PTV Clearance Measuremet to Figure Out How Much To Mil Heads
#1
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Long story short I am trying to measure PTV before I send my heads out to be ported and wanted to get an idea of how much can be milled off. I am trying to use the dial indicator / checker spring method and feel like I am doing it wrong.
I measured PTV at TDC by pressing the valves down until they hit the piston and got .265 with the exhaust side and .270 with the intake with a felpro 26192 PT head gasket.
I used an adjustable pushrod and set the rocker on each valve to 0 lash and made sure the motor turns over without hitting, and it was fine. I am pushing down on the valves every .050 of valve drop to make sure there is no ptv contact and it seems fine as well.
Fwiw, the combo is a sbe lq4 with a custom grind cam motion cam (230/238 113+3 .621"/.604") and 799s. Is there any way to determine the amount I can mil the heads based on the cam specs?
I measured PTV at TDC by pressing the valves down until they hit the piston and got .265 with the exhaust side and .270 with the intake with a felpro 26192 PT head gasket.
I used an adjustable pushrod and set the rocker on each valve to 0 lash and made sure the motor turns over without hitting, and it was fine. I am pushing down on the valves every .050 of valve drop to make sure there is no ptv contact and it seems fine as well.
Fwiw, the combo is a sbe lq4 with a custom grind cam motion cam (230/238 113+3 .621"/.604") and 799s. Is there any way to determine the amount I can mil the heads based on the cam specs?
#3
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PTV is closest at approximately 9 degrees before and after TDC. Checking at TDC will not work. Check every degree from about 5 to 15 degrees before and after TDC to find out where your combo is closest.
#4
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Give this thread a read, way easy way to check PtV
https://ls1tech.com/forums/generatio...ve-method.html
https://ls1tech.com/forums/generatio...ve-method.html
Looks like ill be looking for a degree wheel now.
#5
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So I got around to trying to measure again tonight using the method of putting play-dough between the valve and rocker, as well as putting play-dough on the piston. All measurements were with a digital caliper.
Using the rocker/valve method, I got .083 for the intake and .101 on the exhaust. I had a hard time getting an accurate measurement and had to do this multiple times and this was the most accurate reading I got.
When using the play-dough on the piston, I got just under .210 on the intake and .273 on the exhaust. Since this is an lq4 with dished pistons and a stock thickness head gasket, I'm guessing the piston measurements are more accurate. There was a nice thick chunk on there and the pistons barely made a dent.
Do these numbers seem typical for this size cam and head / head gasket setup?
Using the rocker/valve method, I got .083 for the intake and .101 on the exhaust. I had a hard time getting an accurate measurement and had to do this multiple times and this was the most accurate reading I got.
When using the play-dough on the piston, I got just under .210 on the intake and .273 on the exhaust. Since this is an lq4 with dished pistons and a stock thickness head gasket, I'm guessing the piston measurements are more accurate. There was a nice thick chunk on there and the pistons barely made a dent.
Do these numbers seem typical for this size cam and head / head gasket setup?
#6
TECH Junkie
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This is just my opinion and someone smarter is going to have to chime in but with 799 heads I would say there is no way you you have almost .250" clearance.
What did you set your adjustable push rod checker at ?
What did you set your adjustable push rod checker at ?
Last edited by 98CayenneT/A; 09-08-2017 at 08:21 AM.
#7
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Also when you measured the clay from putting it on the piston, where did you take your measurement from, the lower sitting dish of the piston or the higher outside. Reason I ask is the very outer edge of the valves may barley hit the outer skirt of the piston.
Again just my opinion but I do think using the clay in between the rocker and valve tip is your more accurate measurement in this situation due to the valve possibly slightly hitting the raised outer part of the dished piston.
Again just my opinion but I do think using the clay in between the rocker and valve tip is your more accurate measurement in this situation due to the valve possibly slightly hitting the raised outer part of the dished piston.
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#11
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Looking at the pictures is does look like at the very least the intake valve does continue over the non dish part of the piston.
You may want to try modeling clay also for it's more stable and less springy. I would also cover the outer part of the piston and take that measurement also.
How deep does the dish measure, .050" ?
You may want to try modeling clay also for it's more stable and less springy. I would also cover the outer part of the piston and take that measurement also.
How deep does the dish measure, .050" ?
#13
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So I got around to trying to measure again tonight using the method of putting play-dough between the valve and rocker, as well as putting play-dough on the piston. All measurements were with a digital caliper.
Using the rocker/valve method, I got .083 for the intake and .101 on the exhaust. I had a hard time getting an accurate measurement and had to do this multiple times and this was the most accurate reading I got.
When using the play-dough on the piston, I got just under .210 on the intake and .273 on the exhaust. Since this is an lq4 with dished pistons and a stock thickness head gasket, I'm guessing the piston measurements are more accurate. There was a nice thick chunk on there and the pistons barely made a dent.
Do these numbers seem typical for this size cam and head / head gasket setup?
Using the rocker/valve method, I got .083 for the intake and .101 on the exhaust. I had a hard time getting an accurate measurement and had to do this multiple times and this was the most accurate reading I got.
When using the play-dough on the piston, I got just under .210 on the intake and .273 on the exhaust. Since this is an lq4 with dished pistons and a stock thickness head gasket, I'm guessing the piston measurements are more accurate. There was a nice thick chunk on there and the pistons barely made a dent.
Do these numbers seem typical for this size cam and head / head gasket setup?
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#14
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You need to take apart a hyd lifter and shim it up until it is solid, make sure it has no slop. then put the heads on with (NO ) head gasket. With a checker spring on 1 intake valve and 1 exhaust valve check the clearance 8-10 degrees before and after TDC. No rockers on any other valves. Just add the thickness of the head gasket for you results. 8-10 degrees before and after is where the valve is the closest to the piston.
#15
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You need to take apart a hyd lifter and shim it up until it is solid, make sure it has no slop. then put the heads on with (NO ) head gasket. With a checker spring on 1 intake valve and 1 exhaust valve check the clearance 8-10 degrees before and after TDC. No rockers on any other valves. Just add the thickness of the head gasket for you results. 8-10 degrees before and after is where the valve is the closest to the piston.
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Hi MJS, I use EAP "maths" for P/V contact reports.
BELIEVE THAT I have the head model, I only need to know the cam/engine specs ?
You will find, the P/V distance is closest just before/after TDC NOT AT TDC.
I do this for free, LS-1 Tech members.
Just post the specs ?
Lance
BELIEVE THAT I have the head model, I only need to know the cam/engine specs ?
You will find, the P/V distance is closest just before/after TDC NOT AT TDC.
I do this for free, LS-1 Tech members.
Just post the specs ?
Lance
#17
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Hi MJS, I use EAP "maths" for P/V contact reports.
BELIEVE THAT I have the head model, I only need to know the cam/engine specs ?
You will find, the P/V distance is closest just before/after TDC NOT AT TDC.
I do this for free, LS-1 Tech members.
Just post the specs ?
Lance
BELIEVE THAT I have the head model, I only need to know the cam/engine specs ?
You will find, the P/V distance is closest just before/after TDC NOT AT TDC.
I do this for free, LS-1 Tech members.
Just post the specs ?
Lance
Hey Lance, engine is a stock bottom end lq4, cam specs are 230/238 113+3 .621"/.604", heads are stock 799s that I will be sending out to port after I figure this out, and I have a stock thickness head gasket.
#19
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I was unable to push the plunger down on my lifters by hand so figured modeling clay would not be able to either.