My LS bike build

[isiahstites]

Got the boxes all cleaned up for all of the new gaskets as well as got the roller rockers installed,


Filled the valve reliefs with clay to check piston to valve clearance.


Lifters have been bled down and installed and the motor is ready to be turned over.


Here is what it looked like after the motor was rolled over.


Here is how I measured the thickness of the clay. I have over .100 on the intake and the exhaust was not even close. I also have plenty of eyebrow clearance where the relief gets closer to the valve on the side of the piston.


Motor is pretty much done FINALLY! Just need to finish installing the cam and primary cover and anything that hooks to them or runs through them. I still need to install all of the oil lines, ignition, starter, oil tank and make up some spark plug wires.

[bvillercr]

looking good are you racing El Mirage in sept?

[isiahstites]

looking good are you racing El Mirage in sept?

That's the goal, are you going?

[1212FBGS]

why didn't the ex touch? is the cam timing right? i wouldn't think the piston designer would have been so far off on the ex relief
kent

[isiahstites]

why didn't the ex touch? is the cam timing right? i wouldn't think the piston designer would have been so far off on the ex relief
kent

It did touch Kent, but just barley. Here is something off of there website.

"The piston chases the exhaust valve closed, where the intake valve chases the piston down, so valve float can cause contact with the exhaust valve, but not the intake. So the exhaust clearance needs more margin. The intake clearance conversely is just to accommodate thermal expansion and piston rock."

[1212FBGS]

"and therefore reduce compression" eehhh laziness in designing the optimum piston... looks likes a street piston to me.
kent

[isiahstites]

"and therefore reduce compression" eehhh laziness in designing the optimum piston... looks likes a street piston to me.
kent

So an optimum piston would have a tighter tolerance on the exhaust side valve relief similar to what I had on the intake side?? The piston itself is coming with in .032 - .034 of the head depending on where it is measured.

Scott

[1212FBGS]

yep... a race piston would have all measurements as tight as possible.... looks to me as the ex cutout is as big as the intake cutout... is your ex valve the same size? or is the piston interchangeable with the front piston?

[isiahstites]

yep... a race piston would have all measurements as tight as possible.... looks to me as the ex cutout is as big as the intake cutout... is your ex valve the same size? or is the piston interchangeable with the front piston?

You are correct Kent, the reliefs are exactly the same size. The intake and the exhaust valves are different sizes. As this is my first motor build I have learned quite a bit and am grateful for my new knowledge, however I am at the mercy of others when it comes to certain things until I gain the necessary knowledge. This will be one of the "little things" that I will write down and make right on the next bike I build, thanks Kent.

Scott

[NArias3]

"and therefore reduce compression" eehhh laziness in designing the optimum piston... looks likes a street piston to me.
kent

So an optimum piston would have a tighter tolerance on the exhaust side valve relief similar to what I had on the intake side?? The piston itself is coming with in .032 - .034 of the head depending on where it is measured.

Scott

Nope.  The exhaust valve relief requires more clearance than the intake.  Scott, didn't you say these were borrowed pistons?

Nick 3rd.

[1212FBGS]

the ex doesn't need to be as big as the intake... this is typical of Harley pistons because they can be interchanged from front to rear but this practice is only a cost savings for production purposes... the Harley race pistons i had made were specific for front or fear and had different size reliefs for int and ex.... real race pistons do....
kent

[NArias3]

why didn't the ex touch? is the cam timing right? i wouldn't think the piston designer would have been so far off on the ex relief
kent

It did touch Kent, but just barley. Here is something off of there website.

"The piston chases the exhaust valve closed, where the intake valve chases the piston down, so valve float can cause contact with the exhaust valve, but not the intake. So the exhaust clearance needs more margin. The intake clearance conversely is just to accommodate thermal expansion and piston rock."

We're talking valve relief depth (piston-to-valve lift clearance) here, not diameter.

Nick 3rd.

[JackD]

Proper clearance for the radius of the valve and depth of the pocket are 2 of 3 considerations.
Valves tend to not follow the dimensions observed during setup that addresses material expansion, flow, and hot spots that can produce detonation.
Valves will actually close twice during a high speed cycle because they bounce up off the seat a bit when the weight and speed exceed the springs ability to hold the undampened (float) event.
Lighter weight in the valve train and stiffer springs raise the level before it happens , but it is at the expense of the system. 

[isiahstites]

Nope.  The exhaust valve relief requires more clearance than the intake.  Scott, didn't you say these were borrowed pistons?

Nick 3rd.

Yes, but they were what I was supposed to get from the start. The guys I bought them from made it right with me with some other parts I needed and ordered me a another set with the right compression height because I had originally ordered two sets.

You now have me wondering about why the exhaust barley touched, I know it requires more clearance than the intake valve, but my intake and exhaust cams both have the same lift. Is the exhaust valve seating deeper in the head than the intake??

Scott

[isiahstites]

You now have me wondering about why the exhaust barley touched, I know it requires more clearance than the intake valve, but my intake and exhaust cams both have the same lift. Is the exhaust valve seating deeper in the head than the intake??

Scott

I think it has to do with the orientation of the cams, however I am not sure.