Briggs Flathead Mods and aftermarket carb

[Thepartsguy]

Ok thanks for the measurements, would a 3hp flywheel be a safe replacement for the 5hp flywheel? If not where can i find a cast aluminum one.

You need arc‘s drop bracket to make the 3hp flywheel work. 3hp flywheels cost more on arcs sight then 5hp’s I’m pretty sure..

 

[Rat]

Ok thanks for the measurements, would a 3hp flywheel be a safe replacement for the 5hp flywheel? If not where can i find a cast aluminum one.

Ebay most likely, but if you can go billet do so because it's even better than just being aluminum.

I dont think its safe to remove the governor until i have a flywheel that can withstand the extra rpm.

It's a matter of opinion really. First of all the valve orientation prevents the possibility of floating a valve hard enough to jump a rod and having the crank punch it through...because THERE ARE NO PUSHRODS in a flathead. The lifters hit the valve stems directly.

You also don't have to worry about a rod letting go and getting hammered through the chamber either.

What YOU DO Have to worry about most with a Briggs is the oil dipper snapping off which it usually does in the range of 5500 iirc. That will eat the engine internals not just because you've effectively got a razorblade ratting around in the oil, but also because the oil isn't getting flung around anymore. Not properly anyhow.

They make nylon ones which don't do any damage when the break off, but you still lose lubrication when it does let go.
The Briggs Raptor uses a rod like an OHV/OHC has where the oil slinger is part of the rod cap casting... that's what you want if taking the governor out.

 

[Scrambler]

Ya I've heard about those rods, but tbh I'm more worried about the flywheel than the rod, I've heard many people say that the cast iron ones can explode at ungoverned rmps And the shrapnel can go through your back like a frag grenade, or mabey some people are over exaggerating idk. Anyway I will keep a lookout for a aluminum flywheel and if I can't find one I'll have to fork out 150 for a billet.

 

[Rat]

Ya I've heard about those rods, but tbh I'm more worried about the flywheel than the rod, I've heard many people say that the cast iron ones can explode at ungoverned rmps And the shrapnel can go through your back like a frag grenade, or mabey some people are over exaggerating idk. Anyway I will keep a lookout for a aluminum flywheel and if I can't find one I'll have to fork out 150 for a billet.

Exaggeration... not so much.
Realistic threat to you... probably not.

The fact is you'd need to be able consistently turn 6k to be in any real danger.

I say 6k because of tachometer inaccuracies, and the fact that even an OHV needs work to even have a chance to turn faster than 4800.

The thing is no one can tell you exactly what rpm is most dangerous because ot comes down to casting imperfections, harmonics, and contaminants at the time the cast was poured, all at the microscopic level.

Some flywheels have been known to frag at only 4500, where most are good for 5500, then there's others that are an anomaly by turning 6500 regularly without failing.

You aren't likely to turn more than 5k on an old Briggs flywheel, especially not like the one I have where the fan is cast with the flywheel and the ignition magnets are set in aluminum and held to the the flywheel with roll pins... easily a 10lb iron flywheel.

 

[Thepartsguy]

I had a governor deleted 5hp with some backyard mods but I geared it 10t 60t and it had soooo much torque. I would rev it up till just that point it COULD break the rod. But I must of only been doing 23mph it was the slowest thing ever but again the torque was different i‘m used to speed and almost zero off the line.

 

[panchothedog]

Are you really in love with that old engine, or just using it because it is what you have? My reason for asking is because the modifications and list of new parts you will be buying might very well add up to as much as a new overhead valve engine, capable of a lot more horsepower. If you have a soft spot for the old iron
that's totally understandable. Just trying to point out some economic facts.

 

[Rat]

Are you really in love with that old engine, or just using it because it is what you have? My reason for asking is because the modifications and list of new parts you will be buying might very well add up to as much as a new overhead valve engine, capable of a lot more horsepower. If you have a soft spot for the old iron
that's totally understandable. Just trying to point out some economic facts.

That's mostly what made me back off doing anything the B&S I have. Like yeah it does run, but it needs a head gasket and crank seals at the least.
I find that a Flatty has a unique and angry exhaust note when straight piped that really can't be replicated by any other engine... even as a free engine it's not worth what it needs to make so little power for its given displacement and weight (which is 70% all flywheel weight)

 

[Scrambler]

Are you really in love with that old engine, or just using it because it is what you have? My reason for asking is because the modifications and list of new parts you will be buying might very well add up to as much as a new overhead valve engine, capable of a lot more horsepower. If you have a soft spot for the old iron
that's totally understandable. Just trying to point out some economic facts.

im using it right now becuase its all i have at the moment, and i really like briggs engines. However, i am considering going to harbor freight and getting a predator 212 for 120 bucks. A billet flywheel for the Briggs is probably around the same price as a brand new 212 which i know has tons more available mods for. Are the 212 flywheels stronger or not?

 

[Thepartsguy]

Are the 212 flywheels stronger or not?

1000% weaker then a briggs flywheel. I have run a few ungoverned Briggs 3-8hp engines.

The 212cc they just put a dab of glue on the magnet and then press/hold or to the flywheel till the glue dries.

Going ungoverned on a 212cc is actually less of an option than an ungoverned briggs 5hp...

You can find whole split 212cc flywheels on YouTube.. The one guys flywheel shrapnel was only stopped by the backing of the seat padding in that one YouTube video of a 212cc flywheel explosion.

 

[Rat]

1000% weaker then a briggs flywheel. I have run a few ungoverned Briggs 3-8hp engines.

The 212cc they just put a dab of glue on the magnet and then press/hold or to the flywheel till the glue dries.

Going ungoverned on a 212cc is actually less of an option than an ungoverned briggs 5hp...

You can find whole split 212cc flywheels on YouTube.. The one guys flywheel shrapnel was only stopped by the backing of the seat padding in that one YouTube video of a 212cc flywheel explosion.

True but the upside is that there are more aftermarket flywheel options than there is for an old flatty.

Getting that flathead to spin that heavy a$s flywheel fast enough to frag out is not even likely.
It's not impossible but you'd have to put stupid money into upgrades to get it there because as mentioned the conrod is more prone to fail than anything else.

 

[Thepartsguy]

True but the upside is that there are more aftermarket flywheel options than there is for an old flatty.

Getting that flathead to spin that heavy a$s flywheel fast enough to frag out is not even likely.
It's not impossible but you'd have to put stupid money into upgrades to get it there because as mentioned the conrod is more prone to fail than anything else.

There selling Mike clements flathead 5hp Briggs flywheels for about $65 shipped on the forums.

 

[Rat]

There selling Mike clements flathead 5hp Briggs flywheels for about $65 shipped on the forums.

Speakin greek guy... I'm not into B&S like that

 

[Scrambler]

Exaggeration... not so much.
Realistic threat to you... probably not.

The fact is you'd need to be able consistently turn 6k to be in any real danger.

I say 6k because of tachometer inaccuracies, and the fact that even an OHV needs work to even have a chance to turn faster than 4800.

The thing is no one can tell you exactly what rpm is most dangerous because ot comes down to casting imperfections, harmonics, and contaminants at the time the cast was poured, all at the microscopic level.

Some flywheels have been known to frag at only 4500, where most are good for 5500, then there's others that are an anomaly by turning 6500 regularly without failing.

You aren't likely to turn more than 5k on an old Briggs flywheel, especially not like the one I have where the fan is cast with the flywheel and the ignition magnets are set in aluminum and held to the the flywheel with roll pins... easily a 10lb iron flywheel.

so do you think it would frag if i just put a 22mm flat slide carb on? It is the kind with the fins cast into the wheel. I believe you when you say it weighs 10 lbs., that engine is HEAVY for its size. That's probably all i will do, maybe with a thinner copper head gasket.

 

[Scrambler]

i can always mount a thicker metal plate on the front of the sidecover just incase.

 

[Rat]

so do you think it would frag if i just put a 22mm flat slide carb on? It is the kind with the fins cast into the wheel. I believe you when you say it weighs 10 lbs., that engine is HEAVY for its size. That's probably all i will do, maybe with a thinner copper head gasket.

I wouldn't go with a 22, a 20 sure. Odds are the Pz19 was flooding because it was too small.

A carb that is too small will tend to flood, be rich and hard to lean out because the negative intake pressure will be too high and relieve itself by any means necessary.

A carb that is too large is the same but in reverse, it will be too lean and hard to tune because the negative intake pressure will struggle to draw any fuel at all.