Calculation for Valve to Piston clearance

[Doorkicker]

I was hoping someone could check my math.

For argument sake let's assume my piston to valve clearance is 0.000. Let's assume my intake valve is 2.02 and I'm changing to a new head that is 2.19. The valve angle is 15°.

Is the following calc correct...

Change in valve diameter is 2.19-2.02=0.170, therefore the delta from center is 0.085 (aka change in radius). To calculate change in depth (added distance to piston) take SIN of 15°=0.2588. Therefore, 0.085*0.2588=0.022. so if the starting clearance is 0.000 the new clearance would be -0.022.

Correct or...what did I miss?

Keep in mind I'm just trying to confirm the math. Clearly, I need more clearance to address heat expansion and I don't have zero clearance now, of course. I'm just trying to confirm the use of SIN in the relative calculation to the angle in the change of the valve size.

Thanks in advance.

 

[33 IMP]

I don't know anything about your math, only that it's wrong. A bigger valve is closer to the piston, so clearance HAS TO BE less.
Bottom line: measure . Don't calculate, and don't guess.
(I'm guessing your math has a +/‐ problem.)
Edit okay, after reading remchargers post, I see that your conclusion is a negative (oops).
I Still say measure. (Duration has more effect on p/v than lift, usually)

 

[RemCharger]

I don't know anything about your math, only that it's wrong. A bigger valve is closer to the piston, so clearance HAS TO BE less.
Bottom line: measure . Don't calculate, and don't guess.

Yes he said it would be negative .022
And I agree calculus might be fun ( not for me!) But there is too much going on to calculate such a thing.
How about some actual parts and specs?

 

[Curiousyellow71]

Using Sin was correct....your figures should work for a flat top with no valve reliefs.

 

[Mick56]

You can use modeling clay to get a measurement

 

[Doorkicker]

Thanks fellas!

@33 IMP - yeah... negative result meaning impact with piston.

@RemCharger - So current situation is I have flat tops, no valve relief, .525 lift, valve to piston clearance at 8-10 degrees is 0.045 (a bit close, I think?) on 2.02 intake and a whopping 0.300 on 1.78 exhaust. I'm running numbers on a new head with a larger intake valve (2.19) and contemplating cutting a valve relief. Everything else is the same in the new head and I'm currently planning on using the same head gasket (0.049 compressed). IF my math is right, I know I'm - AT LEAST - looking at an increased distance (closer to piston) of -0.022. I have a crap load of other concerns, most notably how far is too far into the piston, which has a top thickness of 0.315. I See people post all kinds of numbers on cutting depth, but seems everyone agrees don't go over 0.100. I hear different clearances for intake... everything from .040 to .080 (and exhaust most say 0.100). But if I assume meet in the middle and call it .060 clearance for the intake, with the added valve size and current distance of .045 I'm looking at a relief of .037 (math .060-.045=.015, .015+.022=.037 cut in the piston). Call it .040 to be safe.

@Curiousyellow71 - Thanks!

@Mick56 - I did when I built the motor, but honestly I have mixed experiences/results. I felt the clay was a bit hard to measure (caliper digs in). Nevertheless, got roughly the same number .044 as I did with assembled measurement using testing springs on the head and a gage on the valve stem.

My fundamental issue is I have **** pistons and they're limiting my head and cam options. Just that simple. I'm about 2 minutes away from getting a stroker and trickflows and calling it a day, but that's a lot of $$ right now and I'm still working on building a new rear end. Therefore, looking for a short-term "fix".

 

[MoparLeo]

Short term hope... How thick is the piston head and is it cast or forged ?? Many questions.
My advice to my children many years ago was always " If in doubt, don't do it"

 

[RemCharger]

Assumptions;
360?
Hft?
Been run before?
Checked clearance with solid lifters?

 

[Doorkicker]

Assumptions;
360?
Hft?
Been run before?
Checked clearance with solid lifters?

440, 030 over, 452 heads
Not sure what Hft means... sorry
Running now
When I built the motor (about 500 miles ago) I used a solid lifter, and used the hydraulic flat tappet when I measured with testing springs

 

[Curiousyellow71]

452 heads came with 2.08 Intake 1.74 exh making your calculation off a bit that was done w 2.02.
Hft...Hydraulic Flat tappet. Pretty much any of the oem replacement pistons you can remove .100 off the top. That is what it used to say in the old trw books which is likely the origins of the pistons your running...now sold as sealed power.

 

[Doorkicker]

452 heads came with 2.08 Intake 1.74 exh.
Hft...Hydraulic Flat tappet. Pretty much any of the oem replacement pistons you can remove .100 off the top. That is what it used to say in the old trw books which is likely the origins of the pistons your running...now sold as sealed power.

Crap, you're right! 2.08 and 1.74 - thank you! I completely messed that up.
Thanks for the HFT explanation Seems totally obvious now...
And... thank you for the advise on .100! It's nice to hear that from someone directly. Big help.

If I may trouble you for one piece of additional advise/info...

What is the recommended clearance for intake and exhaust valve to piston?

 

[Curiousyellow71]

.080 intake
.100 exhaust

 

[RemCharger]

If your #s are correct using a solid lifter for measuring.. you could try retarding it 4 degrees and remeasure. Should give you more room on intake, less on exhaust.
If you have an adjustable crank sprocket

 

[zyzzyx]

Too much math! Makes my head ache. I put the head on the engine with the head gasket and finger tighten the bolts.
Put weak springs on the intake and exhaust valves on one cylinder that you can push open by hand. Put in two lifters
and push rods and two rocker arms. Mount your degree wheel and set it to TDC. Rotate the engine five degrees at a time
and keep pushing down on the valves until you "feel" them start contacting the tops of the pistons. When you get close,
you can put a dial indicator on the valve and measure the actual clearance. Easy-Peasy!

 

[66Satellite47]

Measure, measure, measure. I'd do valve reliefs, with a little extra valve diameter in mind.

 

[1 Wild R/T]

How big? & How deep???

 

[dvw]

What you have to watch is radial clearance. You need .050" or more. You can install the head without the exhaust valve. As far as depth. Are you using the same cam? Same centerline? Advancing the cam tightens up the intake clearance and opens up the exhaust clearance. Duration effects clearance more than lift. I'm you disasembling the short block? Take the new head w/o valves and center punch the piston at TDC. That'll give you you correct center. If using the same cam checkvalve opening with a dial indicator befor disassembly. If you know how far it opens at 10 BTDC and 10 ATDC Just cut ita touch deeper. .070"intake and .090" at zero lash is as tight as you dare. I'd like to see ,090" .110" for safety.
Doug

 

[66Satellite47]

Follow dvw's advice. Make sure that the relief has radial clearance. I suggest planning on one size larger valve. 2.14/1.81 in a 2-08/1.84. That worked for me, with my early 440's.

 

[Doorkicker]

Too much math! Makes my head ache. I put the head on the engine with the head gasket and finger tighten the bolts.
Put weak springs on the intake and exhaust valves on one cylinder that you can push open by hand. Put in two lifters
and push rods and two rocker arms. Mount your degree wheel and set it to TDC. Rotate the engine five degrees at a time
and keep pushing down on the valves until you "feel" them start contacting the tops of the pistons. When you get close,
you can put a dial indicator on the valve and measure the actual clearance. Easy-Peasy!

Yeah... that's kinda what I did when I put it together, but clearly not that well Nevertheless, thanks for sharing because know I know I wasn't off my rocker (pun intended)

 

[Doorkicker]

What you have to watch is radial clearance. You need .050" or more. You can install the head without the exhaust valve. As far as depth. Are you using the same cam? Same centerline? Advancing the cam tightens up the intake clearance and opens up the exhaust clearance. Duration effects clearance more than lift. I'm you disasembling the short block? Take the new head w/o valves and center punch the piston at TDC. That'll give you you correct center. If using the same cam checkvalve opening with a dial indicator befor disassembly. If you know how far it opens at 10 BTDC and 10 ATDC Just cut ita touch deeper. .070"intake and .090" at zero lash is as tight as you dare. I'd like to see ,090" .110" for safety.
Doug

Thank you - very helpful! I did talk to (I think) David (?) over at Lindy. He was awesome to talk to and I basically gave him all the info on the new valves and head and he custom made the tool with the radial clearance, just as you highlighted.

I am using the same cam. Your point about duration is spot on and my next hurdle. This all surfaced because I was looking at 1:1.6 rockers and that started this whole thing. Assuming all the numbers and measurments work out... I have to see what's possible from there. Eventually... this is getting a 512 stroker. I just don't have the $$ at the moment.