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How much force required to turn a good stock valvetrain?

939 views 8 replies 4 participants last post by  NN4S 
#1 ·
Sorry if the wording of the title is a bit iffy; here's what I need to know.

I am reworking a D16Z6 head for my del Sol so that I can just swap it on to replace the one on it that is warped and leaking oil (car's currently running fine, just loses a bit of oil out of the corner under the water outlet). I've already gone through it and checked for straightness / flatness and have reassembled the spare head with assembly lube. However, while adjusting the valve clearance, it seems to require a good bit more force to turn over than most of the engines I've worked on.

I am working on the bench with the head sitting on a couple of layers of thick cardboard and turning the cam with a rubber strap wrench on the timing pulley. It seems to be very reluctant to pull through the valve actuation instead of going through the transition smoothly. Is this normal for the stock cam and valvetrain? I've seen it with high lift cams in other engines, but most of the stock stuff I've worked with has been relatively smooth when rotating through the cycle. I'm not holding the head hard against the table and limiting the valve movement against the cardboard; the only pressure holding it on the table other than gravity is the 1/4 turn or so I'm giving the strap wrench (from past experience, I should be able to feel a smooth compression of the cardboard instead of the jerky movement I'm getting).

What I want to know is if this sounds like there is something binding and causing this, or is the actuation I'm attempting to describe here the norm for this head? Everything looks good, it's all torqued to spec and the valves are now adjusted with the head ready to swap. I would just like a little input from some folks more familiar with this engine before I take the car off the road for the head swap/water pump/timing belt replacement, as it is my current DD and I can't really afford for it to be down any longer than necessary. Thanks in advance for any help you can provide!
 
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#2 ·
It should not be super hard to turn. I would pull it back apart and check for binding. I had a similar thing happen on a friends failed mini-me attempt. We thought that was normal and slapped the head on and it ended up binding up and broke the cam gear keyway. Check the rocker arms cam caps and lma's.
 
#3 ·
Thanks; that's what I was afraid of. There's a definite catch as it pulls through each set of lobes instead of the motion I expected. I'll go ahead & pull it apart again... better now than after I stuff it in the car!
 
#6 ·
As I said in my initial post, there should be a smooth compression of the cardboard (it's two layers of the thick, soft stuff).

This isn't the first head I've done this type of work on, just the first D16Z6. The action I'm getting out of it is more of a catch & release, like something is hanging somewhere. As such, it is taking a lot more torque to pull through the cycle than I felt necessary. I've only had a hard catch like this in the past on high-lift cams, so it was reasonable to ask if the stock setup in these heads behaved this way or if I was experiencing an aberration.

I'm going to go with turbostd's suggestion & tear it apart again just to be sure there's nothing I'm missing... I don't believe that it's acting as it should, especially considering all of the assembly lube on all of the moving surfaces.
 
#8 ·
It's cool, I just wanted to clarify the situation after the Beaver's post. ;) After all, this isn't HT... I believe everyone here expects relatively serious thought to be put into posts here.

I could have just waited to see how it compares to the head I'll be removing since I know it's working properly, but I'd prefer to know everything's ready to go when I start taking the car apart. Like I said, it's my DD and I can't have it down any longer than necessary.
 
#9 ·
Well, I went back through the head this morning and found a little binding in one of the lost motion assemblies and one of the exhaust rocker spreaders had turned out of position... went ahead and disassembled / reassembled / relubed everything again just to be safe.

I spun the cam over with everything loose (no bolts installed at all) & noticed that, even with the adjuster assemblies as loose as possible, there was still pressure on valves at various points in the cycle (in other words, the cam is never totally unloaded in it's operation; the rockers would lift the cam caps as they tried to press the valve down). Once I installed the bolts and tightened them through the correct sequence & torqued them, the turning torque was about what I would expect from a head with everything adjusted and ready to go even though the adjusters were as loose as possible on all rockers. Readjusting all of the valves for operation brought the force required to turn the cam over back to a little less than what was required before I reworked everything. The redo seems to have helped some in making it a bit smoother to rotate through the valve cycles (eliminated the "catching"), but it definitely requires more torque to pull through the valve cycles than other heads I've worked on. I am satisfied that it's working correctly now, even though it behaves in a different manner than what I'm used to. 8)

Thanks to everyone who offered suggestions up; you just never know when working on something different to your personal experience. :TU:
 
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