Zero lash questions
Thread Starter
Intermediate
Joined: Jul 2004
Posts: 34
Likes: 0
From: Naperville IL
Zero lash questions
I adjusted the valves on my 77 350 per Lars Zero lash doc. I started at tdc by moving the crank to the zero mark with the rotor pointing at the #1 plug. I scribed marks every 90 dgr then adjusted in the firing order until zero lash then went 1/2 turn.
When I moved back to the zero mark - the pushrods still spin freely is this normal?
I also checked the compression and my readings seemed low around 120 when they were at 140 before when the car was running.
I am a newbie to engine work and started by replaceing the carb which was dripping and would not hold an idle. Since I had the carb off i decided to remove the intake,water pump etc so I could repaint and clean the engine. Getting ready to restart the engine.
Tom
When I moved back to the zero mark - the pushrods still spin freely is this normal?
I also checked the compression and my readings seemed low around 120 when they were at 140 before when the car was running.
I am a newbie to engine work and started by replaceing the carb which was dripping and would not hold an idle. Since I had the carb off i decided to remove the intake,water pump etc so I could repaint and clean the engine. Getting ready to restart the engine.
Tom
Le Mans Master
Joined: Mar 2001
Posts: 6,640
Likes: 287
From: Ann Arbor Michigan
The subject of lashing valves came up a couple weeks ago. The best way to find "zero lash" was to move the push rod up and down while turning the nut until there is no more movement, then another 1/4 to 1/2 turn. You will still be able to rotate the push rod.
Gary
Gary
Thread Starter
Intermediate
Joined: Jul 2004
Posts: 34
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From: Naperville IL
Yes, the carb is on but I didn't open the throttle, I thought the compression readings may not be acurate on a cold eng. Still not sure whether I tightened the nuts on the rockers too much, each one only took a slight turn to stop the push rod from spinning. So overall I probably tighten the nuts about 3/4 turn. Thinking I should back them all off 1/4 then start the engine let it warm up and recheck compression.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
You don't want the pushrods to stop spinning. If that happens, you've locked the lifter up. You just want to remove all of the free 'slop' out of the lifter/rod/rocker system so that the rod has no play left. It should still turn if you work your fingers. The "..till it doesn't spin..." language means that if you give it a twist with your fingers and let go of it, it shouldn't spin. This terminology has always been a point of misunderstanding. Another way to find the 'start point' for setting hydraulic lifters is to hold the pushrod between thumb and forefinger and shake the rod lightly in an up-and-down motion. When there is 'play' in the system, it will feel like it is rattling. Continue this movement as you slowly tighten the rocker nut until you feel that the rattling stops. Both methods [if done correctly] will get you to the same start point. Once there, just tighten the nut 1/2 to 3/4 turn clockwise to set the lifter.
Melting Slicks
Joined: Mar 2008
Posts: 2,989
Likes: 198
From: Meriden CT
Yes, the carb is on but I didn't open the throttle, I thought the compression readings may not be acurate on a cold eng. Still not sure whether I tightened the nuts on the rockers too much, each one only took a slight turn to stop the push rod from spinning. So overall I probably tighten the nuts about 3/4 turn. Thinking I should back them all off 1/4 then start the engine let it warm up and recheck compression.
Instructor
Joined: Jun 2005
Posts: 140
Likes: 0
From: Bovingdon Hertfordshire
One point worth mentioning : if you are setting your start point (TDC on Number 1) from the marking on the harmonic balancer (damper) be sure that it hasn't moved. There are plenty of articles on finding TDC by removing the Number 1 spark plug and finding / feeling for the top of the stroke.
Jeremy
Jeremy
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Zero lash means zero - zero - play in the valvetrain. In my experience, for many the moving up and down approach is tough to feel and doesn't give consistent results - especially for new builders/mechanics. Try rolling the pushrods between your fingers while slowly tightening and the the first time you feel ANY DRAG AT ALL you're at zero lash. Spins freely...then a hint of drag...you're there. If you need to, back it off a bit and creep up on it again - experiment a bit to find this "sweet spot". This approach has worked consistently for me and everyone I've demonstrated it to. No debate, please - I'm not saying what's "best" - I'm just offering an alternative that the OP is free to explore, or not.
The preload should be exactly the number of turns that your cam mfgr says it should be.
The preload should be exactly the number of turns that your cam mfgr says it should be.
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Thread Starter
Intermediate
Joined: Jul 2004
Posts: 34
Likes: 0
From: Naperville IL
Thanks everyone for all your input. Having never done this before, I evidently misunderstood the wording and had locked up the lifters the way I adjusted them I glad I asked here before starting the engine! I backed off all the nuts to about where they were at before I started just to start the engine so I could check for leaks. I will be removing the valve covers again and trying to find that sweet spot of zero lash and also as mentioned trying to make sure the harmonic balancer 0 mark is acurate.
Tom
Tom