tecumseh-ohh build
- Thread starter delray
- Start date
- Tags build tecumseh-ohh
I built a stock ohh this summer for the thunderbolt with just some very light mod's that anybody can do. engine I use was 5.5 and up block . they all come with a 2.795 bore. 5hp has a much smaller bore.
I did use a 5hp head because they come with a smaller chamber. milled the head and ported the bowl's into the runners little. use the stock compression relief steel cam with 1.3 ratio rockers. ran 22mm carb,billet rod,dyno retainers,20 pound springs. very happy how it runs. still could use just little tunning on the carb maybe. for a engine with small valves still and a stock cam it pulls very easy up to 6000 rpm's. big help having big sprocket on the back and a 7inch driven.
I also built a ohh drag motor and did some crazy stuff to it. try to get something posted in the future on it.
I did use a 5hp head because they come with a smaller chamber. milled the head and ported the bowl's into the runners little. use the stock compression relief steel cam with 1.3 ratio rockers. ran 22mm carb,billet rod,dyno retainers,20 pound springs. very happy how it runs. still could use just little tunning on the carb maybe. for a engine with small valves still and a stock cam it pulls very easy up to 6000 rpm's. big help having big sprocket on the back and a 7inch driven.
I also built a ohh drag motor and did some crazy stuff to it. try to get something posted in the future on it.
first thing I had to address was one of the bolt holes needed to be slotted.
see one head above the other is slotted from factory. that would be a ohh head. the ovrm is not.
kind did this the old school way when it came to installing the larger seat. mounted on my lathe and centered it up and cut out the old seat.
and wallah it came out.
see one head above the other is slotted from factory. that would be a ohh head. the ovrm is not.
kind did this the old school way when it came to installing the larger seat. mounted on my lathe and centered it up and cut out the old seat.
and wallah it came out.
next step was to open it up to a 32mm seat. YES a 32mm valve will fit in this head.
with the new seat installed you can see how much material I will have to remove.
no problems yet!
open all the way. looks like I went though.
this end up being a good thing. went back and welded up from the inside bowl area and on the outside making this area very rigid and also allowed me to have enough welded material to make a good radius bowl area. allowing the air flow to direct to the valve/seat.
I did little finishing porting on the lathe.
wow can I pump a lot air though this motor...lol
little more cleaning up and we will be good.
with the new seat installed you can see how much material I will have to remove.
no problems yet!
open all the way. looks like I went though.
this end up being a good thing. went back and welded up from the inside bowl area and on the outside making this area very rigid and also allowed me to have enough welded material to make a good radius bowl area. allowing the air flow to direct to the valve/seat.
I did little finishing porting on the lathe.
wow can I pump a lot air though this motor...lol
little more cleaning up and we will be good.
exhaust side I decided to go ahead and cut the old seat out. at first wasn't going to do it. that valve size was already ay 27mm and to go to 28mm.
i don't think I would of seen a difference in performance. but I went ahead and did it anyway.
also note I made a cutting tool to relief the area around the valve and the side of the chamber for better air flow. eventually I will blend the new radius cuts into the chamber and also mill the head. it appears that I will be able to dicate how much compression I will have and that's a good thing.
i don't think I would of seen a difference in performance. but I went ahead and did it anyway.
also note I made a cutting tool to relief the area around the valve and the side of the chamber for better air flow. eventually I will blend the new radius cuts into the chamber and also mill the head. it appears that I will be able to dicate how much compression I will have and that's a good thing.
for the valve train I decided to go with the OHH setup. the ovrm valve train is only setup for very low lift cams. not a lot of valve travel.
with the ohh I can take advantage of the longer valve and factory heavy duty push rods/guild plates and the stock rockers are about .015 thicker then a honda or clone rockers.
for the valve it self I will be using a new flathead briggs ss narrow stem valves and cutting them down to length(ohh valve) and going with a animal lock setup. it's a little better positive lock setup then the flathead's are and at the rpm's I will be spinning am not going to take that chance.
with the ohh I can take advantage of the longer valve and factory heavy duty push rods/guild plates and the stock rockers are about .015 thicker then a honda or clone rockers.
for the valve it self I will be using a new flathead briggs ss narrow stem valves and cutting them down to length(ohh valve) and going with a animal lock setup. it's a little better positive lock setup then the flathead's are and at the rpm's I will be spinning am not going to take that chance.
by using the stock push rods and valve length from a ohh motor like I said previously. It also allowed me to dictate my spring height by making these little aluminum spacers under the valve springs and giving me correct valve travel......off to the lathe.
aslo made them with a small step to self center the valve spring.
aslo made them with a small step to self center the valve spring.
by using the stock push rods and valve length from a ohh motor like I said previously. It also allowed me to dictate my spring height by making these little aluminum spacers under the valve springs and giving me correct valve travel......off to the lathe.
aslo made them with a small step to self center the valve spring.
aslo made them with a small step to self center the valve spring.
next I made a aluminum block spacer get the correct height for the push rods/rockers and all.
this piece of aluminum started out as a larger piece and machine down to correct height.
with the extended height I was dealing with I had to change the rocker arm studs.
the original style had the allen head built into the ball cup and threads for adjusting the valves.
new style would be a longer allen bolt and the threads would be tap farther in to the head. I also would take the old stud and cut the ball cup off and drill though it and now become just a half ball cup that I could slip over the stud and use a jam nut below the rocker to hold the assy together.
final valve train setup end up working very good. also you can see how much lower the ovrm head is over the ohh head.
I would have to make a new valve cover by using the original bottom part only from the ovrm and the top from the ohh. reason why ,one the ovrm fit good on to the head and for some reason the ohh doesn't and I had to make it just little extra Tall to insure everything would fit correct under the cover.
this was the easy part. the next part of the build is where it becomes really fun and doing things to a Tecumseh motor that has never been done.
this piece of aluminum started out as a larger piece and machine down to correct height.
with the extended height I was dealing with I had to change the rocker arm studs.
the original style had the allen head built into the ball cup and threads for adjusting the valves.
new style would be a longer allen bolt and the threads would be tap farther in to the head. I also would take the old stud and cut the ball cup off and drill though it and now become just a half ball cup that I could slip over the stud and use a jam nut below the rocker to hold the assy together.
final valve train setup end up working very good. also you can see how much lower the ovrm head is over the ohh head.
I would have to make a new valve cover by using the original bottom part only from the ovrm and the top from the ohh. reason why ,one the ovrm fit good on to the head and for some reason the ohh doesn't and I had to make it just little extra Tall to insure everything would fit correct under the cover.
this was the easy part. the next part of the build is where it becomes really fun and doing things to a Tecumseh motor that has never been done.
I did little test fitting with the 356 cam and found out that the travel for the lifters just about max out by a few thousands.
I had to machine little material off first to be on the safe side for lifter travel
before
https://ibb.co/sWKt8pr]
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after
https://ibb.co/PYjZXS7]
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I had to machine little material off first to be on the safe side for lifter travel
before
https://ibb.co/sWKt8pr]
after
https://ibb.co/PYjZXS7]
next step was to free up some drag. seeing that I was going to run a 356 lift cam I would have to run 40+ pound valve spring and that would put some what a good amount of load on the factory stationary bushings and create little bit drag in the cam spinning.
I first had to make couple pillow blocks out of a chuck of round stock aluminum.
https://ibb.co/dGfst75]
https://ibb.co/kXnqr5x]
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after making two of them I went back and drilled hole from the top so oil would feed into the bearings.
https://ibb.co/0XgQ3xX]
https://ibb.co/vsThT5b]
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both the block and side cover would get machine out and replace the bearing setup.
https://ibb.co/yN0WYSr]
https://ibb.co/g650g8K]
[/URL][/url]
I first had to make couple pillow blocks out of a chuck of round stock aluminum.
https://ibb.co/dGfst75]
https://ibb.co/kXnqr5x]
after making two of them I went back and drilled hole from the top so oil would feed into the bearings.
https://ibb.co/0XgQ3xX]
https://ibb.co/vsThT5b]
both the block and side cover would get machine out and replace the bearing setup.
https://ibb.co/yN0WYSr]
https://ibb.co/g650g8K]
Wow Del Ray you are just blowing my mind lol
Did you drill a hole in the block there to get support and then weld it up?
Such a smart idea
My Blockzillas have bearings for the cam and it makes such a huge difference. Instantly spins to the moon.
Do you mind if I ask what filler wire you are using?
Thanks
Did you drill a hole in the block there to get support and then weld it up?
Such a smart idea
My Blockzillas have bearings for the cam and it makes such a huge difference. Instantly spins to the moon.
Do you mind if I ask what filler wire you are using?
Thanks