valve adjustment and/or lash???

[Cadillakin'98]

Alright folks, as I mentioned in a recent thread, my neighbor and I are just about to fire up this new motor in his '88 c1500 (5.7L). We think we found the problem. That is lack of compression. Well, we have narrowed it down to improper valve adjustment. We redid it according to the Chilton's manual and the Haynes conveniently says "take it to a professional". Never did like Haynes. Anyways, my (our) question is what exactly is valve lash? Also, what is the proper way to adjust the valves in this motor (5.7L)? When we backed off the nut on rocker arm approx. 1/4 of a turn, we now have some compression (finally)! However, since the Chiltons manual is obviously incorrect, we have no way of knowing the proper procedure but know that there has to be one. I'm staying on here for a while in hopes someone can help us out......

[Cadillakin'98]

YES!!!!! It fired up!!!! Now we just gotta adjust those valves properly. Anyone who can help us out I thank you in advance...

[J-Ri]

The best way is to get a junk set of valve covers, otherwise you'll be shooting oil all over the place. Drill a hole in the junk cover over the rocker arm nuts. Start the engine and loosen one nut until you hear a clicking sound. If it doesn't start clicking after a couple turns, start tightening it. Tighten it until it stops clicking, no further. Move on to the next rocker arm, and do this to all the cylinders. Turn the engine off, and tighten all the nuts 1.5 turns, and let the engine sit for a bit (until lifters bleed down).

[Cadillakin'98]

Thanks J-Ri for coming to the rescue! Been waiting for someone who could help me out. Anyways, I am curious as to the tightening an additional 1.5 turns after getting them to quit clicking. My neighbor did go buy some clips to adjust them with motor running so that part we were planning on doing but we just aren't sure beyond that. The reason we question the additional 1.5 turn is because it seems like we are having this compression problem when we adjust it according to Chiltons. I know you have given me some very logical, sound advice before so I believe you know what your talking about. Also, how do you explain valve "lash"? We have a theory and/or a good idea what this is referring to but maybe if you could explain it then we can see where we are misinturperting things. Thanks for your help again.

[J-Ri]

As the camshaft turns, the hydraulic lifters are pushed up into the push rods. The direction of movement is changed from up to down by the rocker arms, which opens the valves.

Your problem is probably the valves are being held open slightly all the time. Loosening the rocker arm bolt increases the distance in the valve train, and the valve will be allowed to close. When you start hearing the clicking, there is not enough of the valvetrain to fill the distance, so there's a gap and you hear when the valve is opened (push rods are striking the rocker arms, and the rocker arms are striking the valve stems). Tightening the nut down decreases the distance. When the clicking stops, the hydraulic lifters are fully extended, but there's no gap. Tightening the nuts an additional 1.5 turns compresses the lifters slightly so they will adjust automatically to wear.

If it doesn't have hydraulic lifters, only adjust to where they stop clicking. If your manual says 1.5 turns and that didn't fix it, try 1 turn.

[J-Ri]

Oh, and the lash is the gap between parts, it's what causes the clicking.

[Cadillakin'98]

Ok not sure if they are hydraulic lifters or not. It's a 350 small block, 5.7L, TBI. Goes in an '88 model C-series truck (1500). According to Chiltons, it said to start with the rocker arms loose, then begin tightening nut just to the point where there no more lash. Book goes on to say that all lash is removed when the push rod no longer has any movement by hand. Once tightened just up to the point that there was no lash, we then tightened the nut on rocker arm an additional 1 full turn (360 degrees) This was to be done on certain intake/exhaust valves while #1 cylinder was @ TDC. After those valves listed were complete, we then had to turn motor (via harmonic balance of course) 1 full turn. this made #6 cylinder @ TDC and the remaing valves were then adjusted in the same manner.

So lash by your definition is basically the same as we inturpreted it to be by Chiltons explaination. Neighbor is already asleep so I can't find out for certain if that motor has hydraulic lifters or not. But based on what I've told you, if you would know, and think the way your explaining how to adjust the valves still is the way to do it, please let me know. And again, your assistance is greatly appreciated.

[J-Ri]

I would do it the way I suggested. I adjusted the valves on an early '90s 4.3L this way and it turned out great.

The way your manual suggests could be flawed by having #1 on tdc exhaust rather than compression. Also, going by feel isn't usually a good way to do anything. The engine could be gummed up a bit, making it feel right when it's not.

[Cadillakin'98]

Well, it is a newly rebuilt motor so gumming should definantly NOT be the issue. In any case, you have been more than helpful and I (we) will give it a try sometime this week. Thank you

[J-Ri]

You're very welcome, always happy to help.

[mbumgua]

After reading the previous posts I decided to enlighten you on why the valves were not adjusted right when you did it by chiltons. They assume that your lifters already have oil in them-So when you tightened them down you were bottoming them out at the point of turn/no turn- then any additional tightening started opening the valves and therefore no compression. It takes a light touch to adjust the valves with no oil in the lifters-Basically you slowly tighten the rocker nut until you feel a very light drag. After you feel this drag you should push down on the pushrod to make sure you did not bottom out. If you did it correctly you will feel the spring pressure from the spring inside the lifter, and you will feel it bottom out. Then tighten the rocker nut 1/2 to 3/4 turn. This will adjust the valves and generally you will not have to do a final adjustment. After they have oil in them you can adjust them running, but only turn them 1/2 to 3/4 turn after they quit clicking. 1 and 1/2 turns will lead to premature camshaft wear.

[Kevcules]

Some good sound advice here in this forum.
I agree that is why you had so much trouble at first because your lifters weren't charged with oil yet. If you followed the manual correctly , it should get you to the starting stage only for you to go back and set them properly , as mentioned above my post , to prevent premature cam shaft lobe wear. Once engine running and at operating temp, back off on rocker nuts untill they start to tick, then tighten untill tick is gone, then tighten another 1/2 turn.(180 degrees) Don't forget, too loose on the rocker nut leads to a little tick and can be redone. Too tight leads to heavy wear on your cam ,your choice. Good luck.

[J-Ri]

How would 1 or 1.5 turns cause more wear than 1/2 or 3/4 turns? Maybe I'm just missing something, but shouldn't the lifters compensate for being tightened further than 1/2-3/4 turns? I'm not saying 1/2 turn wouldn't be sufficient for many miles, assuming quality oil was used and it was changed every 3,000 miles, but I don't see how the camshaft would wear out faster if the lifters were compressed further, after all, it has the same oil pressure pushing up.

[Kevcules]

Cam shaft lobes have disappeared on cam shafts in engines that have had the rockers tightened too much. I've seen this first hand with a friends camaro. The cam lobe is forcing the push rod up which forces the rocker to "rock". lol. This is metal on metal with a little oil between them. The lifters don't compress very much so the less pressure the better, just enough to take backlash away.
Maybe you could get away with 1 or 1.5 turns but why would you take a chance when 1/2 to 3/4 turns is all it calls for.

[mbumgua]

Kevcules--I couldn't have said it better--I have been rebuilding chevy engines for 30 years and have learned a lot in that time. I have never had a problem with premature wear on camshafts by using the 1/2 to 3/4 turn method. I have always changed my oil at 2000 to 3000 miles. I ran a 1991 S-10 with the 2.8V-6 for 300,000 miles and the day I sold it it did not use any oil between changes.