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Safe exhaust valves clearance

General engine tech -- Drag Racing to Circle Track

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John@RED
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Safe exhaust valves clearance

Post by John@RED »

Hi,
I found an Euro manufacturer that sells camshafts with a lash ramp for an exhaust valve clearance (0.0078-0.0086) being smaller than the minimum advised by the engine manufacturer (0.0110 to 0.0149):
isn't 0.0078 a bit too tight for a turbo engine exhaust valve, considering the valve stem elongation under high temp?
Thanks
mag2555
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Re: Safe exhaust valves clearance

Post by mag2555 »

The Cam manufacturer likely found that when the expansion of everything is taken into account that there recommendation is still safe and better longevity wise for there lobe profile.

Actually when you averaged out the numbers there is only a .0047” difference.

If you want to be on the safe side then run the original manufacturers stated clearance and then see how much that clearance may have closed up or opened up once the motor has been run hard.
You can cut a man's tongue from his mouth, but that does not make him a liar, it just shows that you fear the truth he might speak about you!
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CamKing
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Re: Safe exhaust valves clearance

Post by CamKing »

The lash the engine manufacturer lists, are only for the manufacturer's cams.
Is the aftermarket cam company's lash recommendation for the Hot Lash or Cold lash?
Is this an overhead cam application?
Is the head aluminum ?
Is there a rocker or finger follower, if so, what's the ratio ?
Mike Jones
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Jones Cam Designs' HotPass Vendors Forum: viewforum.php?f=44
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dynoflo
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Re: Safe exhaust valves clearance

Post by dynoflo »

Many years ago i was building quite a few 305 sbc with 416 heads for circle track. I was looking for an edge when my cam grinder recommended a solid lifter with very tight lash disquised as the mandated hydraulic. The lash was .004. First one a did i was skeptical but made several dyno pulls and checked lash and it was still .004. Motor ran all season with many wins and tech. One night tech ask him if he had fast bleeddown lifters and he said yes and they let him have the win.
David Redszus
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Re: Safe exhaust valves clearance

Post by David Redszus »

John@RED wrote: Tue Jul 20, 2021 11:30 am Hi,
I found an Euro manufacturer that sells camshafts with a lash ramp for an exhaust valve clearance (0.0078-0.0086) being smaller than the minimum advised by the engine manufacturer (0.0110 to 0.0149):
isn't 0.0078 a bit too tight for a turbo engine exhaust valve, considering the valve stem elongation under high temp?
Thanks
There is a difference between the valve clearance set point (lash) and the total ramp height.
A cam with a low ramp height cannot entertain a large lash setting.

Valve clearances undergo changes during the warm-up period.
Starting with a cold setting, the clearance may be reduced as the valve heats up and the valve length grows.
As the cylinder head heats up and grows, the clearance is reestablished as the hot running clearance.
It is during the warm-up transition period that problems can emerge.

Several factors must be considered; valve material, head material, clearances and temperatures.
If you can determine the actual ramp height, yo might set the lash at mid-ramp height as a starting point.
John@RED
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Re: Safe exhaust valves clearance

Post by John@RED »

mag2555 wrote: Wed Jul 21, 2021 8:00 am If you want to be on the safe side then run the original manufacturers stated clearance and then see how much that clearance may have closed up or opened up once the motor has been run hard.
Unfortunately you shouldn't, as the hit on the lifters would be very hard.
That's the point
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Re: Safe exhaust valves clearance

Post by John@RED »

CamKing wrote: Wed Jul 21, 2021 9:29 am The lash the engine manufacturer lists, are only for the manufacturer's cams.
Is the aftermarket cam company's lash recommendation for the Hot Lash or Cold lash?
Is this an overhead cam application?
Is the head aluminum ?
Is there a rocker or finger follower, if so, what's the ratio ?
Hi CamKing
1. cold lash
2. yes, dohc
3. yup, aluminum
4. no
Thanks
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CamKing
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Re: Safe exhaust valves clearance

Post by CamKing »

John@RED wrote: Mon Jul 26, 2021 3:43 pm
CamKing wrote: Wed Jul 21, 2021 9:29 am The lash the engine manufacturer lists, are only for the manufacturer's cams.
Is the aftermarket cam company's lash recommendation for the Hot Lash or Cold lash?
Is this an overhead cam application?
Is the head aluminum ?
Is there a rocker or finger follower, if so, what's the ratio ?
Hi CamKing
1. cold lash
2. yes, dohc
3. yup, aluminum
4. no
Thanks
You will have no issue, running the aftermarket cams, set to the recommended cold lash settings from the aftermarket cam manufacturer.
The lash will grow from Cold to Hot, so you don't have to worry, about the aftermarket cam lash, being less then the stock cam lash.
The Reason why it's less, is that the aftermarket cams were designed with a slightly shorter lash ramp, then the stock cam.
Mike Jones
Jones Cam Designs

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jonescams@bellsouth.net
http://www.jonescams.com
Jones Cam Designs' HotPass Vendors Forum: viewforum.php?f=44
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Truckedup
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Re: Safe exhaust valves clearance

Post by Truckedup »

dynoflo wrote: Wed Jul 21, 2021 6:51 pm Many years ago i was building quite a few 305 sbc with 416 heads for circle track. I was looking for an edge when my cam grinder recommended a solid lifter with very tight lash disquised as the mandated hydraulic. The lash was .004. First one a did i was skeptical but made several dyno pulls and checked lash and it was still .004. Motor ran all season with many wins and tech. One night tech ask him if he had fast bleeddown lifters and he said yes and they let him have the win.
Was it a Lazer cam?
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire
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