Installing oversized valves in a Z1/KZ900/KZ1000/K

Installing oversized valves in a Z1/KZ900/KZ1000/KZ1100/ZX1100A head

In order to install oversized valves in a KZ head, there are a number of things that you need to keep in mind. Since the KZ head has a hemispherical combustion chamber and the valves as they open and close are crossing the path of each other, they can’t both be full open at the same time as they would contact each other. They can’t even both be open very much at all at the same time to prevent contact. As it turns out, even with stock camshafts, the timing of the camshafts must be correct to prevent this. As camshaft duration increases, the valves will get closer and closer to each other at the closest point. As you change camshaft timing, no matter the profile of the camshaft, the same thing occurs. Advancing the intake camshaft timing and/or retarding the exhaust camshaft timing will bring the valves closer together at their closest point. This closest point occurs during the valve overlap, where both valves are open at the same time. That is when the exhaust valve is closing and the intake valve is opening. The below graph shows a stock camshaft profile against an aftermarket camshaft profile. Both camshafts are set at the same centerline of approximately 105 degrees. Camshaft center line is the middle of the camshaft profile, or the highest point of lift. However, it can’t be measured simply as the highest point as the camshaft will dwell at the highest lift for some time. Setting both camshafts at the same centerline is splitting the overlap. The graph is likely a little too small to make out specific details. The aftermarket camshafts have the same profile whereas the stock exhaust camshaft has a little less duration and a little less lift than the stock intake camshaft. So the point where both stock camshafts are open the same amount is a little before TDC where the aftermarket camshafts, in this instance of identical profiles, occurs at TDC. It is easy to see that the two valves are both open at the same time at about .080” using stock camshafts whereas the two valves are both open at the same time about .160” using the aftermarket long duration camshafts. The point where the two valves get the closest to each other is not at this exact point, since the two valves are of a different diameter, but it is close enough for the purpose of this discussion.


In stock configuration, when both valves are closed (on the seat), the distance measured between the nearest edge of them is approximately .160” to .180” at the closest point. When you are installing oversized valves in the head, it is imperative that this minimum distance with the valves on the seat be maintained to prevent damage. The only way to maintain this minimum distance is to sink the valves further into the seat. I use .180” as the minimum distance between the valves on the seat to prevent contact.
This sinking of the valves presents other problems that must be overcome somewhere down the line. I start on one combustion chamber with stock sized valves and stock seats and measure how much of the valve stem is protruding out of the valve guide to determine how far I need to go with sinking the valve seat. I then sink both valves about .040” measuring the amount the seat has been sunk before making my first check with the oversized valves on the seat. I then put the oversized valves in and check valve to valve distance on the seat. If I do not have the minimum .180” distance then I sink each valve a little more based on the distance. I continue in this way until I get to the minimum .180” distance with the oversized valves. It normally ends up being somewhere between .050” to .060” sinking the valve seats to get to the minimum clearance. Once I have established the amount the valves need to be sunk on this particular head, I then do the other three combustion chambers the same amount, I check each combustion chamber valve to valve distance when done. A valve seat and guide machine would make this work much easier.
Now we get to the part that causes some consternation on the part of some head recipients. The valve stem length as it protrudes out of the valve guide is critical to valve adjustment. If the valves have been sunk .050” from stock, then you will likely need to remove .050” from the valve stem in order to get back to your starting point. When you remove .050” from the top of the valve stem, the keeper is getting closer to the end of the valve, in some cases past the end of the valve requiring that the keeper be shortened. In some cases, the valve spring retainer will extend past the end of the valve as well requiring that the thickness of that part be reduced. The oversized valves that are available from APE come in sizes that are the largest that they recommend for installation on stock seats. However, until just recently, they were all the same length as stock valves. They recently added 37.5mm valves (the largest that can be installed on stock 1973-1980 KZ seats) with stems that are .055” shorter. Thank you Jay. There are, of course other ways around these problems. If they are made and you know where to get them, you can buy valves like the new APE 37.5mm valves with shortened stems. Or, you could buy blank valves and make them to the correct length.
In trying to accomplish the goal of installing oversized valves in a head with stock seats, I would opt for the least costly route of trimming the valve stems, the keeper tops and the retainer tops as required.
Hopefully, Larry Cavanaugh will see this and take a few minutes out of his busy schedule and add to it as I respect his opinion and can learn from it.

joehooper wrote: Installing oversized valves in a Z1/KZ900/KZ1000/KZ1100/ZX1100A head

In order to install oversized valves in a KZ head, there are a number of things that you need to keep in mind. Since the KZ head has a hemispherical combustion chamber and the valves as they open and close are crossing the path of each other, they can’t both be full open at the same time as they would contact each other. They can’t even both be open very much at all at the same time to prevent contact. As it turns out, even with stock camshafts, the timing of the camshafts must be correct to prevent this. As camshaft duration increases, the valves will get closer and closer to each other at the closest point. As you change camshaft timing, no matter the profile of the camshaft, the same thing occurs. Advancing the intake camshaft timing and/or retarding the exhaust camshaft timing will bring the valves closer together at their closest point. This closest point occurs during the valve overlap, where both valves are open at the same time. That is when the exhaust valve is closing and the intake valve is opening. The below graph shows a stock camshaft profile against an aftermarket camshaft profile. Both camshafts are set at the same centerline of approximately 105 degrees. Camshaft center line is the middle of the camshaft profile, or the highest point of lift. However, it can’t be measured simply as the highest point as the camshaft will dwell at the highest lift for some time. Setting both camshafts at the same centerline is splitting the overlap. The graph is likely a little too small to make out specific details. The aftermarket camshafts have the same profile whereas the stock exhaust camshaft has a little less duration and a little less lift than the stock intake camshaft. So the point where both stock camshafts are open the same amount is a little before TDC where the aftermarket camshafts, in this instance of identical profiles, occurs at TDC. It is easy to see that the two valves are both open at the same time at about .080” using stock camshafts whereas the two valves are both open at the same time about .160” using the aftermarket long duration camshafts. The point where the two valves get the closest to each other is not at this exact point, since the two valves are of a different diameter, but it is close enough for the purpose of this discussion.


In stock configuration, when both valves are closed (on the seat), the distance measured between the nearest edge of them is approximately .160” to .180” at the closest point. When you are installing oversized valves in the head, it is imperative that this minimum distance with the valves on the seat be maintained to prevent damage. The only way to maintain this minimum distance is to sink the valves further into the seat. I use .180” as the minimum distance between the valves on the seat to prevent contact.
This sinking of the valves presents other problems that must be overcome somewhere down the line. I start on one combustion chamber with stock sized valves and stock seats and measure how much of the valve stem is protruding out of the valve guide to determine how far I need to go with sinking the valve seat. I then sink both valves about .040” measuring the amount the seat has been sunk before making my first check with the oversized valves on the seat. I then put the oversized valves in and check valve to valve distance on the seat. If I do not have the minimum .180” distance then I sink each valve a little more based on the distance. I continue in this way until I get to the minimum .180” distance with the oversized valves. It normally ends up being somewhere between .050” to .060” sinking the valve seats to get to the minimum clearance. Once I have established the amount the valves need to be sunk on this particular head, I then do the other three combustion chambers the same amount, I check each combustion chamber valve to valve distance when done. A valve seat and guide machine would make this work much easier.
Now we get to the part that causes some consternation on the part of some head recipients. The valve stem length as it protrudes out of the valve guide is critical to valve adjustment. If the valves have been sunk .050” from stock, then you will likely need to remove .050” from the valve stem in order to get back to your starting point. When you remove .050” from the top of the valve stem, the keeper is getting closer to the end of the valve, in some cases past the end of the valve requiring that the keeper be shortened. In some cases, the valve spring retainer will extend past the end of the valve as well requiring that the thickness of that part be reduced. The oversized valves that are available from APE come in sizes that are the largest that they recommend for installation on stock seats. However, until just recently, they were all the same length as stock valves. They recently added 37.5mm valves (the largest that can be installed on stock 1973-1980 KZ seats) with stems that are .055” shorter. Thank you Jay. There are, of course other ways around these problems. If they are made and you know where to get them, you can buy valves like the new APE 37.5mm valves with shortened stems. Or, you could buy blank valves and make them to the correct length.
In trying to accomplish the goal of installing oversized valves in a head with stock seats, I would opt for the least costly route of trimming the valve stems, the keeper tops and the retainer tops as required.
Hopefully, Larry Cavanaugh will see this and take a few minutes out of his busy schedule and add to it as I respect his opinion and can learn from it.

Thanks for the insight Joe.

WE will put this to good use in our technical data base

Dave

Take a piece of small welding rod. Squeeze it in a vise to flatten one end. Grind it so that its .185" wide. See if it will slide between the valve heads while they are seated. If it doesn't and you have more than stock cams, OUCH! Larry told me this a few years ago.

69.46.28.106/forum/2-engine/594223-for-peter-elr-head