oversize valves head work w/pics

[Guest]

I am opening up my seats for oversize valves, I cut the seats at 45, then a 60 then a 75 to open up the throat. After the 75 cut I am grinding the area more to blend in the cut to the port as has been done some on the second picture.
Question is how much more grinding should be done to realize the potential of the bigger valve?
Sure wish I had a flow bench, but any help/ideas from guys experienced with this work would be much appreciated.

[1980GS1000E]

The chamber roof looks very rough and will need lots of work. Looks as if someone went crazy with a power wire brush.

[sharpy]

This tread be interesting to see who will give up there ideas and who shoots those ideas down. Lots of "experts" and/or "mates" that will put there 2 bobs worth in im sure. Suppose you have to start somewhere and any help SHOULD point you in the right direction. Or am i just a grumpy old man?

[Big Jay]

Throat should be around 88% of the valve size. First bore the seats out, then blend them to the ports, then do the valve job.

[gearhead13]

Throat should be around 88% of the valve size. First bore the seats out, then blend them to the ports, then do the valve job.

88% of the overall size of the valve (28mm) or the width of the new seat?

[Big Jay]

88% of the valve head size. We do some a little larger. For the 28mm valve, you would bore the seat throat to .970"

[rapidray]

I can see a BUTTLOAD of potential for airflow still in the seat areas but that's because I have a flowbench & a couple thousand hours using them over the past 34 years. Ray.

[gearhead13]

I can see a BUTTLOAD of potential for airflow still in the seat areas but that's because I have a flowbench & a couple thousand hours using them over the past 34 years. Ray.

Yes, it is a work in progress.
Thanks to Jay for getting me on the right track. I plan on making/buying a flowbench in the future.
I have moved the valve seat area further out to the margin of the valve and looking to open the throats to 88%.
I will post some more pics when I am done.

[headsbikesmopars]

88% of the valve head size. We do some a little larger. For the 28mm valve, you would bore the seat throat to .970"

What he said..

[headsbikesmopars]

I can see a BUTTLOAD of potential for airflow still in the seat areas but that's because I have a flowbench & a couple thousand hours using them over the past 34 years. Ray.

What he said...

[gearhead13]

Bike is back together now and after a couple tanks of gas, it is performing well, I have had the front wheel come up a LOT easier now.
I know the port work I did wasn't top notch as far as max air flow, but I think that port velocity is also as important. I didnt want to hog them out and lose velocity. All I need is a new clutch and in the spring I plan to bring it to the local 1/8th mile track to see what it will do

[posplayr]

Bike is back together now and after a couple tanks of gas, it is performing well, I have had the front wheel come up a LOT easier now.
I know the port work I did wasn't top notch as far as max air flow, but I think that port velocity is also as important. I didnt want to hog them out and lose velocity. All I need is a new clutch and in the spring I plan to bring it to the local 1/8th mile track to see what it will do

I agree .......if I was going to port my own head, I would not port my own head

[gearhead13]

I agree .......if I was going to port my own head, I would not port my own head

I have ported everything from 2 stroke dirt bikes to V8 car engines since I was in my early teens, so I do have experience. If I had a ton of money to throw away like you I *might* pay someone else to do it.

[posplayr]

I have ported everything from 2 stroke dirt bikes to V8 car engines since I was in my early teens, so I do have experience. If I had a ton of money to throw away like you I *might* pay someone else to do it.

I was agreeing with you, you posted that you removed as much as you felt comfortable doing without affecting port velocity.

It is real easy to F up a head taking out too much. The skill is in knowing where that point is. Without a flow bench there is no way of knowing unless someone that knows tells you. Since two people that know just told you, you can be feel comfortable you acheived your original objective (not going too far).

Bottom line is in knowing how far you can go; you have to stay away from going too far depending upon how well you know what you are doing.

I have no idea, and would not want to trust my head to my hand (with a grinder), so I had Terry do mine.