tecumseh-ohh build

delray

Well-Known Member
#81
tecumseh power
Yes, I think you're right. I must be mistaken, because it doesn't look 3.125" would go
yes,more then likely you had something just over 2.8?? and anything larger then 2.831 you would of had other problems you would of had to deal with.
piston i had was wiseco racing piston for a 2.831 and the bore was Nickel Silicon Carbide plated.

i run 255 dyno cam in my mild built ohh-motor on
my thunderbolt. pulls real hard out of the corners right up to 6000+ rpm's with no problems.
cold start on my thunderbolt. no compression relief
https://youtu.be/Di9nn2kSKp0
project build thunderbolt
https://www.oldminibikes.com/forum/projects-and-rides/115101-thunder-bolt-5.html


cam i ran in my drag bike was a isky cam and that had no problems pulling up to 8000+ rpm's
you mentioned earlyer about getting parts cheap. i just pickup another 3inch crank for only $35 ship to my door.
bearing pto covers too.:thumbsup:
 
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#82
Very cool! What is the part number for those cranks you are getting? I think I still have a ball bearing Motorsports side cover.

I bought some 245, 255, and 356 dyno cams on eBay a while back, and I think I still have a Motorsports OHH cam left.

Man, I had a bunch of one off stuff at one time that I wish I still had. I used to work in a CNC machine shop, and I had access to make rods, custom valve seats, lifters, and I was able to bore blocks and mill heads. I started out running HS flatheads, then moved up to the H50 Motorsports stuff. I started fooling around with OHH later on, and for a while before the Animals came out I was the only fool I know messing with OHV stuff. It seemed so exotic back then!

I still have a Motorsports H50 complete , an OHH55, and a OHH60.

I'm planning on putting together another OHH engine just for the heck of it. I'm collecting parts now. Are you using the ARC rods in your build?

bb

I made these also for stock carbs, but I have a few of them that not drilled to adapt to other carbs. They are made of black delrin, so they are light and in theory should stay cooler.



 
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#83
Nice Jobs on the stacks! Do either of you guys have a HS50 ball bearing crank you want to part with? I have one on order from Jacks small engine parts but it keeps saying backordered, and that they are waiting on the part from the supplier. There is no supplier so I expect it will be cancelled.
 

delray

Well-Known Member
#84
sorry i don't ole4,but depending on what type of engine your running? points or electronic. you could modify a different crank or just the bearing in the pto cover. it just depends on what your trying to do?
 

delray

Well-Known Member
#85
tecumseh power
What is the part number for those cranks you are getting
funny thing is both times i purchase a 3 inch crank on ebay they had the wrong number listed for it. but i could tell by just looking at it that it was a 3inch crank. neighbor kid had a ohh in a gokart and did not want it anymore. that engine came with a 3inch crank. still have the numbers on the recoil cover. thoses numbers should be good. i have a number down in my note book as a 37241 long? with a question mark?
need to double check .
i see you got the good coil too. that will advance the motor from 20 to 30 degrees.
don't try running that 356 unless your really ready to modify your engine. i have the same came. couple things can really cause some problems.
255 cam is a great cam for that engine and the isky is a very good mid to top end cam and is very easy on the drive train. you only need 26 pound spring,has only a 275 lift making good valve clearance. can't say enough how good that cam is....:thumbsup:
my last motor had a briggs rod i machine to fit the rod journal. i won't go that route this time. i got some stroker ideals now....:wink:


 
#86
Nice Jobs on the stacks! Do either of you guys have a HS50 ball bearing crank you want to part with? I have one on order from Jacks small engine parts but it keeps saying backordered, and that they are waiting on the part from the supplier. There is no supplier so I expect it will be cancelled.
I don't think I do, but I'll check and see. I have a few HS engines out there, but they were just engines I picked up for parts long ago.
 
#87
tecumseh power
funny thing is both times i purchase a 3 inch crank on ebay they had the wrong number listed for it. but i could tell by just looking at it that it was a 3inch crank. neighbor kid had a ohh in a gokart and did not want it anymore. that engine came with a 3inch crank. still have the numbers on the recoil cover. thoses numbers should be good. i have a number down in my note book as a 37241 long? with a question mark?
need to double check .
i see you got the good coil too. that will advance the motor from 20 to 30 degrees.
don't try running that 356 unless your really ready to modify your engine. i have the same came. couple things can really cause some problems.
255 cam is a great cam for that engine and the isky is a very good mid to top end cam and is very easy on the drive train. you only need 26 pound spring,has only a 275 lift making good valve clearance. can't say enough how good that cam is....:thumbsup:
my last motor had a briggs rod i machine to fit the rod journal. i won't go that route this time. i got some stroker ideals now....:wink:


Good to know about the Isky cam. Is that a custom thing, or readily available?

On that 356, I believe there would be some clearancing involved and probably beefing up the lifter bore area, if they are anything like the old fast ramp Briggs flathead race cams. You'd need a lot of compression, and heavily ported head and good carb to take advantage of a cam that size. A billet flywheel would pretty much be a must turning that kind of RPM.

I'm intrigued with your ideas on the stroker. I used think about trying to modify a Briggs crank to fit the block (mainly because tons of rods, and flywheels were readily available back then) but I never looked at what it would take to make it happen.
Hopefully you can pull that off and share with your fellow Tecumseh nuts (all 6 of us that are left!)
 
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delray

Well-Known Member
#88
on the isky cam you need to send him a old style points cam. must be the one with the small bump machine on the back lobe. bump is for the compression relief. that will be gone when he welds it up and regrinds the cam. thats the only big draw back with it. so then need to watch how you pull the engine over or your arm will come off.........in a round about way:cursing:
the newer cams he seams to have a small problem welding them. steel casting is little different. but i have seen one newer cam welded up from him and that newer cam also had the compression relief built into it.
newer steel cams have this style compression relief. works pretty slick. just a very lite spring pressure on the counter weight and when the cam starts to spin the compression relief comes off.

another place you can look into welding a newer cam might be dyno cams . they may have better luck welding that type of metal. still little loss on how the tim isky did the compression relief cam. reason i say that is because that newer cam has a bigger base circle and that puts the compression relief arm out farther and when he regrinds them he goes with the old style base circle cam(small). i have been looking at that setup for awhile and want to some how incorporated it into one of my race cams. it doesn't look hard. just alot of time setup to make a jeg and all.
i think the 356 cam you would be ok on the lifter bores,but like you said too it needs lots air and fuel(porting),good carb, billet flywheel....etc... and that cam will hit the crankshaft(both lobes) so the crank will need little machining or grinding.
one thing you don't need to touch is the push rods. they must be twice the thickness has a honda/clone:thumbsup:
also you need to watch the clearance on the valve guides that protrudes out of the casting. retainers could hit them unless you machine them down little.
here are some automotive type retainers that work with tecumseh valves. also the animal spring works good.
left animal retainers/keepers center dyno cam(need little machine work done first) right tecumseh motorsports(heavy duty)
i like the animal's the best......bolt in and go and have a little better off set to them


and yes there is only 6 tecumseh gearhead guys left on this web site....:laugh:

they all gone to the dark side..........clones:doah:
ok with me,just means more clones to race against......:scooter::scooter:
 
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#89
on the isky cam you need to send him a old style points cam. must be the one with the small bump machine on the back lobe. bump is for the compression relief. that will be gone when he welds it up and regrinds the cam. thats the only big draw back with it. so then need to watch how you pull the engine over or your arm will come off.........in a round about way:cursing:
the newer cams he seams to have a small problem welding them. steel casting is little different. but i have seen one newer cam welded up from him and that newer cam also had the compression relief built into it.
newer steel cams have this style compression relief. works pretty slick. just a very lite spring pressure on the counter weight and when the cam starts to spin the compression relief comes off.

another place you can look into welding a newer cam might be dyno cams . they may have better luck welding that type of metal. still little loss on how the tim isky did the compression relief cam. reason i say that is because that newer cam has a bigger base circle and that puts the compression relief arm out farther and when he regrinds them he goes with the old style base circle cam(small). i have been looking at that setup for awhile and want to some how incorporated it into one of my race cams. it doesn't look hard. just alot of time setup to make a jeg and all.
i think the 356 cam you would be ok on the lifter bores,but like you said too it needs lots air and fuel(porting),good carb, billet flywheel....etc... and that cam will hit the crankshaft(both lobes) so the crank will need little machining or grinding.
one thing you don't need to touch is the push rods. they must be twice the thickness has a honda/clone:thumbsup:
also you need to watch the clearance on the valve guides that protrudes out of the casting. retainers could hit them unless you machine them down little.
here are some automotive type retainers that work with tecumseh valves. also the animal spring works good.
left animal retainers/keepers center dyno cam(need little machine work done first) right tecumseh motorsports(heavy duty)
i like the animal's the best......bolt in and go and have a little better off set to them


and yes there is only 6 tecumseh gearhead guys left on this web site....:laugh:

they all gone to the dark side..........clones:doah:
ok with me,just means more clones to race against......:scooter::scooter:
Ok, cool. I have several older HS40 and 50 cams. I'm thinking about building one of them mild with the Dyno 255, and try to build a hot version later. I know what you mean about pulling one of those beasts over. I they'll bite you if you're not careful!

Speaking of your mild 255 cammed engine, what kind of intake setup do you have? I noticed the carb was on the front of the engine. All the pics you had posted no longer show because of photobucket.

I think I'll run a milled H50 head with stock size valves in it and save my welded head (with bigger valves installed and more porting) for the 356 cammed engine.

I remembered another thing we used to do those engines; I used to make billet lifters for them and I put a crown on the lifter face. I put a 30" radius on the face of the lifter (which is a little aggressive that a stock automotive lifter) and it seems to free up a fiction and helped the lifters spin a little quicker. The high lift custom welded cams we used to run seemed to like it.
I also modified a Briggs flathead billet flywheel for one. I don't remember the angles, and I can't remember if I changed the angle on the crank or the flywheel on that particular engine (I've done it both ways). I do remember having to make a bracket to move the coil. One of the ones we did had to have another keyway put in the crank to index it the flywheel properly, but I don't remember if it was the OHH stuff or not.

Speaking of clones, I'm currently working on a Predator for a friend's son. It has rekindled my desire to put together some of this old Tecumseh stuff, so I guess it's not all bad!
 
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delray

Well-Known Member
#92
tecumseh power
what kind of intake setup do you have? I noticed the carb was on the front of the engine.
thats was a one piece wrap around intake i made for it. it work good. i now have my drag bike intake on it to see how that one works.

yes, a 172cc head would be good for the 255 cam. stock valves are small,but they will still flow good with that cam. little head porting and mill .040 off the head and the good tecumseh(advance 30degrees) coil and it will run good. i still use the stock cast iron flywheel on my mild motor and seams to work good.
i also almost need to have it on that bike because i am still running a comet 30 series and they don't like billet aluminum flywheels.
just to much under balance material for a lite flywheel to absorb. people still do it,but they really don't realized the damage they can do in the long run.
ran some numbers(you may already know this or can figure it out)
Engine Item Inches/Measurement
Engine Bore 2.795
Engine Stroke 1.938
Deck Height * .040
Combustion Chamber CC's 15.5
Your Compression Ratio is 10.7
perfect if your local gas station sell's the ethanol free 91 octane
i was wondering little about that head you did,looks good. i do agree you need to save it for a big build and also install bigger valves.........easy:thumbsup:
you would need to put that on a big bore to get your compression up again after you opening it up. one thing about open chamber heads they do seam to flow better then a close chamber head...:thumbsup:
funny thing you mention about lifters. i pickup a new set of hs-small block lifters and they are a dark brown/black color(some kind of coating/heat treated)
make a story short, i am running them on a new cam in a flathead. WOW do they spin them valves. i won't every f-around with uses lifters on a new cam every again.:doah:
another option maybe to look into for a billet flywheel is the new adjustable animal billet flywheel where the center piece unbolts from the flywheel(hub). a guy maybe could just make a new hub with the correct tapper shaft...:shrug:
 

delray

Well-Known Member
#94
here is something I purchase last summer. I have only heard about and I believe only seen in the motorsports ohh-motors. this is a factory head that comes with larger valves. I believe only difference was the motorsports engines came with stainless valves. this is still something I need to verify still? head design on the motorsports and this head was the large cc and would need little milling to get you compression up in the 9's. I have use the small valve heads in the past with just milling the head and porting in the bowls with a stock cam and even a 255 dyno and still works good for hot rodding around on a minibike. i'm sure the big valve head would work good with a 245,255 or even a mild isky cam.
 
#95
Hey delray, how much stall are you using on the dragbike?
Do you want the driven to shift up slowly or quickly with a big-torque motor?
Is 1-7.6 gearing for drags about right?
 

delray

Well-Known Member
#96
I was running 3000 stall on my drag bike and just the stock comet spring in the rear driven. in the pass I tried to use the yellow comet spring and that seemed to create a lot of havoc with the belt and engine trying to turn high rpm's. just in the short time I use the rear driven unit the stock spring also became very weak. I like to try a red spring out of a clone 30 series 7 inch driven I believe. that spring in another bike I ride for fun seems to work good and the spring tension seems to be holding. still have some more testing in the spring to really see what is the best for my application.
 
#97
The 3000/3300 is all I have experience with and for years I haven't even thought of changing.
I.ve only used a yellow spring(yes they wear out!) and just recently put in #3 hole because I figure I have enough
torque already out of the hole so let the TC 1-7.6 and motor head for the mountains right away.
I tried a 3600 in my shed 2 days ago and there is a ton of difference good grief coming in
at 3600 it was WANTING TO GO. Don't the big clutches lock at 4000? I'm wanting to smoke the
tire on what I'm building so I'll need extremes that won't break. Like you, testing is what I need
for, like you say,my application.
 
#99
I believe you, massacre, it will be a rush for me as well no doubt.
Hello all
As you know, (from a car site)
"Heavier flywheel helps with momentum of the engine to offset dumping the clutch. Lighter flywheel helps engine rev faster. Since you have fairly light weight and some fairly low gears, a lighter flywheel should give a lower ET; although you may have slightly lower 60 ft time with light flywheel vs the heavier one. The engine revving up faster will overcome the starting line gain"

I gave away an Arc 3.5 I wish I had back but am going to switch an Arc 1.75 to an Ambush 2.7 laying on the shelf.
Comments, questions, snide remarks?
 
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