Rebuilding a 3HP Briggs *Photos*

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Tommy2

Member
#1
#1
I found this engine on my property after I bought it. It was on a water pump and turns over. The tank is pretty nasty inside, but no holes. Just want to rebuild it for fun... Not really worried about the lack of cost effectiveness that comes with restoring an old engine.

Numbers on the side cover: 80232 0379-01 76051703

I'm thinking of building it for a small mini bike. My plan is to clean/sandblast/sodablast everything and put in new rings, electronic ignition, and maybe different carb/tank, new rings, lap the valves, etc.

Questions:
1: Does anyone know the part # for the electronic coil? I don't want to use points.
2: Will this carb be OK for a mini bike? The throttle linkage will need to be rigged up somehow with a return spring. I've also considered a different carb/intake design with an intergrated float bowl so I can run a separate tank. Is there an intake/carb I can buy that would bolt right on this?
3: What is the best way to hone the engine? It still has some crosshatch showing. I don't want to use anything too rough. Ball or stone hone? What grit and size?
4: I plan to remove the governor. Any concerns with this?
5: Should I attempt to port the intake/exhaust ports in the head?
6: Any ideas for the exhaust? Is a straight pipe ok?
7: Should I upgrade the valve springs?

Sorry for all the questions.. Just thinking outloud and thankful for any suggestions!


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Minimichael

Minimichael

Well-Known Member
#2
#2
Ball or stone depends on whether the bore is aluminum or iron and whether you're reaching for an oversized piston size, or just wanting fresh hash marks. I understand oversized chrome rings could be your most efficient upgrade here.

That carb will work, and yes you'll have to configure a springy linkage of some sort. Shouldn't be hard. That tank could prove too large for certain mini frames, but I'd say keep things stock for now.

Straight pipe will be loud. The bigger, stock hot dog muffler for 5hp sounds way better.

I'd leave the governor for now, and instead learn how to adjust and work with it.

Electronic coils are easy to find — for 5hp. Check B&S manuals here, and then check eBay.
 
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T

Tommy2

Member
#3
#3
Minimichael said:
Ball or stone depends on whether the bore is aluminum or iron and whether you're reaching for an oversized piston size. I understand oversized chrome rings could be your most efficient upgrade here.

That carb will work, and yes you'll have to configure a springy linkage of some sort. Shouldn't be hard. That tank could prove too large for certain mini frames, but I'd say keep things stock for now.

Electronic coils are easy to find — for 5hp. Check B&S manuals here, and then check eBay.
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Appreciate it. I don't plan to bore out the block/jug and am intending to use the original piston with NOS Briggs rings.

The bore is aluminum. No iron sleeve.

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VeritableFox

VeritableFox

Active Member
#6
#6
1: Does anyone know the part # for the electronic coil? I don't want to use points.

Another method that can be used is to install a NOVA electronic ignition system. It lets you keep the original style coil while just removing the points guts. Did this with my Tec HM80. Granted the HM80 is a bit trickier since the coil is under the flywheel with the points on that engine.

2: Will this carb be OK for a mini bike? The throttle linkage will need to be rigged up somehow with a return spring. I've also considered a different carb/intake design with an intergrated float bowl so I can run a separate tank. Is there an intake/carb I can buy that would bolt right on this?

The carb on it is a diaphragm carb and is honestly a better carb style as it removes the issues a bowl carb has with overflowing. Not to mention it's built to work with that gas tank. There should be rebuild kits available for it. Also, using the carb the engine came with tends to make it easier to get running again. The ungodly amount of testing and number of spark plugs I've fouled out tuning my Chikuni to an HM80 and Briggs 5hp would probably frustrate a lot of people into just giving up.

3: What is the best way to hone the engine? It still has some crosshatch showing. I don't want to use anything too rough. Ball or stone hone? What grit and size?

Ball or adjustable deglazer. If you're just looking to get the crosshatch back then I like the deglazer personally. Less likely to oversize it and get a good hone back on the cylinder with a quick 5-10 second run at it.

4: I plan to remove the governor. Any concerns with this?

Yea, with no billet rod or flywheel it's pretty easy to rev them up into the danger zone. There is billet flywheels made for the 3hp though. Otherwise, get a cheap tach and try not to take it over 5k RPM. Having talked with an old timer that used to test the flywheels in Briggs engines, they used to spin up the flywheels to 5500 RPM in a destruction test for 30 seconds. If it exploded, or shook beyond a certain tolerance limit it wasn't put on an engine according to him. However, it's hard to tell how much age will do to a flywheel as it gathers rust pitting and loses its manufactured balance.

Personally, I'd leave the little guy governed. It can probably still get up to street speeds with the right gearing.

5: Should I attempt to port the intake/exhaust ports in the head?

At most, polish the exhaust and clean up the casting imperfections. Porting is really only done when you intend to start dumping lots of flow through the engine. At that point you'd be honing out out to near 5hp piston size and doing mods like shaving the brows for increased flow.

6: Any ideas for the exhaust? Is a straight pipe ok?

Straight pipe works but is basically as loud as just running it open header. If you live in the sticks and no one will really hear it within the 1/2 mile radius it will be audible and you like that sound? Go for it. Otherwise a cheap hotdog or RLV weld on muffler will likely save you from going completely deaf.

7: Should I upgrade the valve springs?

If you're keeping the engine largely stock and governed there is no point to upgrading the valve springs. In fact, increasing the spring rate can actually lead to other issues down the line, like wearing out the lobes on the stock cam really quickly.

Some other thoughts in Briggs engines:

The valve springs themselves tend not to have upper retainers on the flathead models. Buy some upper retainers meant for a Tecumseh, I know they'll work since I recently rebuilt a 5hp Briggs and used them. The reason to do this on the valve springs is so that the spring doesn't wear down the upper part of the chamber, which is incredibly common on Briggs flatheads.

Briggs flatheads have some fairly rough casting on the intake and exhaust. Take a Dremel to the obvious seams. Polish the exhaust with some 300 grit wet/dry but don't bother porting it out. Not sure if the 3hp has it but on the 5hp there is a casting defect on the intake side valve guide that actually catches the intake valve as it moves, it's sanded smooth easily though. You can tell if it has the defect by moving the intake up and down without a spring on it.
 
Harquebus

Harquebus

Well-Known Member
#7
#7
Why do anything to it?

It looks like it has VERY LOW hours on it. All I saw was pics of dirt, carbon staining and a greasy piston. I didn't see a worn out bore or anything grossly amiss. Clean it all up and assess it then. You're overthinking this for an old 3HP Briggs....unless I am missing something.

Did it have low compression? It could need a valve job/valve lap and that's it. Again, the copper color and originality is fabulous, don't go overboard with the sandblast and I-must-tear-it-down-and-recreate-it-in-my-image routine. That copper paint is mint.

Part of the charm is the points ignition but I understand your aversion. It is however pretty reliable on an engine you don't leave outside for 20 years.

If you do want to throw money at a Briggs project, the venerable 5 horse 13 c.i. motor is where you should be focusing.
 
Rick C.

Rick C.

Member
#8
#8
I have the same 3HP Briggs in my Maverick. Same Carb too.
Early today I ordered a carburetor kit for it , just to have one.
Hook it up like mine ( pictures to come if you want. )
Well, when you get the new rings, put it back together. and run it.
She's a peach !
 
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T

Tommy2

Member
#9
#9
VeritableFox said:
1: Does anyone know the part # for the electronic coil? I don't want to use points.

Another method that can be used is to install a NOVA electronic ignition system. It lets you keep the original style coil while just removing the points guts. Did this with my Tec HM80. Granted the HM80 is a bit trickier since the coil is under the flywheel with the points on that engine.

2: Will this carb be OK for a mini bike? The throttle linkage will need to be rigged up somehow with a return spring. I've also considered a different carb/intake design with an intergrated float bowl so I can run a separate tank. Is there an intake/carb I can buy that would bolt right on this?

The carb on it is a diaphragm carb and is honestly a better carb style as it removes the issues a bowl carb has with overflowing. Not to mention it's built to work with that gas tank. There should be rebuild kits available for it. Also, using the carb the engine came with tends to make it easier to get running again. The ungodly amount of testing and number of spark plugs I've fouled out tuning my Chikuni to an HM80 and Briggs 5hp would probably frustrate a lot of people into just giving up.

3: What is the best way to hone the engine? It still has some crosshatch showing. I don't want to use anything too rough. Ball or stone hone? What grit and size?

Ball or adjustable deglazer. If you're just looking to get the crosshatch back then I like the deglazer personally. Less likely to oversize it and get a good hone back on the cylinder with a quick 5-10 second run at it.

4: I plan to remove the governor. Any concerns with this?

Yea, with no billet rod or flywheel it's pretty easy to rev them up into the danger zone. There is billet flywheels made for the 3hp though. Otherwise, get a cheap tach and try not to take it over 5k RPM. Having talked with an old timer that used to test the flywheels in Briggs engines, they used to spin up the flywheels to 5500 RPM in a destruction test for 30 seconds. If it exploded, or shook beyond a certain tolerance limit it wasn't put on an engine according to him. However, it's hard to tell how much age will do to a flywheel as it gathers rust pitting and loses its manufactured balance.

Personally, I'd leave the little guy governed. It can probably still get up to street speeds with the right gearing.

5: Should I attempt to port the intake/exhaust ports in the head?

At most, polish the exhaust and clean up the casting imperfections. Porting is really only done when you intend to start dumping lots of flow through the engine. At that point you'd be honing out out to near 5hp piston size and doing mods like shaving the brows for increased flow.

6: Any ideas for the exhaust? Is a straight pipe ok?

Straight pipe works but is basically as loud as just running it open header. If you live in the sticks and no one will really hear it within the 1/2 mile radius it will be audible and you like that sound? Go for it. Otherwise a cheap hotdog or RLV weld on muffler will likely save you from going completely deaf.

7: Should I upgrade the valve springs?

If you're keeping the engine largely stock and governed there is no point to upgrading the valve springs. In fact, increasing the spring rate can actually lead to other issues down the line, like wearing out the lobes on the stock cam really quickly.

Some other thoughts in Briggs engines:

The valve springs themselves tend not to have upper retainers on the flathead models. Buy some upper retainers meant for a Tecumseh, I know they'll work since I recently rebuilt a 5hp Briggs and used them. The reason to do this on the valve springs is so that the spring doesn't wear down the upper part of the chamber, which is incredibly common on Briggs flatheads.

Briggs flatheads have some fairly rough casting on the intake and exhaust. Take a Dremel to the obvious seams. Polish the exhaust with some 300 grit wet/dry but don't bother porting it out. Not sure if the 3hp has it but on the 5hp there is a casting defect on the intake side valve guide that actually catches the intake valve as it moves, it's sanded smooth easily though. You can tell if it has the defect by moving the intake up and down without a spring on it.
Click to expand...
Thank you so much for taking the time to reply and answer all the questions I had!

Looks like that billet flywheel is about $175. https://www.arcracing.com/6605-arc-billet-flywheel-briggs-3hp-flathead-2-75lbs/

That's pretty steep. However, if that would make running without a governor safer, maybe it's worth ordering? If I ran that flywheel and stiffer springs, would it be safer to turn higher RPMs?
 
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T

Tommy2

Member
#10
#10
Harquebus said:
Why do anything to it?

It looks like it has VERY LOW hours on it. All I saw was pics of dirt, carbon staining and a greasy piston. I didn't see a worn out bore or anything grossly amiss. Clean it all up and assess it then. You're overthinking this for an old 3HP Briggs....unless I am missing something.

Did it have low compression? It could need a valve job/valve lap and that's it. Again, the copper color and originality is fabulous, don't go overboard with the sandblast and I-must-tear-it-down-and-recreate-it-in-my-image routine. That copper paint is mint.

Part of the charm is the points ignition but I understand your aversion. It is however pretty reliable on an engine you don't leave outside for 20 years.

If you do want to throw money at a Briggs project, the venerable 5 horse 13 c.i. motor is where you should be focusing.
Click to expand...
Yea, nothing about what I'm doing makes any sense financially...I don't really care about that. I'm not worried about throwing a few hundred into this project, just for the fun of it. But I also don't want to make the project too aggravating, so retaining the original carb and tank will probably be the way to go.

The engine isn't too bad, but the carbon on the head makes it look like it had some hours on it. And/or was running bad gas in it. The bore is pretty good though. Not sure what the compression was/is. I assume it was fine.

The paint isn't terrible, but it all around needs some clean up. I hate to disappoint anyone, but it will be painted a different color when complete. Probably something pretty ridiculous actually like bright green lol.. Some pretty wild hi-temp engine paint colors available these days.
 
VeritableFox

VeritableFox

Active Member
#12
#12
Tommy2 said:
Thank you so much for taking the time to reply and answer all the questions I had!

Looks like that billet flywheel is about $175. https://www.arcracing.com/6605-arc-billet-flywheel-briggs-3hp-flathead-2-75lbs/

That's pretty steep. However, if that would make running without a governor safer, maybe it's worth ordering? If I ran that flywheel and stiffer springs, would it be safer to turn higher RPMs?
Click to expand...
Eh, safer. The connecting rod is still a fail point. And like I said, the stock flywheel is destruction tested to 5500 RPM. In all honesty, just keep it governed and adjust the governor to allow some more RPM. Save the money to build a Briggs 5hp I/C if you want to build a flathead to be a screamer. Aftermarket parts are still made for the 5hp and readily available and the engine itself is easy to find for $50-$100.

I'd still fix up the 3hp, I'd just find a small frame to stuff it in like a scat cat. Make it a fun little bike to putz around on at 30ish. To start going fast you're honestly going to want to start looking at a 5hp flathead you can build or an OHV like a GX200 or one of its clones like a Predator. And if you don't want to spend time wrenching on an engine then something like a Predator Ghost, Tillotson 212r or Ducar 212 are decently priced race engines coil limited to 6500ish RPM.

I'm not trying to be a downer or drive you off or anything, just the reality of the 3hp doesn't leave a ton of room to get stupid like you can with other engines out there. I'd also like to keep a person as safe as possible while getting into mini bikes. It may seem slow to do it by building something like a small 3hp bike that tops out on a flat surface at 30 before moving on to bigger and faster. However, having taken a bike from a 28mph putzer to a 55mph cruiser it feels WAY faster than it really is because you're on a 125lb bike that likely doesn't even have a 24" seat height.
 
T

Tommy2

Member
#14
#14
VeritableFox said:
Eh, safer. The connecting rod is still a fail point. And like I said, the stock flywheel is destruction tested to 5500 RPM. In all honesty, just keep it governed and adjust the governor to allow some more RPM. Save the money to build a Briggs 5hp I/C if you want to build a flathead to be a screamer. Aftermarket parts are still made for the 5hp and readily available and the engine itself is easy to find for $50-$100.

I'd still fix up the 3hp, I'd just find a small frame to stuff it in like a scat cat. Make it a fun little bike to putz around on at 30ish. To start going fast you're honestly going to want to start looking at a 5hp flathead you can build or an OHV like a GX200 or one of its clones like a Predator. And if you don't want to spend time wrenching on an engine then something like a Predator Ghost, Tillotson 212r or Ducar 212 are decently priced race engines coil limited to 6500ish RPM.

I'm not trying to be a downer or drive you off or anything, just the reality of the 3hp doesn't leave a ton of room to get stupid like you can with other engines out there. I'd also like to keep a person as safe as possible while getting into mini bikes. It may seem slow to do it by building something like a small 3hp bike that tops out on a flat surface at 30 before moving on to bigger and faster. However, having taken a bike from a 28mph putzer to a 55mph cruiser it feels WAY faster than it really is because you're on a 125lb bike that likely doesn't even have a 24" seat height.
Click to expand...
I totally get where you're coming from. I'm not building anything to race... This is more of a fun experiment than anything. I don't want to get crazy complicated, but don't mind spending some money at this point while it's apart. I don't think I can get a billet connecting rod for this engine? Or if I can, I have no idea which one to buy.

Yea, I wish the coil could have a limiter built into it. That would be a good fail safe when removing the governor. I might put a tach on the engine and/or leave the governor. We'll see.
 
sparkwizard

sparkwizard

#15
#15
That governor is an air vane above the flywheel. I would leave it there and ride the bike. You can always tweek that governor or even remove it later without taking anything back apart. (I have been known to use tin snips to adjust 3 horse governors.)
I am a big fan of the tank and carburetor system. No lines to leak, and very good, reliable power.
 
Minimichael

Minimichael

Well-Known Member
#16
#16
I use a tach
Tommy2 said:
I totally get where you're coming from. I'm not building anything to race... This is more of a fun experiment than anything. I don't want to get crazy complicated, but don't mind spending some money at this point while it's apart. I don't think I can get a billet connecting rod for this engine? Or if I can, I have no idea which one to buy.

Yea, I wish the coil could have a limiter built into it. That would be a good fail safe when removing the governor. I might put a tach on the engine and/or leave the governor. We'll see.
Click to expand...
I use a tach on my 5hp and have it set to flash red at me near 4500rpm. It's plenty fast for me at around 25-30s.

Chikuni's are another option and add a lot of fun in terms of responsiveness. Then you'll need a separate tank though, and maybe a fuel pump (which will then need a pulse). But then you'll feel like you're really building something :cool:

$50-75..
 
sparkwizard

sparkwizard

#19
#19
Tommy2 said:
Stupid question - is there no reasonable way to add an electric starter to one of these engines?
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Those are some of the easiest engines ever, to start, Adding a starter (if there even is an option) and a battery would be about the same weight as your engine. What type of "small mini bike" are you planning to install it into?
 
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