tecumseh-ohh build

delray

Well-Known Member
Cool stuff! Where did you get the hardened crank sleeve.
I got lucking and was just doing my research on ebay for that and found something that work. crazy thing that the sleeve ID was only couple thousand larger then the crank seal. so i didn't loose my seal area for the flywheel side.
 

delray

Well-Known Member
So does this mean we have to start differentiating between hemi and non-hemi OHH's...? :D

Great looking stuff!
hemi design head would be interesting with 55 degree ports with 30-32 mm intake port runner. that should blow something apart.....lol or just scare the little people when the engine turning over 8000+ rpm's.....
 
I got lucking and was just doing my research on ebay for that and found something that work. crazy thing that the sleeve ID was only couple thousand larger then the crank seal. so i didn't loose my seal area for the flywheel side.
Years ago when I was rebuilding BSA engines for my street tracker builds a machinest BSA tuner friend used to make sleeves like you did to renew the bushing side of the BSA cranks, you would grind down the worn end and heat and press the new sleeve on which had a inside groove and hole to provide oil to the rods. It was a hardchromed hi silicon steel and it stopped wear which used to reduce oil to rods and then left side rod would depart the cases!
 

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delray

Well-Known Member
interesting ole4, was that something made for that engine repair or a universal part that just happen to fit the engine. someone else had mentioned to me over he summer after hearing what I was doing to my motor that they would do this to some older Harley engines. what convinced me to go this route on my flathead build. after running it very hard last spring on a dirt circle track and taking it apart and seeing the rollers and sleeve surface look like it never ran. I knew at that point this was going to be the ticket for me. the only concern I had was the couple thousands up and down play when I assembled my flathead. good thing I just also happen to be talking to someone that was older gentleman that use to build two stroke go karts in his day. first thing he said was that's perfect clearance for those rollers. all that will expand right away when you start it up. you need that clearance in there for sure or the parts could expand and gouge everything up.( that makes sense.) like I said earlier after taking the flathead apart it was perfect still and I have never had a motor spin so easy. funny part I had couple friends ride the bike last summer and both could not believe it did not have any unwanted vibrations. just real smooth high revving engine. that could just also be a good balance motor. also had two different guys come forward and told me that when they ran briggs flatheads they didn't like the ball style bearing on the flywheel side because of the load on the pto side would put a side load on the other bearing and roller ball bearings don't like a lot of side load. causing the bearing to bind little. why this doesn't happen on clone stuff? I thought that was interesting to know. with my needle roller bearing it's kind of hard to create a side load with it being so wide. so that just might be a plus for my little flathead build.
 

delray

Well-Known Member
delray, what is the part number on that flywheel? I've seen it once or twice as well on eBay and may just have one laying around unknowingly.
couple i have found never had a part number to go with them. they are kind of hard to find because they are different from most of them i have seen for sale. there is no casting edges or casting flash on them just really smooth like the one i posted on my italy made engine and like I said earlier the magnets are built into the flywheel and not roll pin in like most are built. making the roll pin setup more unsafe to use because magnets are mounted on the outside of the flywheel and I have seen them with a steel keyway taper shaft casted in the center of them,unsafe too. just to remind everybody this flywheel I am using I would not use it for riding around at high rpm's with a cheap unbalance clutch or even a 20-30 series .this flywheel is way to light for that kind of application.
 
My friend made a run of about 20 of them for the BSA racers. When Warren Sherwood (raced the most career miles at Daytona) passed my friend and I bought out his basement I found a couple of them. They really solved the problem of wear. Prior to that guys were installing a special needle and ball bearing and then converted the cranks to a quill feed to oil the rods like triumphs.
 

delray

Well-Known Member
My friend made a run of about 20 of them for the BSA racers. When Warren Sherwood (raced the most career miles at Daytona) passed my friend and I bought out his basement I found a couple of them. They really solved the problem of wear. Prior to that guys were installing a special needle and ball bearing and then converted the cranks to a quill feed to oil the rods like triumphs.
that would of been a very cool thing to do back in the day. any plans on building other engine like that in the future?
 

delray

Well-Known Member
Are you going to put this engine on the dyno? Looks like it will be healthy.
I do have a connection to dyno the engine with it on the bike. dyno is setup for atv's and dirtbikes…..perfect for a minibike. I personally would want to have a good street tire on the back and run a clutch only so it's more of a direct drive. guy that i know also feels that a torque converter may slip little and create a inaccurate reading and the way my unit was slipping on top end last year....not good. really like to dyno my hs-40 i built with some alcohol in it.
 

delray

Well-Known Member
piston I use for my project was for a flathead Kawasaki that would come out to a 2.910 bore and the pin bore was only a 15mm bore. that would only put me over .029 from the factory pin. so when enlarging the hole i only had to take about .0145 of material off the the pin bore.

plan on running gas so I gas ported the piston from the side. this will allow the gas ports not to get carbon up from the top if I did go that route

for the piston it self when it came how well it was made. look to be very good. rings where much thinner then a standard ring for a Tecumseh engine. making it a plus for less drag. material of the piston look to be a lot like you would find in a performance piston made out of lighter material and look stronger . not like a factory heavy casted Tecumseh piston's are. more like a hypereutectic piston where they look more silicon casted.

with the big bore and stroking the crank this little guy went from a 195cc to a 218cc motor and still had little more room to go bigger.

I got the engine to fire up and I was almost spot on for jetting. pilot was way off. it still took little more time to get it dial in correct. I wasn't use to this new 26mm flatside carb I was using.

first couple passes i was only pulling 8800+ rpm's and it seem to want more gear.

change the gearing on the jackshaft and seem to make the motor come more alive on the top end ,but also started to develop a small amount of belt slipping.

end up running multiple start stages for just taking off out of the hole. so that point I didn't have to make the motor pull hard rpm's. I wanted to get the pilot spot on which didn't seem really to matter with running a 4500 stall. still a learning curve for me,but I think I got it figure out.
here is the down fall of the engine. when I had it idling and was about to do some adjustments and the engine quits.
well look what came unglued. the crankshaft gear. this was no big surprise to me. gear looks to be a casted material and only a press fit. so this winter I will look into making a harden steel gear and keyway it too

all this happen right before my big race this last summer and would of been a fast bike in my class. so much power. I end up running at the last minute my rupp bike I use for circle track racing only. that had a built clone and a clutch only and only a 3400 stall and the gearing was just off little too. just no time left to dial it in. end up getting second with that. but well worth getting beat by roccosbike(member) daughter. still had lot fun racing still. no second place next year...lol
little help with the neighbor coming over with the bob cat.


yes I have a testing area in my back yard for this.....



I am in no real big hurry to get my engine glued back together. winter has come early and the track is done....lol
 

delray

Well-Known Member
haven't started on the gear yet. just busy with other things going on right now. i did have little down time to play with another head and motor that i will be installing on my thunderbolt.
head was originally a 5hp-ohh small chamber style head that i modified couple years ago with some briggs stock flathead valves and seats i stoled out of a briggs block. 1.125 intake and 1.00 exhaust. for you clone guys that would be a 28.5mm intake and 25.4mm exhaust.
head is also modified with dual springs and dyno flathead briggs retainers/keepers. yes dual springs. i will be running a 255 dnyo cam with some clone 1.3 ratio rockers. total lift will be .331+
head was on a big bore cylinder(2.835)
now it is going back on a stock bore with a factory steel sleeve engine.
so the first thing i need to do is mill little more off the head.


my goal was to try to get the compression into the 11's +
here is where it sits now...in the pall bark.


now here is what i am trying to accomplish. as everybody knows when building any type of Tecumseh ohh or flathead hs-40 or hs-50 the racing cam you get from dyno or even isky does not have a compression relief on it. well for the flatheads with the 245 cam and maybe the 255 too there not bad to pull over once you learn how to pull them over,but for the overhead valve engines. you better have it spot on when you pull it over or your arm will be coming off. i know in the pass with a overhead engine with 30 degrees advance, heavy springs and high compression it's game on when pulling it over. doing little research i found some parts that just might work.
first i had to find a spot on the head if i could install a remote spot for a external compression relief unit that was originally made for a small chain saw.
here is the spot i pick and the only spot...lol
casting hole that was aready in the head.


next was to see if i could drill a hole through the side of the head and all the way through into the chamber right above the intake valve seat.




next was to machine a .075 aluminum plug. i will need to go back and plug the outer hole area and after tapping out the threads.
the compression unit/threads will keep the plug from ever coming out again.


tap i needed to run through was a 10mm.


i will also need to run a small washer spacer so the compression unit will clear fully when open.



completely installed.
OPEN

CLOSE

nice thing about installing it on the intake side. it doesn't really build up carbon and when it might i should be able to spray some carb cleaner down through the vent hole on the compression relief unit if indeed it ever plugs up.
 

delray

Well-Known Member
got to test my compression relief unit this weekend and it works and it also doesn't. it will not pop over with the valve open. just to much lost of air to ignite the fuel,but not really a big deal either. what it did help a lot was the prestart of the engine. so when the engine was cold I can open the valve and then set the choke and pull the engine over couple times without kick back.. this will allow the carb to prime the engine. then shut the valve off and choke and then just pull the engine over slowly unit I get the sweet spot and then pull it just once and off it go's. I might try to restrict the hole little smaller in the future for testing purposes,but for now it's easy to pull over with that small quick procedure.
for the engine setup i am using a 5.5 and larger style block. all ohh-engines that are 5.5 and higher horse power rate come with a 2.795 bore. this block was a big plus. it had a steel sleeve. staying with the lower half of the block i had a arc billet rod installed with a new set off rings and a quick hone with 400 grit stones. cam was a 255 dyno with a set of clone 1.3 rockers modified onto the ohh head. nice thing about the push rods they are built very big(thick). i don't think they will move around(bend). the head i installed came off a 5hp engine. they have a much small open style chamber and milling about .065 off. I got a compression rate around 11.8 and this may drop so slighty when added the piston to cylinder spacing at the top that's not calculated into the finally cc's rating. so I would put it maybe closer to 11.5. perfect with 91 ethonal free gas that is ready available in my area. set of briggs valves(seen in picture above)and ported. for the springs i had to cut the spring pockets down to run a taller spring that would be rated at 32 pounds and a set of dyno retainers/keeper.for a coil i ran a tecumseh hot coil and a aluminum flywheel of a vertical engine. this was not just any flywheel. it was a certain type with the mags casted into the aluminum like the old hs-40's where done and the casting was very smooth. i have seen them come in different ways. so i don't recommend installing just any type of stock flywheel. good example they make one aluminum flywheel that can bolt up to this engine,but the mags are roll pin into the aluminum flywheel.......not safe looking at all(stay away from them)
here is the crazy part. the carb is a 22mm mikuni/china carb with a 142.5 jet a 15 pilot that I my change OUT. reason i say that is at low cruise speed I will get a very small stumble,but if you hit the throttle it would rocket right off again right up 7000+ rpm's

 
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