[Land-speed] Bad vibes

[Jim Dincau]

Don,
     I run a 3 liter Chevy II 4 banger with a Fontana head. I have had good 
luck (2 Speedweeks and 8  El Mirage meets) by following the instructions for 
my 10,000 RPM 2 disc clutch. That is to use stock genuine Chevrolet flex 
plate bolts with no washers and red locktite. I have no locating dowel in 
the crank flange and am amazed that it works. Understand that this is with a 
super light aluminum flywheel not a heavy steel dyno wheel. I also have a 
flat crank, if you are using a V-8 crank your mileage may vary.
    I agree that a four can have strange harmonics. I have noticed some 
fretting between the camshaft OD and the inside of it's keyed drive flange 
and the timing pointer seems to be touching the crank hub in two places on 
the OD. This is with about 1/16" static clearance on the pointer. I could 
not find a harmonic damper that would clear the Fontana gear drive and cover 
so I have not been running one.
      Another problem I had was starter drive sprags, I destroyed a heavy 
duty Summit starter the first time I tried to start it. Tilton told me to 
use their pro stock starter and a 16 volt battery. A four with 14/1 
compression and 31 degrees in the mag is hard on the starter. Against Don 
Zig's advice I also put a mechanical start retard in the mag base (he 
doesn't like them), it worked but I suspect it made the timing scatter a 
little. We have switched to an MSD ignition with start retard (and a rev 
limiter), next month at El Mirage I will find out if it helps. I hope this 
helps you.
Jim Dincau

> Anyone silly enough to cut an engine in half should probably expect  to 
> encounter some "unusual" problems along the way. During a recent  dyno 
> pull, our half Windsor (3 liter inline four) sheared off all six  Locktite 
> secured 7/16" ARP flywheel bolts, and almost welded the  flywheel to the 
> crank. Seems that we have a harmonic vibration  problem that has created 
> more force than our system can tolerate.  So.......... we probably need to 
> strengthen the parts and reduce the  "bad vibes".
>
> The most obvious action would be to strengthen the parts by  increasing 
> the bolt diameter, adding some dowels, and making sure  that everything 
> fits. Reducing the the force could be a little more  difficult.  The 
> balancer (cheapo fluid type) is clearly not up to the  task and should to 
> be upgraded to something more in tune with this  engine's harmonic 
> characteristics.  I really don't have any  experience in this area and 
> would  greatly appreciate any thoughts  that list members would care to 
> share.
>
>                  Thanks, Don