mjs1012

iTrader: (36)

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?

98CayenneT/A

Give this thread a read, way easy way to check PtV
https://ls1tech.com/forums/generatio...ve-method.html

NEstyle

iTrader: (1)

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.

mjs1012

iTrader: (36)

Just saw this, looks like a pretty basic way to check.

Looks like ill be looking for a degree wheel now.

mjs1012

iTrader: (36)

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?

98CayenneT/A

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 ?

98CayenneT/A

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.

mjs1012

iTrader: (36)

I set the pushrod to where I'd have 0 lash and then took the checker springs off and tested.

I measured on the piston at where the deepest point of contact was.

mjs1012

iTrader: (36)

Looking at my pictures more, it looks like I didnt have enough play dough on the outter part of the piston.

CNC-Dude

You need to use a "solid" lifter to ensure the hydraulic one isn't collapsing once you make contact with the play-doh and giving you a false reading.

98CayenneT/A

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" ?

mjs1012

iTrader: (36)

I haven't measured the depth of the piston dish. I was thinking the dough was not sturdy enough since it would conform around the razor whenever I'd try to cut it so I'll look for some modeling clay tomorrow and try it again.

01ssreda4

iTrader: (96)

My Cam Motion 228/232 had .120 and .100 clearance. So yes I milled 30 and had no issues.

NHRAFORMULA00

iTrader: (2)

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.

mjs1012

iTrader: (36)

Ill try to find an old lifter and degree wheel. I don't really want to take apart my brand new lifters.

pantera_efi

iTrader: (1)

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

mjs1012

iTrader: (36)

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.

mjs1012

iTrader: (36)

Random thought, but do checker springs have enough pressure to even push the lifter plunger down? I can collapse the springs completely with just my thumb and index finger.

98CayenneT/A

I was unable to push the plunger down on my lifters by hand so figured modeling clay would not be able to either.

01ssreda4

iTrader: (96)

No, which is the point (of having them) and why a solid lifter recommendation is retarded.