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Cold lash after 500 miles, yikes!

General engine tech -- Drag Racing to Circle Track

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MadBill
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Re: Cold lash after 500 miles, yikes!

Post by MadBill » Mon Sep 03, 2018 1:15 pm

Krooser wrote:
Sun Sep 02, 2018 7:16 pm
CamKing wrote:
Sun Sep 02, 2018 2:20 pm
Krooser wrote:
Sun Sep 02, 2018 1:44 pm
Maybe I'm just an old b*stard but doesn't the valve lash decrease when the engine is hot not increase?
In most cases, no.
The block grows when it gets hot, so now the distance from the cam centerline to the deck has increased. The cylinder head also grows when it gets hot, so now the distance from the deck to the rocker pad has increased. So, when the engine gets hot, the distance from the cam to the rocker increases. The lifter and pushrod also grow when they get hot, but not as much as the block and heads.
Hit the wrong button...I meant the valves get tighter not looser. Been a long week!
And longer still; every pushrod engine I've worked with gained lash when hot*. More with aluminum heads, more still with AL blocks. *(Hot as in shortly after shut down from warmed up. 8000 RPM with glowing exhaust valves is a different story. I read that a problem with burnt valves in factory road race Corvettes in the fifties was traced to tight lash specs closing to <zero on track... #-o )
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: Cold lash after 500 miles, yikes!

Post by F-BIRD'88 » Mon Sep 03, 2018 1:28 pm

Looking at that UDHarold/Lunati cam and the cam lobe family that the intake and exhaust lobes are from I see no reason you cannot run the lash a LOT tighter.
Eg: cold lash settings of .016" to .024"
This ensures that the running lash point is not at the end (or gets beyond) the lash ramp when it's running.

I would set it a LOT tighter than .030" hot , on the street and for long life.
Use the correct setting sequence when setting the valves. Setting them cold is a lot easier.

Getting the method of locking the rocker adjustment nut and lock takes a bit of practice to get it right.

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Re: Cold lash after 500 miles, yikes!

Post by pamotorman » Mon Sep 03, 2018 3:06 pm

when using poly locks I set the lash .003 loose when I tighten the set screw. I crank down that last .003 just turning the poly lock nut. the set screw bites into the stud that way . if I just had the hot setting I set one cylinder hot and the next day I checked that cylinder cold to see what the lash change was and then set the rest cold

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Re: Cold lash after 500 miles, yikes!

Post by tenxal » Mon Sep 03, 2018 3:52 pm

Bishop540 wrote:
Sat Sep 01, 2018 8:54 pm
Yikes! I have about 675 miles on my 540 now and i pulled the valve covers off today (last time was 50 miles or so, when new). Most of the cold lash readings were in the .040's. Thats about .017-.025 too much. I originally set the cold lash at .024 and the hot lash at the recommended. .030. They all ranged from .038-.049, and one of them was .029 (which was weird).

Now, I did set both valves at TDC when I did it at 50 miles. This time I checked them at EOIC, and set them that way too. I went ahead and set them a bit tighter than recommended this time because I have been wanting to try a different lash for a while. Tonight I set them cold at .020, which should be around .026 hot.

Is that much variation in lash normal for the "1st check after 500 miles"?

Aluminum AFR heads
Dart block
Lunati 40110515 solid roller cam
1.8/1.7 rockers
Cut the oil filter apart. If everything looks ok, simply set the valves using the EO/IC method and recheck after a bit. Hot or cold doesn't matter...just recheck it the same way.

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Re: Cold lash after 500 miles, yikes!

Post by stokerboats » Tue Sep 04, 2018 12:06 am


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Re: Cold lash after 500 miles, yikes!

Post by MadBill » Tue Sep 04, 2018 12:29 am

Decent info, but why does he call valve clearance "cooling time"? #-o Also, he suggests tightening the lock screw after getting the lash correct. As anyone who has lashed solids knows, doing that opens the clearance a couple of thous due to slack in the threads and does not allow the polylock to be as firmly tightened as does following pamotorman's method above.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: Cold lash after 500 miles, yikes!

Post by Bishop540 » Sat Sep 08, 2018 6:59 pm

I appreciate all the replies....I started the car today after setting the valves at .020 cold and I do NOT like the way it idles and drives. WOT is undetermined, since all it does is spin but it didn't feel like it had more top end with tighter lash. I am going to open it back up. But not to .049, of course. I'm going back to the upper end of UDHAROLD's recomendation (Google search 502A5LUN):

"Well, the 1st answer is.....That's where it was designed when used with a 1.7:1 rocker arm. The cam was designed in April 1980, and that isn't a wide lash for a big block. Everyone has been used to tight-lash cams for the past 10 years or so, but that cam works fine all year at .030" hot. The adjustment range is from .020" to .034", hot. Run it tighter if you need to kill off some bottom-end". https://www.chevelles.com/forums/148-20 ... c-cam.html

Maybe I should have ran 1.7 rockers instead of my 1.8 but Mr Harold told me personally that 1.8 would be fine. Maybe I should have set the ICL at 102 with 1.8 rockers instead of the recommended 101 ICL with 1.7 rockers (I did 101). I sure wish I would have taken advantage of my dyno time with different lash settings and maybe different ICL settings.

Either way, I will probably set the cold lash to .025 -next chance I get- with EOIC (and see what the reading is at TDC too, after setting it with EOIC)......
Eric

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Re: Cold lash after 500 miles, yikes!

Post by Old School » Sat Sep 08, 2018 7:33 pm

Why don't you just get the engine up to operating temperature, let it sit a few minutes for the heat to equalize, then set the valves at operating temperature? After you set the first side warm the engine back up and repeat process?

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Re: Cold lash after 500 miles, yikes!

Post by Warp Speed » Sat Sep 08, 2018 7:52 pm

Why don't you just set them hot?

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Re: Cold lash after 500 miles, yikes!

Post by In-Tech » Sat Sep 08, 2018 9:49 pm

Warp Speed wrote:
Sat Sep 08, 2018 7:52 pm
Why don't you just set them hot?
Because it's friggin HOT :shock: What's a couple thou between friends anyway? :mrgreen:
Heat is energy, energy is horsepower...but you gotta control the heat.
-Carl

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Re: Cold lash after 500 miles, yikes!

Post by MadBill » Sat Sep 08, 2018 10:23 pm

I think the greatest need for very accurate lash setting doesn't relate to valvetrain dynamics, but rather to the need for a fixed baseline from which to assess any change. E.g., if the lash is set +/- 0.002", how can you make an early diagnosis of a failing roller?
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: Cold lash after 500 miles, yikes!

Post by F-BIRD'88 » Sat Sep 08, 2018 11:59 pm

cooling time refers to the time that the valve is closed on seat each cycle
The valve transfers heat to the valve seat and cooling system during the "cooling time" when the valve is closed. A bit more critical on the exhaust valve and on extended WOT operation and or Supercharged NOS applications.

UD Harold was pretty sharp and good at explaining stuff.

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Re: Cold lash after 500 miles, yikes!

Post by MadBill » Sun Sep 09, 2018 12:24 am

Right, but the purpose of closing a valve is sealing. Cooling is just a useful side effect and design-spec. valve clearance does not contribute to it.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: Cold lash after 500 miles, yikes!

Post by Geoff2 » Sun Sep 09, 2018 2:44 am

Have tools & feeler gauges ready.
Get the engine to operating temp & switch off.
Remove a valve cover & find an int & exh valve that is loose [ has lash ]. Measure & note the lash.
Re-check the same valves when engine has cooled down.
Knowing the hot/cold lash difference, set the valve lash cold, as desired.

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Re: Cold lash after 500 miles, yikes!

Post by Warp Speed » Sun Sep 09, 2018 8:24 am

That would be ok, but lash won't be the same from cold to hot through out. Not sure why hot lashing is such a big deal. I know it is a struggle with a stud girdle, but these days, if you need a stud girdle, you really should have a shaft system. There are plenty of affordable shaft options these days.

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