Topic: Kibblewhite Cb550 +1mm OS Valves

[KrautKoffin]

I just bought a set of +1mm oversized kibblewhite valves from cycle X, anyone have any experience with these. Should I be replacing my valve guides or will the existing guides work? Any info is appreciated!

- Jordan

[MCRider]

You're going to have to cut new seats to fit the OS valves, so that means a valve job and unless you're real lucky I'd say guides as well. I'd plan on it.

Usually the new valves are fitted to the guides with a ream, I think. Old guides would make that harder to achieve.

I think.

[KrautKoffin]

You're going to have to cut new seats to fit the OS valves, so that means a valve job and unless you're real lucky I'd say guides as well. I'd plan on it.

Usually the new valves are fitted to the guides with a ream, I think. Old guides would make that harder to achieve.

I think.

thanks for the input, I was expecting to have to but new guides but the machinist said "You shouldn't have to get that deep into this head." I beg to differ, but Im no machinist. I would think it would be hard to align the seat and guide with the valve.. Also, Im getting a port and polish on the head so it shouldn't be an issue to cut the throat larger to accept the valves.

[MCRider]

You're going to have to cut new seats to fit the OS valves, so that means a valve job and unless you're real lucky I'd say guides as well. I'd plan on it.

Usually the new valves are fitted to the guides with a ream, I think. Old guides would make that harder to achieve.

I think.

thanks for the input, I was expecting to have to but new guides but the machinist said "You shouldn't have to get that deep into this head." I beg to differ, but Im no machinist. I would think it would be hard to align the seat and guide with the valve.. Also, Im getting a port and polish on the head so it shouldn't be an issue to cut the throat larger to accept the valves.

ITs not the throat at issue. ITs the seat. And the rim of the valve. That's where the oversize occurs which is all on the combustion side of the head.  Enlarging the throat/port will be a good thing but not necessary.

Seat cutters are guided by the guides, as you mention. Hence my opinion new guides are  in order.  often a portsmith will like to remove the old guides for better access to the ports.

Completely different tools: rotary porting tool handheld for the ports. Machine guided seat cutters.

[KrautKoffin]

You're going to have to cut new seats to fit the OS valves, so that means a valve job and unless you're real lucky I'd say guides as well. I'd plan on it.

Usually the new valves are fitted to the guides with a ream, I think. Old guides would make that harder to achieve.

I think.

thanks for the input, I was expecting to have to but new guides but the machinist said "You shouldn't have to get that deep into this head." I beg to differ, but Im no machinist. I would think it would be hard to align the seat and guide with the valve.. Also, Im getting a port and polish on the head so it shouldn't be an issue to cut the throat larger to accept the valves.

ITs not the throat at issue. ITs the seat. And the rim of the valve. That's where the oversize occurs which is all on the combustion side of the head.  Enlarging the throat/port will be a good thing but not necessary.

Seat cutters are guided by the guides, as you mention. Hence my opinion new guides are  in order.  often a portsmith will like to remove the old guides for better access to the ports.

Those are my thoughts exactly, but he said he shouldn't have to remove them. If they work and it saves me $150 plus labor Im happy.

[MCRider]

Sure thing, if he thinks he can do it and save the $$, I defer.

[MRieck]

I just bought a set of +1mm oversized kibblewhite valves from cycle X, anyone have any experience with these. Should I be replacing my valve guides or will the existing guides work? Any info is appreciated!

- Jordan

that valve works well....I have installed them on about 6 heads. The old guides will work BUT they have to be in good condition. Adding the larger valve won't do much unless the seat is opened up to 90% of the OS valve.

[KrautKoffin]

I just bought a set of +1mm oversized kibblewhite valves from cycle X, anyone have any experience with these. Should I be replacing my valve guides or will the existing guides work? Any info is appreciated!

- Jordan

that valve works well....I have installed them on about 6 heads. The old guides will work BUT they have to be in good condition. Adding the larger valve won't do much unless the seat is opened up to 90% of the OS valve.

Thanks Mike,good to know. I talked to Pat@APE and he confirmed my suspicions that these heads respond well to OS valves when they are ported well. I'll have my machinist inspect the guides before installing the valves.

[Big Jay]

Installing oversize valves without opening the throats of the seat is pretty much a waste of time.

On these older heads we even open the throats on stock size valves when porting.

[KrautKoffin]

Installing oversize valves without opening the throats of the seat is pretty much a waste of time.

On these older heads we even open the throats on stock size valves when porting.

Jay, have you been talking to Pat? do you have any flow numbers Jay or Mriech?

[turboguzzi]

500/550s are definitely super strangled at the valve seat throat cross section, the big flow numbers come from opening them up exactly there. not something you can do with a hand held grinder though.

[bwaller]

These o/s valves, plus all the above mentioned work to increase flow gave us nearly a 10% power increase in a race engine.  As mentioned, there is much unleashed power in these heads, choosing which improvement steps to follow will determine the outcome.

[KrautKoffin]

These o/s valves, plus all the above mentioned work to increase flow gave us nearly a 10% power increase in a race engine.  As mentioned, there is much unleashed power in these heads, choosing which improvement steps to follow will determine the outcome.

Good to hear! I'm boring it out to 600cc's, knife edging the crank, and porting the head to accept the new valves. This thing should make decent power

[Big Jay]

Seat boring

[SOHC4 Cafe Racer Fan]

These o/s valves, plus all the above mentioned work to increase flow gave us nearly a 10% power increase in a race engine.  As mentioned, there is much unleashed power in these heads, choosing which improvement steps to follow will determine the outcome.

Good to hear! I'm boring it out to 600cc's, knife edging the crank, and porting the head to accept the new valves. This thing should make decent power

Damn, Jordan.  Pulling out the stops for the 550!

[KrautKoffin]

Haha might as well do it right the first time