Rebuilding a Briggs Flatty

[REDNECK GOCARTS]

I have a Briggs 5hp flathead that I want to rebuild. I also want to remove the governor on it. I was thinking about putting in a billet connecting rod and cam so I can hold the engine at high RPM. If i am already doing that should I get new valve springs or should I keep the old ones. I don't need this engine turning 8k or anything because its only going on a yard kart. I was thinking any where between 5000 to 6000 which I know is valve float for stock springs. I just want to be able to hold the gas down for a long time with out blowing her up.

 

[Joe-405]

If your hard on stuff or a lead foot then I would recommend the springs. The old springs could pop after long periods of high rpm use. And then you’d be rebuilding a lot more than what your doing now and cost a lot more also. I would also recommend a cheap tachometer to keep tabs on your rpms also.

 

[REDNECK GOCARTS]

Besides also a new set of rings and a good cleaning and honing, is their much else i would need to do, also, is their anything i can do to the carb to get more power from it, and does shaving the head do much to. I have heard it does and it would make sense. I also plan on porting and polishing. Also I'm not hard on my stuff but I want my friend /family to be able to drive it and I'm kinda paranoid that they will blow up the engine.

 

[Randy H]

Be careful with your cam selection. Some of those cams are intended to meet rules for certain racing classes. i. e. slapper cams. Stock lift, but aggressive profiles that with appropriate springs, not to heavy, will loft the valves. Many of these cams require modification of the block. Welding of the lifter bore area especially the exhaust side.

Cams like Dynocams 94ss and 107ss are a better choice, if not trying to race in a specific class. Possibly requiring longer lifters (maybe billet) because frequently they are reground cams with a reduced base circle. New valve springs, manufacturer recommendation. For piece of mind split retainers and keepers. Maybe this.

https://www.dynocams.com/item/gp-960kit/fham-springs/

Flatheads flow so poorly that sacrificing compression for better flow is common. Eyebrow shaving is an accepted practice. IMO, I say stay away from the bore. Kind of depends on piston compression height and ring package.

https://m.youtube.com/results?q=Briggs flathead eyebrow&sm=3

A free flowing air filter and exhaust, cheap header, will likely require richer jetting. http://www.out2win.com/catalog/raptorjets.html

IMO hand drilled jets suck.

Flywheel advance keys, or, and preferred, flywheels lapped to the crank taper = cheap performance boost. To much timing advance can make hand starting difficult or dangerous.

The exhaust port on these engines was intended to have a screw in muffler. With a bolt on header the port is to big. Simple trick is to screw a pipe nipple in the port, strategically cut to be flush with the port or slightly longer and tapered to extend into the tapered entrance that may exist on an aftermarket header.

 

[REDNECK GOCARTS]

Kaaaa boom. That was my brain exploding. I knew you could do all that but i was hoping for under 100 bucks. Turns out the rods i was looking at were stock, oops. I feel like the best way is to go down and dirty. Throw a new set of rings in, remove the governor, and just send it. I thought it was to good to be true. I guess other people get away with doing governor removals and their engines run fine. I will just be like the rest of society, but if theirs anyway to make cheap power, my ears are open. Also what else should I replace for the rebuilding? All I can think of is honing and new set of rings.


Edit. How much RPM can these rods handle.
http://www.out2win.com/catalog/raptorrods.html
Also do you really need a cam or can you do just the rod?
Might get roasted for this one and where its from.
https://www.ebay.com/itm/Crane-Cam-...511856&hash=item213e951127:g:cyAAAOSwKvJaxR7w
Would both the rod and cam hold up to 5000k

 

[Kentucky Boy]

I just got done rebuilding one that had a broken rod. The rod broke because the previous owner rigged the governor with a zip tie. If your block is aluminum don't hone it, you will ruin it. If it is aluminum you will need chrome rings with NO honing. Measure your bore first to see if it out of round. If it's out of round it's probably toast.

 

[REDNECK GOCARTS]

Its not going to be out of round, it still ran fine. I also have three engines to choose from so out of those I should have a candidate but that still doesn't answer my questions about the rod and cam.

Edit. All three engines are aluminum, doesn't sound like there are many options now. If I can't hone the cylinder then there is really no point to rebuilding them. There is very little scoring but still. What can I do?

 

[ezcome-ezgo]

Recycling?

 

[Randy H]

This post is worth a read

https://karting.4cycle.com/showthread.php?93187-Block-Prep

http://www.out2win.com/catalog/raptorrods.html Use the best you can afford.

The cam your looking at is a stock lift racing cam, meaning if you check it with dial indicator it will indicate stock lift. I would assume, that it is a slapper cam that needs block strengthening in the lifter bore area.

I mean otherwise you can assume it isn't and break your block.

Don't sweat honing. Hone it or don't. There are many other clearances to be worried about. Slap it together and run it.

 

[REDNECK GOCARTS]

What normally breaks first, the cam or the rod. I wish I could find a cam that would work well with out having to change the block or breaking my wallet. I think at this point I will just get the rod and a new piston and run it like that.

 

[Randy H]

The rod breaks the cam. The cam breaks the block. Lol.

Sorry I wish I could explain the cam situation better. Maybe think of it this way. The cam appears stock. Measure it and it's the same lift as a stock cam. But they are designed, to meet rules for racing.

Think of a ski jumper dude or motocross guy. The cam has a ramp. Faster=higher lift and more duration. But increase gravity or put a stiffer spring on a valve and they /it will follow the ramp.

This makes me think of Evel Knievel. Back in them days I had my Dad, Richard Petty, Marty Smith, Marland Whaley, and Mr. Knievel as role models. Except for Marland (and King Richard LOL) , them guys seemed to enjoy defying gravity. Most readers will have to do some research to have any idea what I talking about.

There are cams that give the performance of "cheater cams", or better. I can only recommend Dynocams 94ss and 107ss. The are undoubtedly others. Used cams are a pig in a poke. Sometimes cam cards don't tell the whole story.

I miss Paul Harvey.

 

[Kentucky Boy]

Its not going to be out of round, it still ran fine. I also have three engines to choose from so out of those I should have a candidate but that still doesn't answer my questions about the rod and cam.

Edit. All three engines are aluminum, doesn't sound like there are many options now. If I can't hone the cylinder then there is really no point to rebuilding them. There is very little scoring but still. What can I do?

It can be out of round and still run. Check your compression on all three and pick the best one to rebuild.