390 Spring Pressure
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390 Spring Pressure
I am having the heads serviced for this engine. The machine shop says that the valve spring pressure is 150 lbs; way too much. They told me that full race engines don't go much over 120 lbs. What is the correct valve spring pressure for this engine?
PJX
PJX
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From: Near Fresno, California
Better go to a different machine shop - the Crain specs on a mild cam (343941) call for a spring that provides 90 pounds closed (compressed to 1.828") and 276 pounds with the valve open (compressed to 1.288 inches). They state the valves will start to float at 6500RPM.
http://www.cranecams.com
My 72 shop book states 85 to 95 pounds @ 1.820", and 209 to 231 pounds @1.38" The ware limit is 186 pounds @ 1.38, so, if I understand correctly, even Ford wants the stock springs replaced if they are less than 186 pounds.
I am not an expert, just repeating what I read.
http://www.cranecams.com
My 72 shop book states 85 to 95 pounds @ 1.820", and 209 to 231 pounds @1.38" The ware limit is 186 pounds @ 1.38, so, if I understand correctly, even Ford wants the stock springs replaced if they are less than 186 pounds.
I am not an expert, just repeating what I read.
Posting Guru
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From: Evanston, WY
Mine is a little shy of a full race engine, and I have 210 closed and 576 open. On a stock engine, use the shop manual specs. On an aftermarket cam, use the manufacturers recommendation.
-Scouder
-Scouder
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From: Near Fresno, California
"a little shy of a full race engine"? There is not a person on this website that wouldn't give his left ARM for that engine - not even sure I would install it (it might get dirty!) just set it in the living room as a work of art.
That being said, a machine shop that thinks 150 pounds to compress a valve spring is too much would worry me. I depend on the machinist to keep me from making expensive mistakes and expect them to be experts.
That being said, a machine shop that thinks 150 pounds to compress a valve spring is too much would worry me. I depend on the machinist to keep me from making expensive mistakes and expect them to be experts.
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Thanks to all of you for the answers. I am not sure if the guy was saying that 120 lbs was the closed valve or not. I bought the truck that it is in used. It was used to tow a race car and probably has been modified but I don't know what cam is in it.
These guys have had my heads since the middle of August; needless to say I am never going back.
PJX
These guys have had my heads since the middle of August; needless to say I am never going back.
PJX
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OK, I went and got the Haynes manual that came with the truck. It says that for my year, 1974, Valve Spring Pressure, first check is 76-84 @ 1.69". Valve Spring Pressure, second check, is 190-210 @ 1.31" So I still have to ask the guy which one of these he is referring to. Stay tuned....
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390 Spring Pressure
Another thing, I don't know what cam is in the engine. I think that dis assembly of the engine is required.
PJX
PJX
Last edited by PJX390; Sep 18, 2004 at 05:52 AM. Reason: Addition to Message
