Floating valves

[2or3wheels]

At what RPM does a stock briggs flathead float? keep in mind mine is old so im sure theyre weak. Just wondering if i could just rev her up and have the valves floating be a restrictor of sorts.

 

[Russ2251]

Depends on engine. I can easily hold my old cast iron flatties wide open with no load and valves don't float.
Haven't tried it with newer aluminum blocks. May try it on 3hp Tecumseh which I have no use for...unless somebody makes me an offer.

 

[jr dragster T]

Depends on engine. I can easily hold my old cast iron flatties wide open with no load and valves don't float.
Haven't tried it with newer aluminum blocks. May try it on 3hp Tecumseh which I have no use for...unless somebody makes me an offer.

Never thoght I would ever hear you say that Russ. No load and wide open is asking for trouble and we have already had someone around here learn the hard way.

 

[Russ2251]

I have posted extensively on this. Most engines will tolerate this provided they are unmodified and not clones.

 

[jr dragster T]

Yeah But still no load and a rod and flywheel only desihned for 3600. I know they overrate parts like this for safety but I wouldnt be the person to do this.

 

[Russ2251]

I will post video soon!!!
Any bets on what happens???
Flywheel explosion?
Thrown rod?
Anybody???
I will wire throttle to full open and just let it run wild while on camera. No edits.

 

[jr dragster T]

I dont think anything will break. But all I'm saying Russ is that the less you do it the better!

 

[Russ2251]

...all I'm saying...is that the less you do it the better!

I agree 100%!
My point is that when some folks ask about removing governor (in total), the immediate response (from some posters) is to get billet this and billet that when it is totally unnecessary for a stock setup. There are 'built in' limiters other than governor.

 

[jr dragster T]

I agree 100%!
My point is that when some folks ask about removing governor (in total), the immediate response (from some posters) is to get billet this and billet that when it is totally unnecessary for a stock setup. There are 'built in' limiters other than governor.

Such as soft valve springs, Small ports, Smaller cam and such.

 

[Russ2251]

Precisely. No fears.

 

[sayre315]

if anything happens to the tec it will be a thrown rod

but will an ungoverned briggs 5hp brake anything if it has a load?

 

[Kenny_McCormic]

I hear that a briggs 5 hp flathead floats on the intake side at 4000 rpm to protect the rod. I dont have a tach so I cant say for sure.

 

[Jerryburger]

I hear that a briggs 5 hp flathead floats on the intake side at 4000 rpm to protect the rod. I dont have a tach so I cant say for sure.

It might be higher than that. My junky 5hp (gas powered blender prop) held together at almost 2 miles of going down a road by our house WFO and maintaining between 42-47 mph, which now, I'm learning, was up to 4500 rpm. Not a stutter from it- I was just shocked that it went that fast- going down a fairly steep hill is what helped. The only motor (flatty) that I've ever seen fail was a kid's gokart. (Rod through the front of the motor.) Oil looked like black tar and who knows if there was enough of it in there. I think jrTyler's right. These motors are mechanically stronger than their ability to breathe.
There was an article in a motorcycle magazine stating that most mechanical rpm limits for a typical engine are around 4000 piston-feet-traveled per minute. In the case of a motor with a 2.5" stroke, that gives you 9600 rpm... WAY above what a stock flatty can breathe at. I think valves will float before that, of course... and then there's the infamous dipper problem: Too high a speed or too thick of oil, and it snaps- leaving the motor to keep running with little or no lubrication. I wonder if anyone makes a retro-fit for just the rod cap/dipper?
That 5hp build-up article I posted in another thread never stated if the motor was a stock B/S 5hp, or one of their "stock" racing motors, awaiting mods. But they ran it up pretty high in RPM.

Russ- Are you going to use your TinyTach for the experiment? Those things are HANDY! THX for steering me towards getting one.

 

[oscaryu1]

On eBay I saw a few billet 5HP dippers.

 

[sayre315]

ok, this is gonna sound dumb, but what does it mean when you say "the valve will floadt"?

 

[oscaryu1]

Valve doesn't close or stay closed when it's supposed to.

That's just a dumbed down definition. Wiki it for a more detailed explanation.

 

[jr dragster T]

ok, this is gonna sound dumb, but what does it mean when you say "the valve will floadt"?

Its when the RPM's of the motor are above the RPM rating of the valve spring. The valve opens so quickly at high RPM's and the spring cannot pull it down fast enough and the motor sputters and back fire's and such. Click link to see a indepth view of valve float under the valve cover. Speicly watch the end of the video how they show the valve actually bouncing off the seat!


http://video.google.ca/videoplay?do...KSK-7NIGE_AGn_7i6Ag&q=valve+float&vt=lf&hl=en

 

[jr dragster T]

So wheres this video of the briggs?:toetap05:

 

[2or3wheels]

yeah lets see it.

 

[sayre315]

oh, that must be why we use heavier valve springs