Awesome guide to modding Briggs 5 hp flatheads
If you thought their was a chance that the plane your about to get on would crash because it was improperly maintained would you? Airplanes are owned by corporations, strictly maintained by trained people, and made of high grade materials.
The flywheel is cast iron, was probably left for a good amout of time in open air, and ,unless you had a boxed motor, it has seen other owners that may have already abused it to :censure:.
Also a plane crashes, it's headline news. Grenade your flywheel, you probably aren't going to be bragging about it to people..... possibly from your hospital bed or crutches.
A billet flywheel weighs less than the cast iron one. So even if your governor is still on, it will help performance and let you de-govern when ready. But if your running the stock 3400-3600 the original one should be fine and safe.
But this is an opinionated topic. It's all what your willing to risk to save a bill.
The flywheel is cast iron, was probably left for a good amout of time in open air, and ,unless you had a boxed motor, it has seen other owners that may have already abused it to :censure:.
Also a plane crashes, it's headline news. Grenade your flywheel, you probably aren't going to be bragging about it to people..... possibly from your hospital bed or crutches.
A billet flywheel weighs less than the cast iron one. So even if your governor is still on, it will help performance and let you de-govern when ready. But if your running the stock 3400-3600 the original one should be fine and safe.
But this is an opinionated topic. It's all what your willing to risk to save a bill.
Unless you intend on running at something above 10,000rpm, you're wasting your money.
There is no risk.
Search it out (the "risk") before laying out the $$$.
Valves will float or rod will let go long before the FW lets go.
Briggs flywheel explosion
There is no risk.
Search it out (the "risk") before laying out the $$$.
Valves will float or rod will let go long before the FW lets go.
Briggs flywheel explosion
Thought I would chime in on a cool build on the 5hp flatheads. A couple things i would do on a stocker to hop it up on the cheap is to start off with putting an offset key to advance the timing usually a #5-7 key works the best on pump gas, also if you have a pipe on your Briggs i would buy a Exhaust port reducer to put in the exhaust port, this will really torque up the engine, also a copper head gasket in the .030" range will hop it up, but don't go to thin as this will hurt air flow.. A good 4 angle valve job on the intake always helps 30* seat, 15* topcut along with a 45* cut under the 30* seat and try to keep that the same width on the 45 followed buy a 60*. Along with a 15* backcut on the intake valve. The exhaust seems to like a 3 angle with a 45* seat and 30* top cut and a 60* throat. I would still use the stock cam but recomend at least a good billet rod. Even with a stock carb on pump gas this will make in the 7-8 hp range on my dyno, great for a cruiser mini bike :thumbsup: Adding a small cam, lifters and springs will get you in to the 10hp range.. Plus a little port work will help, just breaking the edges and radiusing the short turn will do wonders.. Hope that helps..
Dustin Lee
Dustin Lee
Here is another way you can help out a briggs (or any engine).
Crank case evacuation via the exhaust:
pulls a vacuum on the crank case and improves ring seal plus no re-burning the blowby. Works best with an open header but still does the job with a muffler.
I just bent up a piece of steel brake line, cut the one end off at 45 degrees, drilled a hole in the header and welded the tube in so that the end is about in the middle of the header. Normally you'd run a check valve as well but i wasn't too worried about that in this case.
More info: Google
Crank case evacuation via the exhaust:
pulls a vacuum on the crank case and improves ring seal plus no re-burning the blowby. Works best with an open header but still does the job with a muffler.
I just bent up a piece of steel brake line, cut the one end off at 45 degrees, drilled a hole in the header and welded the tube in so that the end is about in the middle of the header. Normally you'd run a check valve as well but i wasn't too worried about that in this case.
More info: Google
this idea intrigued me has anyone tried it with successful results on a briggs?
That is true on the 2.5hp to 3.75hp Briggs motors, but I don't think that goes for the 5hp. I am going to be removing the gov on a few of my 5hp Briggs and I am going to spend the cash to get the billet aluminum flywheels for them because even if I don't mind risking a flywheel grenading, I sure as hell don't want to risk it grenading if a friend of family member is riding my bike. :thumbsup:
I know most of this stuff applies to the smaller flats as well (3hp) how about the cam grind, I just got off the phone with dymocams and I am going to send it out just don't want to spend the money if it's not the right grind. Got a few more questions in my thread here if anyone has some imput. http://www.oldminibikes.com/forum/briggs-stratton-engines/74156-building-up-3-hp-briggs.html
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briggs project
nice posting ...building me three at once all 5hp briggs flat heads an im to the point of the carb set up an i really hate the stock carb (with the tank on bottom) so what after market advice u got or u ever set up something different on the briggs ...
p.s. i took the carb off my kx 80 2 stroke dirt bike put it on with a mikuni fuel pump it fired an revved up top end revving pops an misfires?????
nice posting ...building me three at once all 5hp briggs flat heads an im to the point of the carb set up an i really hate the stock carb (with the tank on bottom) so what after market advice u got or u ever set up something different on the briggs ...
p.s. i took the carb off my kx 80 2 stroke dirt bike put it on with a mikuni fuel pump it fired an revved up top end revving pops an misfires?????
It worked well on the flathead in that pic (which will return once my server is fixed), It does need a check valve though.
I haven't put it back on with the nasty Raptor 3 i just built though, i decided to build something a little more stylish to go with it. :thumbsup:
FWIW, i use the same setup on my drag car and it works well on it.
