Setting Valve Lash - A Few Tips

[davepl]

I've seen this done incorrectly more and more recently, and I'm unsure why, but I thought I'd throw this out there.

When you go to set lash (hydraulic), don't do it running. I used to do it that way, with the little clips that only let 95% as much oil get in your eyes and on the headers. Ugly stuff. Google how to do it statically based on valve opening/closing periods.

Anyway, what people get wrong is finding zero lash. Is is NOT when start to feel drag trying to rotate the pushrod back and forth. By the time you feel binding there, you've got plunger down already.

Zero lash is when you move the pushrod up and down as you tighten the nut, and then -just- as there's no slack when you move it up and down.

Then set it from there (1/4 turn or 3/4 turn or whatever you neighbor across the back alley taught you).

If you do it based on the rotating the pushrod approach and then add a turn (or whatever) you'll run the risk of having so much preload that when oil pressure comes up the valves can hang open.

Not sure if that could cause piston-to-valve issues, but I imagine it could in some close engines. But in any case if a valve hangs open the car won't run right, and could backfire through the carb (intake hung open) or exhaust (exhaust hung open).

Others may have more and better input, just throwing this out there in case it saves someone a headache down the road.

Cheers!
Dave

[jtp67-72]

Warm the motor .....idle down to about 5-600 rpm's....set of cheap tall valve covers with top cut out...take each one and loosen till "ticking" then tighten until ticking stops..then 1/4 turn down....never failed me....but before all of this I would do the same process as u described to get me close....but the above procedure gets me exactly where i want to be....and gm wants 1 full turn past zero lash.........most engine builders say no way on my motor!!!.......jim

[imjeff]

Originally Posted by davepl

I've seen this done incorrectly more and more recently, and I'm unsure why, but I thought I'd throw this out there.

When you go to set lash (hydraulic), don't do it running. I used to do it that way, with the little clips that only let 95% as much oil get in your eyes and on the headers. Ugly stuff. Google how to do it statically based on valve opening/closing periods.

Anyway, what people get wrong is finding zero lash. Is is NOT when start to feel drag trying to rotate the pushrod back and forth. By the time you feel binding there, you've got plunger down already.

Zero lash is when you move the pushrod up and down as you tighten the nut, and then -just- as there's no slack when you move it up and down.

Then set it from there (1/4 turn or 3/4 turn or whatever you neighbor across the back alley taught you).

If you do it based on the rotating the pushrod approach and then add a turn (or whatever) you'll run the risk of having so much preload that when oil pressure comes up the valves can hang open.

Not sure if that could cause piston-to-valve issues, but I imagine it could in some close engines. But in any case if a valve hangs open the car won't run right, and could backfire through the carb (intake hung open) or exhaust (exhaust hung open).

Others may have more and better input, just throwing this out there in case it saves someone a headache down the road.

Cheers!
Dave

I'm with you Dave! I still have the clips, but haven't used them in many years. I like to assemble my motors in the shop, run the cam in after install and final tune/oil change after about 500 miles. Im too old to be leaning over my fenders setting lash by ear with an eye full of oil and smoke. I still haven't found the picture of the parking lot where GM sets lash while running lol!

[Ol Blue K20]

I set mine statically on the stand. Zero lash is as you describe and 1/2 turn beyond....done

[davepl]

Indeed. I don't know how to hot-oil running thing ever got started. Maybe its for flatheads or something and people just kept doing it. If it works for you and you don't mind it, all the power to you, I suppose.

Tangential, but I always wondered why GM didn't have to do cam-breakin on the engine line. I've heard they fired them up on natural gas, probably just to make sure the rods didn't come out, but not much more.

[imjeff]

Originally Posted by davepl

Tangential, but I always wondered why GM didn't have to do cam-breakin on the engine line. I've heard they fired them up on natural gas, probably just to make sure the rods didn't come out, but not much more.

I never heard how long they ran the motors, but I do 20 minutes around 2000. I don't know if it's needed, but I'm on a fourty year good streak!

[davepl]

Originally Posted by imjeff

I never heard how long they ran the motors, but I do 20 minutes around 2000. I don't know if it's needed, but I'm on a fourty year good streak!

I used to do it up at 3000 but I've watched older mechanics do it at 1500 to 2000 as you say. All that matters is the cam gets splash-lubricated by oil thrown around off the crank, so there's nothing magical going on. I suppose the better your windage control and crank scraper, the harder it is to oil the cam during breakin.

First time I ever did it the plastic oil gauge line (I know, but that's what Autometer gives you) touched the header, big ball of flame, car on fire. Saved it, but I'm still scared when I start a new engine, and that was 30+ years ago. Probably why I don't like oil on the headers when setting valves, come to think of it.

I don't know if it was my idea, a friend's, or my mom's for all I know, but someone suggested a bucket of water be on hand. That's what I used to put out the flames, so even though there are extinguishers around I still do the bucket of water thing. I should do it while welding too, but I don't... until my first welding fire, I'm sure.

[geezer#99]

The rpm needed for break in isn't solely for splash lubrication. It's so the lifters rotate and don't flatten the cam right away.

[davepl]

Originally Posted by geezer#99

The rpm needed for break in isn't solely for splash lubrication. It's so the lifters rotate and don't flatten the cam right away.

Why would you think they do not rotate at normal RPM? All flat tappet cams are ground on a slight taper and the lifter bore sits at a bit of an offset from the cam lobe centerline, which induces rotation no matter how slowly the engine is turning.

I suppose there's a scenario of massive spring pressure where it could prevent it. I'm not saying you're wrong, just wondering if its urban legend or mechanical reality.

Not quite related, but useful, I stole this from Crane Cams when checking my facts:

"Big Block Chevrolets have an oil-priming idiosyncrasy. When priming a Big Block Chevy with a drill motor and priming tool, it is often necessary to prime for as much as 20 minutes (while rotating the engine) to get oil to all of the lifters and rockers. It is advisable to prime these engines with the valve covers removed so you can check to see oil coming out of all of the rocker arms before firing the engine. This last step is advisable on all engines, but particularly on Big Block Chevrolets."

[geezer#99]

Didn't say they didn't rotate, but you need sufficient rpm at first fire so they rotate fast enough for break in. If you let an engine with fresh lifters idle at 600 rpm some lifters won't rotate enough to prevent flattening the lobes. It's fresh metal. It needs to get freindly.
The lifter needs to mate with the lobe. The lobe face and the lifter base might look smooth but they need to wear in togethor so they'll always rotate at first fire cold.
And fwiw I set my lifters with a slightly different method. Hot, running but I loosen till they clack, tighten till they quit, do them all like that, shut her down then set the pre-load 1/4 turn down.

[imjeff]

Originally Posted by davepl

First time I ever did it the plastic oil gauge line (I know, but that's what Autometer gives you) touched the header, big ball of flame, car on fire. Saved it, but I'm still scared when I start a new engine, and that was 30+ years ago.

I had one of those plastic lines hit a header on a Buick I had. I saw smoke trailing, looked at the oil pressure gauge and saw around 60 psi. I shut it down and pulled over as smoke and a fireball erupted from under the hood. Oil pressure (mechanical) reading 60 with the motor off. After beating the fire out with an apron from the grocery store I worked at I found that when the line was burned in two, the side from the engine remained open and the side to the gauge fused shut with pressure in the line. Those were the days!

[69chevytrucker]

2000rpm heats the metal parts expands them and puts pressure on everything and if after 20min of running like that and no boom or bad noises the engine is good and everyt

[kxmotox247]

I've been running solid lifter cams in my last few builds and this is a handy tool.

http://valvetrax.com/index.php?osCsi...cgsmtnkle81jl5

[jaros44sr]

Originally Posted by kxmotox247

I've been running solid lifter cams in my last few builds and this is a handy tool.

http://valvetrax.com/index.php?osCsi...cgsmtnkle81jl5

Why is everything 19.95?

[PowerdbyChevy79]

Originally Posted by geezer#99

Didn't say they didn't rotate, but you need sufficient rpm at first fire so they rotate fast enough for break in. If you let an engine with fresh lifters idle at 600 rpm some lifters won't rotate enough to prevent flattening the lobes. It's fresh metal. It needs to get freindly.
The lifter needs to mate with the lobe. The lobe face and the lifter base might look smooth but they need to wear in togethor so they'll always rotate at first fire cold.
And fwiw I set my lifters with a slightly different method. Hot, running but I loosen till they clack, tighten till they quit, do them all like that, shut her down then set the pre-load 1/4 turn down.

thats how ive always done em...and my old man taught me..its never failed him or me..