Pushrod length checker: what am I doing wrong?
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Pushrod length checker: what am I doing wrong? I posted a thread a few weeks ago regarding lining the timing marks up before installing the timing cover....
So I pulled the plugs, put a pushrod into cylinder 1's intake valve, turned the motor over until the pushrod rose and then fell.... Then I took an inspection camera, put it into the spark plug hole, and turned the motor over just until the cylinder reached its peak....
So now I'm using a comp pushrod length tool, and I got the intake port measure to 12.5 turns to zero lash.
But when I try the exhaust port it comes to about 11.5 turns to zero lash.
What am I missing here? (BTR stage 2 cam, and Trick flow 220 heads)
So I pulled the plugs, put a pushrod into cylinder 1's intake valve, turned the motor over until the pushrod rose and then fell.... Then I took an inspection camera, put it into the spark plug hole, and turned the motor over just until the cylinder reached its peak....
So now I'm using a comp pushrod length tool, and I got the intake port measure to 12.5 turns to zero lash.
But when I try the exhaust port it comes to about 11.5 turns to zero lash.
What am I missing here? (BTR stage 2 cam, and Trick flow 220 heads)
Are you turning the motor over after you take the intake lobe measurement in order ot get the exhaust valve on its base circle? The checker has to be on the base circle to get an accurate reading however just because you are on the intake lobes base circle doesnt mean its on the exhaust lobe's.
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Are you turning the motor over after you take the intake lobe measurement in order ot get the exhaust valve on its base circle? The checker has to be on the base circle to get an accurate reading however just because you are on the intake lobes base circle doesnt mean its on the exhaust lobe's.
So if the method above tells you when the intake is on the base circle, what is a good method of telling that the exhaust is? I was under the impression that doing the above would ensure I was on the base circle of both
Last edited by wayland1985; Jun 23, 2015 at 07:28 PM.
Make sure the lifters are down against the cam good. They will stay up unless you push them down. If that doesn't correct it, try turning the motor a little bit with the pushrod in the exhaust and see if it moves at all. Then re-measure. Since it's on the power stroke, the measurement should be the same.
If the same, they I would check the valve stem height to the machined base of the rocker stand to ensure the valve stems heights are the same (within tolerance). Wouldn't be the first time a new head came through with valve seats different.
If the same, they I would check the valve stem height to the machined base of the rocker stand to ensure the valve stems heights are the same (within tolerance). Wouldn't be the first time a new head came through with valve seats different.
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Yea, I've pushed the lifters down onto the cam.
I'm getting some what more consistent measurements with the middle two cylinders, but for some reason cylinder 1's intake is off by .025.
And then the exhaust vs the intake on each is off by 0.25.
I'm getting some what more consistent measurements with the middle two cylinders, but for some reason cylinder 1's intake is off by .025.
And then the exhaust vs the intake on each is off by 0.25.
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the BTR cams have less lift on the exhaust side, so the base circle of the cam will be around .025" larger diameter than the intake base circle. Half of that or .0125" is how much higher in the tray the lifter will be sitting when measuring
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Anyways, heres what I come up with: using 13 turns on my Comp Pushrod checker (13 includes my 0.050 preload), I come up with 1 and 1/4 turns to 22ft lbs on the intake side, and 1 and 3/4 turns on the exhaust side.
Using the 7.475 pushrods I purchased, I cam up with 1.75 turns to 22ft lbs intake side, and 2 full turns to 22ft lbs on the exhaust side.
So, knowing that, I think I need either a 7.45 length pushrod, or a 7.425 length pushrod to give me a preload of about .050 (intake side).
Or, do you think I'll need to be super picky and order separate pushrods for the intake and exhaust sides?
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I'm wondering if using copper gasket spray is causing this? Or perhaps there is a difference from milling the heads?
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Your cam could also not be centered in the block casting...putting one whole bank of lifters slightly closer to the cylinders.....slight casting/machining imperfections can magnify the further away from the source you are measuring.
Did you check deck clearance on both banks....I've seen on here where a guy got two different measurements and ultimately choose to run different thickness head gaskets to make the bank to bank compression ratios identical but IIRC he ended up using several different length push rods as well.
I agree that 7.425 should be fine. This is certainly an exception to the rule but i think you're reading too much into it lol. The preload window of ls7 lifters is pretty big so having a little different on the other isnt going to hurt anything and it happens more than most realize.
Truthfully any aftermarket cam with ~.600 lift give or take is going to need 7.425 pushrods with stock heads. I've installed quite a few cams and it always works out that way unless it has aftermarket heads, lifters, or milled heads. How much were yours milled?
Truthfully any aftermarket cam with ~.600 lift give or take is going to need 7.425 pushrods with stock heads. I've installed quite a few cams and it always works out that way unless it has aftermarket heads, lifters, or milled heads. How much were yours milled?
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I agree that 7.425 should be fine. This is certainly an exception to the rule but i think you're reading too much into it lol. The preload window of ls7 lifters is pretty big so having a little different on the other isnt going to hurt anything and it happens more than most realize.
Truthfully any aftermarket cam with ~.600 lift give or take is going to need 7.425 pushrods with stock heads. I've installed quite a few cams and it always works out that way unless it has aftermarket heads, lifters, or milled heads. How much were yours milled?
Truthfully any aftermarket cam with ~.600 lift give or take is going to need 7.425 pushrods with stock heads. I've installed quite a few cams and it always works out that way unless it has aftermarket heads, lifters, or milled heads. How much were yours milled?
The heads were killed to 61cc... Or at least supposed to be. I have no way of checking at this point That they were both milled correctly.
TEA did have to re-do the valve job on one head before it was delivered to me. I'm waiting to hear back to find out exactly what happened and whether it has any effect on my issue I'm seeing.
I really do hope they milled both sides correctly.
I was able to use a 7.40 prs as my 241s were cut .030" and I had .0236" longer LS6 valves
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Also, assuming it's the valves, will I need to run different rods on the left and right? Or will the lifter negate any difference?