloy tecumseh flywheel is so i can use a rounded blower housing, for that pre-1973 tecumseh look. i don't think spending $50 to $100 for an alloy flywheel is worth it, from a performance point of view.
personally i don't increase the size of the block's ports. that block area seems thin to me. it just seems like an easy way to ruin a motor, if you don't have experience doing it. also i would really need to see some 'before' and 'after' performance tests to believe that the risk is justified in doing that modification.
Cam and springs allows you to continue making power at high RPMs as long as you have enough fuel.
gotta jet up.
thin aluminum flywheel is a win-win, motor spins up quicker and can fit a thin shroud.
Hs40 should come stock with an aluminum flywheel anyways.
also did anyone notice that the beautiful engine in H Dave’s post is a side popper?
love it. And in the video the exhaust sounds sooooooo good lol
gotta jet up.
thin aluminum flywheel is a win-win, motor spins up quicker and can fit a thin shroud.
Hs40 should come stock with an aluminum flywheel anyways.
also did anyone notice that the beautiful engine in H Dave’s post is a side popper?
love it. And in the video the exhaust sounds sooooooo good lol
the problem with increased spring tention on the 245 cam is wear. the lobes are not hardened. so dynocam recommends not using stiffer springs. i guess on the other cams the lobes are hardened/welded, so stiff springs work. that's what the guy from dynocam told me on the phone.
i'm not big on doing any of these mods on less than a HS50. it costs exactly the same on smaller motors, so why not start with the bigger HS50. also on an H35 there's no billet rod available. so that's a good reason not to go too crazy with that motor.
i'm not big on doing any of these mods on less than a HS50. it costs exactly the same on smaller motors, so why not start with the bigger HS50. also on an H35 there's no billet rod available. so that's a good reason not to go too crazy with that motor.
I think what you and at dyno cams where talking about must of been some miscommunication on stiffer springs. 16 or even 18 pound springs are no means a stiff spring. that's if indeed you spoke to someone, maybe there where under the assumption that you where going to install real stiff spring. for example a 26 or 36 pound spring some of the more common springs they sell on a daily basis. 16 and 18 spring we Tecumseh guys have use in are projects is normally found in a animal engine with the factory cam. that too doesn't carry much of a lift either. I can't see how anybody would want you to use a stock 50 yr old valve spring in a motor that could see 7000+ rpm's I also can see you not having a problem with stock spring in your projects, because they never spin type rpm's the cam is made for. good thing if you start to bounce the valve your not going to smack the piston. it's still going to rev, just not going to have the power it should have.
I don't see how the 245 is made different then the 255 or even the 356 cam. when i was first looking into building my hs-40 I called dyno and spoke to a tech guy and he gave me a list type of valve springs he recommend for all three cams. 245-18 255-20 and the 356-36 I have run all three cams in different type of Tecumseh's. mainly ohh-style engines. my 356 engine I set the springs little on the tight side at 42 pounds. I see now on there web site they too say to set them at 42-44. back to this gentlemen I spoke to at dyno. he was the guy that told me about the little trick you can do with a briggs flathead dyno retainer. use a dual spring retainer and just machine off just little so the single fat style spring(animal) would fit correct with the retainer. not to get off the subject to much. dyno will also grind you a 308 cam. I know of one gentlemen that had one done.
at the end of the day are you really going to go faster then a clone? maybe not, but who really cares. the last time I look we where under the Tecumseh flathead and the money spent to me is nothing. not like your going to go broke or your trying to build a 7000 rpm big block chevy. it's one little cylinder engine. if you really want to spend some money. try building a clone motor. nothing to spend up to $2000 or more. especially for the guys that can't do any of the machine work.
there can be a Big difference in performance on how you build you little hs-motor. good example is in this video.
the one bike that's in the inside lane has a hs-40 rupp block. block it self is ported,bored .080 over with a wiseco 2-ring piston. 19mm dellorto ,rupp header,installed a steel ohh cam with a compression relief. 16 pound animal springs...etc.. turns max rpm about 5000+ that day. still think these is a strong stock mod hs-40. if a kid had this setup back in the day on is black widow. that would be cool....
outside bike is my hs-40 extreme built,maybe the only like it and it passes the other bike like it was standing still. tons of crazy mod's done to it. 7000+rpm motor with a 245 cam with 18 pound springs. motor has gone to the moon and back several times and has been torn down and inpected and shows no signs of cam wear. also note I run a zinc oil in this engine.
engine build thread https://www.oldminibikes.com/forum/index.php?threads/hs-40-build.161335/
I don't see how the 245 is made different then the 255 or even the 356 cam. when i was first looking into building my hs-40 I called dyno and spoke to a tech guy and he gave me a list type of valve springs he recommend for all three cams. 245-18 255-20 and the 356-36 I have run all three cams in different type of Tecumseh's. mainly ohh-style engines. my 356 engine I set the springs little on the tight side at 42 pounds. I see now on there web site they too say to set them at 42-44. back to this gentlemen I spoke to at dyno. he was the guy that told me about the little trick you can do with a briggs flathead dyno retainer. use a dual spring retainer and just machine off just little so the single fat style spring(animal) would fit correct with the retainer. not to get off the subject to much. dyno will also grind you a 308 cam. I know of one gentlemen that had one done.
at the end of the day are you really going to go faster then a clone? maybe not, but who really cares. the last time I look we where under the Tecumseh flathead and the money spent to me is nothing. not like your going to go broke or your trying to build a 7000 rpm big block chevy. it's one little cylinder engine. if you really want to spend some money. try building a clone motor. nothing to spend up to $2000 or more. especially for the guys that can't do any of the machine work.
there can be a Big difference in performance on how you build you little hs-motor. good example is in this video.
the one bike that's in the inside lane has a hs-40 rupp block. block it self is ported,bored .080 over with a wiseco 2-ring piston. 19mm dellorto ,rupp header,installed a steel ohh cam with a compression relief. 16 pound animal springs...etc.. turns max rpm about 5000+ that day. still think these is a strong stock mod hs-40. if a kid had this setup back in the day on is black widow. that would be cool....
outside bike is my hs-40 extreme built,maybe the only like it and it passes the other bike like it was standing still. tons of crazy mod's done to it. 7000+rpm motor with a 245 cam with 18 pound springs. motor has gone to the moon and back several times and has been torn down and inpected and shows no signs of cam wear. also note I run a zinc oil in this engine.
engine build thread https://www.oldminibikes.com/forum/index.php?threads/hs-40-build.161335/
All i know is what the guy told me. i wrote down his name, but it's at the shop. he said that the 245's were cut from existing tecumseh cores, and using a stock spring was proper, a stronger spring would wear the lobes. (but i didn't ask him about pound ratings on springs.) he also said the larger cams were welded and then cut. this made the lobes harder, and stronger springs were fine. you can call them. maybe i misunderstood or he misunderstood. but i actually took notes so i wouldn't forget what he said!
i'm not sure what cam they where using as their core. i know the Mechanical release cam is easier to grind. because it has that huge lobe, it doesn't need to be welded to grind it. or maybe they were getting 'raw' cams from tecumseh, before tecumseh ground them. either way he said the 245 wasn't heat treated and wasn't welded. that's the best i could come up with. i should have asked more questions...
not sure what the guy was trying to tell you that day? or how they do there process.
here is something interesting to look at. I sent a newer cam out of a ohh with the compression relief to tim isky. for some reason he could not weld on it,so he had to get a older style cam to do it. for some reason he sent back the cam he couldn't weld on with the other good cam. 275 lift. awesome cam in my ohh motor. spun that guy all day at 8500 rpm's very strong power with that cam(in a Tecumseh overhead valve engine)
note how he had to regrind completely around it before welding on it. just something to look at...
here is something interesting to look at. I sent a newer cam out of a ohh with the compression relief to tim isky. for some reason he could not weld on it,so he had to get a older style cam to do it. for some reason he sent back the cam he couldn't weld on with the other good cam. 275 lift. awesome cam in my ohh motor. spun that guy all day at 8500 rpm's very strong power with that cam(in a Tecumseh overhead valve engine)
note how he had to regrind completely around it before welding on it. just something to look at...
wow that looks weird. i've ground a bunch of my own cams and haven't had any problems welding on them. maybe the surface was somehow contaminated. i just grind it before welding, and it clears up that problem. but i don't know how they are doing this. obviously they have a lot more experience doing this than me! maybe he knows when a cam is "no good", and just stops and picks up another one.
i believe when Tecumseh was in business their job was easier, as they could buy cores direct from Tec. Now that isn't an option. Like i said, maybe they were buying cams before Tecumseh ground them? They are cast iron, and the surface have to be ground. if they could get a stock cam 'raw', maybe that's the perfect core for a 245 cam. then they don't have to weld them. that was the impression i got from the dynocam guy.
i believe when Tecumseh was in business their job was easier, as they could buy cores direct from Tec. Now that isn't an option. Like i said, maybe they were buying cams before Tecumseh ground them? They are cast iron, and the surface have to be ground. if they could get a stock cam 'raw', maybe that's the perfect core for a 245 cam. then they don't have to weld them. that was the impression i got from the dynocam guy.