Incorrect Valve Lash Symptoms - Chevelle Tech
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  #1  
Old Mar 10th, 04, 7:35 PM
71chevelleconvtble 71chevelleconvtble is offline
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Earl
 
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I need a better understanding of what can happen to an engine with incorrect valve lash. Is there any symptoms that would indicate you need to check your settings? I am not having a problem, just a thirst for more knowledge. Thank you.
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Old Mar 10th, 04, 8:25 PM
427L88 427L88 is offline
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Gene
 
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The vacuum gauge always gets a flutter in it when a valve or two are off.
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Old Mar 10th, 04, 9:20 PM
69LS1 69LS1 is offline
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Here's one for you guys....

A guy a work who is now in his late 50's and finially has the kids out of the house decided it was time to play hot rodder again.Way back in the day he had a car with a 327 in it with an ancient old Engle solid lifter cam that he had since the late 60's.So he builds a fresh 355 and procedes to start playing around....

Hmmmm... somethings wrong... this very cam used to pull 7400 RPM in his old 327...but it's only going about 6500 in the new 355....Whats up ?

So after chasing his tail for a while trying to figure this out he decides to call Engle and talks to Mark..... Well this cam is so old they no longer had any info on it.... But Jack Engle just happened to be there .... so Jack gets on the phone and they talk about this. Well my friend had lost the cam card but remembered that it was ground on a 108 LSA so he installed it there.... He Couldnt remember what the valve lash was suspose to be ...so to be on the safe side he set them @ .018....

So after a few minutes Jack remembered that cam and asked what he set the lash at ? He said .018...
Jack said....ohh no that wont work....thats the problem.... it will never pull set there... set them at .028 !

Well he did..... BINGO...pulled 7300 RPM... opened the lash and gained 800 RPM !..... That normally dont happen quite that dramatically.

Kinda just the opposite of what many would think.
But does go to show that some cams are quite sensitive to lash changes.

This is a drastic example but some combos will hardly respond to lash changes at all and others respond alot.

If the lash is too loose you can really start to hurt parts.... if they are set too tight you can burn up valves.....Generally with most normal type lobes you can vary the lash several thousands either way...maybe .004 -.006 looser to .010 tighter if you have a relitively wide lash to begin with....But I wouldnt set them a .004 if it's suspose to be .012....

The lash pretty much defines where the valve events take place....If you loosen the lash then the valves will open later and close sooner...if you tighten the lash the valves will open sooner and close later.....This will generally have an effect on manifold vacuum and how the engine runs so will often times show up on a vacuum guage.This is one of the ways I tell if I need to adj my valves.I have a vacuume guage in the car and after a while you get to know how the guage is responding to the engine.
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Old Mar 11th, 04, 9:01 AM
71chevelleconvtble 71chevelleconvtble is offline
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Earl
 
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Great info. So if you notice vacuum flutter, that would indicate valves may need to be adjusted. How much flutter is normal or would that vary? What if you notice a vacuum drop? Would that also indicate a need to adjust? Too tight of lash can limit RPM's and burn up valves. Too loose and what parts may be damaged? How will the engine run under these two scenarios? Could excessive exhaust smoke be an indicator? I hope these are not stupid questions. [img]redface.gif[/img]
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Old Mar 11th, 04, 9:31 AM
427L88 427L88 is offline
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Too tight, and the exhaust valve won't stay on the seat long enough to cool it down - burned valve.

Too loose and the valvetrain starts getting beat up, tighter is easier on parts.

I know Barista tried this and it didnt make a big difference, but when I set my Crane cam loose, WOW, you think it was a different cam. Framer rode in the car before/after, adn he was shocked. ob tried this and there was no difference. Well, come to find out, it wasn't shortening duration, per e, that woke the motor up, but by loosening the lash, now it was using less of the take-up ramp ( it was noticeable louder - which I thought strage going from .022 to .024 )and making the valve acceleration greater.

{Thats kind of when I decided that at some point I need to put a cam in there that has wicked acceleration rates, like the UD I run now. Now it perfer to be set tight. If I set it at harold's .026" spec, it smokes the tires, smokes them wien you hit 2nd gear with street slicks, its a mess!, Tight, no problem down low. ( it must be those old RECT heads I use! )}

Not lower vaccum , but fluttering. I haven't quantified it, but the needle flutters, as it would if the carb was misadjusted.
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Old Mar 11th, 04, 1:07 PM
71chevelleconvtble 71chevelleconvtble is offline
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Really makes sense..thanks.
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Chevelle Tech > Mechanical > Engine      Current Topic: Incorrect Valve Lash Symptoms
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