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So was Sanborn right or wrong about my valve damage...?

What do you think? Is Sanborn an engine guru or should he stick to 2-strokes?

  • Yes, Dave was right - there was NO valve damage.

    Votes: 2 20.0%

  • No, Dave was wrong - there is valve damage.

    Votes: 5 50.0%

  • Who really gives a sh*t.

    Votes: 3 30.0%
  • Total voters
    10
What rockers were/are you running? Comparing the pistons to the valve marks, either the rockers are opening the valves to far or the cam is a lot larger than planned.... I think that timing gear mishap probably saved you a bunch of cracked pistons.
 
i agree, it looks like those piston/valves were hitting long before the timing gear gave way. I would think that the marks wouldnt be so clean if it was just from a few smacks as the motor was shutting down.
 
I think that timing gear mishap....
Click to expand...

...may have been the result of a larger problem. Like too much valve lift.


Are we looking at both heads, or just one? Does the other head look the same way? That will tell us more.
 
both heads are the same Dave.

it's a 70 block with '68 heads w/ stock valves also.

I think I listed my cam spec earlier in the post. And 1.6 ratio roller rockers.
 
When you assembled the engine did you put some playdo (clay) in there to check clearances?

Lika this...

Valveclearance.jpg
 
No I didn't Mark. I ordered everything as a kit and assumed that it was pieced together to work properly.

Guess that may be what I get for assuming...

I'll putty it this time for sure.

That's going to perturb me if that it what it is. But part of me has trouble believing that if the valves have been hitting from day 1, it would have taken this long to fail...
 
it's a 70 block with '68 heads w/ stock valves also.

I think I listed my cam spec earlier in the post. And 1.6 ratio roller rockers.
Click to expand...

Something is not adding up then....

The only thing I can think of now is that just prior to complete timing gear failure, the cam jumped a LOT of timing... and stayed there long enough for all of the exhaust valves to hit the pistons, but not the intake valves.... again, something isn't adding up.
 
I think it started jumping a tooth at at time and started getting out of time little by little. The idler gear had probably 70% of the teeth sheered off. And I don't think it did that all at once.

The exhaust valves are open as the piston is traveling upwards. And if it's tight to begin with, I would think if it was getting out of time if could hit the Ex valves as it did...?
 
I would be more inclined to believe that the cam timing started go hey wire as the timing gear began to fail. I can't imagine that it would have ran long like that plus it would would make an awful noise that couldn't have been missed!
However, it never hurts to check these things, even good quality cams can be out of spec.
 
"tarafied1" said:
I would be more inclined to believe that the cam timing started go hey wire as the timing gear began to fail. I can't imagine that it would have ran long like that plus it would would make an awful noise that couldn't have been missed!
However, it never hurts to check these things, even good quality cams can be out of spec.
Click to expand...

yeah, that's what I was trying to get at as well.
 
"daveSanborn" said:
Something is not adding up then....

The only thing I can think of now is that just prior to complete timing gear failure, the cam jumped a LOT of timing... and stayed there long enough for all of the exhaust valves to hit the pistons, but not the intake valves.... again, something isn't adding up.
Click to expand...

Remember that at 3000 rpm each cylinder is firing 25 times per second so it doesn't take much time for valve/piston damage to occur.
 
If Sanborn was right about your valve damage, shouldn't he be responsible for paying the damage claim?
 
"70_Fastback" said:
His original statement was that there was not any valve damage.
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Well, since Dave was obviously wrong, he's responsible for giving you bad advice...therefore he's liable for damages.
 
"JeffTepper" said:
Remember that at 3000 rpm each cylinder is firing 25 times per second so it doesn't take much time for valve/piston damage to occur.
Click to expand...
Your math's a little off, Jeff;)

3000rpm, divide by 60s/min, divide by 8 cylinders, divide by 2 (each cylinder fires once every two revolutions), you get 3.125 spark events per second. 25 times a second is 24000 rpm :D
 
Thanks for writing it out Tad, I knew the 25 # was high, but didn't have the time to do the math on my last visit. Regardless, if the timing was WAY OFF for 10 seconds, the piston would hit the ex. valve 30 times, which is consistant with the visible damage. Plus, didn't most of us see a video of the troubleshooting after the incident where the engine was turning over, but wouldn't start? Or was the engine not turning over during these attempts?
 
Wow...i'd like to hear the circumstances behind that.

Check your rockers and pushrods for cracks and bendos

Your lucky the valves hit the pistons near the center of the valve instead of on the outer edge...they would probably be bent otherwise.
 
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