[DeTomaso] I *hate* it when that happens....

Guido deTomaso guido_detomaso at prodigy.net
Fri Mar 23 03:39:49 EDT 2012



Fine thread in aluminum seems like an odd choice, even in the stock steel 
flywheel I'd expect coarse thread but could be wrong there.

Changing to 3/8 coarse at least would move the project away from fine thread but 
the number of threads in the flywheel goes down + the pressure plate would need 
to be drilled to match.

I'd just heli-coil the one stripped bolt hole back to 5/16ths fine thread, look 
for longer bolts for more thread engagement.

Re. balance, I've never understood drilling pressure plate to balance the 
engine, since the PP is a wear item and once replaced, there goes the balance.  
I don't know that you'll ever notice the weight of one heli-coil.

GD




________________________________
From: "MikeLDrew at aol.com" <MikeLDrew at aol.com>
To: detomaso at realbig.com
Sent: Thu, March 22, 2012 9:16:29 PM
Subject: [DeTomaso] I *hate* it when that happens....

So, my engine has been sitting on a stand for months now, after the 
distributor gear ate the cam gear at the POCA Fun Rally last year.  The cam has 
been replaced and the motor is all back together, so today I thought I'd take 
care of some last details to get it ready to go back into the car.

When I put the engine back together, I noted that one of the six pressure 
plate bolts was not a genuine Ford pressure plate bolt, but rather a Grade 
Zilch hardware store special.  I decided to buy some whippy dippy ARP Ford 
pressure plate bolts, and swap them out before mating the engine to the 
gearbox.

Today, out with the old, in with the new.  Surprisingly, there is no 
published torque spec for the pressure plate bolts anywhere in the shop manual 
(at least, none that I could find), but a search of the internet showed 
multiple sources consistently saying that the magic number was 35 ft/lbs, 
lubricated.

So I got out my handy dandy torque wrench and started installing them.  I 
figured I'd step the torque up gradually and started with 25 ft/lbs.  The 
first few started tightening up normally, but then one of them started 
getting tight and then...didn't. :<(

I had a good hard look, and discovered that the ARP bolts were marginally 
shorter than the Ford bolts.  What's worse, the thickness of the flange on 
the clutch coupled with the hardened washers left precious little thread 
engagement in the soft aluminum flywheel.  When I removed the not-tightening 
bolt, it came out looking like this:

http://www.poca.com/index.php/gallery/?g2_itemId=35807

Only three threads engaged the flywheel, not nearly enough to do the job.  
To be fair, this flywheel came to me used, and clearly clutches had been 
installed and removed numerous times during its life.  It's entirely possible 
that somebody before me had just about completely trashed the threads, and 
I just finished them off.  All of the holes bore indications of prior 
damage at the hands of another.  I just consider myself lucky that I found the 
problem now, rather than at 6000 rpm on a track.

So what to do?

Fortunately, I had an idea.  Ford pressure plate bolts are traditionally 
rather puny, 5/16-24 affairs, but Chevys use much meatier 3/8-16 bolts.  I 
phoned ARP's tech department and described my problem; they confirmed that 
the Chevy bolts are about .200" longer too.  The larger diameter coupled with 
greater length should solve all my problems.

So a new set of Chevy bolts and some ARP bolt lube are both on their way.  
Since I don't have access to a drill press, I'm going to take the flywheel 
to a machine shop tomorrow to have them drill out the holes and tap them for 
the 3/8 bolts, which should arrive by tomorrow afternoon.  I figure that 
by the end of the day, I should be in business. :>)

Mike
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