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Discussion Starter #1
another question for same mate.

He had a cam pin that locates the cam gear snap off clean while revving fairly new engine.
The cam gear bolt was tight. Any ideas of cause?
It was brand new roller cam.
 

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74 XB Fairmont
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The bolt may have felt tight but was the washer in there to keep the offset washer tight to the cam? I've seen quite a few people forget to put the washer in. They assume it's tight as the fuel pump level takes up any slack they can see if the timing car is put on after the fuel pump.

I've done the same with a 253 Holden V8. Many years ago.
 

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Had this happen twice on the same motor fresh build. First time thought it was a fluke,banged ina new pin and off i went. Got about 100 mile away from home,came into town off a highway run ,stopped at some stop lights and she quit. Pin broken again.. Cam was too tight in the bearings was the outcome. Gl
 

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'60 F100 Q-Code
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Socketman said:
Had this happen twice on the same motor fresh build. First time thought it was a fluke,banged ina new pin and off i went. Got about 100 mile away from home,came into town off a highway run ,stopped at some stop lights and she quit. Pin broken again.. Cam was too tight in the bearings was the outcome. Gl
It is far too easy to measure camshaft bearing clearances/dimensions, however another common cause is valve float. Float the valves and the cam pin will definitely sheer. Moral of the story is never trust valve springs you didn't check. Too many el cheapo rebuilders use CRAP valve springs that float at a moment's notice. Even a 2V Clevo has heavy valves (compared to a POS Chevy/Holden). They need serious springs on the order of a BB engine for everyone else.


:davis:
 

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Discussion Starter #6
davis said:
It is far too easy to measure camshaft bearing clearances/dimensions, however another common cause is valve float. Float the valves and the cam pin will definitely sheer. Moral of the story is never trust valve springs you didn't check. Too many el cheapo rebuilders use CRAP valve springs that float at a moment's notice. Even a 2V Clevo has heavy valves (compared to a POS Chevy/Holden). They need serious springs on the order of a BB engine for everyone else.


:davis:
davis I understand what you're saying but I'm missing something here I haven't run into before. I see how coil bind (locking up) would stress the pin.
What does valve float do to it? This pin has sheared off as clean as.
 

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Valve float is what happens when you don't have enough open pressure,and the lifter,pushrod,rocker and valve weight energy,exceeds the ability of the spring to control all that combined weight...so the valve lift exceeds the designed amount,and the entire valvetrain losses contact with the top of the lobe...and the spring doesn't have the strength to shove all that mass back onto the lobe...

open valve pressure is the pressure against the retainer when the valve is at it's maximum open point...when you don't have enough open pressure the lifter will jump over the nose of the cam...then the lifter strikes the closing flank with a severe impact...this is when the damage occurs...it can do damage to several areas of the valvetrain..as will to much open spring pressure...this can also do the same damage as the above by increasing the pushrod flexing,which in itself increases lofting of the valve and valvetrain seperation...don't use pogosticks for pushrods...
 

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Discussion Starter #8
Knew the colletts could pop out under float situation; didn't think about the lifter coming off the cam.

His engine sounds like it's bent all the valves, no compression on cranking.

Thanks soverign.
 
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