Valve lash on a solid cam question...
Thread Starter
Safety Car
Joined: Jul 2002
Posts: 3,770
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From: St Louis MO
Valve lash on a solid cam question...
According to the Compcams solid lifter cam install instructions, they say to adjust lash per the cam card for cam break-in, which is .016 on int and exh. It goes on to say that after break-in, the engine will be at operating temp and that due to thermal expansion, the lash will now be looser than it was when the engine was cold.
Now, that just doesn't sound right to me. I would think the lash would be tighter due to thermal expansion. According to what I've read here, you should adjust the lash .002 looser (in this case, to .018) when cold and the lash should be real close when warm.
Are the instructions screwy? Should I adjust lash to .018 with the intent of heat getting the lash to the .016 target?
Brett
Now, that just doesn't sound right to me. I would think the lash would be tighter due to thermal expansion. According to what I've read here, you should adjust the lash .002 looser (in this case, to .018) when cold and the lash should be real close when warm.
Are the instructions screwy? Should I adjust lash to .018 with the intent of heat getting the lash to the .016 target?
Brett
Drifting
Joined: Oct 2000
Posts: 1,825
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From: Shawano WI
Originally Posted by Brettmc
Cam card says .016 for the intake and exhaust.
The lash will increase (loosen up) as the motor reaches operating temp. When I have to set the valves cold I always go .002 tighter with a iron head / iron block, .003 with an alum head / iron bock and .006 for an alum head / alum block.
Pete
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Just a general guideline from Crane Cams website
Iron block, iron heads ADD + 0.002"
Iron block, aluminum heads SUBTRACT- 0.006"
Aluminum heads, aluminum block SUBTRACT-0.012"
I have been experimenting with my solid roller and whle it is best to set them hot I set them cold last time and set them - 0.002" ) iron block, aluminum heads ) I will take a valve cover off tommorrow when hot and see what they read.
Iron block, iron heads ADD + 0.002"
Iron block, aluminum heads SUBTRACT- 0.006"
Aluminum heads, aluminum block SUBTRACT-0.012"
I have been experimenting with my solid roller and whle it is best to set them hot I set them cold last time and set them - 0.002" ) iron block, aluminum heads ) I will take a valve cover off tommorrow when hot and see what they read.
Thread Starter
Safety Car
Joined: Jul 2002
Posts: 3,770
Likes: 3
From: St Louis MO
Thanks Pete but why does that happen? You would think when the parts expanded, the lash would close up. Why does it get looser?
Anyway, I should adjust the lash to .014 cold on my all iron engine, right?
Brett
Anyway, I should adjust the lash to .014 cold on my all iron engine, right?
Brett
Last edited by Brettmc; Oct 2, 2004 at 11:42 PM.
Race Director
Joined: Apr 2000
Posts: 17,676
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Dosen't matter it's for either
http://www.cranecams.com/?show=faq&id=4
Just remember this is only to get you close to start up you are supposed to set to factory specs as soon as it heats up
http://www.cranecams.com/?show=faq&id=4
Just remember this is only to get you close to start up you are supposed to set to factory specs as soon as it heats up
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Drifting
Joined: Oct 2000
Posts: 1,825
Likes: 56
From: Shawano WI
Brett:
As the motor increases in temperature the hottest parts will increase in size the most. The block and heads are where the combustion takes place so that will be the hottest part of the engine. As the block expands, the deck surface is moved away from the cam centerline. As the heads expand, the rocker studs are moved away from the cam centerline. As both of these parts expand the distant from the cam centerline to the rocker arm increases, causing an increase in vavle lash. The pushrod and lifter are isolated from the combustion temperature so they do not expand as much as the block and heads. With alum heads or block, the aluminum expands at a greater rate than the steel push rod and lifter so they will increase the lash more than an iron head / block combination.
Pete
As the motor increases in temperature the hottest parts will increase in size the most. The block and heads are where the combustion takes place so that will be the hottest part of the engine. As the block expands, the deck surface is moved away from the cam centerline. As the heads expand, the rocker studs are moved away from the cam centerline. As both of these parts expand the distant from the cam centerline to the rocker arm increases, causing an increase in vavle lash. The pushrod and lifter are isolated from the combustion temperature so they do not expand as much as the block and heads. With alum heads or block, the aluminum expands at a greater rate than the steel push rod and lifter so they will increase the lash more than an iron head / block combination.
Pete
Thread Starter
Safety Car
Joined: Jul 2002
Posts: 3,770
Likes: 3
From: St Louis MO
Originally Posted by Pete79L82
Brett:
As the motor increases in temperature the hottest parts will increase in size the most. The block and heads are where the combustion takes place so that will be the hottest part of the engine. As the block expands, the deck surface is moved away from the cam centerline. As the heads expand, the rocker studs are moved away from the cam centerline. As both of these parts expand the distant from the cam centerline to the rocker arm increases, causing an increase in vavle lash. The pushrod and lifter are isolated from the combustion temperature so they do not expand as much as the block and heads. With alum heads or block, the aluminum expands at a greater rate than the steel push rod and lifter so they will increase the lash more than an iron head / block combination.
Pete
As the motor increases in temperature the hottest parts will increase in size the most. The block and heads are where the combustion takes place so that will be the hottest part of the engine. As the block expands, the deck surface is moved away from the cam centerline. As the heads expand, the rocker studs are moved away from the cam centerline. As both of these parts expand the distant from the cam centerline to the rocker arm increases, causing an increase in vavle lash. The pushrod and lifter are isolated from the combustion temperature so they do not expand as much as the block and heads. With alum heads or block, the aluminum expands at a greater rate than the steel push rod and lifter so they will increase the lash more than an iron head / block combination.
Pete
EXACTLY what I was looking for. Thanks, Pete.
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Originally Posted by Pete79L82
Brett:
As the motor increases in temperature the hottest parts will increase in size the most. The block and heads are where the combustion takes place so that will be the hottest part of the engine. As the block expands, the deck surface is moved away from the cam centerline. As the heads expand, the rocker studs are moved away from the cam centerline. As both of these parts expand the distant from the cam centerline to the rocker arm increases, causing an increase in vavle lash. The pushrod and lifter are isolated from the combustion temperature so they do not expand as much as the block and heads. With alum heads or block, the aluminum expands at a greater rate than the steel push rod and lifter so they will increase the lash more than an iron head / block combination.
Pete
As the motor increases in temperature the hottest parts will increase in size the most. The block and heads are where the combustion takes place so that will be the hottest part of the engine. As the block expands, the deck surface is moved away from the cam centerline. As the heads expand, the rocker studs are moved away from the cam centerline. As both of these parts expand the distant from the cam centerline to the rocker arm increases, causing an increase in vavle lash. The pushrod and lifter are isolated from the combustion temperature so they do not expand as much as the block and heads. With alum heads or block, the aluminum expands at a greater rate than the steel push rod and lifter so they will increase the lash more than an iron head / block combination.
Pete
Thread Starter
Safety Car
Joined: Jul 2002
Posts: 3,770
Likes: 3
From: St Louis MO
Ya know, I've always been partial to cork too. I have cork on my valve covers now. However, the cam change gasket set (Fel-Pro) I got from Summit has rubber ones in it. Dunno how I'm gonna like that...
Brett
Brett
