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Old 02-16-2008, 07:30 AM
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Piston To Valve Clearance Problem - Help

Well I just threw the new BBC together - new cam (roller) and stuff. I put a head gasket on, installed the head, set lash on the valves, installed "temporary" valve checking springs, hooked up a dial indicator, and checked piston to valve clearance. It looks like I have a problem. I've only got about .030" of clearance on the intake. The exhaust is fine.

I was told to have at least .080" clearance. I'm not even close.

I have SpeedPro L2399F60 pistons. Aluminum, domed.

Standard 4" non-stroker crank.

The cam is a custom solid steel roller from Comp Cams. It's the 11-771-8 on a solid billet. (-9 series core).

Now what do I do? I already messed up by installing the oil pan and all gaskets - took me forever to do that. I thought for sure I would have enough clearance. Now I may have to do the whole darn thing over again...

Do I have to get the pistons cut or what? Is that too much material to remove from the pistons? That would mean removing and reinstalling every piston - that's a ton of work for me. Do I have to change the cam?

what should I do? - Help..........

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Old 02-16-2008, 07:47 AM
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Is the cam ground straight up or did they dial in a little advance for you?

Stick a degree wheel on it and make sure of your valve timing before you go any further. If it is advanced you can back it up to 0 degrees and re-check the V-P clearance.



Larry
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Old 02-16-2008, 08:36 AM
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Quote:
Originally Posted by coldknock
Is the cam ground straight up or did they dial in a little advance for you?

Stick a degree wheel on it and make sure of your valve timing before you go any further. If it is advanced you can back it up to 0 degrees and re-check the V-P clearance.



Larry
It's installed straight up - never degreed it. Even if it was off 2-3 degrees advance or retarded I still don't think I would have .080" clearance.
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Old 02-16-2008, 08:44 AM
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Quote:
Originally Posted by leejoy
It's installed straight up - never degreed it. Even if it was off 2-3 degrees advance or retarded I still don't think I would have .080" clearance.
The only thing you can say for sure is that it is "installed" you have no idea of the actual valve timing.

You can either do the job right or do it again the right way later.

I tried to warn you but......

According to the cam card the cam naturally goes in 4 deg advanced.




Degree it in first. Yyou don't even know if you have the right cam in it.
I've had a 9 degree over advance problem on a bbc before. Cause I "thru it in" without checking.

Ok at what crank/piston position is the minimum clearance?
before TDC? after TDC? @TDC?

Last edited by F-BIRD'88; 02-16-2008 at 08:51 AM.
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Old 02-16-2008, 09:02 AM
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Stick the old xe284h-10 cam back in and check the actual .050" valve timing and VtP clearance.

A friend here ran into the same problem with a near identical comp roller cam in a 454.
L2465F pistons .
Had to retard it quit a bit from cam card specs to gain intake VtP clearance.
on a BBC you check at 0 valve lash for .100" minimum clearance.

Last edited by F-BIRD'88; 02-16-2008 at 09:08 AM.
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Old 02-16-2008, 09:06 AM
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P-v Clearance

if you are sure you have .030 clearance on the intake valve, it will be fine. the intake valve is chasing the piston down the bore, the piston is moving at a greater speed than the valve opening rate. you will not have any problems.

sam-missle
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Old 02-16-2008, 09:15 AM
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What is the piston to deck clearance @ TDC? Are your heads shaved?
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Old 02-16-2008, 10:01 AM
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guys - have to run out for a family event - be back in a couple hours - can't wait to get talking about this again with you guys - thanks.

Lee.
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Old 02-16-2008, 02:25 PM
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I would take the time to degree-check it. It also may be as simple as having a 3 key-way bottom gear indexed incorrectly.

tom
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Old 02-16-2008, 02:33 PM
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Quote:
Originally Posted by machine shop tom
I would take the time to degree-check it. It also may be as simple as having a 3 key-way bottom gear indexed incorrectly.

tom
Im sure the cam gear is indexed correctly. There is a dot on one gear and a triangle (I think) on the other gear. They were pointing to eachother when #1 cyl is at TDC.

I'll have to get a degree wheel and then find TDC and see what the heck is going on. It may be advanced a few degrees.

Lee
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Old 02-16-2008, 03:59 PM
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Quote:
Originally Posted by leejoy
Im sure the cam gear is indexed correctly. There is a dot on one gear and a triangle (I think) on the other gear. They were pointing to eachother when #1 cyl is at TDC.

I'll have to get a degree wheel and then find TDC and see what the heck is going on. It may be advanced a few degrees.

Lee
If it was a three key-way bottom gear, you have to have the proper marks and key-ways lined up. Otherwise.......

tom
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Old 02-16-2008, 06:28 PM
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Check Out These Pictures

The clay thickness in that one picture is only about .030" thick all throughout from one end to another - not much room. I'll degree the cam and go from there. If that doesnt give me at least .050" or so, I'll have to use that ISKY tool to cut the pistons or pull them out and have a machine shop do it.

I have 2.19" intake valves. - Help.......



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Old 02-16-2008, 06:46 PM
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I think there's a problem with your timing set if there isn't three keyways cut into the bottom sprocket, and it should also be marked with a dot, square, and triangle. Like previously suggested, I also bet the cam timing is off.
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Old 02-16-2008, 07:11 PM
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Quote:
Originally Posted by baddbob
I think there's a problem with your timing set if there isn't three keyways cut into the bottom sprocket, and it should also be marked with a dot, square, and triangle. Like previously suggested, I also bet the cam timing is off.
here is a picture of my timing set. it appears the triangle on the crank gear is lined up with the dot on the cam gear when the #1 cyl is at TDC.

Is that correct?

The cam was not "degreed". There were no "bushings" installed on the cam gear. I will have to change that and "degree" it to find out what the heck is going on.

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Old 02-16-2008, 07:16 PM
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That means you're 4 degrees advanced+ 4 degrees designed into the grind from Comp means you're a total of 8 degrees advanced. You should definately put a degree wheel on it and verify where you're at.
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