tecumseh-ohh build

#1
when i first look into this motor there was not intention to build this motor. just to make it run good. i think for the most part everybody would agree this motor run's like crap from the factory. it seems like 99 percent of theses motors are found on med to large two seater gokarts. i have 5hp on a med two seater and my neighbor has a 6hp on is large gokart and they both run the same way. fix jet and governor way down and only a 20 degree advance timing and for anybody that does not understand what i am talking about. i would say pretty close to chitty chitty bang bang.....:laugh:


first thing i did was look into the head. actually the first thing i did was to find out why it did not run. engine only less then a hour running time and then the owner replace it with a new engine and put this one back into the factory tecumseh box and then it sat for over 10yrs+ until i got it. keyway was broken....:doah:

right away i notice the casting on the intake was much lower then the exhaust
 
#2
measure the height on the intake with the seal and then the exhaust side. i found that there was .130 difference.
made a spacer on my lathe and also made it so it would center the spring better by making a small raised inner lip.


spring lock in the spacer nicely.
 
#3
the way i figured out that a briggs animal #20 spring would work . i had a intek briggs 6.5 engine and the springs in them where the same has my tecumseh-ohh stock springs.

 
#4
for retainers and keepers, i found that the flathead briggs dual spring retainer and locks would work perfect for my tecumseh valves.



there was one small problem i had to deal with. the inner spring lip on the retainer had to go. so my single (fat) animal spring would sit correct in the retainer.
off to my lathe......
retainer on the left you can see how much material i had to take off.

 
#8
there was not much to clean up for the valves and head. i did clean up the bowls. only ported the bowls into start of the runner. it was not hard to figure out what needed to be clean up. both the intake runner and exhaust runner it self i did not touch. they look to have plenty of airflow.
factory valves are small, but they still proved to flow good power for this project build on a minibike.


before bolting the head back on . i decided to measure thickness of the new and old head gasket and they came out to be .040
i also found some info on the internet saying the gasket was .040 thick.....:thumbsup:



i wet ahead and installed the head without the gasket and found that the valve train look good. everything was lining up real good still.
so at that point i wet ahead and milled .040 off.

lots of room for bigger valves. maybe next project.....:smile:
 
#9
retainers and keepers workout real good.


this thing has a big bore. i believe it was somewhere around 2.800 just under 3inch......:eek: and just think it still only comes out to a 195cc motor......:laugh: piston comes to the top. it does not sit in the hole like the clones do.
i did clay the piston to valves with the cam i installed and still had plenty clearance. bigger cam and valves would still work..:thumbsup:
 
#13
randy, i will make a list of part numbers for all the items you will need to run in that ohh-motor of yours when i am done with this project build write up..:thumbsup:
 
#14
here is a picture of the stock push rod and rocker arm on the right and a honda/clone push rod and rocker arm left. note how much bigger and thicker the tecumseh push rod is and it looks like they both appear to share the same size/ 1 to 1 ratio rocker arm. you know what that means for a future build. maybe some 1.2's or 1.3's rockers....:rolleyes:
 
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#15
i got real lucky when i was building this motor. i found a bearing cover real cheap on ebay.....:thumbsup:

bearing cover next to stock cover.

also note i clip off the governor parts.

when using a bearing cover it takes a different crank. there will be a grove cut in the shaft about .500 from the cam gear. this is for a snap ring that is installed before putting on the crank seal.


i also got lucky and found a new crank real cheap on ebay.



now that i have a grove crank for a bearing cover and know the distance. i can just cut a grove in my next future build and not buy a new crank.....:thumbsup:
 
#17
went ahead and purchase a new performance tecumseh coil that everybody was calling the hot coil.

well it really isn't a hot coil when it comes to spark. i did a quick little test with it and it puts out the same amount of distance spark as the old coil does. i also had a old use ohh-motor with a stock coil on it for my little spark test.



what i did find out is when i went to degree the timing with a timing light. the motor was advance way out. timing was 36+ degrees advance when i was timing it...:doah: motor was not running. i was just turning it over with a high torque drill with a socket on the end of it. so this is what this coil does only. advances the timing.
had to bring the advancement back little. so what i did was chuck up the factory bolts in my lathe that hold the coil and turn done the threads only in the area where the coil sits with a file and also bored out the mounting holes little in the coil. all this allowed me to adjust the timing little and get it more in the ball park.
 
#19
for some of you guy's you already know the engine was done. because you got to see and here it run at windber.
i didn't have alot of pictures,but enough to get ideal what i did to this motor for all you guys that have been asking about it.
engine has been running awesome. i never would of thought in a million years this tecumseh would put out so much power for a 195cc motor. i would still consider this a mild motor. more room for bigger valves,bigger cam,now i believe i found a aluminum flywheel that would work with just little modification to the coil mount.boring the block.aftermarket piston and rings. lot more things i could still do someday on my next OHH-BUILD.....:thumbsup:


this is where it gets little crazy. before going to winder i was trying to jet the bike.
first plug run..........white as a ghost with a 120jet


color stayed like that until i got to a 142.5 jet and that took over a week+ to get that color to change. because i had to reorder jets twice. not thinking this motor would need that big of a jet. when i got to a 142.5 jet it was only two days before i had to go to windber and i ran out of time. so off to windber with just enough color to run the bike.

the other small problem i had with it was the pilot jet was to small. i found that out also two days before windber. at low cruise speed the pilot should keep steady speed. i could feel it slowing down or as they say laying down...:laugh:
i just order a bigger pilot and that also may help the lean just little and then i will see if i need to bump it up to a 145 jet.
once i get that dialed in it should have just little more power or at least running the best it can......:scooter:

question for you honda/clone guys that are building them with a mikuni/clone carbs. when you start to get into a 135 jet and up i have seen some good horse power come out of these motors(for just being on a minibike). is it possible this motor with that big of a jet is doing the same thing?



list of part numbers i use in this project build.
tecumseh coil 36605k
retainers:dynocams DCSH102
keepers: dynocams DCSH103
valve springs:dynocams #20lb animal spring DCS-AN2
cam: dynocam 255
mikuni/clone:MIKUNI VM22 Carburetor Quad ATV Dirt Pit Bike Dirtbike 125CC Carb 26MM
 
#20
mb165
that intake may have a ram effect, helping with additional power.
does it load up at slow speed? just curious, did happen to measure the volume of the manifold versus the engine displacement?
mb165, no loading up at slow speed. just a small lean problem with the pilot. i have not done any volume measuring verus manifold/engine displacement.
back to your first question. enough ram effect that the intake is getting cold and you know what that does.......:scooter::thumbsup:
 
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