sparking

[rimcanyon]

I'm grinding valve seats dry with aluminum oxide stones and I don't see a lot of sparking, although the stone is in contact with the steel and it grinds and the seats look nice. Is the lack of spark an indication the stone needs to be dressed more? I have been dressing the stones every second seat; maybe I need to do it more often. The problem I am running into is slow cutting and I find it takes forever to grind out the high spots on the final cut. The stone turns at 10000 rpm. The grinder is an eccentric grinder, so it makes contact with a single point on the circumference of the seat. The contact point rotates around the seat at 20 rpm, and I usually let it go around 12 times on the final cut (36 seconds), but I am still finding high spots (.001" variation). The seats all get a 30 and 60 degree grind prior to the 45 degree cut. Often the bore of the new guide does not align with the original seat and prior grind, so the 30/60 grinds are quite important to get the seat centered, but even so, the 45 grind has to grind the high side down until the seat is even. That is the issue, it is taking forever.

All I know about the seats is that they are "hard steel", which Porsche changed over to from brass seats in 1960. So I am considering two things, wanted opinions. One is dressing more often. Second is using silicon carbide stones. The grinder mfr. made three types of stones: brown (unknown) for cast iron, grey silicon carbide for "hard seats", and white aluminum oxide for stellite seats. I have been using the aluminum oxide because I have found in other kinds of grinding, it does not overheat the work, while I have had problems with silicon carbide burning steel. So I tend to be cautious.

 

[rimcanyon]

I don't think the seats are stellite. As for hardness, they are soft enough to be cut by hand using a Neway seat cutter. The grinder mfr. is where the "hard steel" label comes from: their 1960 catalog lists Porsche seats as "hard steel" and recommends silicon carbide. What I don't understand is that they recommend al oxide for stellite and silicon carbide for "hard steel". What is the principle behind that recommendation.

 

[Milling man]

I'm grinding valve seats dry with aluminum oxide stones and I don't see a lot of sparking, although the stone is in contact with the steel and it grinds and the seats look nice. Is the lack of spark an indication the stone needs to be dressed more? I have been dressing the stones every second seat; maybe I need to do it more often. The problem I am running into is slow cutting and I find it takes forever to grind out the high spots on the final cut. The stone turns at 10000 rpm. The grinder is an eccentric grinder, so it makes contact with a single point on the circumference of the seat. The contact point rotates around the seat at 20 rpm, and I usually let it go around 12 times on the final cut (36 seconds), but I am still finding high spots (.001" variation). The seats all get a 30 and 60 degree grind prior to the 45 degree cut. Often the bore of the new guide does not align with the original seat and prior grind, so the 30/60 grinds are quite important to get the seat centered, but even so, the 45 grind has to grind the high side down until the seat is even. That is the issue, it is taking forever.

All I know about the seats is that they are "hard steel", which Porsche changed over to from brass seats in 1960. So I am considering two things, wanted opinions. One is dressing more often. Second is using silicon carbide stones. The grinder mfr. made three types of stones: brown (unknown) for cast iron, grey silicon carbide for "hard seats", and white aluminum oxide for stellite seats. I have been using the aluminum oxide because I have found in other kinds of grinding, it does not overheat the work, while I have had problems with silicon carbide burning steel. So I tend to be cautious.

You wrote the speed of rotation of the grinding wheel, but did not write its diameter The normal cutting speed for grinding is about 30 meters per second (or about 100 feet per second).

 

[michiganbuck]

Pretty much you want 4000 to 6500 surface feet per minute with an abrasive wheel to make sparks in steel. likely it is an 80 grit wheel so 10,000 rpm seems slow for a wheel that may be an inch or so diameter. What are the RPM options on your machine? is it a point-mounted wheel (abrasive on a shank)?
At a certain slowness, you are honing not grinding.

X But it looks like most valve seat grinder machines are made for 4500 to 11,000 so my higher speed suggestion is not likely the problem...and you never want to run any grinding wheel higher than the listed RPM.

I used to grind long runs of stellite parting blades at 1/4 x 2"and 10 or more inches long, but that was such a long ago that I forgot how stellite sparks.

We used to make valve seats in iron 2 to 3 tenths wide at the heel of the 45 so they would hit at the top and pound to perfect. Machining not grinding.
For pressed-in hard seats, it was dead on at 45* for both the valve and seat, with bought valves and seats.

Modern fuels like hard seats, or adding a lead supplement.

 

[moonlight machine]

I'm grinding valve seats dry with aluminum oxide stones and I don't see a lot of sparking, although the stone is in contact with the steel and it grinds and the seats look nice. Is the lack of spark an indication the stone needs to be dressed more? I have been dressing the stones every second seat; maybe I need to do it more often. The problem I am running into is slow cutting and I find it takes forever to grind out the high spots on the final cut. The stone turns at 10000 rpm. The grinder is an eccentric grinder, so it makes contact with a single point on the circumference of the seat. The contact point rotates around the seat at 20 rpm, and I usually let it go around 12 times on the final cut (36 seconds), but I am still finding high spots (.001" variation). The seats all get a 30 and 60 degree grind prior to the 45 degree cut. Often the bore of the new guide does not align with the original seat and prior grind, so the 30/60 grinds are quite important to get the seat centered, but even so, the 45 grind has to grind the high side down until the seat is even. That is the issue, it is taking forever.

All I know about the seats is that they are "hard steel", which Porsche changed over to from brass seats in 1960. So I am considering two things, wanted opinions. One is dressing more often. Second is using silicon carbide stones. The grinder mfr. made three types of stones: brown (unknown) for cast iron, grey silicon carbide for "hard seats", and white aluminum oxide for stellite seats. I have been using the aluminum oxide because I have found in other kinds of grinding, it does not overheat the work, while I have had problems with silicon carbide burning steel. So I tend to be cautious.

I would be using the silicon carbide, it worked fine for me on the last set of Porsche heads I did.

 

[rimcanyon]

After doing some checking, I found part of the problem. Its not the stone, its the fit of the grinder spindle to the pilot. Both the spindle and pilot are new, but there is still some rocking. The grinder motor is offset, so the weight pulls the alignment to the side. I found that if I supply a side force to the top of the grinder in the direction of the high spot I can eliminate it. The grinder has a handle with a force gauge built in, but the gauge is no longer accurate so it took some trial and error to figure out - I was not giving it enough force. Now I am getting seats flat to within .0002-.0003", which I am happy with.

 

[rogertoolmaker]

I'm grinding valve seats dry with aluminum oxide stones and I don't see a lot of sparking, although the stone is in contact with the steel and it grinds and the seats look nice. Is the lack of spark an indication the stone needs to be dressed more? I have been dressing the stones every second seat; maybe I need to do it more often. The problem I am running into is slow cutting and I find it takes forever to grind out the high spots on the final cut. The stone turns at 10000 rpm. The grinder is an eccentric grinder, so it makes contact with a single point on the circumference of the seat. The contact point rotates around the seat at 20 rpm, and I usually let it go around 12 times on the final cut (36 seconds), but I am still finding high spots (.001" variation). The seats all get a 30 and 60 degree grind prior to the 45 degree cut. Often the bore of the new guide does not align with the original seat and prior grind, so the 30/60 grinds are quite important to get the seat centered, but even so, the 45 grind has to grind the high side down until the seat is even. That is the issue, it is taking forever.

All I know about the seats is that they are "hard steel", which Porsche changed over to from brass seats in 1960. So I am considering two things, wanted opinions. One is dressing more often. Second is using silicon carbide stones. The grinder mfr. made three types of stones: brown (unknown) for cast iron, grey silicon carbide for "hard seats", and white aluminum oxide for stellite seats. I have been using the aluminum oxide because I have found in other kinds of grinding, it does not overheat the work, while I have had problems with silicon carbide burning steel. So, I tend to be cautious.

The sparks can depend on the alloys in the steel. A high alloyed steel will spark very little. Whereas a low carbon steel may have a large volume of long sparks. It's the way the steel is made to meet a certain requirement. It has nothing to do with how you dress the wheel or the contact with the work piece. Your grinding high alloyed, hard tough material. It won't be rushed. It sounds like your grinding wheel supplier is giving good advice for wheel selection. It requires patients. The only though I have is to use a sharp diamond to dress the grinding wheels. It makes a difference in how a grinding wheel reacts.
You mentioned you have trouble burning when using silicon carbide wheels on steel. Aluminum oxide wheels will cut better grinding steel than silicon carbide wheels. You might say they are more soluble in steel than a silicon carbide wheel.
Roger

 

[majohnson]

There is no mention of what you are doing with the valve guides. Replacing the guides will have small changes in how the valve face sits on the valve seat. If you using the hand held grinder it easy to oblong the seat a very small amount. Cutting the floor and top is in part to narrow the primary 45* angle. Be careful of how much die you use to locate the seat, it can clog the finer stones some. I was taught to redress the 45* stone at least every seat, maybe more if it would start getting a ring in the stone face.

Back when there was lead in the fuel mfg didn't install any bronze guides, it was just a hole in the cast iron. So we knurled and reamed a lot of heads because the car would have oil smoke the valve seal had hardened. Now the problem is parifin build up on the back side of the valve.