Lapping valves on OS Surpass
 

Can anyone please tell me the correct wat to lap valves on a OS Surpass? Pictures if possible. THANKS

RE: Lapping valves on OS Surpass
 

I don't see anything in the photos that indicates you need to lap the valves, Why do you think you should???

If you do decide to go down this path, be warned the lapping the valves in these engines is a case of less is best. You don't have the huge volume of say a car engine, and the valve surface is very small. The wider you make the seat, lapping it, the less compression you will be able to obtain.

I belong to a Yahoo group dedicated to small engine building. Valve lapping is a constant topic. The best results seem to be to machine the valves properly and NOT lap them. They get a better seal with the shapr break on a freshly machined valve. Lapping them dulls this sharp edge and reduces the sealing ability. I would think long and hard about lapping your valves. It may lead to the need for a new head and valves.
Don

RE: Lapping valves on OS Surpass
 

Don, thanks for the advise. After I replaced the bearings of the engine I thought checking the valves. The exhaust valve stem was full of burned castor, so I decided to remove both valves. I removed most of the burned castor on the exhaust stem, not touching the valve edge and valve seats. there was obviosly nothing wrong with the intake valve, so I just put it back. After I put the motor back, I turned it over by hand (with prop) and i could hear a slight hiss from the exhaust port and intake port. checked the valve clearences, still the same. I thought the engine just need to run a bit for the valves to reseat. Saturday I had about 4 flights of 10min, the engine was not performing well. Idles perfectly but could not get enough power. I played with the needle valve but still had no luck. While I was revving up the motor I could see the firewall was full of castor (behind the carb). It was never that bad before, therefore I think the intake valve is not seating properly. I have heard that guys use plain toothpaste to lap the valves of model engines.

RE: Lapping valves on OS Surpass
 

You can use tooth paste.

Hold the valve stem with a pin vise
Get yourself a good pattern on both valves.

You may need to readjust the valves after the lapping.

You may have the cam off a tooth?
http://image2-6.rcuniverse.com/e1/ga.../lg-163571.jpg

RE: Lapping valves on OS Surpass
 

G'day

I did once lap the valves on a Saito with a little tooth paste. Very gentle is the way to go if you do decide to. This particular engine was a FA45 about 15 years old and after its cleanup it ran well. But from your description of low power, are you sure you have not got the timing out by one tooth? My friend's ASP 52 idled and ran perfectly after I had to clean it out for him after a crash but it had no power. A one tooth change in the timing and she was back to her best. Check that when the piston is at top dead centre on the non power stroke that the tappets are rocking by equal amounts ie that at TDC, the exhaust and inlet valves are open by the same amount and the two rockers are parallel.

RE: Lapping valves on OS Surpass
 

Thanks guys, I did not even thought of that. I will have a look at the cam. I will just gently try to lap them again till I can see the edge is all shiny all way round

RE: Lapping valves on OS Surpass
 

Have the crank at top dead center and the dot on the cam should be in line with the lifters and pushrods.

The exhaust lifter has been removed in the picture

RE: Lapping valves on OS Surpass
 

I just rebuilt an Enya .46 4C and tried Brasso - too fine, toothpaste - too fine, Dupont chrome polish - nice but I quit very early in the process. Applying mouth suction to the intake and exhaust runners (with a plastic tube contraption I made up) the valves held a pretty good suction slowly bleeding off. The earlier reference to excessivly wide valve seats holds true - less than perfect sealing but good heat transfer from the valve head to the cylinder head. Heat transfer should not be an issue on an alcohol fueled engine. If anyone is aware of where I could obtain a proper three angle valve seat cutting tool for model engines I would be very grateful.

Bill

RE: Lapping valves on OS Surpass
 

An absolute seal is not necessary. Just a good enough seal.

When one thinks about the duration in milliseconds that the whole transaction occupies in time, it becomes apparent that a purely "perfect" seal would be a waste of effort.

I'm not saying that a sloppy seal is "okay". I am saying that I think that some of us go the extra distance to obtain a near perfect seal and then discover (eventually) that there is a point beyond which the law of diminishing returns makes itself apparent. Four-stroke heads are expensive. I wouldn't lap the valves in a four-stroke glow engine unless the head was nearly useless "as-is".


Ed Cregger

RE: Lapping valves on OS Surpass
 

Ed, would you say then that the slight "hiss" I hear in both intake and exhaust, when I turn the prop over is OK? I recon the compression must eventually bleed off, but not instantly.

RE: Lapping valves on OS Surpass
 

What thin liquid does you guys use to see if the valves seal properly?

RE: Lapping valves on OS Surpass
 

Most of us listen in the exhaust and intake ports to hear the leaks

RE: Lapping valves on OS Surpass
 

....the correct metod is to use polishing compound, and a pin vise to lap/seal
the valve to the seat. ;)

To check the seal, use WD-40 or similar fluid. The valve must seal 100%
to be perfect. If any fluid passes thru the closed valve....

....it is not sealed properly. ;)

FBD. :D

RE: Lapping valves on OS Surpass
 

Thanks FBD, I will give it a go

RE: Lapping valves on OS Surpass
 

.... [sm=thumbup.gif]

....you can use rubbing compound as well. Give it 10 strokes (twists), then rotate the tool
180 degrees, and give it 10 more twists. That should be all you need to remove the fine
bits of carbon. Clean the parts with WD-40, and check the seal with the parts bone dry.

Both surfaces will appear a dull grey when sealed....not shiny. Now you have perfection. ;)

FBD. :D

RE: Lapping valves on OS Surpass
 

Guys, if you can see the dull seat from the lapping compound, you have cut way to much off. Toothpaste is a mild abrasive, most containing aluminuma which I used to polish gemstones. It would be fine for a quick clean up, but keep the abrasives out of the engine. These are tiny engines, not your 327. You cant use the same rules for the valves.

A bit of hissing through the valves when chanked by hand is normal. A little carbon on the valves is OK. What makes a valve bad is a burnt blow by spot, or a bent stem. Pulling the valves and screwing around with them is a good way to bend a stem. Check your timing and leave the valves alone.

Don

RE: Lapping valves on OS Surpass
 

The problem I've seen with model four stroke valves relative to seating where it was not just carbon, dirt, or sticking is bent valve guides.

RE: Lapping valves on OS Surpass
 

What about Dawn Power Dissolver? Does it work for carbon, or only for castor and such?

RE: Lapping valves on OS Surpass
 

Interesting. Aren't the valve seats bronze? Aren't the valves steel? I am of the opinion that the valves are harder than the valve seats. I would think if the valves are true (not bent), then after say a minute of operation at top RPM, the valves would be well seated. And since the valve closed duration is so short, a more perfect seal is of marginal value.

Clean the valve stems, especially the exhaust valve. There should not be any residue on the intake valve. Reassemble, time correctly and run. That should do it.

Cheers,

Chip

RE: Lapping valves on OS Surpass
 

Chip, good advice.

I had a new four stroke that leaked out the exhaust valve a little but it ran fine. I used it 2 or 3 years and sold it to another guy who has used it for a couple. As far as I know it still leaks a little. I tried lapping it 3 times but couldn't get it to seat properly. The lapping pattern would look good on both faces but when you assembled the engine it would still hiss.

RE: Lapping valves on OS Surpass
 

I have checked my cam timing and it is spot on, so that is out of the equision:D

RE: Lapping valves on OS Surpass
 

Good . . . .

What's the next step in our process of elimination?

What about the valve gap confirmation?

RE: Lapping valves on OS Surpass
 

I would run the engine as it is and see how it stacks up to other engines of similar displacement/construction. If it is within a couple of hundred rpm, I would be tempted to let it be until it worsened noticably. Just my $.02.


Ed Cregger

RE: Lapping valves on OS Surpass
 

Here is a nice tutorial on valve regrinding and re-seating:
http://home.hiwaay.net/~langford/corvair/valvejob.html

Notice the color on the valve where the lapping has taken place.
It is grey. This is what happens when you lap a valve, no matter
what grit or compound you use. The grey part shows the rebuilder
the parts of the valve and seat that are making contact. The mechanic
wants to see 100% contact between these two mating surfaces.

If there is an area that is still shiny, and not sealing, the mechanic
will continue to lap the valve until the 100% contact and sealing of
that valve has been accomplished. In this tutorial the mechanic is using
blueing as a visual aid on the valve seat. If the bluing is not removed
100% by the compound, the valve is not fully seating and sealing.

Every engine rebuilder knows these procedures well. Not every engine
rebuilder actually does the valve job. Most heads are sent out to a specialty
automotive machine shop for this work.

In our application, using polishing compound as a paste, we are
simply cleaning the sealing surfaces. This allows us to see the
area of contact and make for a perfect sealing of the two parts.

I have used this procedure of cleaning and inspecting valve components
successfully since 1970 as a professional, factory trained engine rebuilder.
I have used this procedure for 20 years on my four stroke aero-model engines.

Trust me, you cannot hurt a valve or a valve seat by cleaning the surfaces
with polishing compound. ;)

FBD. :D

RE: Lapping valves on OS Surpass
 

I've been using virtually the same procedure as FBD, except I use "Soft Scrub" or Copper bottomed cooking pan cleaner instead of the white polishing compound...

The valve stems are not that fragile...it would take some effort to actually bend a valve stem...but you have to be careful obviously.
We are basically just talking about carbon removal, not removal of any metal. More like burnishing IMO.