GAB Version CHEAP.0 Tecumseh OHH50 172cc 5HP

[bob58o]

OHH50 68025F

http://www.jackssmallengines.com/ja...cumseh/4-cycle-horizontal/ohh-50/ohh50-68025f

Carb stuff. Main jet is also Bowl Nut. Pretty Easy.
http://outdoorpowerinfo.com/repairs/tecumseh_carb_640017.asp


Gov removal. Free

Port n Polish. Free

Air Intake. Free

Carb Jetting. Free

Exhaust. $15

- 2x http://www.homedepot.com/p/3-4-in-R...Mm2H68uB2P-iDNXEf-LykaAsk18P8HAQ&gclsrc=aw.ds

- 2x http://www.homedepot.com/p/3-4-in-Rigid-Conduit-Coupling-64007/100164200

Head Gasket. Diagram no 119 part # 36738 or #36626 $6.50
http://www.ebay.com/itm/NOS-Tecumse...hash=item5889e5e62c:m:mmjRlKlbVLxTYntC-qa6Xrw
^works for ohh50 and ohh55

Side Cover Gasket. Diagram no. 69 part #36624 $4.50
http://www.ebay.com/itm/Genuine-Tec...418888?hash=item41aee99908:g:jHEAAOSwNuxXaU5g


Billet Con Rod (Not for this Build, But for anyone who might want one)
Maybe this is the right one. Hunter at ARC says as far as he knows it works with OHH50
$60

http://www.arcracing.com/6282-arc-billet-rod-tecumseh-5-5-ohv-3-484/

 

[bob58o]

Maybe I'll sell it.

 

[Hellion]

But we know so little about them. Keep it, I say.

What, no photos of the port and polish or the rest of the surgery? I feel cheated.

 

[chancer]

I don't know who you are but you are doing the GAB an injustice.
If it were really Bob,
There would be links,
Chamber CC measurements,
Cam cards,
Plug readings,
HP to Weight ratios,
Phone numbers with first names of "cool" guys from random Tecumseh dealerships.
Parts and tools recently purchased.
and then
and then
and then
and then.

 

[bob58o]

The Exhausting Exhaust Flange and Header

I was going to surprise everybody tomorrow with a custom made exhaust.

I have flat stock left over from mounting the post for the band brake on the buggy.

This will become my exhaust flange. It seems perfectly sized (1.25" by maybe 2.25").
I'll drill some holes for some bolts. I'll drill a hole for the exhaust pipe.
I bought 3/4 conduit which has an ID of ~7/8".
I got some 6" straight and some 90 degrees bends.
I got some Couplers.
The muffler that came with my 212 kit fits the threads as well.


So since you wanted some GAB....
7/8" ID pipe give cross sectional area of

r=0.875/2 = 0.4375"
c/s Area = pi*r^2 = 3.14*0.4375^2 = 0.60132 sq inches

c/s Area = Engine Cubic Inches * RPM / 88,200

172cc = 10.5 cubic inches

0.60132 = 10.5 * RPM / 88,200

RPM = (0.60132*88,200) / 10.5 = 5,050

I'll design this exhaust for this engine and the TS-500 minibike.
I really just want to try a DIY exhaust. I could of bought one for 25 bucks, but wasn't sure the fit.

I'll post some pics soon.

 

[bob58o]

I didn't do anything yet but take the air box and exhaust off.

The exhaust flange needs to have holes for 1/4 - 20 bolts (3/8" long). These are spaced 1 9/16" apart.

EDIT: SHOULD BE 1.50" APRART!!

Going to attempt to drill 3 holes.
2@ 1/4"
1~7/8"

 

[bob58o]

Bobertson gab tube

22-23" w/o optional screw on muffler.

Not set yet. Need to cut some.

But you're beginning to see it, right?

I know. It's awesome!

 

[bob58o]

Maybe like this but I think I like the first one better,

 

[bob58o]

Here's a link to another exhaust header design page.
http://garage.grumpysperformance.com/index.php?threads/calculating-header-design.185/

It gives a simplified, but informative, explanation of how Tube diameter is used to set the RPM where you want a TQ boost and Tube length is used to rock the TQ Curve.

Longer tube means more area under peak torque RPM, but falls off more rapidly above peak torque. Better for lower RPM.

Shorter tube means TQ falls off less rapidly after peak TQ, but less area under peak torque RPM. Better for Higher RPM.

Every time I try a Header Length Calculator I get something like 43 -48"

Like from here
https://bigrockets.wordpress.com/2012/01/29/450/

ED = 180 + [degrees BBDC that the Ex Valve opens (0.050")]
guessing 210 - 220 for this engine. We will use 215

850 * 215 = 182,750

Now divide by RPM....

If peak torque is 2750 then
182,750 / 2750 = 66.4

66.4 - 3 = TOO MANY INCHES

If tuning for 4800 RPM then...
182,750 / 4800 = 38
38 - 3 = 35"

If trying to tune for 5050 RPM (same as what DIA is tuned for) then....

182,750 / 5050 = 36.2
36.2 - 3 = 33.2"



My 23" Tube (now working in reverse)....
23 +3 = 26
182,750 / 26 = 7,025


So the basic idea is that the DIAMETER will give a TQ boost at 5,050 RPM.
Peak TQ will still probably be below 3000 RPM, but this exhaust may shift peak TQ a bit towards higher RPM.

Since an Exhaust length designed to give TQ boost at engine peak TQ RPM would be 3.5 - 4' long, the idea behind the relatively short tube is that shorter tubes rock the TQ curve to give more area under the curve above Peak TQ RPM. So even if Peak TQ is at 3000 RPM, the short tube will keep it from falling off as aggressively as it would with a longer tube.
It will however cause TQ to drop on all RPMs approaching Peak TQ (as opposed to a longer tube).

 

[bob58o]

Stock air box.

 

[bob58o]

I like the design. A hole in the fan shroud blows air into opening in the air box.

From here...

 

[bob58o]

Into here...

 

[bob58o]

These holes could be much bigger.

You can see one square hole. There are two. Both same size.

Also there is a cold weather choke plate.
You can move it to block the intake.

 

[bob58o]

The filter has oil from the first day I rode it.

 

[bob58o]

The rest of the air box...

 

[bob58o]

Intake manifold, carb, and and stock muffler.

 

[bob58o]

I don't know who you are but you are doing the GAB an injustice.
If it were really Bob,
There would be links,
Chamber CC measurements,
Cam cards,
Plug readings,
HP to Weight ratios,
Phone numbers with first names of "cool" guys from random Tecumseh dealerships.
Parts and tools recently purchased.
and then
and then
and then
and then.

Fixed that for ya.
Added some info to first post.

Also decided to buy the Air Filter Adapter and Air Filter. Was going to mod the stock box and make a new filter out of socks and Air Conditioner Prefilter, but I like the look the the K&N style.


Measured to be sure 1 3/8" apart.
http://www.bmikarts.com/Air-Filter-adapter-for-Tecumseh-Briggs-OHV-Engine_p_463.html

http://www.bmikarts.com/Straight-Fabric-Air-Filter-2-716-Inlet-x-4-Tall_p_454.html

Let's see how much this filter gets in my way.

I may end up selling this whole bike complete with engine and use the money to get the

NITRO 909 ROLLER and some of the parts I need to put my 212 on it????
http://909minibikes.com/products/nitro-44-drag-bike-roller

Hhhmmmmm????

 

[chancer]

GAB Nation!!!!
Cool that is more like it.

I like the first exhaust down the middle up and over the fender.
Also the Ram air is a cool idea.
FR and a couple guys always talk about adding a Leaf blower or smog pump.
That is such a simple design idea to take forced air off the Cooling fan and Shroud.

But Like you did; Forget it the K&N style looks Cool.

 

[Hellion]

...I like the first exhaust down the middle up and over the fender.

Ditto, very artsy looking. I'd like to see it wrapped in 1" titanium header wrap (must be the hottest color these days).

 

[bob58o]

So exhaust Trial 1 did not work.

My 1/8" flange attempt didn't work so great.

Welding the Galvanized steel from the Rigid Conduit to the plate wasn't easy for me. I suck at welding.

I drilled holes 1 9/16" inches apart. That is what most of BMI's Tec's Pipes were labeled???
Ebay had a bunch labeled at 1.5".

I need 1.5".

---------- Post added at 01:52 PM ---------- Previous post was at 01:39 PM ----------

My new exhaust flange will be different!!!!!

Thicker and threaded.

3" x 3" square washer.
0.25" thick
0.938" ID (for 7/8" bolt)

http://www.mcmaster.com/#standard-washers/=13p264d
I picked this washer specifically because it was drilled to 15/16".
I needed (wanted) bigger than 2x2", so this galvanized 3x3" one was only option.


15/16" is an alternate pilot bit size to 59/64" which is the recommended size for 3/4" - 14 NPT Pipe Tap.

I don't have either size bit, so I got a washer already drilled.

Now my first new Toy for this project!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
http://www.harborfreight.com/6-piece-pipe-taps-42432.html
6 piece pipe taps!

I asked when the next 20% sale was and the girl just gave me 20% off. One of the benefits of going there every day!!!!!
$36 not to shabby!!

I will have 3.5 threads of tapered pipe thread holding the exhaust?????

Pics to come after I drill the 1.5" spaced holes for 1/4" bolts (studs maybe)