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Auto Decompression

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When turning over the engine by hand. I noticed that the lobe on the auto decompression ticks against the valve bucket. To break things down, I had a blown head gasket. Went from 440 back to stock cylinder. New piston and gaskets, after reinstalling everything. I heard a nasty knock. Tore everything down once again and noticed that my valves were hitting the piston. (Exhaust only).  

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I have always used the specs from the hotcams. But back to my other question. Is the auto decompression supposed to tick off that bucket?

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Isn't there a thicker base gasket and head gasket needed for this mod? or else you cam timing is off and the reason the valves hit.

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I have always used the specs from the hotcams. But back to my other question. Is the auto decompression supposed to tick off that bucket?

 

Here are the specs for E model cams

IN .351 lift 227 dur.... EX .366 lift 243 dur

 

And for S/SM

IN .334 lift 227 dur…. EX .323 lift 243 dur

 

Yes the auto decomp is supposed to "tick" the valve bucket. That's how it releases some compression to allow the starter motor to turn over the engine easier. Once the RPM's are above a certain speed (somewhere between cranking speed and idle speed) the auto decomp mechanism will rotate that cam so it no longer contacts the valve bucket. If you have the valve cover open you can move it around with your finger and see for yourself how it works.

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Here are the specs for E model cams

IN .351 lift 227 dur.... EX .366 lift 243 dur

And for S/SM

IN .334 lift 227 dur…. EX .323 lift 243 dur

Yes the auto decomp is supposed to "tick" the valve bucket. That's how it releases some compression to allow the starter motor to turn over the engine easier. Once the RPM's are above a certain speed (somewhere between cranking speed and idle speed) the auto decomp mechanism will rotate that cam so it no longer contacts the valve bucket. If you have the valve cover open you can move it around with your finger and see for yourself how it works.

I think he meant valve lash not lift and duration..... In which case yes should be .10-.20 intake and .20-.30 exhaust

The auto decomp has been known to fail, which will give you a nasty ticking sound while it's running. ImageUploadedByThumper Talk1402250896.418558.jpg

Here is a pic of my failed decompression. There is a smaller pin that locates into the larger pin visible in my pic. Kind of looks like a "T" shape. This smaller pin can shear and allow the larger pin to move freely and smack the bucket.

Video of decomp noise:

Edited by Gsxrstuntdrz
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