1mm or 2mm over valves

@Liftedzuki
Uuurgh with what jack refered to i can only marginally assist as I have other ways of approaching the same target/goal.
Thinking now I could imagine measuring the inner diameter on the seat (yamaha usually likes very wide seats on the valves) that you might be almost there and just need to grind down a hint on the seats in order to arrive at the needed inner diameter, thus cutting just down on the outer circumference of the valve should be no issue in my book.
Tell you what, I think I have a original non touched head laying in my current stack of to be ported work of which I could measure the needed dimensions.
If you measure me as precise as possible (dial calipers a must!) the inner seat diameter on the seat I will see if I can help you a lil tomorrow doing some assumptions and calculations.
Sorry for my somewhat tardy reply but I'm not regularly in the forums for lack of time (family, studies and assorted competition porting work).

Btw from what I can tell, replacement valves are over here still wo any Prob's available although not for discount prices.
If they are OEM I did not investigate but usually there is quite good availability of xs parts in europe.

Kind regards

Christian
 
273974311627
273974311889 ebay numbers for xv750
valves, the valves are exactly the same length and stem size, just have to grind the seats and they can bore into the port at the same time
20210503_180958.jpg
 
That part is up to you, I'm sure Jack would tell you, I had mine line bored to match the valves then smoothed around into the ports, but you do need to watch clearances if you look at the picture you'll see a flat spot on the spark plug where the valve has been skimming the edge
 
I just got done putting in the +1mm intake and exhaust valves and shell #1 cam from Hoos Racing in my motor. Without indexing the plugs as described above the intake valve would hit the ground electrode. Clearances are tight with 1mm over int and exh so 2mm over may require some outside the box thinking
 
I just got done putting in the +1mm intake and exhaust valves and shell #1 cam from Hoos Racing in my motor. Without indexing the plugs as described above the intake valve would hit the ground electrode. Clearances are tight with 1mm over int and exh so 2mm over may require some outside the box thinking
so even with the 1MM oversize you are having clearance issues?
 
Which do you think would be better 1mm over kibblewhite valves or 2mm over xv valves, if it was just down to size the answer would be obvious the kibblewhite are stainless so should have smoother flow across them against the heavier steel larger xv valves

Not sure where you got your information, Stainless Steel is not lighter than other Steel, in fact depending on the alloy it's often marginally heavier though not so much as would make a difference.
 
Not sure where you got your information, Stainless Steel is not lighter than other Steel, in fact depending on the alloy it's often marginally heavier though not so much as would make a difference.
Was talking to someone st a race meeting and he made reference to the extra size and weight versus the kibblewhite valves, must be said I've not noticed any difference in performance since fitting the 2mm over valves but have had to increase the size of the main jet substantially from 132 to 165
 
so even with the 1MM oversize you are having clearance issues?

With 1mm over I was having clearance problems between the intake valve and spark plug if the ground electrode wasn't directly opposite the intake valve. Once I indexed the plugs there wasn't any more interference. Everything seems to be happy now, although I only have 1 heat cycle on the motor. I did pull the plugs after the initial start to check for interference. The plugs were pretty black from using the enricher/choke with no telltale shiny spots on the electrode tip
 
I have been told the way to solve valve to valve clearance issues is to cut the valve seats deeper into the head. Never done it myself I have always had head work done by others.
 
I have been told the way to solve valve to valve clearance issues is to cut the valve seats deeper into the head. Never done it myself I have always had head work done by others.

Interesting that you bring this up. I had the head work done by a local machinist and in order to get proper spring height for the Rd springs I used the machinist had to cut the valve seats 30 thousandths deeper. I wonder if that is why I had no valve to valve clearance issues with 1mm oversized intake and exhaust valves
 
Never had a problem valve to valve with 1mm or 2mm over with either of my cams, just the plug,
 
Out of curiosity and it may also help in your decision making I measured stock valves and the valves I have for a Lillie replica head that is earmarked for a special race engine.
The Lillie valves are + 1.25 mm on the inlet and + 1.1 on the exhaust. I believe they used modified Harley valves back in the day.
We had very good results using another Lillie head. When I start to learn porting I will be using Jacks notes and use the Lillie head as the gold standard it is that good in my opinion.
I understand that Jack likes the XV valves for 2 reasons in that they are bigger but also the stems are better shaped for flow.
 
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