Tuesday, April 10, 2007

Porting, cleaning up head ports, head work.

Dismantled the head today, nice easy work on a proper head thing.
Got the exhaust valves refaced and cleaned the carbon off.
Had the head face skimmed, 0.002" all that was needed to clean some tiny marks off. Risky facing before porting, but I got a rubber tipped extension on my dremel tool and taped up the face.
To be honest I was expecting the ports and valve seat areas to be worse, they weren't too hot but not too bad. There were alot of ridges, sharp angles and mess as the seats were larger than the ports, some quite big, so ridge was on the bad side (fighting incoming gas)...

Also as shown above the bend before the seat at the back is a VERY sharp angle, which is pants, rough and a mess. Seat inserts also have a convex radius on the non seat area which is a bit crap.

Untouched port above, showing the ridge on the port. They look ok cause you can't see the ridge on the seat inserts which is up to 0.75mm in places. Stick your finger in and its a different ballgame, pretty crap. Ideally you want to punch the guides out and remove some roof area in the port, but thats just not worth the hassle atm. Maybe next time.
Roughly reshaped, I had to use a grit stone on the seat inserts to grind them away, took about 5minutes a port, just till they met the alloy of the port, showing the ridge was removed then flap wheeled the rest and the port.

At this stage I left some distance to the seat till I had done all the ports, then I flap wheeled right up to the seat and a bit further, I don't want to cut the seats again as they are fine so this was delicate work, but I didn't mark any seats working right up to them.

Finished port exits. Flap wheeled right up to the seats, I reduced the seat width very slightly. Once I grind the valves in i'll go back and remove some more material leaving a 1.5mm seat area. I had to use flap wheel as a burr is too aggressive and dangerous in such fine work.

I will not be flap wheeling the entire port, just the exits, i'll leave it rough like it left the factory to help fuel atomisation on the carbs. Plus I can't do some areas without removing/replacing the guides.
Here you can see above that the port meets the seat with no ridge, shame I didn't take a pic before as the ridges were pretty bad.

I see DVA (main K man) doesn't cut another angle before the seat, he runs the ports straight onto the seat and runs a thin seat. So I copied him, he gets up to 250HP from a 1.9 stroker motor so he's clearly in the know.

This is by no means a port job, this is a fettle of the seat area copying a DVA job here and removal of production imperfections...A full port job is different.

This work alone should be worth just over 10HP also it will help torque as cylinder filling at lower valve lifts will be better.

Once the valves are ground in they will be backed off, ie a chamfer cut at a shallow angle right up to the lapping marks on the valves, so reducing the unused valve seating area, so improving flow at lower lifts...

Took me 3hrs to do that work.

Will do the same to the exhaust valve ports tomorrow night. No doubt i'll go back and have another poke in the inlets.

All helps.

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