valve lapping need or not need

[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!

[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.

[flyingace]

I thought you didn't lap Suzuki valves because they had a hardend surface material that can be ground away with lapping compound. And once this material is gone, valve wear is rapid.

Is this not so?

[Addy Leung]

no, they are stock valves. When I get it from the seller, it was installed with 28.5 and 24 S/S valves I think. I found "F05" marks on in-take valves and "F07" on exhaust valves.
the exhaust valves seem to be more hard than the in-take valves.

One thing I learn is that do not lap the each valve too long time to make the valve seat width too large. as state in the manual it should be only 0.9mm to 1.1mm.
My first valves lap too long and make it have 1.9mm width valve seat.

[rphillips]

Didn't the 16 valve GS 1100's come stock with Stainless steel valves. It seems I remember people buying & installing aftermarket stainless valves, thinking they were getting a better valve, when actually they were just swaping stainless for stainless.