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

[70_Fastback]

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...

[daveSanborn]

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.

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.

[70_Fastback]

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...?

[tarafied1]

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.

[70_Fastback]

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.

yeah, that's what I was trying to get at as well.

[JeffTepper]

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.

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.

[Midlife]

If Sanborn was right about your valve damage, shouldn't he be responsible for paying the damage claim?

[70_Fastback]

His original statement was that there was not any valve damage.

[Midlife]

His original statement was that there was not any valve damage.

Well, since Dave was obviously wrong, he's responsible for giving you bad advice...therefore he's liable for damages.

[70_Fastback]

That'd be like getting blood from a turnip!

[daveSanborn]

That'd be like getting blood from a turnip!

You've got that right.....

[Starfury]

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.

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

[daveSanborn]

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?

[70_Fastback]

Oh no, we turned it over a bunch of times, like a fat girl looking for da wet spot.

[blackford]

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.

[70_Fastback]

Hey Tracy!  The valves are bent fairly good.

If you didn't see my previous postl my gear drive grenaded on me and let the timing slip to the point of failure as seen here.

I'm now in the process of trying to find replacement valves. 

[JeffTepper]

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

Tad:

First, I am NOT a math major so I'm not trying to bust your chops.  I am, however, having a difficult time visualizing your math.  Follow me for a second:  If each cylinder fires 3.125 (your number) times per second and there are 60 seconds in a minute (3.125 x 60) then that cylinder fires 187.5 times per minute.  If that cylinder fires once every two revolutions than the engine speed would be 187.5 x 2 = 375 rpm.

Using the same formula, here's how I got to my figure of 25 sparks per second per cylinder.  25 sparks per second times 60 seconds = 1500 sparks per minute.  With a spark every other revolution the engine speed would be at (1500 x 2) 3000 rpm.

Going from the other end, at 3000 rpm an 8 cylinder engine generates 12,000 spark events per minute (3000 x 8 divided by 2).  Dividing 12,000 spark events by 60 seconds = 200 spark events per second.  Dividing 2000 spark events by 8 cylinders = 25 spark events per second per cylinder.

To simplify further, if we have a one cylinder engine firing once every other revolution as it is turning 3000 rpm we have 1500 spark events per minute (3000 divided by 2).  To calculate the per second rate of spark events, divide 1500 by 60 results in 25 spark events per second.

Help me understand where I miscalculated.....................

[blackford]

Hey Tracy!  The valves are bent fairly good.

If you didn't see my previous postl my gear drive grenaded on me and let the timing slip to the point of failure as seen here.

I'm now in the process of trying to find replacement valves. 

Oh...bummer.  I am a FNG...huh? 

[Midlife]

Tad:

First, I am NOT a math major so I'm not trying to bust your chops.  I am, however, having a difficult time visualizing your math.  Follow me for a second:  If each cylinder fires 3.125 (your number) times per second and there are 60 seconds in a minute (3.125 x 60) then that cylinder fires 187.5 times per minute.  If that cylinder fires once every two revolutions than the engine speed would be 187.5 x 2 = 375 rpm.

Using the same formula, here's how I got to my figure of 25 sparks per second per cylinder.  25 sparks per second times 60 seconds = 1500 sparks per minute.  With a spark every other revolution the engine speed would be at (1500 x 2) 3000 rpm.

Going from the other end, at 3000 rpm an 8 cylinder engine generates 12,000 spark events per minute (3000 x 8 divided by 2).  Dividing 12,000 spark events by 60 seconds = 200 spark events per second.  Dividing 2000 spark events by 8 cylinders = 25 spark events per second per cylinder.

To simplify further, if we have a one cylinder engine firing once every other revolution as it is turning 3000 rpm we have 1500 spark events per minute (3000 divided by 2).  To calculate the per second rate of spark events, divide 1500 by 60 results in 25 spark events per second.

Help me understand where I miscalculated.....................

Dr. Midlife here...anyone need aspirin?  I'm writing prescriptions right now!