Measuring piston to valve clearance
Thread Starter
Staging Lane
Joined: Oct 2024
Posts: 51
Likes: 1
Measuring piston to valve clearance Hey guys, very new to engine building and slowly learning as I go… quick question here on piston to valve clearance.
I have a forged ls2 short block that I had a shop machine and put together for me (very reputable). I decided I would do the rest. Had the heads resurfaced, installed some new Che trunnions, new BTR stage 2 boost cam, melling pump, ARP main and head studs, BTR platinum spring kit etc, it’s an s480 big turbo build.
Purchased and installed Johnson 2116lsr lifters because I’m too paranoid of fake ls7’s or just the lifters turning in trays in general…. anyways, I measured my pushrod length 3x (triple checked lol) and sent the numbers to Manton.
Got my custom length pushrods yesterday…. Now I need to measure piston to valve clearance is my understanding of last step before I put accessories on.
Here’s my question… since my cam is somewhat large I understand it’s proper to measure PTV since it’s not a short duration cam. So, I plan to do the method where you add clay to cylinder 1 exhaust and intake, rotate engine, get the impression on clay and then measure impression for clearance.
My question here is, when I turn the engine over it will likely compress the lifters and oil content, so will I get a false measurement?
I have a forged ls2 short block that I had a shop machine and put together for me (very reputable). I decided I would do the rest. Had the heads resurfaced, installed some new Che trunnions, new BTR stage 2 boost cam, melling pump, ARP main and head studs, BTR platinum spring kit etc, it’s an s480 big turbo build.
Purchased and installed Johnson 2116lsr lifters because I’m too paranoid of fake ls7’s or just the lifters turning in trays in general…. anyways, I measured my pushrod length 3x (triple checked lol) and sent the numbers to Manton.
Got my custom length pushrods yesterday…. Now I need to measure piston to valve clearance is my understanding of last step before I put accessories on.
Here’s my question… since my cam is somewhat large I understand it’s proper to measure PTV since it’s not a short duration cam. So, I plan to do the method where you add clay to cylinder 1 exhaust and intake, rotate engine, get the impression on clay and then measure impression for clearance.
My question here is, when I turn the engine over it will likely compress the lifters and oil content, so will I get a false measurement?
You can make some solid lifters from used hydraulic lifters and if you have an adjustable push rod length checking tool and some lightweight valve checking springs you should be able to check P-V with that but to answer your question, yes it will give an inaccurate reading due to the lifters in the engine but you may have enough P-V anyway that it would not be a concern.
It would help to post actual cam specs instead of "stages." Stages are for actors, or for horses to pull. IDK about others, but not many here are going to go to the BTR website and look up specs. I'd offer my opinion if I knew the specs....
Thread Starter
Staging Lane
Joined: Oct 2024
Posts: 51
Likes: 1
let me say this though, I DO have valve relief cuts, they are summit PRO pistons
Thread Starter
Staging Lane
Joined: Oct 2024
Posts: 51
Likes: 1
You can make some solid lifters from used hydraulic lifters and if you have an adjustable push rod length checking tool and some lightweight valve checking springs you should be able to check P-V with that but to answer your question, yes it will give an inaccurate reading due to the lifters in the engine but you may have enough P-V anyway that it would not be a concern.
Launching!
Joined: Mar 2024
Posts: 291
Likes: 92
From: Bradentucky Florida
Pull the snap ring on the lifter and replace the spring in it with a stack of washers
Use a check spring under the valve keeper
I normally use playdough to check clearances
Because a solid lifter set to zero lash will give you a much better indication of true P-V clearance than your hydraulic lifters. I prefer to use a degree wheel and a dial indicator to measure P-V and confirm with the clay.
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I have heard thru the years that play dough can give incorrect measurements. Another way to do this is to mount a dial indicator over the rocker arm or spring retainer at the valve stem end (of course), and slowly rotate the engine over. Slowly push the rocker down by hand (checking springs) at various points in the rotation, and note the distances you've had to push the rocker to make the valve contact the piston. Not a good description, sorry. But hopefully you'll know what I'm trying to convey...
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Verdad Gallardo I have heard thru the years that play dough can give incorrect measurements. Another way to do this is to mount a dial indicator over the rocker arm or spring retainer at the valve stem end (of course), and slowly rotate the engine over. Slowly push the rocker down by hand (checking springs) at various points in the rotation, and note the distances you've had to push the rocker to make the valve contact the piston. Not a good description, sorry. But hopefully you'll know what I'm trying to convey...
During an engine build P-V is often checked after TDC has been determined, a degree wheel has been setup, the camshaft has been installed and the valve events have been verified against the cam card. The closest P-V measurements are typically within 10° before and after TDC.
Hey guys, very new to engine building and slowly learning as I go… quick question here on piston to valve clearance.
I have a forged ls2 short block that I had a shop machine and put together for me (very reputable). I decided I would do the rest. Had the heads resurfaced, installed some new Che trunnions, new BTR stage 2 boost cam, melling pump, ARP main and head studs, BTR platinum spring kit etc, it’s an s480 big turbo build.
Purchased and installed Johnson 2116lsr lifters because I’m too paranoid of fake ls7’s or just the lifters turning in trays in general…. anyways, I measured my pushrod length 3x (triple checked lol) and sent the numbers to Manton.
Got my custom length pushrods yesterday…. Now I need to measure piston to valve clearance is my understanding of last step before I put accessories on.
Here’s my question… since my cam is somewhat large I understand it’s proper to measure PTV since it’s not a short duration cam. So, I plan to do the method where you add clay to cylinder 1 exhaust and intake, rotate engine, get the impression on clay and then measure impression for clearance.
My question here is, when I turn the engine over it will likely compress the lifters and oil content, so will I get a false measurement?
I have a forged ls2 short block that I had a shop machine and put together for me (very reputable). I decided I would do the rest. Had the heads resurfaced, installed some new Che trunnions, new BTR stage 2 boost cam, melling pump, ARP main and head studs, BTR platinum spring kit etc, it’s an s480 big turbo build.
Purchased and installed Johnson 2116lsr lifters because I’m too paranoid of fake ls7’s or just the lifters turning in trays in general…. anyways, I measured my pushrod length 3x (triple checked lol) and sent the numbers to Manton.
Got my custom length pushrods yesterday…. Now I need to measure piston to valve clearance is my understanding of last step before I put accessories on.
Here’s my question… since my cam is somewhat large I understand it’s proper to measure PTV since it’s not a short duration cam. So, I plan to do the method where you add clay to cylinder 1 exhaust and intake, rotate engine, get the impression on clay and then measure impression for clearance.
My question here is, when I turn the engine over it will likely compress the lifters and oil content, so will I get a false measurement?
I ALWAYS use modeling clay for finding PTV. I use checking springs on cyl #1, so hydraulic lifters aren’t a factor. The clay won’t lie. Turn the engine over two full revolutions to do this. I use .030 steel valvespring shims under the heads while turning it over by hand. If I’m using a .040” headgasket…which 98% of my builds use…I simply ADD .010 to my numbers i found in the clay. It’s super easy. Snug the head while doing this, so you don’t hurt the head with the shims. The shims have the correct .500 hole in the center of them for the head dowels and headbolts to go through. I use 6…4 at the corners and 2 in the center for support. I only use a few headbolts, again hand tite snug. Pushrod length to do this step is determined during a mock-up stage….it’s usually VERY close to stock length for the style of engine. I determine my final pushrod length…all 16 valves…in my final step after heads are final torqued. That’s the last step, unless it’s a solid roller…in which case setting lash would be my final step before valve covers go on, and it’s ready to fire.
Problem #1….you measured pushrods before you checked PTV. That’s a no-can-do. If you need to alter PTV with headgaskets, which I don’t recommend, those pushrods are going in the trash. I preach it all the time here guys…YOU HAVE TO BUILD THE ENGINE BEFORE YOU BUILD THE ENGINE. Mock everything up. Sure it takes time. Sure it’s tedious. But it’s the right way to do this. I don’t recommend using headgaskets to alter PTV because your compression target trumps everything. Compression target is set on paper before ANYTHING gets purchased. It’s etched in stone. I cut pistons to alter PTV. It’s determined on day one of mock-ups.
I ALWAYS use modeling clay for finding PTV. I use checking springs on cyl #1, so hydraulic lifters aren’t a factor. The clay won’t lie. Turn the engine over two full revolutions to do this. I use .030 steel valvespring shims under the heads while turning it over by hand. If I’m using a .040” headgasket…which 98% of my builds use…I simply ADD .010 to my numbers i found in the clay. It’s super easy. Snug the head while doing this, so you don’t hurt the head with the shims. The shims have the correct .500 hole in the center of them for the head dowels and headbolts to go through. I use 6…4 at the corners and 2 in the center for support. I only use a few headbolts, again hand tite snug. Pushrod length to do this step is determined during a mock-up stage….it’s usually VERY close to stock length for the style of engine. I determine my final pushrod length…all 16 valves…in my final step after heads are final torqued. That’s the last step, unless it’s a solid roller…in which case setting lash would be my final step before valve covers go on, and it’s ready to fire.
I ALWAYS use modeling clay for finding PTV. I use checking springs on cyl #1, so hydraulic lifters aren’t a factor. The clay won’t lie. Turn the engine over two full revolutions to do this. I use .030 steel valvespring shims under the heads while turning it over by hand. If I’m using a .040” headgasket…which 98% of my builds use…I simply ADD .010 to my numbers i found in the clay. It’s super easy. Snug the head while doing this, so you don’t hurt the head with the shims. The shims have the correct .500 hole in the center of them for the head dowels and headbolts to go through. I use 6…4 at the corners and 2 in the center for support. I only use a few headbolts, again hand tite snug. Pushrod length to do this step is determined during a mock-up stage….it’s usually VERY close to stock length for the style of engine. I determine my final pushrod length…all 16 valves…in my final step after heads are final torqued. That’s the last step, unless it’s a solid roller…in which case setting lash would be my final step before valve covers go on, and it’s ready to fire.
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