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Old 12-17-2008, 07:31 AM
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Reducing Valve Lash on Solid Roller - Is It Ok To Do?

This is a follow up to an earlier post I made about Valve Lash. It's more of a general question - not really application specific.

What is the downside of reducing valve lash on a solid lifter cam? Say for example, the cam card specs .020" of lash (hot). If you reduce valve lash to say .010".......what are the likely problems if any?

Perhaps a "refresher course" on the purpose of lash is in order here. On hydraulic lifter setups, the lifters pump up just enough to eliminate lash. What is the purpose of lash on a solid lifter setup? I believe it's necessary to ensure that the valve is fully seated when the cam lobe/lifter is on the base circle - and to allow for thermal expansion changes. Without lash, there may be times when the valve is not fully seated - especially at high rpm. Is that correct? Or, does this have to do something with "coil bind" on the valve spring? With reduced lash, the valve lift is higher and the valve spring is compressed more - so there better be enough clearance between valve spring coils to allow for this right - or a push rod gets bent.

I know that by reducing lash, you make the cam appear "bigger" (longer duration and more lift). By increasing lash, you make the cam "smaller" (shorter duration and less lift). Ok fine, I understand that. But that is not the information I am seeking here. My question concerens wear and tear, mechanical failure, etc.

The reason I ask all this is because like I said in my earlier thread, when I set lash to the cam card specs, the valvetrain became very noisy, and the awesome lopey/lumpy idle quality sound diminished noticeably.

I will leave my lash at the current cam card specs (.017") until I learn more about this.

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Old 12-17-2008, 07:35 AM
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Tighter won't really hurt anything as long as you don't get into coil bind.Loose can kill a valve train quick.
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Old 12-17-2008, 07:38 AM
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When you close the gap, you run the risk of the valve not completely closing. If that happens, you WILL burn the valve/valves. The hot mixture goes past the valve/seat at increadible speeds and combined with the heat, it will burn a track in either the valve face or seat. NOT something i'd recommend.

Loosening the lash can help some in changing the lift and duration but you get to a point where you can hear it (more than now) and you can also mushroom the stem from the hammering.

Mark
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Old 12-17-2008, 08:04 AM
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Water is wet...the sky is blue....solid rollers are noisy. Put some RPM to that thing (the reason you went with solid roller) and you won't hear it over your pipes and or the screming of your passenger......lol
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Old 12-17-2008, 08:13 AM
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As stated you can reduce it some, but be CAREFUL so you don't burn a valve.
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Old 12-17-2008, 08:33 AM
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You have three different heat expansions situations relitive to what you are asking.
1. Is the effect of cold lash compared to the hot lash (2)
The third condition is the heat expansion caused tot he valves when running hard at WOT and creating heat. Especialy on the exhaust valve.
So typically the valve lash when set cold at say .017" will increase a little bit once the motor is fully warmed up to operating temp.

Then, when running at WOT for an extended time (like marine or oval track racing) the heat of combustion at WOT will heat up and expand the valves which will tend to reduce the net valve lash. (a little bit)
As long as you maintain some net running valve lash under all these conditions, you won;t burn any valves. This is why the exhaust lash it typically about .002" bigger than the intake lash. At extended WOT the exhaust valve runs hotter and expands more.
You have some room to fine tune things a bit to your liking within reason by varying the lash a bit without worry of burning a valve.
The idea being that you must keep the running "lash point" within the area of the lash clearance rams on the cam with an eye to the valvetrain and engine block expansion characteristics discribed above.
Did you try the hot lash/cold lash check on your motor yet to see for yourself how much your valve lash will vary with a hot or cold engine?
It will take a full 24 hours for your BBC to cool right down to "stone cold" to see the real difference in hot and cold valve lash.
With our present cold weather you probabily want to restrict airflow thru the radiator or shut off an electric fan to allow you to get the motor hot enough while idling. Some cardboard or paper sheets in front of the rad will do to restrict the airflow.
You;'d want to get the motor good and hot (but not overheated) (say 210F water temp) like a hot Texas summer day to simulate the hot lash idling condition before checking the hot lash.
Cast iron takes time to fully warm up. When you get 'er good and hot, shut the motor off and remove 1 valve cover and quicky check 1 valve.
Check 1 valve say at .017" hot lash or what ever its at. (you don't need to change the lash setting, just check what it is while hot) and check it the next day (24 hours) when dead "stone cold". You won't be driving the car at WOT so no fear of burning a valve while idling in the driveway to perform this simple test. Yes, it takes that long for a BBC to cool off completely.
Call or email Comp cams "CamHelp" tech service and they will advise on allowable valve lash tuning variation for your cam.
As I said you typically can go .008" tighter than cam card or .004" looser than cam card recomended lash settings without fear of damaging anything.
I have some 30 years experience playing with BBC's including playing with valve lash on solid lifter cams and have never burned a valve yet. Even with a lot of nitrous. You just need to understand the various engine operating temp conditions /camshaft/valve lash ramp design limits and stay within them.

For a guy that has no problem skinning the cat close with valve to piston clearance on your motor, you sure worry a lot.

Last edited by F-BIRD'88; 12-17-2008 at 09:03 AM.
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Old 12-17-2008, 09:17 AM
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Quote:
Originally Posted by F-BIRD'88
You have three different heat expansions situations relitive to what you are asking.
1. Is the effect of cold lash compared to the hot lash (2)
The third condition is the heat expansion caused tot he valves when running hard at WOT and creating heat. Especialy on the exhaust valve.
So typically the valve lash when set cold at say .017" will increase a little bit once the motor is fully warmed up to operating temp.

Then, when running at WOT for an extended time (like marine or oval track racing) the heat of combustion at WOT will heat up and expand the valves which will tend to reduce the net valve lash. (a little bit)
As long as you maintain some net running valve lash under all these conditions, you won;t burn any valves. This is why the exhaust lash it typically about .002" bigger than the intake lash. At extended WOT the exhaust valve runs hotter and expands more.
You have some room to fine tune things a bit to your liking within reason by varying the lash a bit without worry of burning a valve.
The idea being that you must keep the running "lash point" within the area of the lash clearance rams on the cam with an eye to the valvetrain and engine block expansion characteristics discribed above.
Did you try the hot lash/cold lash check on your motor yet to see for yourself how much your valve lash will vary with a hot or cold engine?
It will take a full 24 hours for your BBC to cool right down to "stone cold" to see the real difference in hot and cold valve lash.
With our present cold weather you probabily want to restrict airflow thru the radiator or shut off an electric fan to allow you to get the motor hot enough while idling. Some cardboard or paper sheets in front of the rad will do to restrict the airflow.
You;'d want to get the motor good and hot (but not overheated) (say 210F water temp) like a hot Texas summer day to simulate the hot lash idling condition before checking the hot lash.
Cast iron takes time to fully warm up. When you get 'er good and hot, shut the motor off and remove 1 valve cover and quicky check 1 valve.
Check 1 valve say at .017" hot lash or what ever its at. (you don't need to change the lash setting, just check what it is while hot) and check it the next day (24 hours) when dead "stone cold". You won't be driving the car at WOT so no fear of burning a valve while idling in the driveway to perform this simple test. Yes, it takes that long for a BBC to cool off completely.
Call or email Comp cams "CamHelp" tech service and they will advise on allowable valve lash tuning variation for your cam.
As I said you typically can go .008" tighter than cam card or .004" looser than cam card recomended lash settings without fear of damaging anything.
I have some 30 years experience playing with BBC's including playing with valve lash on solid lifter cams and have never burned a valve yet. Even with a lot of nitrous. You just need to understand the various engine operating temp conditions /camshaft/valve lash ramp design limits and stay within them.

For a guy that has no problem skinning the cat close with valve to piston clearance on your motor, you sure worry a lot.
I will try the valve lash test as you suggest - just for my own understanding and knowledge. Right now the car is sitting in my freezing cold garage. I'll check lash in these "cold" conditions as you suggest, then I'll get her real hot and check lash again. I'll report my findings back to this thread. I'm beginning to understand this all a bit better. The idea of burning a valve is new to me.

Does anybody out there have a photo of a burnt valve that they can email to me or post to this thread? If so, please include a caption explaining which the situation was that caused the valve to burn.

Here is my email address: chevywaldo@yahoo.com

thanks

Lee
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Old 12-17-2008, 09:21 AM
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Quote:
Originally Posted by BBCMudbogger
Water is wet...the sky is blue....solid rollers are noisy. Put some RPM to that thing (the reason you went with solid roller) and you won't hear it over your pipes and or the screming of your passenger......lol
Hi Mudbogger: I agree with what you said. You are correct. The last time I ran this motor with the solid roller in it - and opened up the throttle - it took off like a bat of out hell and the exhaust noise was so loud and beautiful that the valvetrain became a non-issue. But you have to admit, a lumpy, lopey idle sound is equally as enjoyable to listen to, and that seems to sound much better when lash is tighter. Just an observation.
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Old 12-17-2008, 10:01 AM
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Quote:
Originally Posted by leejoy
I will try the valve lash test as you suggest - just for my own understanding and knowledge. Right now the car is sitting in my freezing cold garage. I'll check lash in these "cold" conditions as you suggest, then I'll get her real hot and check lash again. I'll report my findings back to this thread. I'm beginning to understand this all a bit better. The idea of burning a valve is new to me.

Does anybody out there have a photo of a burnt valve that they can email to me or post to this thread? If so, please include a caption explaining which the situation was that caused the valve to burn.

Here is my email address: chevywaldo@yahoo.com

thanks

Lee

f'bird is a sharp guy, I wouldn't use the full .008" tighter, probably more like .005", but start with what he said to get you started.
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Old 12-17-2008, 10:13 AM
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If I remember correctly, this is a 454 and the cubes will soak up the cam pretty quick. I have a .680 lift I think like a 258 duration cam in a 396 and at about 1600 rpm idle it sounds great but if I were to put the same cam in a 454 inch engine it wouldn't be as noticable at idle .......and as far as I have been told, most solid roller lifters shouldn't be idled excessively anyways.....but it is a street ride....when you smoke a few Mustangs and ricers light to light your idle sound won't be the talk of the town, it will be the screaming big block nova they talk about, not the one that sounds good at the stoplight and most of them don't know what a healthy big block should sound like anyways.....only what it soundls like from behind...lol
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Old 12-17-2008, 04:57 PM
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Check out this site, nice pic of a majorly burned valve. http://www.aa1car.com/library/ar1192.htm

Weak springs or insufficient valve lash can also prevent good valve-to-seat contact and allow excessive heat to build up in the valves. A loose seat or poorly fitting guide can also hinder heat transfer to the head and contribute to burning.

Mark
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Old 12-17-2008, 06:55 PM
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What about piston clearance , or lack of.
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Old 12-17-2008, 09:23 PM
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Piston clearance does come into play, kinda sorta anyway. If making an 8 thousands change in valve lift creates piston to valve interference, then it was built way to close to begin with.

It should not make a difference if everything is as it should be.

Mark
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Old 12-18-2008, 03:06 PM
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Here's another way to look at it. You researched your build in detail, selected the ideal cam, spent all you can afford to buy from the most reputable and knowledgeable cam grinder you can find. He gives you the exact valve clearance for best power and durability. Then, you ignore everything he tells you. What is wrong with this picture?

thnx, jack vines
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Old 12-19-2008, 10:11 AM
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Quote:
Originally Posted by Packard V8
Here's another way to look at it. You researched your build in detail, selected the ideal cam, spent all you can afford to buy from the most reputable and knowledgeable cam grinder you can find. He gives you the exact valve clearance for best power and durability. Then, you ignore everything he tells you. What is wrong with this picture?

thnx, jack vines
That's not really what's going on here. I'm just trying to learn more about this. I'm not prepared to actually reduce valve lash at this point until I know all the facts. So far I havent heard enough to make me change anything. I'm leaving lash at the cam card specs for now until something changes. I may reduce it a tiny bit (.005") in the future if I'm sure there will be not harmful results.

As far as piston to valve clearance goes - it was pretty tight when I did the build. Some cylinders were like .050" clearance (that's tight), so I had to retard the cam 2 deg. If I recall the tightest spot was about 15 deg ATDC. When I checked clearances during the build, the valve lash was set at 0. So that gave me a "safety cushion" of real PTV clearance. Once you add lash, the PTV clearance increases.
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