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Old 05-02-2011, 09:02 AM   #1
71z28camaro
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Default Solid Roller Valve Lash,Help Please

I have asked this question before, on a BBC is there any problems (valve train damage) i would be facing by reducing the valve lash on a solid roller, cam card called for .026/.028 hot, set them at .014/.016 and gained allmost 2 tenths. I realize the motor wants more cam,but am i tearing something up by doing this? No visable signs,just wondering. Thanks for any help.
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Old 05-02-2011, 09:17 AM   #2
mike schill
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Default Re: Solid Roller Valve Lash,Help Please

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Originally Posted by 71z28camaro View Post
I have asked this question before, on a BBC is there any problems (valve train damage) i would be facing by reducing the valve lash on a solid roller, cam card called for .026/.028 hot, set them at .014/.016 and gained allmost 2 tenths. I realize the motor wants more cam,but am i tearing something up by doing this? No visable signs,just wondering. Thanks for any help.
You should not have any problems running them tight like that, but i would call the grinder of the cam and ask them. There are a few lobes with such aggresive ramps that they can be hard on rollers when they are tightened up.
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Old 05-02-2011, 09:38 AM   #3
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Default Re: Solid Roller Valve Lash,Help Please

I never go tighter than .016 HOT, but run most BBC rollers between .016 and .022 HOT depending on lobe profile. 2 exceptions off the top of my head are Comps RX lobes and Ersons "F" lobes, these like between .022-.026 HOT as well as a few aggressive LSM and Bullet lobes. Definately call cam grinder (or post grind # here) to be sure
Only go tighter than .016 if you have a tight lash roller (designed for this)
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Old 05-02-2011, 10:44 AM   #4
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Default Re: Solid Roller Valve Lash,Help Please

tight lash is fine , its the .045" lash cams that you gotta be careful with
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Old 09-27-2011, 04:02 PM   #5
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Default Re: Solid Roller Valve Lash,Help Please

Be carefull, to tight a lash can burn a valve, especally a exhaust, the momentary closing of the valve(lash) helps to cool the valve, the heat is drawn up from the seat and through the guide. would not recomend any more than .006 from what the cam card says.
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Old 10-02-2011, 09:34 PM   #6
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Default Re: Solid Roller Valve Lash,Help Please

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Originally Posted by gtotomm View Post
Be carefull, to tight a lash can burn a valve, especally a exhaust, the momentary closing of the valve(lash) helps to cool the valve, the heat is drawn up from the seat and through the guide. would not recomend any more than .006 from what the cam card says.
I dont agree with this. The heat transfered out of the valve and into the head is dependant upon 2 things. Valve seat width and duration. Tightening the lash up with increase the duration but not by 30 degrees. I will change it by 4 or maybe 6. IMO no enough to burn a valve unless something else is wrong
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Old 10-04-2011, 05:55 AM   #7
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Default Re: Solid Roller Valve Lash,Help Please

Quote:
Originally Posted by 71z28camaro View Post
I have asked this question before, on a BBC is there any problems (valve train damage) i would be facing by reducing the valve lash on a solid roller, cam card called for .026/.028 hot, set them at .014/.016 and gained allmost 2 tenths. I realize the motor wants more cam,but am i tearing something up by doing this? No visable signs,just wondering. Thanks for any help.
Below is some information from an older post of mine

Quote:
Originally Posted by trmnatr View Post
I have had a couple people ask about adjusting lash, so today while I was doing a 355 and was done setting the camshaft in I checked opening/closing points @ .0005" tappet lift and .0005" valve lift with the rockers mounted (Shaft mounted I used as the stud rockers are not here yet for this engine, I used my spare shafts)

Timing @ Camshaft .020" tappet lift to .020" tappet lift, spec on the lobe was dead on the money (Crane custom lobe)
IVO 51.5 btdc IVC 75.5 abdc
EVO 86.5 bbdc EVC 46.5 atdc

Thats what it was at the lifter, so we will compute the seat duration as follows
Intake - 51.5 + 75.5 + 180 = 307 seat duration
Exhaust - 86.5 + 46.5 + 180 = 313 seat duration

With cast iron heads and block, you set the lash cold .002" larger and the hot lash will be .002" tighter (with in .001"). This camshaft calls for .020"/.022" hot so I set them @ .022"/.024",,, here are the opening and closing points @ the valve @ .0005" valve lift
IVO 57 btdc IVC 82.5 abdc
EVO 90.5 bbdc EVC 51 atdc

Now we can compute the seat duration at the valve with .022"/.024" lash to give us .020"/.022" hot lash
Intake - 57 + 82.5 + 180 = 319.5 seat duration
Exhaust - 90.5 + 51 + 180 = 321.5 seat duration

Now many people ask how lash effects it and rockers, I checked lash, I will check different rockers when I have time (Which I don't at this moment). This camshaft is safe to run @ .012"/.012" lash, but how much do we really gain from just tightening up the lash .008"-.010"????? See below

Here are the timing specs with lash set @ .014" on both intake and exhaust, The opening points are taken at .0005" valve lift, thats as close as a human can get
IVO 60.5 btdc IVC 86.5 abdc
EVO 95 bbdc EVC 54 atdc

Now lets compute our seat duration and how much we gained
Intake - 60.5 + 86.5 + 180 = 327 seat duration
Exhaust - 95 + 54 + 180 = 329 seat duration

We tightened up the lash on the intake .008" and .010" on the exhaust. As you can see we gained a good amount of seat duration at the valves, see below

Original seat duration @ .022"/.024" cold lash 319.5/321.5 @ the valve
Our new seat duration @ .014"/.014" cold lash 327/329 @ the valve

Now every rocker and every lobe will be different (between different lobe profiles, different brand rockers and/or ratios, but this gives you an idea as to what can be there)

By tightening up lash .008" on the intake we gained 7.5 seat duration and on the exhaust by tightening up the lash .010" we gained 7.5 duration

I hope this gives those interested an idea or example to look at. You can also check this yourself too after you degree your camshaft

Also this will effect valve lift a little too, if you have say 1.5 rockers and a .450" lobe lift, you will have .675" at the valve before lash, now you have to minus the lash from that number

I understand this is not your every day street camshaft here, but its a good example
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