85 I6 valve adjustment question
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85 I6 valve adjustment question
My I6 valve rockers are bolted to the head. I pulled a push rod to confirm there is a hydraulic lifter in the hole.
I was expecting some kind of rocker adjustment like a lock nut on a stud but mine all seem to be cinched up and torqued to the head with a bolt. Do I have to change the push rod length to adjust the values in such a setup? And how do I make the measurement since the lifters are hydraulic?
I was expecting some kind of rocker adjustment like a lock nut on a stud but mine all seem to be cinched up and torqued to the head with a bolt. Do I have to change the push rod length to adjust the values in such a setup? And how do I make the measurement since the lifters are hydraulic?
Last edited by longreins; May 16, 2013 at 01:11 AM. Reason: left off a question
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From: Virginia
Yes, you have to change the pushrod length. There are other ways that some people use, like small shims under the rockers.
You should not need to adjust the valvetrain if everything is original. If some head work has been done, they are supposed to keep it correct and no adjustment is needed, but we all know we don't get a proper job sometimes. Also if you have a aftermarket cam sometimes you also need to adjust them.
You can tell if you need adjustment by bringing that cylinder around to TDC. Loosen the rockers, slowly tighten them till the play in the pushrod just goes away, then count the number of turns it takes to lock down the bolt. 1/2 turn you are on the borderline too loose, 3/4 to 1 turn you should be ok. Anymore than that you are too tight.
You should not need to adjust the valvetrain if everything is original. If some head work has been done, they are supposed to keep it correct and no adjustment is needed, but we all know we don't get a proper job sometimes. Also if you have a aftermarket cam sometimes you also need to adjust them.
You can tell if you need adjustment by bringing that cylinder around to TDC. Loosen the rockers, slowly tighten them till the play in the pushrod just goes away, then count the number of turns it takes to lock down the bolt. 1/2 turn you are on the borderline too loose, 3/4 to 1 turn you should be ok. Anymore than that you are too tight.
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I have 8 valves that are too tight and 2 that are crowding tight. I need to replace more than half the push rods. I hope the part store has a big caliper. Is it okay to swap push rods if any happen to be the right length for a different spot?
I can convert degrees of bolt turn into thousandths of an inch at the bolt; the fulcrum of the rocker. But I don't know the rocker ratio and length needed to turn that number into thousandths of an inch at the push rod. Is there published table for a stock rocker?
When I start changing rods, I will target the center of acceptable; 3/4 turns.
These are my measurements in turns from finger tight to torqued using EOIC by eyeball.
E1=1 3/8, I1=1 1/8
E2=1 5/8, I2=1 1/2
E3=1 3/8, I3=1
E4=0 3/4, I4=1 1/8
E5=1 1/8, I5=0 5/8
E6=1 0/8, I6=1 3/8
I can convert degrees of bolt turn into thousandths of an inch at the bolt; the fulcrum of the rocker. But I don't know the rocker ratio and length needed to turn that number into thousandths of an inch at the push rod. Is there published table for a stock rocker?
When I start changing rods, I will target the center of acceptable; 3/4 turns.
These are my measurements in turns from finger tight to torqued using EOIC by eyeball.
E1=1 3/8, I1=1 1/8
E2=1 5/8, I2=1 1/2
E3=1 3/8, I3=1
E4=0 3/4, I4=1 1/8
E5=1 1/8, I5=0 5/8
E6=1 0/8, I6=1 3/8
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From: Virginia
I don't believe they sell many different lengths. I have never bought any, but heard some people talking about getting a pushrod that is .01 shorter or longer.
Since you have some that are too tight, you could try shims. I guess you have had the rocker completely off before? If so, you will notice the head has a little slot machined in it where the rocker bolt hole is located. This slot is where the slide fulcrum sits, and holds everything in alignment to the valve tip.
The slot is deep. So you can cut small brass or whatever shim stock, and place it under the fulcrum. Hopefully you can keep it in one piece, I think I would punch the hole in the shim first, and then cut around the hole for it to fit in the slot. As long as the fulcrum is still down in the slot some, you should be ok.
I can't tell you how much shim you will need. What I would do is experiment till you get the correct number of turns when you tighten the bolt down.
Since you have some that are too tight, you could try shims. I guess you have had the rocker completely off before? If so, you will notice the head has a little slot machined in it where the rocker bolt hole is located. This slot is where the slide fulcrum sits, and holds everything in alignment to the valve tip.
The slot is deep. So you can cut small brass or whatever shim stock, and place it under the fulcrum. Hopefully you can keep it in one piece, I think I would punch the hole in the shim first, and then cut around the hole for it to fit in the slot. As long as the fulcrum is still down in the slot some, you should be ok.
I can't tell you how much shim you will need. What I would do is experiment till you get the correct number of turns when you tighten the bolt down.
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I realize now that there is no need to think about the rocker ratio. If a valve rocker needed 1 1/2 turns to torque down but I wanted it to torque at 3/4 of a turn. Then I simply need a shim that is as thick at 3/4 of the height of one bolt thread.
It took me a while to realize the engine-off measurements were only compressing the spring in the lifter but that when the engine is running, the oil in the lifter would not let it do that; the valve would move instead. The acceptable window of half a turn to one whole turn must include all that rocker ratio stuff I was trying to figure out as if I had solid lifters.
My 85 does not have a grove to align the fulcrum but some channel stock between intake and exhaust fulcrums that works like a wrench holding the pair aligned. The shim stock will be trapped inside that channel with the fulcrum.
Thanks again Dave.
It took me a while to realize the engine-off measurements were only compressing the spring in the lifter but that when the engine is running, the oil in the lifter would not let it do that; the valve would move instead. The acceptable window of half a turn to one whole turn must include all that rocker ratio stuff I was trying to figure out as if I had solid lifters.
My 85 does not have a grove to align the fulcrum but some channel stock between intake and exhaust fulcrums that works like a wrench holding the pair aligned. The shim stock will be trapped inside that channel with the fulcrum.
Thanks again Dave.
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Unless the head has been milled, the motor's valve train has significant wear, or you have changed from stock components, no need to change push rods.
The proper way to check for proper push rod length on a motor like this with positive stop rocker arms is to torque down all the rocker arms to spec, then use a lifter bleed-down tool to collapse the lifters. Once that's done, you take a feeler gauge and see what the gap is between the tip of the valve stem and the rolled hump that the rocker arm rides the valve with.
If the gap between the valve stem and the rocker arm is too large, get a longer push rod that will shrink the gap and bring it into spec.
If the gap between the valve stem and the rocker arm is too small, get a shorter push rod that will open up the gap a hair and bring it into spec.
The idea here is to get everything within the proper range so the hydraulic lifters can automatically adjust for lash once the motor is cranked up.
The proper way to check for proper push rod length on a motor like this with positive stop rocker arms is to torque down all the rocker arms to spec, then use a lifter bleed-down tool to collapse the lifters. Once that's done, you take a feeler gauge and see what the gap is between the tip of the valve stem and the rolled hump that the rocker arm rides the valve with.
If the gap between the valve stem and the rocker arm is too large, get a longer push rod that will shrink the gap and bring it into spec.
If the gap between the valve stem and the rocker arm is too small, get a shorter push rod that will open up the gap a hair and bring it into spec.
The idea here is to get everything within the proper range so the hydraulic lifters can automatically adjust for lash once the motor is cranked up.
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