valve seat/guide question

Looking for some guideance here (pun intended.)

For my 650/810 project I am keeping my ported 650 head but putting in Kz750 cams, springs and valves. Does anyone have any experience on valve seats and guide requirements with this combo?

I was looking to mill 15 thou off of the head and was advised to also take 15 thou off the valve stem length. Will the bigger 750 valves be fully compatible with the 650 seat and guides? I couldn't find the 650/750 seat part numbers to cross-reference on the kawasaki web site.

Any opinions or experience would be appreciated.

Cheers-Colin Firth-Ontario Canada

Restored '77 Kz 650 Custom had Wiseco 700. Second season back on the road after a 12 year sleep. Re-doing bike again with 810 Wiseco kit, Wired George Mikuni 28 carbs, 650 Head with Kz 750 valvetrain, Dyna Ignition, 13 tooth sprocket, Barnett Clutch, MAC pipe, Filters, 130 rear tire. Going back to stock factory Metallic Moon Dust Silver/Red Striping. Goal is to have a stock looking sleeper that will wake up other bigger bikes at stop light grand prix events!

Someone must have done this, or knows how to do it... I need the same info, except Im not milling the head (dont want to get into slotted cam sprockets).... anyone?

The valve guides for the 650 and the 750 are the same part number, so I see no reason to replace them unless they are bad.
I don't know if the valve seats on the 650 are large enough to enlarge them to fit the 750 valves and still be thick enough to prevent cracking (or even possibly falling out of the head).
I'd guess they can "probably" be enlarged, but I suggest having a local machinist look at them and tell you.

I don't know why you would need to cut .015" off the stem though, it has nothing to do with milling the head, since the cams are fastened to the top of the head and are not going to change their position relative to the valves
.

Thanks Steell for the info on the guides. This is the correct info as shown on the kaswasaki parts site.

I ruled out milling the head for a number of reasons. Hassles notching the cam sprockets, degreeing the cams and the higher compression ratio.

From my recent research I have learned that using the 810 Wiseco piston kit - 10.25 to I with the smaller KZ650 combustion chamber the compression ratio will rise. Milling the head will only add to this higher than stock rating and I plan on running this thing on high octane pump gas. Once you start getting near the 11 to 1 ratio you may experience detonation issues at higher rpm's unless you start putting in the champagne go-juice (race or av-gas) or play around with the timing. So milling the head is now a dead issue.

However I still would like to hear from anyone on whether or not they have experience on if the Kz750 valves will fit into the Kz650 seat with minor machining or should new 750 seats be pressed into the head?

Cheers-Colin Firth

Post edited by: reborn650, at: 2006/03/27 20:22

We use the same guide for the 650s thru 1100s, so they won't be a problem.

Acording to my info, a 650 can take a 34.5 mm intake valve on the stock seat, and a 750 std is 34mm.



Exhaust can take 29 mm, 750 std is 30. Wouldn't be hard to make 29s out of 30s.

Jay

Thanks Jay-that's the info I was hoping to hear.
Cheers-Colin

APE Jay wrote:

Acording to my info, a 650 can take a 34.5 mm intake valve on the stock seat, and a 750 std is 34mm.


Exhaust can take 29 mm, 750 std is 30. Wouldn't be hard to make 29s out of 30s.

Jay

Can you (or anybody else) explain this out for me, or point me to where I can learn more about this sort of thing? Steell mentioned enlarging the valve seats, does this also make the ports bigger, or let you make them bigger? I really want to know as much as possible before I start doing anything more than swapping cams. thanks a lot
Scott

A valve seat is approximately 1/4" thick, and when you cut a new seat for a larger valve you normally just cut the seat face (the part the valve touches). From that point on it's porting, and IIRC, the port should be about 80% of the size of the valve (actually the area of the ID of the seat). I'm not going into the details of porting (because like everything else, I disagree with most people), but there is not much sense in installing larger valves if you don't increase the size of the ports to allow more air to flow through those larger valves. I suggest doing a lot of reading about porting before you ever start grinding metal though, it's easier to cause harm than it is to do good.

IMHO, it would be a lot cheaper and easier to use the 750 head, shave it and slot the cam sprockets.

Post edited by: steell, at: 2006/03/28 02:09

When we do a modification like this, we bore out the throat of the seat however much oversize the valve will be. Then the seat is machined for the valve. It is then necessary to blend the larger valve throat with the port, or port the head to match the new seat throat.

Jay

APE Jay wrote:

When we do a modification like this, we bore out the throat of the seat however much oversize the valve will be. Then the seat is machined for the valve. It is then necessary to blend the larger valve throat with the port, or port the head to match the new seat throat.

Jay

That's what happens when you send it to a professional motorcycle machinist, not so likely at your local shop though.

APE generally does things the right way

I have a GPZ style 750 cylinder head which have some damage to the seats and also to the combustion chambers surfaces. I don't know what caused it, neither do I care. It could be as easy as a stone chip or nut falling into the hole on a spark plug change.
The engine is in parts, and I'm rebuilding it from scratch. Taking the time and money it takes, to get it to specs and fully operational again. Yes, I have the FSM and I know how to inspect and measure an engine. I just need to hear Your first hand experience.
I was hoping to find more specific info on valve seat REPLACEMENT in here, but no one seems to touch on that topic.
So! Who has done it, and who knows what to look out for?

ErlingW

wrote:

I have a GPZ style 750 cylinder head which have some damage to the seats and also to the combustion chambers surfaces. I don't know what caused it, neither do I care. It could be as easy as a stone chip or nut falling into the hole on a spark plug change.
The engine is in parts, and I'm rebuilding it from scratch. Taking the time and money it takes, to get it to specs and fully operational again. Yes, I have the FSM and I know how to inspect and measure an engine. I just need to hear Your first hand experience.
I was hoping to find more specific info on valve seat REPLACEMENT in here, but no one seems to touch on that topic.
So! Who has done it, and who knows what to look out for?

ErlingW

Sorry, I can't answer your question.  What I can say is to encourage you to check ebay for replacement heads that don't need so much work.