Building up a 3hp briggs

[chain]

So I've located a Briggs 3 hp I/C and it's on it way. I've built a few bikes but this is my first engine overhaul/ for performance. I'm looking for a happy medium for power and reliability. Any help will be sincerely appreciated.

I'm going to go by the 5 hp guide for the most part for mods. I have a couple questions.

Governor will go and aluminum flywheel will be purchased.

Eyebrows- when shaving how deep is a good depth(using a flatbar across the head and measuring with a feeler gauge)

Cam- I've gotten a couple steel cams for this model so I wont have to use plastic.

Rod- what can I do to make the stock rod less prone to failure

Dipper- weak point from what has been posted. There isn't a specific nylon dipper for a 3 hp that I can find. What is the bolt spacing on a 5 hp rod where the dipper attaches.

Carb- right now I've got a few 2 pc flo jets so I will be using one to start with.
Any suggestions on valves , lifters, and springs would be great.

Thanks

 

[smgs92]

I'd suggest for a minibike starting with a bigger engine. I can fit a 420cc 15hp on my minibike so a predator 212 with be a good engine. It's cheap, it's powerful and it has a huge aftermarket.

 

[chain]

I am committed to using a 3hp that is the largest that will fit in my frame. I also am committed to using the frame I have. Thank you for the response.

 

[smgs92]

Just curious post some pics of the frame you are using. I'm not familiar building on briggs but I can offer suggestions based off other engines I've built.

 

[cumminsbayou4x4]

you can polish the rod and drill the oil journal out bigger so it wont throw a rod. they make 3hp billet fly wheels just google that you'll see them. i think they make a 3hp briggs billet dipper but not sure. you can put a exhaust spring in the intake side to make the valves not float, and if you have a welder i would build up the cam to

 

[chain]

Just curious post some pics of the frame you are using. I'm not familiar building on briggs but I can offer suggestions based off other engines I've built.

It's not for a kart but you can see the frame type I prefer to use the last two pics are of the same frame I am using.

http://www.diygokarts.com/vb/showthread.php?t=12521

 

[chain]

i think they make a 3hp briggs billet dipper but not sure.o

If you happen to see one or any 3 hp non standard parts, if you remember please let me know because I have been looking everywhere.

 

[OzFab]

Just FYI, being a 3hp, it will more than likely only have a vane type governor

 

[zbuck]

Years ago, some 1/4 midgets used to run the 3hp briggs. You might look around on the net, and find some old 1/4 midget sites. Or some old vintage go-kart race sites. For 3hp performance parts. Good luck with your endever.

 

[smgs92]

It's not for a kart but you can see the frame type I prefer to use the last two pics are of the same frame I am using.

http://www.diygokarts.com/vb/showthread.php?t=12521

Yes you stated already it was for a bike frame. In the 1st pic of the last 2, that is either a gx160 or gx200 so you would be able to fit a bigger engine you'll have to remove the tank and get an exhaust but you'll be much happier with the outcome and you won't have to build the engine near as much to get the same outcome, and parts are cheaper.

 

[chain]

It is a hf79cc with tank removed, Which Took work to get in there and have everything line up only had 1/4 to 1/2 inch clearance each side.. Briggs 3.5 too large. 5 hp waaaaaaaay to big. This is my third one using this type of frame and without frame mods the 3 is the biggest. To get an idea of the space available that red air filter in the pic is a tuna can.

 

[landuse]

Just FYI, being a 3hp, it will more than likely only have a vane type governor

Yup, I was going to say the same thing. It doesn't have an internal governor like other engines. Looks like this

 

[cumminsbayou4x4]

isn't the vane type governor better to have tho

 

[Doc Sprocket]

Better? Well, I can think of 2 major benefits. If it fails, it will not scatter parts inside your crankcase. If you wish to remove it, it's a VERY basic operation, oh, third thought- if you wish to bypass it, you're not gonna hurt anything.

 

[cumminsbayou4x4]

well i meant better if your gonna remove it i remove all mine every once in a while ill get my mini bike to 3/4 throttle and im probilly going 25 then the valves float

 

[jamyers]

As far as shaving the 'eyebrows' (aka Relieving the bore), I don't think there's a magic number for depth - rather you're trying to take off the edges and provide a nice smooth surface for the gasses to flow across on their way between the valves and bore and back again. On second thought, there is one thing you do NOT want to exceed. That is, you don't want to take the side of the bore down any lower than the highest point that the piston rings will see - easy to tell on a used engine, there'll be a ridge at the top of the bore. Check out my Texas Terror build thread for some pics of what I did on my Briggs 8hp - same ideas will apply to any flathead.

Also imho, cleaning up the intake and exhaust ports will be a MAJOR gain, the stock ones are atrocious!

 

[chain]

Managed to get a nos Wiseco Jrdragster piston with a higher pin height which will give a bit more room for a longer rod and a bit closer to a billet rod and dipper... now to try and get a hold of someone over at ARC.

 

[chain]

There are no billet rods that would fit a 3 hp. So I would like to get the motor to get to max at around 6000rpm. Let me know if something sounds wrong
I'm going port in and out, the exhaust has the threads as well as holes for bolts so I'm going to smooth out threads and go with 1 in. header. Lighter billet flywheel or is that needed at 6000
Now the questions
I need to get a cam ground, the 5 hp guide recs. 94ss grind- I've also heard 312ss any suggestions here? Will this grind be ok ?

Scrap the flo jet if it isn't helping - suggestions?

Exhaust spring on intake ?

5 hp lifters cut down to 3 hp length ?

And grind down towards piston ?

Would like to order parts this week, anything else I may have missed?

Thanks in Advance.

 

[chain]

Help needed

Don't know why it double posted.

 

[cumminsbayou4x4]

There are no billet rods that would fit a 3 hp. So I would like to get the motor to get to max at around 6000rpm. Let me know if something sounds wrong
I'm going port in and out, the exhaust has the threads as well as holes for bolts so I'm going to smooth out threads and go with 1 in. header. Lighter billet flywheel or is that needed at 6000
Now the questions
I need to get a cam ground, the 5 hp guide recs. 94ss grind- I've also heard 312ss any suggestions here? Will this grind be ok ?

Scrap the flo jet if it isn't helping - suggestions?

Exhaust spring on intake ?

5 hp lifters cut down to 3 hp length ?

And grind down towards piston ?

Would like to order parts this week, anything else I may have missed?

Thanks in Advance.

the rod should hold up to 6000 rpm if you drill out the oil hole and polish it up. i don't think you can get rid of the threads in the block. It wouldn't hurt to put a billet fly wheel in it at 6000 rpm.
get a 224 or a 243 lift cam or try to weld them up around that much. try to find a old tecumseh carb or something like that you can make a tilly intake for it to bolt up.