Valve Lash Adjusting.

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SR Racing
Posts: 1205
Joined: June 24th, 2006, 1:58 pm

Valve Lash Adjusting.

Post by SR Racing »

I don't think I have posted this here before, but...

I often see guys struggling with 3 arms, a flashlite, feeler gauges, screwdriver and 13mm wrench to adjust the lash.

It can be a lot easier than that. The valve adjust screws are 1mm per thread. Or one full turn of the adjuster is 1mm of lash. You typically want about .003 inch of lash. 1 mm is .040 in. So move the camshaft to the low side (no lift) and lightly snug the adjuster down and then back it off slightly less than 1/2 of a nut flat (1/12 turn). Tighten the adjuster and make sure you can feel the lash. No feeler gauges needed.

Those .003 feeler gauges get bent up so quick anyways. (I don't undestand why they don't make them thicker. :lol: )

A complete valve check/adjust should take no more than 5 minutes.

It is also a good quick check to rotate the engine through 2 full revolutions while making sure that every valve has some lash most of the time during the rotation.

Another point. The intake valve is seldom an issue and the closer you can get to .002-.003 the better. It gets plenty of cooling from the intake charge. However, the exhaust valve gets its cooling during it's seat time and from the valve guide. The closer the tolerance on the valve guide clearance and the bigger the lash the more time the valve gets cooled. A broken valve head in the chamber is ugly. Plus, the exhaust flow (at the head) on a ACVW engine is already more than needed.
tiagosantos
Posts: 389
Joined: June 20th, 2010, 12:10 am

Re: Valve Lash Adjusting.

Post by tiagosantos »

Of course I had never thought of that..

Thanks for posting this and the induction flow article. Good stuff!
billinstuart
Posts: 201
Joined: July 17th, 2006, 8:53 pm

Re: Valve Lash Adjusting.

Post by billinstuart »

Good method.

The lash increases with temperature. We used to set 0 lash cold or just barely warm. Sometimes it would run on 3 cylinders cold til it warmed up enough for the valve to seat. NO! valve issues in 10 years.

Too much clearance is bad..shouldn't sound like a thrashing machine!
FV80
Site Admin
Posts: 1195
Joined: June 27th, 2006, 9:07 am

Re: Valve Lash Adjusting.

Post by FV80 »

billinstuart wrote:...
Too much clearance is bad..shouldn't sound like a thrashing machine!
Be sure to note ... too LITTLE is 100 times worse than too much. If you set your lash at 0.006 instead of 0.003, you would never be able to tell the difference from the driver's seat.... HOWEVER, if you set it to -0.001, rest assured, you WILL be able to tell - it's gonna HURT you!

I always prefer to err on the "too loose" side.. *IF* I decide to make an error, that is :lol: .
Steve, FV80
The Racer's Wedge and now a Vortech, FV80
billinstuart
Posts: 201
Joined: July 17th, 2006, 8:53 pm

Re: Valve Lash Adjusting.

Post by billinstuart »

Steve:

No argument. However, my experience is the clearance increases with temperature on our VW stuff.

I have the utmost respect for you and Rollin, and I'll defer to you guys judgement with no hesitation. My experience, since the '70's, is that clearances increase. Been doing this for decades with no adverse effects..even with the old round boss heads. We did "finger tight" cold..no screwdriver. We'd always have a few thousandths race temp hot.

We did both maximum lift analysis and "area under the curve" stuff. The sooner we started lifting the valve, the sooner flow would start. it seems. Tight clearances seemed to increase the "area under the curve" while keeping maximum lift within allowances...but just barely. "course this was combined with the usual pushrod/rocker arm optimization.

No dyno time, but we held our own with most national motors..except Cricket Farm...................
brian
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: Valve Lash Adjusting.

Post by brian »

Reminds me of the old statement: "Valves, I rather hear them, than smell them." Clearances do increase on vw motors when hot and that's rare, so clearance when cold is less critical. If you want to run zero cold, you should never have it tight enough to drop a cylinder until it heats up. That's too tight. There could be an entire book written about clearances, valve float and stem damage. Yes as mentioned, lift area does increase as clearances decrease but so does valve float. Float is described as anytime any component in the valve train separates from adjacent component. Valve clearance is a preset separation and that contributes to float. Even minor floating will damage the valve stems and adjusting screws. Check the health of the adjusting screws the next time you do an adjustment. If they're all banged up or chipped, your floating the valves.

When heads are fresh, the valves will seat in a bit and tighten the clearance. I run clearance for at least the first hour of run time on fresh heads. Once I can see that the valves are settled in and the clearances are not changing, I go to 0 lash. I tighten the adjusting screw to tight and back off til the pushrod rotates freely. If you want to run a clearance, I would suggest that you set the valves hot and no more than .004. That setting will cool to .002 or less when cold.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
CitationFV21
Posts: 272
Joined: July 6th, 2006, 10:49 pm

Re: Valve Lash Adjusting.

Post by CitationFV21 »

Okay,

Found this on You Tube:

http://www.youtube.com/watch?v=6S5Uapc8GjE

I need to look at cam to see if it works.

ChrisZ
sharplikestump
Posts: 183
Joined: January 12th, 2009, 2:28 pm

Re: Valve Lash Adjusting.

Post by sharplikestump »

CitationFV21 wrote:Okay,

Found this on You Tube:

http://www.youtube.com/watch?v=6S5Uapc8GjE

I need to look at cam to see if it works.

ChrisZ
As far as this video goes, (along with some of the others) all I care to say is....Goodness!
As for what I consider the proper technique: Go to TDC as marked on the pulley and rock it back and forth. If both #1's intake and exhaust take turns moving, you are on #3. Either start w/ #3, or spin the pulley 1 rev. (of course, you can also verify this by removing the dist. cap).
Let's assume you are on #1. While pulling back on the adjustor screw, check the clearance with your feeler gauge. Adjust to your desired spec, again while pulling back on the screw. Now, rotate the pulley CCW 1/2 rev (180 degrees), and repeat for #2, another 1/2 rev, for #3, and finally for #4.
One of the reasons that I like this technique especially for Vees is that we run more oil than in stock. By doing one side at a time, it allows jacking the car, doing that side and then replacing the valve cover without dumping a quantity of oil.
Now, on the subject of "proper clearance". I say it varies per engine, and per track for that matter. What is called the "valve lash take-up ramp" on our cams is in the area of .010-.012 inch. It's design purpose is self explanatory. It affords a wide range of adjustment or wear without getting into serious slamming. While I would never suggest setting them anywhere that loose, It does allow for moving the torque/power band a surprising amount. Depending on the readings I get on the engine stand, only partially determined by the cam key I choose, I may then wish to make my final adjustment by altering the valve clearance. In general, tighter valves will move the power band higher, while looser valves will pull you out of the turns better. Long straights and you have a short box.....tighter. Running on some goat path of a track.....I might loosen them to .007. This will only do so much. Goat path, with a long box.......can't help ya.
Many other factors, amongst which may be: individual engine characteristics, driver ability, tire sizes, rain or dry, etc.
Now, who will be the first to figure out how to come up with variable valve lift??? :lol:
Mike P.
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