JonPMH53

So I measured my PTV with a dial indicator and checker springs, the closest I got was .052 on the intake valve at 10 degrees after TDC...I know .080 is the recommended minimum for intake valves...is .028 gap pushing it too much?

Again this was 10 deg ATDC so the piston is on the way down (.063 at 15 deg ATDC), it should never get any closer than that right?

I also have 1.8 rockers on there as well, if I switch back to 1.7, I will gain approx .033 and be solidly at .085...but I would like to avoid getting rid of my expensive rockers if at all possible. Whats the alternative, retarding the cam a couple degrees to gain more clearance?

I welcome all thoughts and ideas...thanks.

badazz81z28

iTrader: (6)

What size cam are you running? Heads milled?
With clearences below spec, you are risking it. Keep in mind rods will stretch during running. What may be close now, may be ever closer at 6000 rpms

underacheiver

think about heat expansion also.

JonPMH53

Patriot Stage 2 heads milled down to 59 cc combustion chambers (not sure how much that equals in inches), stock GM head gasket, new cam is a Comp custom by Pat G : 226/230 .569/.572 (.602/.606 w/ 1.8 rockers).

I think the lifter may be screwing up my readings, I know I should use a solid one for this measurement but I'm not pulling the head off if I don't have to. Do I need an adjustable pushrod checker to get accurate measurements with the lifters in?

RonSSNova

iTrader: (3)

With checking springs? Absolutely you need to be using an adj pushrod set to 0 lash and left that way for the whole test.
You are holding your valves open by whatever amount of preload you had dialed into your pushrod length.

Ron

vettenuts

iTrader: (4)

You need to double check. How exactly did you measure?

Also note that while rods will stretch, the pushrods and rockers will flex and your actual valve motion will be less than measured with the dial indicator. I am running less than 0.080" but not as low as you although some motor builders have told me they run tighter then your measurements but valve control is key.

JonPMH53

Here is my latest dilemma:

Stock rockers, checker springs, and adjustable Comp pushrod checker give me zero lash at just about 7.312" (10 and 1/4 turns on the checker), but drop my PTV clearance to .062 at its closest. When I unwind the adjustable pushrod to 7.300" (10 turns), the PTV clearance goes up to a normal .082, but leaves just a bit of looseness between the rocker and the top of the valve, which will translate to lots of ticking noise.

If I understand everything right, 7.312 + .080 lifter preload should be approximately 7.400 correct pushrod length. I just happen to have some 7.400 rods laying around so I tried one and my PTV drops even further into the .050 range.

So would a 7.400 pushrod still be the correct size and hope that when the lifter does depress it gives back that critical .020-.030 clearance that I need?

Am I doing all the math right? it just makes me nervous when I see the PTV drop like that....HELP!

vettenuts

iTrader: (4)

You can't/shouldn't measure PTV with a pushrod that is longer than zero lash as it will depress the lifter plunger and skew the readings. If the hydraulic lifter is in place you need to ensure the plunger isn't moving downwards during the PTV reading or it will be incorrect. This is why your values are all over the map.

Can you explain exactly how you are making the measurements? Are you starting at around 15-20 degrees before the piston gets to the top and measure in 2 deegree increments until 20 degrees after the piston passes TDC?

Tainted

iTrader: (9)

you are one missed shift or other small glitch away from having a set of notched pistons and bent valves with that little clearance. Minimum I would ever run is .065

JonPMH53

I've been measuring the PTV clearance with checker springs on the #1 cylinder and a dial indicator on the top of the valve retainer, normal lifters still in the head, stopping every 2 degrees as recommended between 20 BTDC to 20 ATDC.

Intake valve starts opening around 6 Deg. BTDC and clearance is fine until I hit 2 ATDC, thats when it drops below .080 and gets down to .062 by 10 ATDC. At 15 ATDC, its at .068 and moving in the right direction again.

This is at zero lash on the base circle and 7.312" on the adjustable pushrod checker. I'm confident on all the other measurements, ICL is within a half degree from the card, TDC is right on dot to dot.

According to my cam card, the intake is not supposed to be opening until 1 deg BTDC, do I need to retard it 5 deg? I'm guessing that would give me back some clearance on the intake valve...the exhaust valve is way clear by the way, no issues there.

I know its the milled heads that are killing the clearance, I'm just hoping I don't have to buy a smaller cam to over come it....

badazz81z28

iTrader: (6)

Thats exactly why I don't understand why people are milling heads with stock bottom ends. Not only is your compression high, now you need a big cam to bring the DC down which is now creating PTV clearence issues. That .035"+ that is milled off those heads is your clearence! You will have to fly cut those pistons, and your cam duration really isnt that much.

RonSSNova

iTrader: (3)

What ICL does the cam card call for? And what is the lobe sep?
My cam is dang similar. 226/230 .598/.608 114 lobe sep, 113 ICL. And I have .095" clearance on the intake. Plenty on the exh.
Heads milled .032 (AFR) with the GM .051" MLS gaskets.
How sure are you about your TDC setup? How did you do that?

Ron

JonPMH53

Cam card says 112 ICL, with 113 LSA...I came up with 111.5 ICL after checking it so I want to believe the grind is good....

I found TDC with a spark plug hole piston stop and the degree wheel (small 9" Comp wheel) per the instructions: rotate 20 deg back from dot to dot, screw in the stop, mark the wheel, rotate 20 deg forward, mark the wheel, took the average value in the middle and moved zero to that value...

I'm going to redo the TDC calculation and basically start from scratch again. After checking many times at zero lash, the closest value I come up with is .067 at 8 deg ATDC on the intake...this is with 7.3125" dialed on the adjustable pushrod checker.

Hopefully if I do it all over and be really precise with not shaking the dial indicator, I can get to the neighborhood of .070....I think that is a little closer to the realm of safety, but if not I may have to buy an adjustable timing set...

My big question is is it worth it to retard the cam a couple degrees in hopes of more clearance? I'm thinking just a 2 deg move would probably do the trick...and hopefully not mess anything else up in the process...

RonSSNova

iTrader: (3)

After you screwed in the stop, you rotated CW until the piston hit it and marked the wheel. Right?
Then the same thing rotating all the way CCW?
TDC is half way in between. It is best to be able to just move the pointer rather than loosen the wheel.
Then recheck to verify.
Not doubting you did it right, just checking.

How did you check the ICL?

JonPMH53

Ron-
I turned the crank CCW from dot to dot first 20 deg, screwed in the piston stop, and then continued CCW until it came up and hit the stop again, marked it then rotated CW (in the direction of engine rotation) until it came up and hit the stop, marked it....took the center between those two.

That's the way it is described in the instructions that came with the wheel...it shouldn't matter which direction you go first as long as you are marking it correctly right? The piston should be in the same position no matter which way you turn first right?

I did ICL using the dial indicator on top of the valve, rotated to max lift, reset dial indicator to zero. Backed it off (CCW) until it read .100, then moved forward to .050, recorded the number on the wheel. Rotated forward until the indicator read .050 on the closing side, recorded the number. Added together and divided by two and got 111.5...which I believe is close enough to the advertised 112 ICL.

I'm going to do it all over again using the adjustable pushrod locked at 7.3125 (zero lash) and see if anything moves...

Thanks for the input, I welcome any other ideas and questions. I really want to make sure I get this right....

JonPMH53

One thing I noticed in the Comp degree wheel directions is that starting from approximate TDC both valves should be closed...

I just noticed that my intake begins opening before TDC...it is actually starting to move at 20 deg before TDC even though the cam card says it should start at 1 deg....could this be the issue? Is this cam jacked or are my calculations way off?

Lined up dot to dot the intake valve is already open about .075 at zero lash...what am I doing wrong here???

RonSSNova

iTrader: (3)

TDC proceedure is correct. Doesn't matter which direction first.
You did the ICL measurements on the valve. I did mine on the lifter. I didn't have the lifter trays in the engine, they really messed the measurements up because they hold the lifters up.

When you do ICL on the valve, you have the rocker ratio in the measurements. I think the instructions want you to do it .050" either side of full lift at the lobe (lifter). You might go back and re-do that but use .100 or .090. either side and see what you come up with. These modern lobes might not be real symetrical. You also might ask Pat G. What he thinks.

My cam has EPS intake lobe. Interesting stuff huh?

PowellSixO

iTrader: (1)

Does it have to be tdc on the compression stroke? If you are not at tdc on the compression stroke that would explain why both valves are not closed.

JonPMH53

So I took everything apart and walked away for about a day to re-think this...then came back and started from scratch, reaccomplished all the measurements from TDC, to ICL, to PTV clearance. Here is what I came up with:

Intake PTV clearance- Lowest was .122 at 8 deg ATDC
Exhaust PTV clearance- Lowest was .191 at 10 deg BTDC
ICL- 111.5

I did each one a minimum of three times and took the averages, each measurement all within +/- .003 of each other. I'm pretty confident this is accurate, the only thing that bugs me is why the measurements were all over the chart before. Only thing I can think of is that maybe the pushrod wasn't seated all the way in the lifter cup and just riding on the edge, That would easily produce readings that would be .050-.060 less I believe.

I'm putting back together and going with it....whats the worst that could happen...I bend all the valves and smack all the pistons? Big deal...if that happens I'll just take a loan from my retirement account and get a new LS7 longblock!

vettenuts

iTrader: (4)

When I degreed my cam, I did the intake centerline method and then check the 0.050" position of the cam. Both methods provided the same answer so I was good. Sometimes a double check using another method will tell you if you missed on the first method. Don't feel bad, took me several attempts to get things straight as it is harder with the motor in the car. I think even with 0.070" you were OK. Let's face it, if 0.010" on the intake is an issue you would likely have a problem at 0.080" as well.