cam problems - Team Camaro Tech
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post #1 of 6 (permalink) Old Jul 18th, 00, 06:26 AM Thread Starter
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Bruce
 
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Location: PA
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anyone ever have this problem ? i'm pulled out my 396 this weekend,(where was everyone, pizza and beer was on me....), went to install my new cam,(comp cam xe294h), which by the way is a smaller cam, and when i went to set the pre-load on the lifters, the intake valve hit the piston(s). confused, you bet...
i called up comp cams and they told me that from the numbers i gave them off of my old cam spec sheet, i should have plenty of clearance. still confused, you bet...
called a local shop, the mechanics brother works for grumpy jenkins, and both of these guys no there sh#!. i told him what the cam company said and he kind of laughed. then i remembered, my crank gear was set on four degrees advanced, and the cam was made with four degrees in it, so i asked him if this could be the problem, should i set the crank gear back on zero ? he told me that this could be a big problem seeing that i had a total of eight degrees advance, and he did say set it back. so i'm going to find out as soon as i get a gear puller. anyone out there have one ??? pizza and beer is still on me....
what do you guys think ?
later,
bruce
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post #2 of 6 (permalink) Old Jul 18th, 00, 07:23 AM
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Bruce,

The fact that you are not running the cam straight up DEFINATELY can affect your valve clearance. I run approx. a .600 lift cam on my 396 and I have about .120 piston to valve clearance BUT I am runnning the cam straight up. Secondly, 242/248 duration at .050 is ALOT of duration. It is possible that due to the valve opening and closing points and the duration with which the valves are staying open COMBINED with the fact that you are running the cam 8 degrees adavanced led to your valve clearance problem.

I would install the cam straight up and see what happens. If you are not running large domed pistons you shouldn't really have a problem staright up.



[This message has been edited by sr71bb (edited 07-18-2000).]
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post #3 of 6 (permalink) Old Jul 18th, 00, 07:06 PM
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Lonnie
 
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Moving the cam back 4 degrees probably won't give you .080 clearance, and if your valve hit the piston, you will need more than that. You better pull at least one head and check clearances properly or you might regret it. Different pistons have different size valve reliefs.

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post #4 of 6 (permalink) Old Jul 19th, 00, 12:58 AM
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Bruce,

Lonnie, is right about that. I know it is an absolute pain in the butt but I would take one of the heads off and run a clay check for valve clearance. You need a minimum of .100 to be safe. You didn't say what pistons you are running so it is possible that you will need deeper valve reliefs if all else fails. Some people try to fudge this by running a thicker than normal head gasket but that is a BAD IDEA.

That being said, it is possible to check for valve clearance WITHOUT removing your heads. You could remove a spark plug and VERY CAREFULLY insert a piece of solder (say .180 thickness) that is bent at a 90 degree angle into the spark plug hole. You then, manually turn the the motor through a a complete cycle. The solder will be squeezed between the piston and the valve during this process. Then, take a micrometer and measure the thickness of the solder at the "squeeze" point. It should be .100 or THICKER. This method was taught to me by an old machine shop guy. I have not used it myself because I changed out my heads so I used the old "playdough" method.

Good Luck.
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post #5 of 6 (permalink) Old Jul 19th, 00, 03:24 AM Thread Starter
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Bruce
 
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thanks for the info. i really hate the idea of pulling the heads off, it's not the part that it's a lot of work, it's that i just put these head gaskets on and i hate to waste new gaskets. one guy told me to reuse them because they are new. in fact, the is no miles on them, just running time. the pistons are 12.5:1 comp full floating pistons, made for closed chamber heads. my heads are oval port, open chamber. the old cam spec's were 610", 310 dur., 274 @.050. the guy at comp cams told me the i should not have any problems with valve to piston clearance. well i am. me wanted me to take a retainer to guide measurement. not sure how to take this?
well i'm getting a gear puller this weekend and i'll let you know what happens.
thanks,
bruce
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post #6 of 6 (permalink) Old Jul 19th, 00, 03:28 AM Thread Starter
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Bruce
 
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sorry, i forgot to mention this. when i had the 610" cam in, i did have at least .100 valve to piston clearance. we did check it with playdough, and i was ok. so that is why i believe it may be with the crank gear. i hope i'm correct.
later,
bruce
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