valve lapping need or not need

[Addy Leung]

I have got my gs1100 head from US which just have done the 3 angles valve job. But under the sun light, I see light can through the valves seats - 15 out of 16, it is very fine light.
Do I still need valve lapping job to make perfect?
Or just install it and let it run it?

Hope someone can share the experience to me.

 

[Billy Ricks]

Suzuki doesn't recommend lapping. Their theory is the valves will seat themselves in the first few seconds after it fires.

 

[Guest]

I hand lapped the valves on my 4v 750. I did it to final seat them & smooth out any imperfections. It seemed to work out fine.

Paul

 

[Addy Leung]

Thanks for input.
My Local workshop old man told me that I can use the lapping-fine-sand-materials to lap the valves and also do the hammer action during the lapping to make it perfect.
my valves are now s/s valves, not the stock valves. So I think it would not have the stock hard plating on the valves.

Do you think I still go to do some mirror lapping?

 

[rphillips]

It's no secret, You all know I'm not a master mechanic, but I wouldn't think you should be able to see light thru any of the valves with a new valve job, weather they were lapped in or not. Surely not thru 15 of 16

 

[Addy Leung]

it is true. I can see very little light through valve seat when my eye very close to the in-port and out-port. When I use my hand to cover the valves area, all the ports are dark. when I remove my hand and the velves is under the sun light, very little can pass through the valve seat but just little.
I mann 15 valves out of the 16 valves is like that.

 

[BadBillyB]

This is what you should do. Rotate the valve 90 degrees on the seat while you are seeing daylight through it. Rotate it another 90, then again and again. If it goes from light to dark to light, the valves are not straight. If the light remains the same, the seats are not concentric with the guide and the valve job was done poorly. Lapping the valve and seat should not be necessary........It just hides a poorly done valve job....Billy

 

[hungryman]

You shouldn't be able to see light and you don't need to lap them. Take the head back to the shop who did the work for you.

 

[jimg]

You shouldn't be able to see light and you don't need to lap them. Take the head back to the shop who did the work for you.

FWIW. I don't know about motorcycles, but Dad was an International Harvester/Case IH mechanic for 55 years and I can't tell you how many valves I have lapped. He worked on engines from 4hp mowers to 400hp diesels. He would turn over in his grave if I didn't lap a valve. He was a perfectionest and when doing an overhaul, expected the engine to perform as it came from the factory.

Here's what he said. Every machine has tolerances, from the valve grinder to the seat grinder to the valve guide reamer. The ONLY way to insure the valves match perfectly is to lap them in the seat they are going to be used in.

Maybe Suzuki's seats and valves are different and can seat themselves under heat, but I wouldn't bet on it.

 

[Addy Leung]

I think Jimg is right. I said little light is mean that only a very small spot of light source but it can not bright up the port all, the port is still look dark.
Anyway it is good to try to turn the valve by 90 degree to see the what I can find.

I would not say which shop did my heads as it is already a second-hand head I got it from ebay. I just let him to make refreshment valve job. The 3 angle valves job is done by his Serdi Valve machine. I think it shoud be not bad.

I will try to lap it as carefully as I can. it is my first time.

 

[hungryman]

I suggest you talk with any top engine builder and see if they lap their valves. They don't.

I'm not sure about tractors and what tools they use on them, but for high performance engines, no one I know or has written on the subject laps valves.

Your dad propably lapped the valves because his grinder didn't have the precision that modern machine shops have. If you are using a hand grinder guided buy a stem inserted into the valve guide, then yes, you will not get a perfect valve seat, especially if the stone isn't surfaced properly, or there is any slop in the stem. (I'll bet dollars to donuts that's what your dad used).

Personally, I don't care what you do to your bike. Just stating a fact that valves should not need lapping after a precision valve job.

 

[BadBillyB]

I am going to have to agree with Hungryman, lapping should not have to be done, it only covers up a poorly done valve job. If the seats were done on a Serdi machine, I'm betting the valves were not ground straight. That is why I told him to rotate the valve on the seat, seeing if the light appears and disappears. This is how you check the valve for straightness. Here is a little test I do to check the valve and seat....With the valve seal removed, you drop the valve onto the seat from about a 3" height. If the valve and seat are properly done, the valve will bounce 3 or 4 times before coming to a rest on the seat. If you drop it and it sticks (with no bounce), you have problems.....The reason it sticks is because it is deflected to the side instead of upwards. This can wreak havoc on your valve guides and seat.......From experience, I have found that in most cases where the valve was not ground straight, the end of the stem was not faced squarely or the chamfer on the end was not true to the stem........Some machines, including mine, use that chamfer to center the valve in the chuck. I always face the stem, machine the chamfer, then grind the valve........But as my friends always said, "Theres a right way, a wrong way, and theres Billy's way"......I also am a perfectionist, thats why I bought my own machine.......Billy

 

[Footy.]

Having spent over 30 years in the engine reconditioning trade, i have used all manner of valve and seat grinders and cutters.

Our company in Cheshire, was one of the first in England to invest in the then novel Serdi valve seat machining equipment.

But i have to say, even the Serdi can produce poor results if the operator is not properly trained, particularly if non-carbide mandrel's are used when cutting three angle seats in one operation. Machines like the Serdi with air floating centering, depend on presise air pressures and "clean" air! If not, the free floating centering can "stick" slightly producing in-accurate work.

What the machinist should do is check the seat by dropping the valve in whilst still on the machine, and use a port vacuum device to test the seal. At the very least it is easy enough to just use a thin coat of engineer's "blue" on the valve face, then fit and "spin" it on the valve seat. This clearly highlights any lack of concentricity and high spots some hand cutters can produce on seats.

It's not rocket science, and for the price people charge for this work, it is just not on to be able to see light as described. I would use some "blue" as described to highlight the problem, and take the head back to the machinist!

It should be noted that in most cases where valve and seat lapping is not recommended, this is because the design uses a half degree difference in the valve/seat angles. This gives a high loading over a small area for the valve to "bed in" quickly. When valves and seats have been re-machined at a shop, this slight angle difference is not always maintained, so again bluing can show the contact area.

I don't really "lap" in valves as a means of actually removing metal. What i do on general engine builds is just give valves a few seconds of lapping with a fine paste. The matt grey finish shows up any pitting or flaws in machining if machining has been done some where else. If the valves and seats are not good, then you can decide on further machining.

I must say i dont go along with some kind of Suzuki hard coating on the exhaust valves, that lapping will destroy? The only such coating i know of is stelite that is used on some exhaust valves. As far as i am aware, GS Ex valves are the standard bi-metal design where the head uses one metal friction welded onto a stem metal that has better bearing characteristics to run in the guide.

When i first got my GS750 in the early eighties, i overhauled the engine including re-facing the exhaust valves on a valve grinder to remove pitting. After around ten thousand miles later, i rebuilt the engine again. There was no real wear on the exhaust valve seats at all, that would indicated i had ground through a hard coating!

So if machine re-facing is'nt doing any harm, lapping certainly won't! Remember like most manufactures, Suzuki want to sell "new" parts.

But back to the original post, take it back it is shoddy work !!

Footy.

 

[DaveDanger]

I agree with jimg. As far as I'm concerned, a valve job isn't completed till each valve has been hand lapped into the individual seat that it's going to run with. You don't have to lap the valve till it falls through the seat, but you want it to seal perfectly.

Back to the original post... when a GOOD machine shop or mechanic completes the grinding part of a valve job, before even lapping, the head (with valves installed) should be flipped upside down and gasoline, alcohol or lacquer thinner should be poured into the combustion chamber in the head. If ANY fluid runs through the valve face and seat, you instantly know that you have an imperfect valve surface. The amount of leakage tells you whether lapping is sufficient or regrinding is the answer. I'll guarantee that if you can see daylight through the valve seats, it won't hold oatmeal, much less fuel

 

[hungryman]

This is one of those subjects that we will just have to agree to disagree on and let it go at that. I've built many engines, never lapped the valves, and never had an issue with valves leaking. Do it right the first time.

 

[Boondocks]

From the 1980 Suzuki GS1100 Factory Service Manual. I will skip to the final part:

If the contact area is too low, use 75° cutter to raise and narrow the contact area. If the contact area is too high, use 30° cutter to low the contact area. After cutting the 75° and 30° angles, it is possible that the valve seat (45°) is too narrow.

If so, re-cut the seat to the correct width.
• After the desired seat position and width is achieved, use the 45° cutter very lightly to clean up any burrs caused by the previous cutting ooperations. DO NOT use lapping compound after the final cut is made. The finished valve seat should have a velvety smooth finish and not a highly polished or shiny finish. This will provide a soft surface for the final seating of the valve which will occur during the first few seconds of engine operation.

• Clean and assemble the head and valve components. Fill the intake and exhaust posts with gasoline to check for leaks. If any leaks occur, inspect the valve seat and face for burrs or other things that could prevent the valve from sealing.

Prior to the valve grinding, the manual specifies using Prussian blue to check the valve contact and valve seat width. Footy has given you good advice which is very similar to the factory manual.

I would not lap the valves in an attempt to compensate for a poor machining job. I would return the head to have the job done properly, or give it to someone who is competent and follows the factory manual procedure.

 

[Addy Leung]

First at all, I would like to thanks for all sineor menber advice. Thank you.

I would really like to return it to the darg racing motorbike shop. But I am living in Hong Kong, it takes 5 months to make the round trip by surface mail and $120 for two shipping cost.
I think I will check the step by step before doing any lapping work. 1/ filling alcohol to the port , 2/ Rotate the valves to see any different, 3/free fall the valves without the valve seal, 4/ blue print checking to the valve seat.
One thing I just think about it that would the valve now is water tight only but still let a little bit sun light go through – I mean that it will be water tight but not gas tight at this moment - just after the proper machine valve job. Once the engine fire up, all valve will be heat up and continues to hit the seat properly to form the perfect sealing and it will be gas tight.

 

[Addy Leung]

I tested by filling alcohol and find that all the valves are leaking. I lapped all the valves now. I found that each in take valves has 1/5 is not seat well before lapping.

Now all the valve seat is OK. The boss of the bike shop tell me that lapping just are speeding the processe for the valves seat well. If I don't lap, it is still Ok after the engine run-in.

But this first lapping exprience tell me lapping is a good thing to ensure your valves are seating well.

 

[Wingnut]

Personally, I think you got a bad valve job. I would go back to the guy and tell him to fix it or refund. When a valve job is done right you should be able to poor gas in the port and it should not leak past the seat. Whether you get to that point by regrinding or lapping doesn't mater but that is where you need to be. I wouldn't put the engine together like it is. It is true they would probably seat themselves eventually but I am not willing to wait 5 or 10K mile for this to happen and for the motor to finally run right. It is not going to idle correctly and you run the risk of burning a valve with the leakage. Incompetent machinists infuriate me. They are everywhere. They know what is right, they just don't want to spend the time to do it. They will always take the time to collect your money though. Go back down there with the head, and attach a tag to it that says "fix this correctly, I have 6 more heads" and throw it through the front window late at night.

 

[argonsagas]

Addy, you did the right thing in doing the lap work.

Under NO circumstances should you be able to see light past the seat of a properly ground valve. At the very least that indicates an unnecessarily rough surface on either or both the valve and seat, and for 15 of 16 to be that way is inexcusably poor quality work.

Given the fact that you had visible light, there is also no way that you could or should believe that use after installation would have the poorly-ground valve seat properly. There are too many possible variables to accept this.

Given the second fact that sending the unit back would have been expensive and taken a lot of time, it was very reasonable to do the lapping, and thus gain a better picture of what you had.


It would have been a very reasonable choice to return the poor work to the shop with a demand that the work be done correctly, but your own effort seems to have paid off, as it appears that the alcohol stays up, and you now have leak-free valves.


Well done!