Hi Arnie,
It sounds like you have the correct head for non-rail type rocker arms.
I also bent a push rod that was caused by excessive clearance. I was
able to replace the pushrod with no other damage. A very positive check
would be to perform a leak down test on the affected cylinder. This will
show you if your valve touched the piston, because it will be bent and
not seal.
Craig Wright
Arnie Sugar wrote:
>
> Thanks for all the input - here's a summary of theories, with my
> comments and further questions for all you enginologists:
>
> * Valve float due to high revving / missed shift / "spirited"
> driving - I don't think this is the case, at least not just prior to
> failure - I was just taking off, and going rather slow. Engine may have
> been a tad cold.
> * Rockers not adjusted - I suppose, but they never made any noise
> prior to this
> * Stock rocker arms may not have enough clearance for high lift
> cam - would this have lasted 3000 miles? How do I check this?
> * Springs too big / not enough clearance - would this have lasted
> 3000 miles? How do I check this?
> * Pressed in rocker arm studs may have pulled out and loosened the
> rocker arm. How do I check this? I think mine are threaded, but not
> sure.
> * Mismatched rockers & heads (e.g., big guide holes and no
> rail-type rockers, or guideplates with non-hardened pushrods) - I don't
> think this is the case, but don't have a sense for how tight the
> clearance in the guide holes should be with flat faced (no rails)
> rockers. My heads have a hole where the pushrod goes in, lots of play
> up and down, and around 0.050" side to side. I'm not sure what a
> guideplate looks like, or what the clearance in the head-hole should be.
> This is likely the origin of the old expression "I need that like a I
> need a hole in the head."
>
> Tim, in specific response to your questions:
>
> * Is it possible that the Rocker bound on the rocker stud? - I'm
> not sure what to look for, but the rocker and stud looked OK.
> * Is it possible that the springs coil bound? Also not sure what
> you mean by this, or what to look for.
> * Is the cam solid or mechanical? Are you referring to a roller
> cam? I have hydraulic lifters. This is something I've always wondered
> about: All cams are solid, no? The lifters are either solid, hydraulic,
> or have rollers. When people refer to "roller cams" or "hydraulic cams"
> does this refer to the cam profile to accept certain types of lifters?
> Sorry if I seem like I just fell off the turnip truck...
> * What is the clearance between the spring coils at max lift? Is
> there a spec for this? Do I just rotate engine until valve is full open,
> then measure clearance between the coils?
> * Were they both Intake valves? Yes
> * Are there valve reliefs milled into the pistons? Not sure,
> rebuild was 15 years ago
> * Did you check valve to piston clearance? I didn't build the
> motor. How is this done, through the intake/exhaust port?
> * Do you have guideplates and if so do they show any wear? No,
> just the holes in the heads.
>
> I think if a valve was hitting a piston, it would have happened earlier,
> believe me, I've done more, uh... "spirited" driving in the past.
>
> Thanks again to all, please let me know what you think some more - I'll
> be tearing into it this weekend.
> Arnie
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