Kirby Tecumseh 2 stroke 12HP

[#28 FASTGRASS]

Hey all,
Thought this might be of interest, (see photo's) a bit historical as these things are wayyyy obsolete. They are a Aussie made Kirby Tecumseh engine STD 4.2HP & 3,600 RPM modified 12+HP & 8,000 + RPM. Bore 2.500" Stroke 1.770" their down fall is the fact the cranks are a bit dodgy in their case hardening on the main rod end.....(and only 0.750" in Dia.)
They go very well though....tuned one so well the drive dogs broke on the maxi torque clutch! It had a savage power band wicked on the pipe in full song but a real pig off the power.....
These were on lawn mowers that use to hover amongst others in the 60 & 70's (maybe earlier???)

They proved popular in Karts but strangley I have trouble finding any references to them (the secret is now out!!)

I have a copy of the factory porting modifications and dynoed power output out of interest (or for the noisy negativists as Stanton Friedman would say).........Also in the mists of building up a reed valve one with a boost port using a Mac10? reed block....
Shame they were not as popular on lawn mowers as the Aussie Victa motor....
Enjoy the pics, I use a 6V Willies Jeep starter on a 12V batt. to start the one in the photo.. more detailed to come in time if the interest is there....

 

[crazyman]

Nice!

 

[anderkart]

Hey cool engine Fastgrass, I'm not sure but I think I might have an engine that's kinda similar here:

It reads Tecumseh AH817MB

This (5hp/139cc???) 2-cycle engine came on this 1972 Fox Tracker I just bought.
Its a little rough but all original. (the dirt and grease all over it is even from the 70's )
It starts on the 3rd pull and rides great!

I dig it, It kinda looks like an old Trials/rock-climber bike, only smaller...

Its got a factory torque converter system, This little thing wheelies off the line with my 235lb a$$ on it, and then it feels like it tops out at like 50mph or something.

 

[#28 FASTGRASS]

Hey anderkart,
yeah nice little unit there! Wonder what it would be like if you doubled the HP!!!! Scary!! but bloody good fun I bet!

The engine looks like it might be from the same family of engines, as the ones over here, which we made under licence from Tecumseh USA in Australia. (I have a few square finned barrel versions too)

It would be good to find out more about these engines, maybe you guys have a cache of spares over there? I think wishful thinking on my part there though....

P.S. I want one of those bikes too

 

[number 37]

man, I want one of those for a chainsaw project...

that bike is great looking anderkart!

 

[#28 FASTGRASS]

More photo's

A few more random photo's, might post a porting before, during and after shots of the reed valve boost port one I'm doing at the moment. The one on the Kart has had the head welded and remachined with better squish too... 145-150 PSI comp...a bit beyond hand starting....

man, I want one of those for a chainsaw project...

Mate you'd be a brave soul to hang on to that grenade!! and you would need another saw engine to start it....it is Nasty...

 

[number 37]

that is just a crazy cool motor

 

[sexyvicta]

i got one for a lawnmower. has been converted from crankcase to piston port induction. Crazy australians

 

[mwmurrell]

I had an AH817mb

So i actually had one of these rare beauties (AH817mb) and it was really cool. I would have kept it if i had a garage rather than a kitchen to build my projects. What i found out about it is:
Tecumseh made the MB model for MiniBikes. It is a two stroke aluminum engine and it is impossible to find parts for them. After making all new gaskets for it I decided that I didnt have the tools i needed to finish the job so i sold it on CL in less thn an hour. If you go to oldminibikes .com and search my user name mwmurrell there are a ton of pics of the engine. It started and ran (not well probably due to tuning). I do know that they are pretty durable and really fun but very sensitive to elevation and temperature.

There were lots of unhappy people when i told them i sold it for 150.... o well i just needed enough to get a gx200. I think the engine would look very nice all cleaned up with JUST the leading edges of the cooling fins polished. sure you could polish the whole thing but that's just too much. I sure would love to spend some time on one that's tuned up and running well. What a cool engine.....im starting to wish i had not sold mine. Hopefully it has a good home

 

[mwmurrell]

Here are the pics of the ah817mb i was fortunate to spend some time with. The mounting is so strange around the shaft like that. I have seen it mounted almost completely horizontally... which i suppose is ok because it is a 2stroke but i would still be worried about even lubrication within the cylinder. I also love the exhaust manifold. It looks like it came straight off the set of starwars. The pic of the piston/ring through the intake is poor quality sorry but you can still see how clean it was. The frame is a Manco Streaker which is what the GX200 is going in this weekend....God willing. You dont even want to see how the engine was mounted to the frame when i got it. It may just make you sick. Looking back at these pics and seeing how clean it was compared to yours makes me want to kick myself for not keeping it. Fabrication just is not possible unless i go to a friends garage which is ok once in a while. I dont want to build a whole project in somebody else's garage tho... I hope that nerdy dude i sold it to is treating it well. Some day i WILL find another one and make it perfect now that I have a sentimental attachment to these crazy things. People have said that they put out some power too... being that they are so small.
And to think i got it for free ,engine and rolling frame, well i had to clean a truck for it. small price. I have more pics if u think they would help. Let me know

 

[#28 FASTGRASS]

Cool motor there...(AH817mb)....good to see its inside detail thanks!...Has anyone double carby'd one? I reckon you could reed induct the base on those as well. You can definatly see the common design thread with both the Aussie and American motors

 

[oscaryu1]

You're gonna warp the hell out of those bridges with it ported so heavily.

 

[#28 FASTGRASS]

Yeah you are right, that one actually had a hair line crack across one in fact. However it ran for 1 season in competition and and about 2 years of messing about afterwards before being stripped down and inspected. When they are running that fine to the limits you do risk chucking a few in the trash...At the time time they were about $10 to $15 each, we only left enough in there to keep the rings from falling out thats racing....on the limits...

 

[andrew n]

Hey mate nice work! I have one of these engines and I'm keen to use it in a go kart set up. How did you know how far to take the port work?

 

[#28 FASTGRASS]

Hey mate nice work! I have one of these engines and I'm keen to use it in a go kart set up. How did you know how far to take the port work?

Thanks andrew n, and Trial and error over 10 yrs........ if you have a Kirby Tecumseh engine just square up the ports (following the drilled angle of the port) with a square file and dont change the timings anywhere (or you may have to bin it, depending on error), blend the radiuses and polish the ports with wet and dry paper.

Take the sharp edges off the ports in the cylinder so the rings dont catch, make your own inlet pipe and put a 3/4 tilliston carb on it (@ $320??). make up an expansion chamber with shallow angles (taper) for good mid range power, with a ~24mm tail pipe and your there! this will give you about 8+hp, depending on what Tecumseh head you have on yours. The single dished one with the large flat squish area over the exhaust side of the head is the more powerful one of the two. There are the usual other tricks as well... if you have a lathe skim 1mm off of the bottom of crank case and from memory about the same off the top of the barrell, check clearances first and make sure things dont hit allowing for the gaskets... for safety leave the squish a bit loose at 1.2mm these extras might give you an extra 2+hp (you have to think outside the square with these heads and how they fit...hint hint)....dont forget to order the free running bearings if replacing the bottom end bearings and do replace the seals. Use a cold spark plug or you will hole the piston try an NGK b8hs? that will be about right. Machine the crank to 5/8" to fit a Maxi torque clutch and get the key way cut, and cut about 6-8 turns out of the spring (feel free to curse me on re-assembly), or buy the racing one (I haven't tried that type yet)

All that said... check the crank first.... you will probably have to bin it (they bend if the big ends get loose, and can also get severe roller "ripple" on the main journal) and then PM me I might be interested in the barrell if you haven't filed it...

Again having said all of that.... get a Victa 160cc from the 70's which does have full round machined crank webs on each side....... You can get most parts for those..... if out right power is your aim...

Because these things are waaaayyyy obsolete, dont go wild thining the port bridges etc. leave plenty there, esp. if your a newbie it will last longer....

OH Edit: and work out a way of starting it because you'll bust your hand and the recoil starter!!

Personally I'd use an Aussie Victa now... (I'm doing 1 for my kids now, a low power 125cc off a trashed reel mower as it has the carb and engine mount to bolt straight in a Kart) you can at least get parts, and the effort you put into the inlet and exhaust fabrication wont be wasted.....

 

[beansdaddy78]

I dig that minibike anderkart, Are you gonna fully restore that HOG???
I actually see a few parts for them around (only since im looking so hard for vintage fox parts for my project) I am trying to find me one of them that you got, or any other old fox projects. I love the way they look kinda like a dirtbike and wanna put a 2 stroke on one.

I got a 69 fox spoiler im working on getting riding then im gonna brake it down and restore it. I have a tecumseh 3hp motor like one of the motors that came on it (3-5hp tec's) its not the original motor though so im gonna slap a 2stroke mc49 saw clone i finished yesterday on it. I hope to test drive it sometime today or tomorrow depending on when the guy who does the roads out here gets up and plows them.

 

[Ahmed]

The AH600 sounds similar, any info on that?

 

[andrew n]

cheers, that will keep me busy for a while. The first thing i noticed was that the big end had let go. I am thinking maybe a custom crankshaft based on a 2 stroke dirtbike crank with a press fit pin. rod length could be altered to change the stroke? not sure if that will benefit the engine or not.

The kart currently has a victa 160 with a few mods which goes good but i think the tecumseh will be better.