John,
I believe that you are under the misconception that a rev limiter would
have prevented this problem, it wouldn't have. A rev limiter will limit
the RPM of an engine when the engine itself is asking for higher RPM
than the limiter is set to, such as flooring the car in neutral, or
missing a speed shift. It will not do anything for an engine that is
being pushed to higher revs by a down shift where the mass and momentum
of the car are causing the engine to be mechanically over-revved. As far
as I know there is nothing to prevent this.
As for things to check, see if the balancer key is sheared. Even if the
timing chains are correct, if the balancer is out of time with the
crank, your valve train is STILL not timed correctly with the crank. You
should be able to do this by pulling out spark plug #1 and looking down
into the cylinder while slowly turning the engine by hand. When the
piston is close to top dead center, see where the timing mark is on the
balancer. As you suggested, the two halves of the balancer may have
slipped. I don't know the relationship of balancer key way to timing
marks, but I suspect someone on this list does!
Good luck getting things figured out, and sorry again about your damage.
Peace,
Pat
jover4x4@aol.com wrote:
>List, racers,
>
>I made a bonehead mistake on the track last weekend. This topic was brought
>up recently and we all talked about the great insurance benefits an MSD 6AL
>box with rev limiter has to offer. Unfortunately my box is just the 6A. On
>the track last weekend I shifted into third but hit fifth, no problem, until I
>went to hit third again and hit first gear. OUCH. I sent the RPMS pretty
>high. I caught it quickly but obviously not quick enough. After the incident
>the car ran fine, but ran slightly rough and had a harmonic vibration like the
>balancer was not doing its job. Anyway, after a quick diagnosis I found the
>upper timing chain had jumped a tooth. Compression was at 90 psi on all
>cylinders so I figured it was a timing issue. After reseting the cam timing I
>started the car and found no change in compression and the harmonic vibration
>was still there. I have not put a timing light on it as I called it quits for
>the night when I made no progress. I didn't want to pull the!
> front cover but it seems I might need to. I guess I can diagnose the timing
>issue if I "degree" the cam. If any of you have experience with this, what
>could be causing my harmonic vibration. I speculate the balancer could have
>been damaged. I am thinking of putting a timing light on it to see if it is
>still timed where it used to be (outer ring could have moved radially on its
>center?) and maybe I can stop/slow the motion with a timing light to see if
>the balancer is damaged and moving around?
>
>Any other ideas on what I should look for? I don't think that I could have
>bent a crank, jackshaft or cam, or affected the clutch/flywheel. I did do a
>quick check on the valve adjustment and all clearances seemed within the
>ballpark. I didn't find any excessive gaps that would indicate a bent valve.
>I also didn't hear any unusual noises when this happened. It just revved high
>and I quickly stomped on the clutch.
>
>Any thoughts are appreciated. Please keep negative comments to yourself. I
>remember some negative remarks towards the last guy this happened to. Hey,
>sh*t happens.
>
>John Over
>68 2000
>
>
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