briggs mod questions

ok guys im new to modding lawn tractors. my background is in trucks so I have three questions to begin.
1)if i take the governor off will i need forged or billit internals.
2)if i do need them where is the best/cheapest place to get them
3) if i have a 12.5 briggs model 28 can i put a 13 hp briggs model 28 crank in to ''stroke it out''
thanks in advanced for replys

Moved your topic to the appropriate section of the forum. My answers to the questions:

1. I would say no in general. The engine is typically not going to rev beyond the speed that is likely to cause destruction of stock internals. My friends and I run 5 tractors without governors, and have had almost no engine problems.

2. See #1

3. No idea, but depending on what you are trying to do, you most likely will not need to do this kind of mod. With the proper gearing (geared tranny + pulley swap etc), a 12.5 HP Briggs is enough engine to easily get to 40+ Mph, plow through mud, climb trails and hills, or have enough power to do some amateur pulling, etc. I run a 16.5HP opposed twin, but not because I really need the extra power, just because it was available and I like the way oppys sound. My tractor does 45Mph and has plenty of power to run in the woods / mud.

thanks on 1&2 and i would want to stroke it for more torque and when i build for torque i go overboard hehehe and i may want to use a bigger head for more flow then stroke it to bring the compression back up

TheRainbowBoxer wrote:

Moved your topic to the appropriate section of the forum.  My answers to the questions:

1.  I would say no in general.  The engine is typically not going to rev beyond the speed that is likely to cause destruction of stock internals.  My friends and I run 5 tractors without governors, and have had almost no engine problems.

2.  See #1

3.  No idea, but depending on what you are trying to do, you most likely will not need to do this kind of mod.  With the proper gearing (geared tranny + pulley swap etc), a 12.5 HP Briggs is enough engine to easily get to 40+ Mph, plow through mud, climb trails and hills, or have enough power to do some amateur pulling, etc.   I run a 16.5HP opposed twin, but not because I really need the extra power, just because it was available and I like the way oppys sound.  My tractor does 45Mph and has plenty of power to run in the woods / mud.

Have you and your buddies ever rev the engines way out? like as far as they can go? My friend does that but never holds it at that rpm, I was wondering if a twin could do that.

and oh does anyone know of any cams compatible with the briggs 12.5 hp that will boost power

We've had 10hp tecs, 11-12hp flattie briggs, 14.5hp OHV briggs, opposed twins, and a v-twin briggs. All have been rev'ed, but not held there. One 12hp flattie we rev'ed full bore, for 45 min! Took that long to run out of oil and lock up... It was smoking and due for replacement.

Flatties did good, tecs would pop a rod sometimes, stock opposed don't seem to rev that high, v-twin revs high. 14.5 ohv briggs would blow smoke if reved too high, and tended to foul plugs.

Stretch44875 wrote:

We've had 10hp tecs, 11-12hp flattie briggs, 14.5hp OHV briggs, opposed twins, and a v-twin briggs.  All have been rev'ed, but not held there.  One 12hp flattie we rev'ed full bore, for 45 min!  Took that long to run out of oil and lock up... It was smoking and due for replacement.

Flatties did good, tecs would pop a rod sometimes, stock opposed don't seem to rev that high, v-twin revs high.  14.5 ohv briggs would blow smoke if reved too high, and tended to foul plugs.

 
WOW, you almost know too much!

LAWN MOWER MUDDER wrote:

Stretch44875 wrote:

We've had 10hp tecs, 11-12hp flattie briggs, 14.5hp OHV briggs, opposed twins, and a v-twin briggs.  All have been rev'ed, but not held there.  One 12hp flattie we rev'ed full bore, for 45 min!  Took that long to run out of oil and lock up... It was smoking and due for replacement.

Flatties did good, tecs would pop a rod sometimes, stock opposed don't seem to rev that high, v-twin revs high.  14.5 ohv briggs would blow smoke if reved too high, and tended to foul plugs.

 
WOW, you almost know too much!

Now that's called experience lol.

mudcrazy wrote:

ok guys im new to modding lawn tractors. my background is in trucks so I have three questions to begin.
1)if i take the governor off will i need forged or billit internals.
2)if i do need them where is the best/cheapest place to get them
3) if i have a 12.5 briggs model 28 can i put a 13 hp briggs model 28 crank in to ''stroke it out''
thanks in advanced for replys

If you want to build one helluva a motor. The first thing I would recommend would be a billet flywheel and rod. Also. is your crank have a nut or a bolt holding the flywheel on? The crank with the nut tend to be stronger. After you get your billet flywheel and rod, you can safely rev your motor to the moon. BUT. that will not make a difference.. that makes it safe. Stretch is one of the lucky ones to never encounter a flywheel go..  I watched one go on a puller when I was younger.. it made one hell of a boom and scared the crap out of me. Another issue is the counterweights on these motors, ARC makes brass ones. ARCracing.com
If your not worried about safety. (not recommended, but do-able) The first thing I would do is a good port and polish job.. It doesnt not require much money. very little actually. If you have the right tools its easy but you dont need them. There are many guides out there. try one!
Next your going to want remove all the carbon off of the piston, valves, head, and give your flathead a nice place to area to flow .
After your get your basics done, your going to want to get a cam. There are many out there, research is key. Alot of places you can talk to and they will tell you what you need. DO NOT SHAVE THE HEAD! Flow is key. Not Compression. another thing is always run the motor with the shroud on. A cool motor is a happy motor!
When you start cranking on a motor and really get heavy into the high rpms, youll notice you will no longer be making any more power.. 90% of the time its because your valves are doing something called floating.. Basically the valves springs are not fast enough for the motor. This is when you start to make power. Dual Valve springs are a nice touch to get power out of these motors.  
Both ECcarburetors.com and arcracing.com carry these.
While we are on the carb subject. The walbro carbs on these are not the best carbs but definately can be made one! or you can buy one at EC pre built.
I know this is all over the place but im sorry lol.
I also know lots of people like to put ohv rods in these because they are said to take rpms better... I believe you should go billet if you can.
So heres a good list for you.
To start,
Port / Polish
Clean carbon.
Oil change to synthetic.
Copper Headgasket and full gasket set..
ARC Flywheel, Rod, and counter weights
Air filter Velocity Stack adaptor EC sells this
Dual Valve Springs and Billet Retainers
Stainless Steel valves
Billet Lifters Do these together if you can. Saves a lot of work
Camshaft
Carb
Have it bored .30 over making it a 31ci have it resleeved too
Depends on every motor but you might want to play with timing.


This otta have you a really strong motor.. and of course there is alot of other stuff you can do after this but this will get you moving fast.
No offense stretch but anyone and hold a motor wide open and watch it... That shows me nothing.

you can also get a scattershield for it to do the same. if you must.

69Huffy wrote:

you can also get a scattershield for it to do the same. if you must.

You can! The scattershield is a great addition if you must run a stock flywheel. Although these dont guarrentee. They certainly help the thought!
They are available at g-team.us (copy and paste it into your browser, for some reason it wont hyperlink) !!!

is there any other flywheel that will fit that is stronger or is there a way to make the stock one a bit stonger/ also is there a way to increase flow and compression or is it a you have to choose deal. plus would a cam from a bigger briggs have a higher lift that will fit and how do i play with the timing im planning on running 93 w/octane booster so im not worried about blowing the motor that way. sorry for all the questions im kinda new to mower modding fixed em all my life but never modded them.

mudcrazy wrote:

is there any other flywheel that will fit that is stronger or is there a way to make the stock one a bit stonger/ also is there a way to increase flow and compression or is it a you have to choose deal. plus would a cam from a bigger briggs have a higher lift that will fit and how do i play with the timing im planning on running 93 w/octane booster so im not worried about blowing the motor that way. sorry for all the questions im kinda new to mower modding fixed em all my life but never modded them.

Running 93 octane with booster is not going to make a difference.
lower octane burns faster in the cylinder and less evenly. Until your motor is modded, you will be fine on just 93 octane.
Fuel has nothing to do with blowin a motor how your thinking.
as far as I know there is no stock briggs cam that fits these besides the original.
The flywheel question.. DO NOT MODIFY YOUR STOCK FLYWHEEL. Leave it alone. These are cast iron and weigh about 15 lbs or so. Def dont want to f with it. No other flywheel will be safe..
look at the scattershields they are cheap and you could easily make your own out of some heavy gauged steel.
With these either go stock w/ scattershield or go safe with billet.
Timing is adjusted with flywheel offset keys. They are fairly cheap like 3-4 bucks. the flywheel is on a key way and all you do is pull fly wheel and swap keys to advance or retard the timing. Always use a proper flywheel puller too. Prying can cause microscopic cracks and weaken it.

What kind of build are you doing? Trail rig? Lifted? Mud? Race?

its going to be a mix high enough to go trail riding and fast enough to be a showoff street mower. i also want to find a way to put shocks on the front for stabilazation and more flex for trails.

and im going to get a scatter shield and renforce it i cant afford the flywheel yet so im just doing valvetrian rod and carb prob a cheap exhaust and pullys

Okay sounds good.. you can get away without carb.. just takes some fine tuning. Valve train.. you can also save your stock lifters until you get a cam.. Be sure to do the port polish job!!! Its definately worth it

i run 18" tires and i hot around 18mph top and am slow enough to mud or even crawl in first. if i put bigger tires it would be faster obviously

can i just switch the front and back pullys

thats all i did to speed up. engine is completely stock

Note: The response below is in no way intended to belittle anyone's views on the subject. No offense intended and take the advice and information for precisely the amount you paid for it.

Honestly, until you start messing with double springs, balanced assemblies etc, the engine is not capable of grenading a stock flywheel in good condition. Valve float alone will keep the RPMs in a safe enough range. For liability purposes, B&S (and every other manufacturer) have to test the flywheels at way higher RPMs than the engine is capable. Governors can and do fail, and the manufacturer would be in a world of legal hurt if a flywheel exploded and injured someone. Don't let them scare you... every time someone brings up that they witnessed a flywheel explode, it is on a high performance tuned/modified engine running far higher RPMs than a stock engine is capable.

TheRainbowBoxer wrote:

high performance tuned/modified engine running far higher RPMs than a stock engine is capable.

Don't know what you missed on that... HE WANTS A HIGH PERFORMANCE ENGINE... Dual valve springs stop valve float dramatically... but what would I know... Allowing him to go beyond the standard stopping point.. Nothing sounds worst than a motor revved to the point where the valves are floating... It sounds like shiit.. I assumed he knew about removing the govenor properly considering he was willing to jump into a project like this..
I understand what ur saying.. A stock motor's chance of exploding a flywheel are slim.. but.. he doesnt want a stock motor..

I am currently building up my oppy for high horsepower but I will not remove the governor for this very fact I dont want to be going 45 down the road have the engine at high rpm and have the flywheel explode on me so its just easier to leave the governor

im going to take the governor off then when i put more performance ie more than a port and polish and exhaust/intake stack in it down the road (prob december) im going to put a shield on it and save up for a flywheel. if it does explode that way ill at least have a shield so i dont get castrated... 

mudcrazy wrote:

im going to take the governor off then when i put more performance ie more than a port and polish and exhaust/intake stack in it down the road (prob december) im going to put a shield on it and save up for a flywheel. if it does explode that way ill at least have a shield so i dont get castrated... 

Yes you can have a shield to protect you but it can and  will destroy an engine so be very careful with this I would just say start saving up for an aluminum flywheel its cheap insurance