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.

[nastyjones]

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.