5HP Koolbore/Non-sleeved Briggs Flathead Questions

[BiniMike]

I have a model 130202 Briggs that I have on my Sears Drover that burns oil and has a fair bit of scoring... It's nothing super severe, but it burns oil nonetheless, so I know it will eventually bite the dust, and there isn't all that much I can do about it...
I am curious about whether I should leave it and let it blow up when it wants to, or should I just pull it apart and do a rebuild asap?
Should I even rebuild it? or find a new piston and block for it like an I/C or Raptor block? After all the output shaft is small (1-1.5"), and I was thinking of getting a new one with a longer shaft to use with a cvt anyway, So I could just get like a whole new bottom end or something.
I have already modded this engine pretty good; shaved head, head work, shaved eyebrows, 22lb valve springs, 3/4" threaded tube (not direct muffler) exhaust, and proper air filter. This is why I am considering a multitude of options and is also why I'd like to save it.
NOTE: It's wild how much power can be free'd up from simply removing some metal in the combustion chamber for flow!

 

[sparkwizard]

I would not bother trying to seal up the bore on a cool-bore engine. Used engines are very reasonably priced on ebay, Craigslist, Marketplace...
All of your parts should swap into an I/C block and you can do the eyebrow mods, maybe some porting and have a very nice engine that should last a long time. As far as the one you now have...maybe switch to 40 Wt oil to slow the burning, check it often and run it until a good used one comes up.

 

[BiniMike]

I would not bother trying to seal up the bore on a cool-bore engine. Used engines are very reasonably priced on ebay, Craigslist, Marketplace...
All of your parts should swap into an I/C block and you can do the eyebrow mods, maybe some porting and have a very nice engine that should last a long time. As far as the one you now have...maybe switch to 40 Wt oil to slow the burning, check it often and run it until a good used one comes up.

I think I'll buy an I/C bottom end (At least the crank, piston, rod, and cam.) and swap everything modified over... Then that opens up the possibility to mod a cam since I'll have 2! Although I may want to look into a billet rod at this point... Not trying to severely blow it up...
Is it worth advancing the timing by shearing the key? I also have a Briggs 3HP on hand that is fully parted out for spare parts and I'm wondering whether I should put the 3HP flywheel on with an adapter or leave it stock, and whether the adapter would advance the timing?
Does putting the 3HP flywheel sacrifice cooling at all? Should I worry about that? What RPMs are dangerous with the 3HP vs 5HP flywheels?
Also, by 40 weight oil do you mean 10w-40?
Thank you

 

[sparkwizard]

I think I'll buy an I/C bottom end (At least the crank, piston, rod, and cam.) and swap everything modified over... Then that opens up the possibility to mod a cam since I'll have 2! Although I may want to look into a billet rod at this point... Not trying to severely blow it up...
Is it worth advancing the timing by shearing the key? I also have a Briggs 3HP on hand that is fully parted out for spare parts and I'm wondering whether I should put the 3HP flywheel on with an adapter or leave it stock, and whether the adapter would advance the timing?
Does putting the 3HP flywheel sacrifice cooling at all? Should I worry about that? What RPMs are dangerous with the 3HP vs 5HP flywheels?
Also, by 40 weight oil do you mean 10w-40?
Thank you

40 means 40. 10w40 is basically 10 weight oil with additives. It will smoke more, burn faster. Use straight 30 or 40 because it is thicker and leaks and burns slower. A billet rod is always a great idea! As far as your timing question: I might try a few different keys. For the answer to the 3 horse flywheel, let's call a friend: @Thepaetsguy

 

[BiniMike]

Thanks, spark! Looks like I should do some research on different oil types...

I have a 3HP carburetor and tank on my 5HP engine... Are there any differences between the 3HP carbs and 5HP carbs? Aside from the linkage stuffs. What kind of modification can be done to them? I left mine stock at the moment and figured I'll switch to something else later down the line, but I do quite like a stock appearing briggs, so I may keep a stock carb on... depends on how much it will limit my engine.
NOTE: My 5HP is an '85 130202 and the 3HP parts engine is a '79 80202

I may come back to this thread for more questions if anything else comes up.

 

[Havasu Dave]

They are different. But I don't know how. I recently (last week) built both a 100202 and an 80202 and those carb part numbers were different. I also had air leaks with a chinese knock off. Ended up buying nOS parts off of Ebay. Side note. You fixing up briggs Flatty and want performance, ditch the carb, and get a Mikuni VM 22-133. Or a Flatside. That is the single greatest improvement for horsepower available to that engine. More than cams even. You'll have to figure out the tank if moving from pulsejet.

 

[creia]

The 5HP is taller than a 3HP and as such the length of the tank support bracket on a 3HP is shorter than the 5HP. If indeed that is a 3HP carb/tank combo the bracket would not be long enough to reach (and bolt into) the 1/4-20 threaded hole at the base of the (taller) 5HP block. Having that bracket bolted to the block is important to support the weight and vibration of the fuel tank when its full of gas. You do not want that fuel tank flopping in the breeze and supported by only the 2 carb to block bolts.
Michael

 

[Thepaetsguy]

Then that opens up the possibility to mod a cam since I'll have 2! I also have a Briggs 3HP on hand that is fully parted out for spare parts and I'm wondering whether I should put the 3HP flywheel on with an adapter or leave it stock, and whether the adapter would advance the timing?
Does putting the 3HP flywheel sacrifice cooling at all? Should I worry about that? What RPMs are dangerous with the 3HP vs 5HP flywheels?
Thank you

I have a Briggs 5hp that has a 3hp drop bracket/non billet 3hp flywheel and a simple Tillotson carburetor from a stihl cutoff saw. It starts extremely easy and I rev the snot out of it. The 3hp flywheel is fine for a mild build.


[QUOTE="
I have already modded this engine pretty good; shaved head, head work, shaved eyebrows, 22lb valve springs, 3/4" threaded tube (not direct muffler) exhaust, and proper air filter. This is why I am considering a multitude of options and is also why I'd like to save it
NOTE: It's wild how much power can be free'd up from simply removing some metal in the combustion chamber for flow![/QUOTE]
The ports in these Briggs 5hp’s are crap… Re-do them.

 

[BiniMike]

They are different. But I don't know how. I recently (last week) built both a 100202 and an 80202 and those carb part numbers were different. I also had air leaks with a chinese knock off. Ended up buying nOS parts off of Ebay. Side note. You fixing up briggs Flatty and want performance, ditch the carb, and get a Mikuni VM 22-133. Or a Flatside. That is the single greatest improvement for horsepower available to that engine. More than cams even. You'll have to figure out the tank if moving from pulsejet.

They seem identical other than the tank (of course) and the throttle actuator shaft (Not sure what it's called...) being slightly different to work with the 3hp air vane governor... I had to drill a hole in it for it to work, which is how I figured that out.

 

[BiniMike]

The 5HP is taller than a 3HP and as such the length of the tank support bracket on a 3HP is shorter than the 5HP. If indeed that is a 3HP carb/tank combo the bracket would not be long enough to reach (and bolt into) the 1/4-20 threaded hole at the base of the (taller) 5HP block. Having that bracket bolted to the block is important to support the weight and vibration of the fuel tank when its full of gas. You do not want that fuel tank flopping in the breeze and supported by only the 2 carb to block bolts.
Michael

So... I may or may not have just the two bolts mounting the carb and tank on... but it is supposed to be temporary! My 5HP tank is full of sediment and needs a clean... been meaning to do that. Means I'd switch back to the 5HP carb too, after a rebuild of it of course. Actually, I never cleaned the 3HP carb, it very surprisingly worked after simply diluting the small amount of gas in that old tank... it's worked great so not a big need to clean it.

 

[BiniMike]

I have a Briggs 5hp that has a 3hp drop bracket/non billet 3hp flywheel and a simple Tillotson carburetor from a stihl cutoff saw. It starts extremely easy and I rev the snot out of it. The 3hp flywheel is fine for a mild build.


[QUOTE="
I have already modded this engine pretty good; shaved head, head work, shaved eyebrows, 22lb valve springs, 3/4" threaded tube (not direct muffler) exhaust, and proper air filter. This is why I am considering a multitude of options and is also why I'd like to save it
NOTE: It's wild how much power can be free'd up from simply removing some metal in the combustion chamber for flow!

The ports in these Briggs 5hp’s are crap… Re-do them.
View attachment 327130 View attachment 327131 View attachment 327132 View attachment 327129 [/QUOTE]
Looks like porting and polishing is next on the list! Any important pieces of advice for someone doing it for the first time?
Combining porting and polishing with advanced timing on the 3hp flywheel (along with all the other stuff I've done) should get me near the most amount of a power increase I can do without spending a whole lot, correct?
I also have some questions:
Is it possible to port a stock carb? is it worth it if so? Again, I do like a stock appearing Briggs, but if I really do need to, I'll swap the carb... I do have a chikuni laying around that needs a use after all.
I heard you can reduce the effectiveness of the compression release for increased compression and more power... Is this true?

 

[Thepaetsguy]

The ports in these Briggs 5hp’s are crap… Re-do them.
View attachment 327130 View attachment 327131 View attachment 327132 View attachment 327129

Looks like porting and polishing is next on the list! Any important pieces of advice for someone doing it for the first time?
Combining porting and polishing with advanced timing on the 3hp flywheel (along with all the other stuff I've done) should get me near the most amount of a power increase I can do without spending a whole lot, correct?
I also have some questions:
Is it possible to port a stock carb? is it worth it if so? Again, I do like a stock appearing Briggs, but if I really do need to, I'll swap the carb... I do have a chikuni laying around that needs a use after all.
I heard you can reduce the effectiveness of the compression release for increased compression and more power... Is this true?[/QUOTE

Uncle franks blue wazoom engine was an out of the box 12hp methanol engine YOU could purchase and it used a standard Briggs 3hp flywheel with drop bracket. I know for a fact my Briggs engines are not making anywhere close to 12hp so I‘m under the assumption the 3hp standard Briggs flywheel is safe within reason.

Leave the ports alone. The governor is deleted and the eyebrows gone. One billet rod and the drop bracket for the flywheel plus you gain a bit of adjustable timing. Maybe make or source a header.


Do not file off the compression release it could become hard to start and could kickback on you. Go with the stock 5hp tank..

 

[Minimichael]

One way to improve flow in a stock carb is by filing down the screw that holds the butterfly to its spindle.

 

[BiniMike]

Looks like porting and polishing is next on the list! Any important pieces of advice for someone doing it for the first time?
Combining porting and polishing with advanced timing on the 3hp flywheel (along with all the other stuff I've done) should get me near the most amount of a power increase I can do without spending a whole lot, correct?
I also have some questions:
Is it possible to port a stock carb? is it worth it if so? Again, I do like a stock appearing Briggs, but if I really do need to, I'll swap the carb... I do have a chikuni laying around that needs a use after all.
I heard you can reduce the effectiveness of the compression release for increased compression and more power... Is this true?[/QUOTE

Uncle franks blue wazoom engine was an out of the box 12hp methanol engine YOU could purchase and it used a standard Briggs 3hp flywheel with drop bracket. I know for a fact my Briggs engines are not making anywhere close to 12hp so I‘m under the assumption the 3hp standard Briggs flywheel is safe within reason.

Leave the ports alone. The governor is deleted and the eyebrows gone. One billet rod and the drop bracket for the flywheel plus you gain a bit of adjustable timing. Maybe make or source a header.


Do not file off the compression release it could become hard to start and could kickback on you. Go with the stock 5hp tank..

Yeah, I figured there would be issues modifying the compression release, so that's a no-go... But i'm still curious, does it affect power?

What kind of timing adjustability would I be looking at with the drop bracket? I assume you're talking about the ARC drop bracket.
Also, do you think it'd be easy to make a bracket, or is it just not worth my time since they're like 15 bucks anyway?

I agree with you on keeping that stock tank, which is why I'd like to explore carb modification... I will for sure do some research on that. Little mods like what MiniMichael said is what I'm looking to do... They add up!

I think investing in a billet rod would be great for that thing, especially considering the fact that I plan to put that 3hp flywheel in... Though, as stated in the earlier parts of this thread, this things pretty worn, burns oil, and requires frequent oil changes to prevent wear.

I can get a billet rod and drop it in anyway, just to move to another, much better conditioned block once this engines had enough. Should I be worried about putting excess wear on the rod by putting it in my worn engine, or am I overthinking this?

Thanks all, for the advice. You guys have been a great deal of help. (and thanks OldMiniBikes.com!)

 

[sparkwizard]

I think the Pulsajet and the Varajet carbs look somewhat similar but there are functional differences. I "BELIEVE" the Varajet does not pump fuel up into the little bowl inside the tank. The Pulsajet does. The Pulsajet has one mixture screw for idle and high speed. I am not sure if the Varajet does or not. I might have a spare Pulsajet and a questionable tank if you need them. Cheap with no claims or promises.

 

[mchadsey1]

Y

Yeah, I figured there would be issues modifying the compression release, so that's a no-go... But i'm still curious, does it affect power?

What kind of timing adjustability would I be looking at with the drop bracket? I assume you're talking about the ARC drop bracket.
Also, do you think it'd be easy to make a bracket, or is it just not worth my time since they're like 15 bucks anyway?

I agree with you on keeping that stock tank, which is why I'd like to explore carb modification... I will for sure do some research on that. Little mods like what MiniMichael said is what I'm looking to do... They add up!

I think investing in a billet rod would be great for that thing, especially considering the fact that I plan to put that 3hp flywheel in... Though, as stated in the earlier parts of this thread, this things pretty worn, burns oil, and requires frequent oil changes to prevent wear.

I can get a billet rod and drop it in anyway, just to move to another, much better conditioned block once this engines had enough. Should I be worried about putting excess wear on the rod by putting it in my worn engine, or am I overthinking this?

Thanks all, for the advice. You guys have been a great deal of help. (and thanks OldMiniBikes.com!)

You will need to clean and inspect all internal parts for wear before putting in new parts . Use a micrometer to measure the crank journal for size and roundness. And your going to need a bore guage to check the bore diameter and straightness. If its burning oil it's going to need a hone at minimum most likely a recut on the bore with an o.s. piston.

 

[Thepaetsguy]

Yeah, I figured there would be issues modifying the compression release, so that's a no-go...

I agree with you on keeping that stock tank, which is why I'd like to explore carb modification... I will for sure do some research on that. Little mods like what MiniMichael said is what I'm looking to do... They add up!

I think investing in a billet rod would be great for that thing, especially considering the fact that I plan to put that 3hp flywheel in...

I can get a billet rod and drop it in anyway, just to move to another, much better conditioned block once this engines had enough. Should I be worried about putting excess wear on the rod by putting it in my worn engine, or am I overthinking this?

Thanks all, for the advice. You guys have been a great deal of help. (and thanks OldMiniBikes.com!)

The crappy tiller engines laying upside down in the swamp full of water are the BEST ONES… No one else has messed with them yet. Simple pull apart clean all parts and add your aftermarket re-assemble..

I buy used rods from the Briggs Facebook page install cheap new rod inserts into those used rods and install them into a Briggs 5hp the engines still run fine today.

For a really fun hotstock skip the drop bracket and 3hp flywheel entirely and go for that arc 5hp billet.

One single billet rod a 5hp arc flywheel and the governor is deleted. Add your header and down the road look for a carburetor swap. It’s the ultimate hotstock. And with that simple rod/flywheel combo makes it safe to modify as far as you think you can possibly go in the future. There is the 212cc option with infinite aftermarket also.

 

[sparkwizard]

One of my most reliable engines is a 5 horse I/C that was on a tiler laying on it's side near a creek. It was stuck and muddy. I filled it up with trans fluid, cleaned the tank and carb. I was planning to tear it apart and go through it. When I drained the fluid, it turned over. I did replace the coil, but I still use that engine. Never even opened it up. It was free. The former owner said it was hard to start so he dumped it out there and bought another tiller.

 

[BiniMike]

So... I may or may not have just the two bolts mounting the carb and tank on... but it is supposed to be temporary! My 5HP tank is full of sediment and needs a clean... been meaning to do that. Means I'd switch back to the 5HP carb too, after a rebuild of it of course. Actually, I never cleaned the 3HP carb, it very surprisingly worked after simply diluting the small amount of gas in that old tank... it's worked great so not a big need to clean it.

Hah! called it! It's clogged now and I need to rebuild it... If it's any more worn than the 5hp carb I'm switching to the 5hp one.
Looks like it's time to take a gander at the 5hp tank! Wish me luck!

 

[Thepaetsguy]

I’ll swear up and down you build a non hemi 212cc with CHEAP INFINITE aftermarket support. I don’t care to build one…

This was a stock Briggs 5hp engine I pulled out of a shed that was falling in.. I pulled it all apart stripped the paint off it and did my best to polish it. Installed the aftermarket billet and re-assembled.

Skip paint removal/polish to save a LOAD of time. Disassemble hit EVERYTHING with soapy water and a pressure washer and make it all clean and bare bones presentable then add want you want.

My vote if you’re going to spend ANY MONEY is one rod and one flywheel. Your governor is deleted and make a cheap as possible header. Parts are not cheap for the Briggs they are cheap for the 212