[Fot] TR4 ARP Flywheel Bolts Question

Wed Jun 7 13:05:45 MDT 2017

Lots of interesting discussion here.  This may surprise some of you, but my experience shows that the Factory knew what they were doing when they were designing the flywheel connection to the crankshaft.
Early in my career, racing a TR-4A (SCCA D Production, then moved to E Production) I sheared off flywheel bolts on a number of occasions, and each time, I tried to figure out the cause of the failure.  Understanding the causes of these failures, and with suggestions from other TR racers, here is the combination I came up with, which I used for the last 17 years I raced.  And, of course, this was the time during which I was producing the most HP and turning the lowest lap times (thus more strain on this connection).
First, I had 2 flywheel dowel holes drilled.  By that time, I was using a Tilton aluminum flywheel and dual disk racing clutch.  The stock crankshaft had 2 dowel holes, but for whatever reason, they only used one dowel.  The stock flywheel came with 2 dowel holes drilled, but they were only 90 dewgrees apart, and they didn't go all the way through the flywheel, and they only used 1 dowel.  I don't recall if the Tilton flywheel came with 2 dowel holes, or if I had to have a second one drilled 180 degrees from the first one.  So, I installed dowels in both dowel holes in the stock crankshaft.  I found some longer dowels that would go to the seat at the bottom of the crankshaft holes, all the way through the flywheel, and still leave about 1/8" sticking out on the flywheel side.  Next is very important!!!  I installed the stock lock tabs, such that the tabs covered the ends of the dowels sticking out.  This kept the dowels from backing out, in addition to keeping the bolts from loosening up.  As a back-up, I also used blue loc-tite on the stock bolts.  In fact, I never purchased a new flywheel bolt.  I had enough used bolts laying around that I just picked out 4 that looked good (threads, wear on the shoulder, etc.), had them magnafluxed, and they were good to go.  Never broke one using this procedure.  I used the factory recommended torque spec.
I know this sounds pretty simple, and it doesn't involve spending a lot of money on expensive parts, but it worked for me.  There may be better options out there, but my concern was always to find something that worked, no matter what part of the car I was working on.  Then "if it ain't broke, don't fix it".  This approach worked for me for a long time.
Footnote:  The last time I sheared off a flywheel was at The Runoffs in 1980 (my first year at The Runoffs).  Turns out I had installed the lock tabs 90 degrees off from where they should have been.  Without the lock tabs to secure them, the dowels backed out, which eventually allowed the connection to loosen up and sheared off the bolts, spinning the engine to 8,500 RPM's (coming down the back straightaway).  This necessitated a change to a back-up engine.  With the approach described above, I never sheared off another flywheel.

Good luck, and I hope you all find a solution that works for you.
Jack

On Wednesday, June 7, 2017, 1:50:57 PM EDT, timmmurphh--- via Fot <fot at autox.team.net> wrote:

Is there a shorter (3/4 inch) 3/8-20 bolt that could be used for the flywheel that you know of?

Tim

From: Fot [mailto:fot-bounces at autox.team.net] On Behalf Of Robert Deanes via Fot
Sent: Tuesday, June 6, 2017 10:42 AM
To: Barr, Scott <sbarr at mccarty-law.com>
Cc: FOT <fot at autox.team.net>
Subject: Re: [Fot] TR4 ARP Flywheel Bolts Question

the shorter ARP bolts are 350-2802.....you don't have to grind the end of the bolt

On Mon, Jun 5, 2017 at 4:36 PM, Barr, Scott via Fot <fot at autox.team.net> wrote:

<< Don't you guys use steel inserts in those flywheel holes? >>

Nope – I’ve always used them as supplied.  And so long as I remembered to check the clearance for the radius under the head, it’s been fine.  Frankly, I always wondered about why it was OK to torque the flywheel bolts down onto a relatively soft aluminum flywheel, but bad to use a steel washer – which was almost certainly harder.  But I’ve always used Loctite on the flywheel bolts: mostly red, though sometimes blue.

Scott (B.)

From: Scott Janzen [mailto:sjanzen at me.com] 
Sent: Monday, June 05, 2017 3:28 PM
To: Barr, Scott <sbarr at McCarty-Law.com>
Cc: timmmurphh at gmail.com; Steve Yott <tr4 at wi.rr.com>; STEPHEN BOROWSKI <biznzman at pacbell.net>; FOT <fot at autox.team.net>
Subject: Re: [Fot] TR4 ARP Flywheel Bolts Question

Don't you guys use steel inserts in those flywheel holes?

Sent from my iPhone

On Jun 5, 2017, at 7:55 AM, Barr, Scott via Fot <fot at autox.team.net> wrote:

This is what it looks like if you forget to chamfer the flywheel holes to clear the radius under the head. 

<image001.jpg>

From: Fot [mailto:fot-bounces at autox.team.net] On Behalf Of timmmurphh--- via Fot
Sent: Sunday, June 04, 2017 5:53 PM
To: 'Steve Yott' <tr4 at wi.rr.com>; 'STEPHEN BOROWSKI' <biznzman at pacbell.net>; fot at autox.team.net
Subject: Re: [Fot] TR4 ARP Flywheel Bolts Question

Thanks for the clarification Steve, that makes sense.

Tim

From: Steve Yott [mailto:tr4 at wi.rr.com] 
Sent: Sunday, June 4, 2017 4:56 PM
To: timmmurphh at gmail.com; 'STEPHEN BOROWSKI' <biznzman at pacbell.net>
Subject: RE: [Fot] TR4 ARP Flywheel Bolts Question

The reason they state to not use washers is they are afraid that the washers used will (1) not be hard enough and will compress under the bolt head and (2) all ARP bolts have very liberal radii between the head and shank.  If there is a tight fitting washer this would be strain on this radius and could break the head.

The 7/16” ARP bolts used on Chevy flywheels is what I fit to TR’6, late Spitfires and modified TR4 cranks.  These bolts come with the special washers to use with them.  I have used a proper washer under the 3/8” ARP bolts many times with no problems using a correct washer.  You can also use an ARP crown wheel bolt for the same purpose and these come with proper washers.

Steve Yott  

From: Fot [mailto:fot-bounces at autox.team.net] On Behalf Of timmmurphh--- via Fot
Sent: Sunday, June 04, 2017 1:59 PM
To: 'STEPHEN BOROWSKI' <biznzman at pacbell.net>; fot at autox.team.net
Subject: Re: [Fot] TR4 ARP Flywheel Bolts Question

FWIW

I just got a set of ARP 206-2802 flywheel bolts from Pegasus for the TR4.  They are for “BMC A series”.  The instruction specifically says, “DO NOT USE ANY WAHERS”, yes, all in caps for emphasis!  They further state that ARP will not be responsible for failures is washers are used.  The instructions also say, “Make sure there is an adequate chamfer under the bolt holes on the flywheel to clear the radius under the head of the bolt.”  Torque is 55 Ft-Lb with specified lubricants on the threads.

I’ve never had that much good luck grinding the ends of bolts and still having it square so as not to start it cocked and runing the female threads.  Maybe it’s just me😊

Tim

From: Fot [mailto:fot-bounces at autox.team.net] On Behalf Of STEPHEN BOROWSKI via Fot
Sent: Friday, June 2, 2017 3:28 PM
To: FOT List <fot at autox.team.net>
Subject: [Fot] TR4 ARP Flywheel Bolts Question

Does anyone have experience using the ARP flywheel bolts sold by Moss and others?

I understand that you may have to shorten the bolt or it breaks the rear seal???

Are they supposed to have a washer or not?

Thxs. Steve

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rob deanes

TR Racer
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