Briggs and Stratton 5hp (Flathead) problems

[Sparkwizard]

Buy longer bolts for the ones going through the tank bracket.
There is no porting to be done on a model 13 flathead Briggs head.
The ports are in the block. Do a lot of research before you start removing the valves to port that block.
With a big carb and stock valve springs, the flathead might make 6 horsepower.
A Predator making 20 HP is a serious investment.

 

[John Roger]

Buy longer bolts for the ones going through the tank bracket.
There is no porting to be done on a model 13 flathead Briggs head.
The ports are in the block. Do a lot of research before you start removing the valves to port that block.
With a big carb and stock valve springs, the flathead might make 6 horsepower.
A Predator making 20 HP is a serious investment.

yea 1,500$ also I meant the block

 

[John Roger]

for a nitromethane burning engine 1 gallon with a 90% pure nitromethane 10% pure methanol would be $130 but in a perfect world Should make 2.5 times the power 12-15hp

 

[Hellion]

Just a note, you are basically wasting your time and money hopping up a Briggs flathead unless of course it is:

(1.) A genuine Raptor of any series (I, II, III)
(2.) A steel/iron sleeve I/C (Industrial Commercial) engine with a dual ball-bearing supported crankshaft
Or an I/C engine that has only one ball-bearing on the crankshaft (some do)
(3.) A Kool-Bore engine with only one ball-bearing (the other is a plain bearing).
These engines, listed from best to worst, are I think the best able to handle the power.

Engine codes on the blower shroud:
132232 Cast iron sleeve dual ball-bearing engine
130232 Aluminum (Kool Bore) dual ball-bearing engine
13X202 Bushing on the flywheel side only

Sparkwizard is correct. The intake and exhaust ports (especially the exhaust) are already too big from the factory. The casting flash or seam you'll find in the intake port some say is perfect for helping atomize the A/F mixture.

 

[John Roger]

then I'll polish them not port when I saw videos on modding them they port and polish the heads using scotch pad to make it very slightly bigger

 

[John Roger]

I also saw some people sand down these parts should I do that

 

[Sparkwizard]

I still have a new, in the bag screw-in exhaust restrictor for the model 13. They were outlawed in Kart racing a long time ago because they made too much torque. (That was the story I remember, anyway)
It screws into the threads in your block and requires the use of a bolt on header or muffler.
$20 shipped.

 

[Master Hack]

Well that's a blatant "disinformation

To be clear l stated the words use in sentences,
Nothing about parts availability. Fact is l still have ceramic main bearings for flatheads as well as the Animal engine. I haven't heard anyone lately use that combination of words, thereby the word rarely came to mind.
Also being of "senior" status (in age only) Ford is what l think of when l hear flathead.
Thats my excuse, l'll take my 40 lashes now!

 

[John Roger]

Photos

 

[Hellion]

Head gasket looks like it's toast. The newer flathead gaskets are a composite sort of malleable graphite material like yours (I think). The old school gaskets were made to last and last because you were supposed to periodically remove the cylinder head and scrape off the excess carbon deposits. I believe the thinking then was that the head gasket had to be able to survive constant removal and installation.

 

[John Roger]

I just did that in the photos Sould I get like a copper gasket? Or just stick with the graphite stuff

 

[Sparkwizard]

Never use copper gaskets unless you are a dedicated racer. They have strict instructions for heat treating them to soften them they demand flat, smooth surfaces and they will never seal unless you do everything correctly.
The old, multilayer graphite metallic gaskets are what you should use.

 

[Sparkwizard]

While you have the head off, find instructions for contouring EYEBROWS on your block.
Be conservative. Do not belt sand the head. Leave it alone. Trying to raise compression by milling the head will reduce flow between the valves and the cylinder. Any real boost will come from billet parts, a better cam and more RPM.

 

[John Roger]

I don’t have a milling machine (sadly) but I see people use like 200 grit sandpaper and just be carful with it

 

[Hellion]

The old, multilayer graphite metallic gaskets are what you should use.

There's older (I think) head gaskets that appear to be stiffer than the "graphite" versions. These gaskets have the material sandwiched between two perforated layers of what looks like thin sheet aluminum. Not saying one gasket type is better than the other though.

As far as milling the head so the gasket (OEM or copper) will fit better, it can be done with a plate of thick 1/2" glass (or maybe a ceramic floor tile) and some medium to fine grit sandpaper taped to it. It's the same process as "milling" the fuel pump diaphragm cover on the Pulsa-Jet carburetor. It's definitely Backyard Bubba level "machining" but you can have very very good results both with the block, the cylinder head and the pump diaphragm cover ....

https://oldminibikes.com/forum/index.php?threads/tech-trueing-your-diaphram-cover.59393/

 

[Sparkwizard]

For truing purposes only. Removing material from the head on a flathead to raise compression will also restrict air flow between the valves and the cylinder. You would need to remove so much material from the block "eyebrows" to make room for airflow, you would be lowering the compression again. Flathead engines are not high compression engines.

 

[John Roger]

thats why I wanted to sand down these parts to allow better airflow for the intake it more of a old school trick that people would do and they should also get better heads to allow more airflow

just realize these are called the eyebrows

 

[John Roger]

There's older (I think) head gaskets that appear to be stiffer than the "graphite" versions. These gaskets have the material sandwiched between two perforated layers of what looks like thin sheet aluminum. Not saying one gasket type is better than the other though.

As far as milling the head so the gasket (OEM or copper) will fit better, it can be done with a plate of thick 1/2" glass (or maybe a ceramic floor tile) and some medium to fine grit sandpaper taped to it. It's the same process as "milling" the fuel pump diaphragm cover on the Pulsa-Jet carburetor. It's definitely Backyard Bubba level "machining" but you can have very very good results both with the block, the cylinder head and the pump diaphragm cover ....

https://oldminibikes.com/forum/index.php?threads/tech-trueing-your-diaphram-cover.59393/

that's what I meant

 

[Denny]

On a flat head that is referred to relieving the block.

 

[John Roger]

the reason i want to up the (just slightly) compression is to make it run on nitromethane I know its dumb or whatever but from looking at other forums it has worked for some people even on a stock briggs a but I want to build a better engine if you want the link to those discussions let me know I even found some videos of people running stock Briggs on nitro but they do work well because of a couple of thing. first is nitromethane burns very slowly so you would have to advance the ignition at least 20 degrees most do almost 45 degrees. nitromethane actually works better at lower compression ratios so I might not up the compression but the reason you don't want to up the compression is that nitromethane can pre detonate with also with such a slow burning fuel will make flames spit out the exhaust because it burns so slow that why you need advance (ignition) timing if you have any other ideas for this to work let me kno.