A boring question...

[Anonymous]

Is it necessary to modify the head to match the increase in cylinder diameter when bored (1 mm over)?

Is there any appreciable increase (decrease) in compression ratio. The volume to be compressed is increased but so is the volume into which it will be compressed. Do they cancel each other?

And one last one (not boring, or about it anyway).
Is the additional cost of a three angle valve job really worth it for a street bike? My first thought is the decrease in the valve face against the seat would cause it wear faster but the somewhat rounding of the edge where the gases flow may make it last longer. I'm so confused :?
Thanks.

[Anonymous]

ill bet that you just should leave it alone. the compression ratio is a mathematical relationship of Volume to volume--probably not noticable. It looks like you are just rebuilding the top end with the 1mm over bore. Ill say just do it and dont worry about anything else. A standardvalve job is fine.

[mcconnell]

I had a full radius cut done on the valve seats when I had her apart for my 1st over bore job. The motor rev'ed easier than it ever had before. Previously, there were flat spots in the power band at about 4k and one at 6k rpm. They were completely eliminated. I can't give the valve job full credit as years before I slotted the cam sprockets and retimed the cams to sacrifice some top end power for more mid range. That had already made the flat spots less noticable. Was all of this worth it? Yes, but only for the tinker and fun factors.

[Anonymous]

A three angle valve seat is what every head has. A five angle valve seat is a step up and a radius valve seat is the hot setup today no angles just a radius allowing the air to flow better. DON'T let anybody sell you a three angle valve job as a hot set up. A 1mm over bore is a small over bore no head mod are required but while the head is off you might want to lap the valves lightly to clean the seats and install new valve guild seals and the top end should be good as new

[focus frenzy]

I put 1mm over sized pistons in my 1000g and it had some affect on compresion, (for the better) my bike now doesnt like anything below premium gas, and even with premium, when the engine is fully warmed up, rolling beyond 1/4 throttle below 5,000rpm triggers some detonanion, on premium it is fairly minor, but on regular, it clatters like a diesel.
Other than that, it runs like a champ.

[KGB]

hmmmmmmm

Stretracer,
I agree and see your point
for those of us running "street" motors, I have a 3 angle done on my 80-1000S, runs fine. 5 angle..don't know, radius yes makes sense.
More for "performance" than for daily riding.
I don't run at redline, but do see it often.
If you have the cylinders bored, regardless of how much,
you should have the head and cylinder deck checked.
I had both "shaved", it upped compression slightly.
It also ensured they seated after the rebuild.
Your middle cylinders run hotter than the outer cylinders, this can cause minor warping of the decks, it's not much more money, a good machinist would check these and just do it.

Keith

[Anonymous]

What would be a typical amount removed when the head and/or deck was shaved? Given that there wasn't severe warpage.

[Hap Call]

When you overbore an engine you will see a increase in compression, sometimes to the point where pinging can become a severe problem. While this is normally not a problem with stock motors going one over with OEM oversized pistons, it can rear its' ugly head on the higher performance engines.

Hap

[redliner1973]

What would be a typical amount removed when the head and/or deck was shaved? Given that there wasn't severe warpage.

Do yourself the favour and remove only enough to straighten it out. Too much and you goof up the compression and have to run high octance, and run hotter also and with the GS...Hot motor is not a happy motor.

[KEITH KRAUSE]

To Focus Frenzy

Not to change the main subject,but many years ago my 1000EN was pinging at the same point as yours.All I had done was put on a 4 into 1 pipe and take off the air filter housing lid under the seat. Too lean. I raised the jet-needle 1/2 notch by using a spacer at Vance&Hines and pinging was gone. KK.