What does it mean to.....
 

In response to an earlier quarry about 4 stokes, someone advised using a tach so as not to exceed 10-11000 rpm while breaking in a new Saito 180 or I may "FLOAT THE VALVES", can someone elaborate on this statement?
Also, from reading around in this site, I find that I can expect a lot of initial vibration, my question, canI just run a couple gallons through before installing this in the plane?
Pardon my ignorance to these 4 strokes, but, can I install this engine in a regular mount and bolt the mount to my work bench, or, will I need some bushings or some type of "shock absorber" between the mount and bench to reduce the vibration stress on the engine?
Any help you can give will be appreciated!

THANKS....

What does it mean to.....
 

Floating valves occur when you over rev the engine past the limit the valve spring seat pressure can handle. In other words...

The valve spring seat pressure is not enough so they cannot bring the valve back into the seat fast enough so the valves flutter, they do not seat properly which results in drastic cylinder pressure leak.

When a lifter is coming off a cam lobe(ramp) it is returning the valve to it's seated position. For example if the intake valve cannot come down fast enough to the seat because of low seat-pressure the combusted gas will then bleed back up through the intake and fire out the carb..


understand ? :)

THANKS
 

If this happens, I assume a major overhaul is in order?
Preciate the info!

What does it mean to.....
 

Don't mount your engine in the jaws of a vice and you'll be ok.

Most people cut a notch in a 1 X 6 and bolt them down. You can nail or deck screw the 1 X 6 to a saw horse.

There are a number of test stands available on the market but you have to screw all of them down to a work bench or saw horse.

I always run my engines on the stand before I mount them on the plane. I like to have everything set the best I can when I go to the field. That way the vibration has settled down too.

Enjoy,

Jim

Re: THANKS
 

Normally not... but it serves no useful purpose, and certainly doesn't "help" the engine any.
Specifically, valve float is when the springs aren't providing enough tension to allow the
lifters to continue in constant contact with the cam, so you are no longer gaining any rpm.
(We'll ignore "controlled valve float" experiments and associated research, for the moment)

Best case, you aren't making any more power than running in the proper RPM range.
Worst case, if allowed to achieve valve float frequently, or for long periods of time,
you will beat the cam and lifters to death in short order, at the very least.

(Not to mention that, being outside MFG's high RPM specs, you're probably killing everything else, too)

What does it mean to.....
 

Valve float occurs when the spring pressure can no longer overcome the inertia of the entire system. It has to accelerate the valve, rocker arm, pushrod and cam follower fast enough to keep everything in contact. When you have excessive floating the valve is no longer where it should be compared to the piston that's hurtling up the bore towards it and it's possible for the piston to hit the valve. Not good!

Floating...
 

THANKS AGAIN!
I REALLY appreciate the information you folks have taken the time to provide.
Its a big help to an engine and all around novice like myself.

What does it mean to.....
 

doesnt valve bounce just mean that the valve springs are too weak to handle the higher revs?
eg I have a 1.5 litre pushrod engine in my datsun and it suffers from it. it (will be) remedied by installing stiffer veedub bug springs in it.
what is the word on hotrodding our 4 stroke engines by installing hotter cams and things such as valvesprings just mentioned?

What does it mean to.....
 

Yes it means that the valve springs have been overcome.
Understand though, that camshafts and lifters are designed to operate together
within a certain range of contact pressure, too. Exceed this, and you can rob the
cam/lifter contact patch of much needed lubrication, and fail cam and/or lifters.
You can also cause lubrication problems between pushrod and rocker, or rocker to valve,
causing excessive wear or failure of those parts of the valvetrain, as well.
Ask me how I know :D
(20+ years working on engines of all sorts... including some dragracing and dirt trackin'.
I've burned up a couple of brand new cam/lifter or cam/follower sets this way.
Of course, a couple times it was because I got sloppy and threw a set of springs in
without paying attention to installed height, coil bind at max lift, etc... to make a race in time.
Go much over "stock" with cam, lifter ratios, or spring pressures/lengths, and you'll
really need to be looking closely at all specs, and possibly be doing some machine work.)

Obviously you're in better shape with a roller setup, but there are still design limits.
Camshaft design has a lot to do with it, too... cams with very high lift and steep ramps
will float the valves at a much lower rpm than a more modest cam, given the same springs.

Also, as mentioned earlier, you have to make sure all the other engine components are
up to the task that you're asking the engine to do. Consider where the valves are
floating, and where you're wanting to be with RPM, and WHY.
Most of the time, simply eliminating valve float, or raising the RPM where it occurs,
is not going to gain you much in the first place, as you are already outside the power curve.
If that's the case, you're needing headwork, pistons, exhaust, carb, etc... before you
even need to think about anything else. Consider grabbing the next gear, or in the
case of our model airplanes, moving to a larger prop ;)
Sometimes an extra few RPM isn't worth it, unless you build an all out "race" motor.

What does it mean to.....
 

I'll chime in and say that engineers usually apply valve spring rates just stiff enough to close the valves just a little bit beyond the engines intended RPM range. Designing with springs employing a heavier rate, or more preload increases valvetrain stress and requires stronger, sometimes heavier,and more costly followers,tappets,pushrods etc. This also adds reciprocating mass to the valvetrain which results in a slightly less efficient valvetrain. Some of the benefit of the added spring rate will be lost moving the now heavier valvetrain. OK now you've got your engine turning 10% more RPM than the bottom end was designed for. What's gonna fail next. I'll put $10 on the connecting rod, $5 on the bearings.

Whew, sorry about the rant. I've watched many people spend their savings building up half of their engine, only so it's capable of grenade-ing the other stock half leaving 5 quarts of oil on the local 1/4-mile track, and no money in the bank. If you want to hot rod properly, you have to sit down, decide what kind of power you want, and then build your engine accordingly, from one end to the other. That's what the engineers did with the stock engine.


Take it easy JJ, we're only talking about model engines, they're only model engines, they're only model engines, they're only................. LOL

What does it mean to.....
 

You beat me to the Submit" button C_Watkins!!

What does it mean to.....
 

Hehe. First race I've won in years :)

I rekon I got er now....
 

Engines whirlin so fast her gutz cant keep up.
Im breaking in a brand spankin new Saito 150, was going to go for the 180, but, I let LHS talk me out of it.
I will be sure and not let this happen, If I really do understand this correctly, as long as the high speed needle valve is set per specs, 2-300 rpm below peak, I shouldnt have to worry about over reving anyhow??

Thanks a bunch.

Roger

What does it mean to.....
 

Roger,
Is the prop your using among those recomended by the web site? What fuel are you using.

You could be over reving it? Eventhough you richened it up some. I'm assuming that you don't have a tach?


Jim

What does it mean to.....
 

Jim,

Im using one of the recommended props per the instruction manuel, its a 16-8.
2 tanks of fuel so far 15% nitro 16% oil.
HS all but insisted this be the fuel used, I HOPE this is right?
I havnt even gotten to half trottle yet, book says 10 mins. at no more than 4000 rpms.
Ive had to stop and let my glow ignitor recharge as its been almost continuously connected because of rich initial setting, at least I hope this is the reason for not cranking.

Thanks
Roger

What does it mean to.....
 

Roger,

Everything sounds OK.

Jim

What does it mean to.....
 

One more thing Jim,

Itd seem that any time a prop change, in size, or pitch, was done, that Id need to re set the high speed needle.
I suppose I need to get a tach to finish my break in proceedure.

Thanks again

Roger.

What does it mean to.....
 

Roger,

You don't have to have a tach. If you follow the guide lines like you have so far, then you'll be OK. Concentrate on other things for now.

Yes you most likely will need to adjust at least the high speed needle if you change props. But most people can adjust the needles by the sound of the engine.

Some people have bad hearing and need a tach if they cannot feel the plane and tell what the engine is doing?

Now, if you need some snob appeal to keep your syche going, then by all means get one. Then you can come back on here with certain bragging rights about how many rpm's your engine turned.

A tach is nice if your really intrested in engines and you want to try to get the last bit of power from one. But you don't have to have one.

I've never seen anyone get their tach out at the flying field. A lot of the fellows probably have them but I suspect the only person I'll ever see at the field with one will be some new guy.

I have a TNC tach which is expensive and no longer made, but it stays in the shop. I don't take it to the field.

Good luck,

Jim

What does it mean to.....
 

Hey Flap,
During the initial break-in, I belive the Mfg. makes a point to not exceed 4,000 rpm on the first initial runs, for only a special duration of time. I belive the first couple of runs, saito wants you to use the glow warmer on the plug during those runs untill it will operate without it. These things, as well as the tach, may not be necessary, but I have found that following these instructions have given me a very powerful and reliable engine-if not that, then piece of mind. You probably will not go above half throttle at first anyhow, so you won't hit those rpms.

W8ye is right, you will seldom see people use these instruments out at the field, for my case, it is because I have spent the time doing those things at home, and have gotten to know my engines and how they operate well enough so I won't have to waist that time at the field when I could be flying.

I'm glad you asked what it means to "float the valves." When I told you to be careful, in an earlier thread you put out, not to "float them valves," I was afraid you wouldn't know what I meant. But, as you have stated, these sights are great to get a lot of perspective, from people with different understandings and experiences.

What does it mean to.....
 

Im not real big on gizmos and gadgets, really dont have a big hobby % on the old budget, which is one reason Im so proud of this engine!
I also really really really dont want to do anything to reduce the life of this one and I havnt built up much 4 stroke confidence yet, so, I may borrow a tach just to be sure as Im not used to the "right sound" of these yet.
Maybe after I get to "get down" on the throttle a little, Ill realize its not so different from the 2 strokers I can easily adjust now, which I knew nothing about a short time ago.
Any how, my knowledge has increased 10 fold just this week by finding this site and you guys to "talk" to.

As always, THANKS

Roger