So how wide of a sealing face is appropriate? It seems that some designs call for a 1° difference in the sealing faces, which would result in line contact. This design relies on the parts wearing into each other. More typically it seems engines call for both the valve and seat to be cut at 45°, with a specified seat width. Model engines seem to use the former, I'm guessing, because it's cheaper. Another question is do production automotive or other engines have lapped valves out of the factory?

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I guess I can't help but keep remembering all of the times I saw fellows ruin brand new engines at the flying field using Fox Lustrox. <G>


Ed Cregger

The less sealing surface, the better. Do some math. Figure the area of a 0.002" wide band around the valve and figure the pressure sealing the valve, figure 50 PSI of compression for a bench mark and and in the couple lbs of valve spring. See what the sealing PSI is. Now do the same math for 0.006" band. There will be quite a difference. Even a minimual use of abrasive will accomplish this amount of band increase very quickly. As the band increases in width, there is an accompanying requirement for more pressure to maintain the same seal. Seeing as our pressure is a fixed element, keeping the band narrow is the way to get the best seal.


As to the car companies lapping valves, I doubt it. With the CNC machinery now used, the manufacturing tollerances are very tight. The only reason to lap a valve to begin withis that the tollerancew were not very tight. It is not unheard of today to keep tolerances within +/- 0.0002" or better. In the 60's, that would have been closer to 0.0015". Remember in the 60's, your new car manual had you not driving the speed limit for the first 2000 miles. Replacing the "break in oil" after 1000 miles, The an oil change every 2000 miles. The valves and rings had to "wear in" for fit. You don't see that in todays cars. The engines are made to run and will right out of the box. I would be absolutely astonished if the valves in our current 4 strokes are lapped in either at the factory. The CNC macining eleminated that need.

Don

....ED, what the heck is Fox Lustrox ?

stuff Fox used to sell? A little dab in the intake while the engine was running, and it would help breakin? Breakout? Breakup?

What brought about the question was FBD's photo with what looks like a .020-.030" seat width, maybe more, I have no idea how large that valve is.

Greg, that is what I was afraid people would look at and think it is acceptable. Even on a 2 1/2" car valve, it looked to wide. Like you ask, a sharp line is the best. A wide line like the photo is going to be a leaker. The least little speck of carbon will prevent it from closing all the way. A sharp line will crack the carbon in half, and still seal.

A couple years back, I bought a set of plans for a 1/6th scale P&W Wasp Jr engine. It uses the bronze valve guide/seat combo. Some of the guys building it complained about the valves wheezing as the engine was cranked over by hand. All reported that lapping only made things worse. These valves were cut by individuals making the engine, or by a guy that makes the valves for that engine and a couple others. They are not the precision CNC cut valves and seats you would expect in engine today, so they probably represent the quility of the parts back when the Wasp Jr was in production, and the need to lap and fit parts. That just isn't the case today.

Another thing just popped to mind. That is the ring. It used to be that when you purchased a set of rings for a car, you had to set the gaps for each ring in the cylinder it was going to be in. That is a thing of the past also. Now, if our guy who stated this thread happened to have pulled the piston out of the sleve, he may have broken the ring replacing it. That could be the source of his problems, not the valves. If that was the case, lapping the valves isn't going to accomplish much other than reduce the life of the head by several years.

Don

I just looked over several engines I have apart on the bench. The seat width in OS engines appears to be ~.015", 0.4mm. A Magnum 91 RFS with loads on time on it was interesting. The valves are visibly worn, but the seats are like new. I noticed my low time Enya 46-4C had worn seats and guides. The Enya appears to have a multi angle seat, the only model engine that I've noticed it on. I don't have many Saitos, the FA-40 appears to have a wide seat, but the valves are relatively small. This FA-40 appears to have a damaged intake valve. There is a blemish on the sealing face. It's in pieces for repair now because it leaks. I'll probably regrind the valve face on the lathe. I have an OS FS-91 SII I picked up as parts with very wide seats. This engine looks like has loads of time on it. Over all I think seat width is intended to be what OS uses. I'll pull a new engine and have a look.

We've found that you can over-grind a valve and seat, even if you only use a polishing or lapping compound. Then the edge of the valve becomes too thin and begins to warp away from the valve seat. The rim of the valve can become so thin that the valve starts to become more and more recessed into the valve seat area, finally becoming small enough that it's well inside the port area. The engine is ruined at that point, and a new cylinder head and new valves are needed.

Valve maintenance should only be performed by trained and skilled personnel. That's why
most shops send the heads out to an automotive machine shop to have the work performed
by a skilled professional. Almost any part of any mechanical apparatus can he hacked to death
by the backyard hackers.

A valve the has been over-ground in the manner that you describe, Bax....has had a drill motor
fastened to it....and the valve and seat ground to death. Lapping compound is about 50 times coarser
than fine polishing compound. Polishing compound is so fine....it is used primarily to remove scratches,
not remove material.

Cleaning a valve and seat in the manner I use will not harm them in any way, shape or form.
I'm quite sure that you know that. How many grams of pressure could be applied with a pin-vise ?

It would take a real idiot to harm a valve with polishing compound. I wonder how many hours it would
take with the drill motor, and how many times he would have to clean the parts and reapply polishing
compound....maybe 50 times....a hundred ?

FBD.

Edit: Dave...you posted just before I did...this isn't in response to your post...I'm in full agreement w/ you FBD.




That may be so, if one is using some sort of power tool to spin the valve and applys too much pressure...uses too coarse a compound...and/or if one is mechanically inept/ham handed.

IMO if you're just talking about cleaning the valve face and seat, you can do it by twirling the stem between your thumb and forefinger with the "Soft Scrub" or Copper bottom pan cleaner like I mentioned previously. The whole process only takes about a minute per valve.

If you are removing any significant amount of metal, then you are doing it wrong.

The Clover valve grinding compound from the auto parts store will grind them away quickly even if you use the fine side of the can.

Will something like oven cleaner work to take off the burned castor on the stem/near the face. I have used my Dremel with a metal brush, but it can only do so much

I've used the crock pot anti-freeze method for carbon removal. It gets most of it and the wire brush in a dremel easily removes the rest.
Edwin

Here's a recent thread where we talked about a similar situation:
http://www.rcuniverse.com/forum/m_8254906/tm.htm

Being a trained mechanic and engine rebuilder I feel competent to add my input. I was taught that when it comes to lapping valves it should be done as a final step in the valve grinding to just obtain that final degree of perfection from a proper head rebuild. Using it to fix problems may invite some of the trouble already covered here. The seat width is considered very important so widening it by excessive lapping is not recomended. Most rebuilders make the mistake when checking the seat with bluing by rotating the valve , if there is a high spot on the valve it will appear as a complete circle using this method and lead one to believe the seal is good. Proper method is to just "pop" the valve straight in and out and check the pattern.
I was also taught that if the valves are not perfectly sealed the hot gasses will burn the seats and lead to failure.
There are enough variables and tenchniques that I can not cover here.

Here are some more discussions :

http://www.rcuniverse.com/forum/m_64...tm.htm#6463732

http://www.rcuniverse.com/forum/m_41...tm.htm#4108460

http://www.rcuniverse.com/forum/m_70.../tm.htm#705940


FBD.

Oven cleaner works good on steel surfaces but absolutely do not use oven cleaner on aluminum.

the aluminum will turn dark forever

Hmmmmmm,,,,,,,,,coloring aluminum,,,,,,,,,,,might look cool. Really, really cheap anodizing looking stuff.
Nah.

I HAVE BEEN DOING MECHANIC WORK FOR OVER 45 YEARS. I DON'T SEE ANY PROBLEM WITH LAPPING THE VALVES IN THIS HEAD. WHEN YOU LAP VALVES YOUR NOT ACTUALLY TAKING VERY MUCH MATERIAL OFF THE VALVES OR THE SEATS. THERE SHOULDN'T BE ANY PROBLEMS LAPPING THESE VALVES AT ALL.

....Welcome to R/C Universe tubetype1....[sm=thumbup.gif]

While it is clear that all the real mechanics agree that the the valves must be sealed 100%
to avoid problems later....it should be noted that real mechanics take the extra step necessary to
avoid any valve leakage, and the possibility of premature valve burning and failure, due to a
leaking valve. While it is rare....even an intake valve can burn if it should leak.

It seems like only the guys that are not really familiar with valve servicing would argue about
valve lapping....using only unfounded Internet arguements to serve their case, not actual experience.

This happens alot on the Internet....but it makes for interesting discussion.

FBD.

2 Strokes............one less thing.

True, but 4 strokes keeps our minds busy

Gents,

A picture of my 30 years old ENYA 60 4 C engine.
I did make the picture when I did repair the thread of the glowplug.

This Is all I can show you because, why should I remove the valves?

The material of the valve is harder than the seat. Even a very little scratch on the valve and in my opion, it is end of story. You can lap a seat but not a valve.
The rocker will hit the stem not exactly in the centre and it is often done this way (motorbikes) to let rotate the valve.

Of course I cannot compare the power with the other engines on the field, but he can pull the Orion, nearly 10 pounds, 70 " span.

Cees

Nice plane