Hamilton Cams
ignorant
- Joined
- Jun 28, 2007
- Messages
- 2,639
I have been asked what I consider to be a "drop in" cam. For a general description it would be any cam that can be put into 99% of the trucks on the road that are how they came from the factory and have had less than
.010" total machined off of either the head or the block or a combination of the two.
That being said, I have seen people run their valves into the pistons with stock cams installed incorrectly, mis-matched components; poor machining to the block, head, pistons or valves, incorrect head gaskets, or bad lash adjusments.
Piston to valve is usually caused by one of the above, but can also be caused by valve float caused by excessive rpm or valves being opened by boost. Both of which are attributed to not enough spring pressure.
All of that being said, things do come out of the factory out of spec. from time to time which can cause issues. To be unambiguous, and so that you can feel safe about what you are installing, I use these figures to make sure things are good to go, If your block deck surface has not been machined, the cam gear you are using is the one that came with the truck, you have a straight keyway and the rocker arms are original on the truck, and the head gasket is OEM CUMMINS, then you will need .040" MINIMUM valve face depth to clear the cam on 24v models and .047" MINIMUM on 12v models.
This gives a little wiggle room so that you should be good to go. This is also assuming that, the lash is set correctly and that the cam was cut on centers correctly and is not a regrind or a cam that was cut on a manual machine.
This is a guide to make sure things don't hit, not to make power.
I like my valves to protrude .010"-.020" out of the head so that the low lift flow of the port will increase. In other words I like my valves up to .060" closer to the piston than I am telling you. For a simple guide use the numbers above.
If you do not have enough room here is how to remedy the situation.
If your valve is not deep enough in the head, you can either grind on the valve and seat to get a few thousandths. If you do not want to do a valve job, then you have the option of a thicker head gasket. to gain clearance.
3283335 STD
3283337 +.010"
3283339 +.020"
If you want the most power and you do not have enough clearance, don't worry about the valve job, or the head gasket, that is when it is time for piston machining.
When people ask how much fly-cut of the piston is needed to clear a cam, I can give you two specs, what will make the engine more efficient or what will make it easiest for you on the install. Please specify what you want to hear when you call.
For instance we say that the 200-220 is not a drop in cam, but it can be if clearances are correct and you will take the time to do the math. If you don't want to do the work, we say that .080" is needed, which is just not true in most instances. On our big cams, I have had people say that our cams are crap because I tell them they need to cut the pistons .150". They say it must be a small cam because Haisley and Scheid tell them to cut .250" off of the piston, so I must be giving them a baby cam even though duration and lift are in the same ballpark.
In short I am a little haggard from all of the misinformation and games. It is really not as hard as a lot of people make it out to be. For what we do with our cams, if all is OEM excepth the cam .040" valve face depth on 24v and .047" 12v will let you run our "drop in" cams.
If there is enough desire for it, I will come up with a formula to account for valve face depth, piston protrusion, rocker ratio, head gasket thickness, centerlines and lash to account for Piston to valve clearance. If any further information is needed, please feel free to post up any questions you may have. I hope that I have put this information in a way that is easily understood.
Zach
.010" total machined off of either the head or the block or a combination of the two.
That being said, I have seen people run their valves into the pistons with stock cams installed incorrectly, mis-matched components; poor machining to the block, head, pistons or valves, incorrect head gaskets, or bad lash adjusments.
Piston to valve is usually caused by one of the above, but can also be caused by valve float caused by excessive rpm or valves being opened by boost. Both of which are attributed to not enough spring pressure.
All of that being said, things do come out of the factory out of spec. from time to time which can cause issues. To be unambiguous, and so that you can feel safe about what you are installing, I use these figures to make sure things are good to go, If your block deck surface has not been machined, the cam gear you are using is the one that came with the truck, you have a straight keyway and the rocker arms are original on the truck, and the head gasket is OEM CUMMINS, then you will need .040" MINIMUM valve face depth to clear the cam on 24v models and .047" MINIMUM on 12v models.
This gives a little wiggle room so that you should be good to go. This is also assuming that, the lash is set correctly and that the cam was cut on centers correctly and is not a regrind or a cam that was cut on a manual machine.
This is a guide to make sure things don't hit, not to make power.
I like my valves to protrude .010"-.020" out of the head so that the low lift flow of the port will increase. In other words I like my valves up to .060" closer to the piston than I am telling you. For a simple guide use the numbers above.
If you do not have enough room here is how to remedy the situation.
If your valve is not deep enough in the head, you can either grind on the valve and seat to get a few thousandths. If you do not want to do a valve job, then you have the option of a thicker head gasket. to gain clearance.
3283335 STD
3283337 +.010"
3283339 +.020"
If you want the most power and you do not have enough clearance, don't worry about the valve job, or the head gasket, that is when it is time for piston machining.
When people ask how much fly-cut of the piston is needed to clear a cam, I can give you two specs, what will make the engine more efficient or what will make it easiest for you on the install. Please specify what you want to hear when you call.
For instance we say that the 200-220 is not a drop in cam, but it can be if clearances are correct and you will take the time to do the math. If you don't want to do the work, we say that .080" is needed, which is just not true in most instances. On our big cams, I have had people say that our cams are crap because I tell them they need to cut the pistons .150". They say it must be a small cam because Haisley and Scheid tell them to cut .250" off of the piston, so I must be giving them a baby cam even though duration and lift are in the same ballpark.
In short I am a little haggard from all of the misinformation and games. It is really not as hard as a lot of people make it out to be. For what we do with our cams, if all is OEM excepth the cam .040" valve face depth on 24v and .047" 12v will let you run our "drop in" cams.
If there is enough desire for it, I will come up with a formula to account for valve face depth, piston protrusion, rocker ratio, head gasket thickness, centerlines and lash to account for Piston to valve clearance. If any further information is needed, please feel free to post up any questions you may have. I hope that I have put this information in a way that is easily understood.
Zach
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