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Mike S.
Mike S., ASE Certified Technician
Category: GMC
Satisfied Customers: 7500
Experience:  GMC N.A.I.S.E. Certified Auto-Mechanic
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I have a 1991 4.3. I installed a set of 1995 heads on it. I

Customer Question

I have a 1991 4.3. I installed a set of 1995 heads on it. I bought ARP rocker arm studs that have a M10 X 1.5 base and ⅜ 24 threaded top to use the 1991 rocker arm stud. I am having valve lash adjusting issues. Can you please inform me of what Im over looking or where my mistake was made. Thanks for your time.
Submitted: 2 years ago.
Category: GMC
Expert:  Toolhut replied 2 years ago.

Hi, My Name is ***** ***** for posting your question to just answer. I am a ASE Certified Master Auto Technician with 20 years experience. I am confident we can resolve your problem together.Please remember I don't know your skill level. I can't see, smell, hear, or touch the vehicle. It may take a few back and forth replies to get to a satisfactory resolution.I also try to give all of the information you may need expecting a positive rating.

How did you adjust the valves? What kind of problems are you having?

Customer: replied 2 years ago.
I tighten the rocker arm until the push rod has enuff tention that I can't spin it between my fingers. The book calls for 1 to 1½ turns after that. As soon as I get a ¼ turn on the locking nut the valve spring begins to compress a considerable amount. If I take it the full 1 to 1½ turns the valve is hanging open. I am not an ASE certified mechanic.... but I was certified for engines, brakes, electrical, smd alignment here in Michigan. Granted it was 20 years ago...but I'm still agear head.
Expert:  Toolhut replied 2 years ago.

Are you sure you are on the proper spot on the cam?

Customer: replied 2 years ago.
While at TDC on #1 this is my sequence of adjustmentIntake, 1, 2, 3
Exhaust, 1, 5,Then I rotate the engine 180 degrees and finish with this sequenceIntake, 4, 5, 6
Exhaust, 2, 3, 4
Expert:  Toolhut replied 2 years ago.

Realistically the lifters should bleed down.

Try turning 1/2 let it set for 10 minutes and see if you can turn pushrod. I suspect you are not allowing lifters to bleed down.

Customer: replied 2 years ago.
I Already tried that... with no success. I'm curious it may be the difference in a rocker arm ratios
Customer: replied 2 years ago.
can you tell me if the valve spring strength is different for a 1991 compared to a 1995 Heads
Expert:  Toolhut replied 2 years ago.

Accordng to service manual and parts catalog they are the same. What I am thinking is when you are tightening you are going to tight.

Adjust until you cannot move the pushrod up and down instead of til it wont turn. then go 1 turn. My manual states 1 turn after the clearance is removed.

Customer: replied 2 years ago.
I can positively assure you that is not the case. I am a Harley mechanic by trade. I'm stuck in the upper peninsula of Michigan trying to fix our cabin truck ( wood hauler) with no manual.
Customer: replied 2 years ago.
I know that GM changed rocker ratio's...lifter travel and rocker arm stud design 3 or 4 times from '89 to '95. I don't know exact specifics on the changes. I would bet my manhood that it is in the configuration of my components. That's why I came just answers.
Customer: replied 2 years ago.
Please look closer at my original message....not to be rude but if I wanted speculation I would have asked anyone at the local tavern.
Expert:  Toolhut replied 2 years ago.

I looked up rocker arm part numbers and spring height specs. The ratios and spring heights are the same 91 and 95. The part numbers are different and I cannot determine the change

Customer: replied 2 years ago.
From 1987 thru 1997 GM also changed thier lifters along rocker arms and studs.AC Delco HL-124 lifters have standard (0.166") travel. From 1992-1995 AC Delco HL-105 long travel (0.237") lifters. The rocker arm ratio's varied along with them. I AM NOT impressed with " just" . I am going to request a refund. I can appreciate the attempt to help... but I feel as if I've have not received any help at all. Have a good day.
Expert:  Toolhut replied 2 years ago.

I can opt out and see if another expert can help

Customer: replied 2 years ago.
I am not dealing with this website any longer. Thank you but no.
Expert:  Mike S. replied 2 years ago.

I always adjust the valves when the engine is idling no matter if I give them an initial adjustment when it's not running or not. What I would do is start off with 1/2 turn down from zero lash, then while the engine is idling back off each adjustment nut 1/8 to 1/4 turns until the lifter begins to clack then tighten back down 1/8 to 1/4 turn at a time, pausing of course, until the noise goes away. That would be zero lash, then go down another 1/2 to 1 full turn depending on the mileage on the camshaft, with 1/2 turn being anything nearing or over 100,000 miles and 1 full on anything under 50,000 miles.

The spring tension, I don't believe really matters, but the rocket arm ratio I believe should. I would think that you would have to adjust your thinking or specifications for how much of a turn or adjustment there is for the valve and lifter since of course it takes less travel of the valve lifter lobe to equal the same distance of valve opening.

If it's a 1.5 times ration rocker arm, I would naturally think that you would divide that 1 full turn down by 1.5 which equals 0.66 turn.

Expert:  Mike S. replied 2 years ago.

Let me backup here. I believe adjusting the valves has to do with putting the lifter plunger down into it's center of travel, so even if the are different ration rockers, the adjustment will still be the same.

Expert:  Mike S. replied 2 years ago.

If your valve springs are starting to compress and valves open, I might come to the conclusion that you are not on the flat side of the camshaft. You never did say on the compression stroke when you said tdc, so maybe that is your problem, you have to distinguish between tdc exhaust and tdc compression stroke, then do those adjustments.