When the locking nut is tightened, it pushs the top nut up, decreasing the clearance. Unless you initially position the upper nut with a little extra clearance to account for this, the valve will be too tight after the locknut is tightened.

i always adjust it by loosening the lock nuts, one key note i have always done is have the wrench in your right hand on the bottom and the wrench in your left hand on top, if the valve is too tight position both wrenches to the left loosen the one in your right and then follow through with the left, if they are too loose start on the right loosen with the left and follow through with the right. i will see if i can make a basic video next time i have to adjust one in the shop.

Valve adjustment with a decent set of wrenches, and done the way the FSM recommends takes 30-40 minutes. Turning both the lock nut and the adjusting cap simultaneously while they are still jammed together is shade-tree in my opinion. Makes me wonder how "Master" that mechanic is.:rolleyes:

Both nuts are threaded onto the valve stem. If the top adjustment nut doesn't spin, and the valve stem doesn't spin, then it will not advance upward. If it pushed over a thread, the valve stem or the nut (or both) would strip. Now, there may be just a teeny-tiny bit of difference from being pushed to one side of the thread rather than sitting in the middle, but that is a whole heck of a less difference than trying to clamp the top nut down on the bottom over and over hoping to get it right.

You can bring the top nut DOWN 1/16 of a turn while you are bringing the bottom locking nut UP if you need to.

Exactly. How many adjustments can you make before you are replacing stripped valve stems?

Depending on the clearance in the threads, that "teeny-tiny bit of difference" might be as much as .003". That's the difference that TF is referring to.

Maybe, I am just pessimistic, but...
 

doesn't this method damage, or potentially damage the threads of the adjuster?
John

In that case, do the 1/16 turn down if needs be.

I suspect that anyone who rechecks their valve clearance after they tighten the locknut would disagree.

What is your explanation of this phenomenon? Is it other than already described?

Having 2 people saves a load of time. :D

I explained it to you in post #21. The clearance in the threads causes the top nut to move upward when the bottom nut applies the upward force during the locking sequenct.

Then that brings up the question of how far it usually rises. Maybe we should set the gap with .12-.13mm intake, .37-.38mm exhaust (Turbo 617) and and then check it at .10 and .35 after its tightened.

Might work........but the clearance in the threads on various valves might not be held to .001". A tolerance of .001" on threads is very difficult to achieve unless the thread is ground........and these most certainly are not. Therefore, the variation in clearance is probably more than would be acceptable for this procedure.

Wanted to add to this post. I just adjusted the valves in the 300TD and the method does work very well. The time adjusting was very minimal compared to my previous method. I had to replace the valve cover gasket due to a leak and, it has been a while since I adjusted the valves. I did take a little longer doing the job. I loosened and tightened each valves jamb nuts to make sure they were not overly tight. After doing that I found the technique and job to to very quickly.
I also made copies of the valve intake-exhaust diagram from the SM and added notes to it. I print it out each time I adjust the valves and use it as a guide. I also wrote down the order that each cam came into position for adjustment so you only rotate the cam once during the adjustment. Whether this saves time, I'm not sure. Moving the large lower wrench may take up more time then rotating the cam a couple of times to adjust each valve in order, front to back. I do leave the injector lines connected while doing this.

Attached is the valve adjustment diagram I made. It is for a 82 300TD.

Dave