[Fot] Center main support

Sun Nov 24 17:57:45 MST 2019

Chris:  That is exactly how we built the roller bearing crank half's for our two stroke GP bikes... well placed blows with a brass hammer and in an hour or so you end up with a straight crank

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On Nov 24, 2019, at 6:27 PM, Chris Marx via Fot <fot at autox.team.net> wrote:

Hi Phil,

If I give a crank to the machine shop for testing and maybe polishing they also correcting straightness.
They using a hammer and a wedge like tool with brass or bronze surface and giving it a big blow at some places to make it straight.
They also checking with magna flux system for cracks.

I run 0.0027” main bearing clearance.

For sure Kas throw in is right. I keep the revs below 6k with the standard crank.
Many people going up to 7k with their engines but I don’t dare. A billet crank might help a little but I saw billet cranks breaking too.

Engine power is not my main concern. Cornering speed is.

Cheers
Chris

Von: Fot <fot-bounces at autox.team.net> Im Auftrag von Phil Gott via Fot
Gesendet: Sonntag, 24. November 2019 22:03
An: Friends Of Triumph <fot at autox.team.net>
Betreff: Re: [Fot] Center main support

Interesting, Chris:
My machine shop said that .002” run out at the center main, with the crank supported and spun on numbers 1 and 3 was a sign that it was developing high levels of internal stress (work hardening) and that it should be retired. They aim for 0 run out under these conditions. Based on what you’ve said, I wonder if they are being overly cautious. As they do not grind cranks themselves ( only polishing and balancing), they had little to gain from that diagnosis.
Thanks for the input.
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On Nov 24, 2019, at 9:26 AM, Tony Drews <tony at tonydrews.com<mailto:tony at tonydrews.com>> wrote:

Wow!  It's very nicely done.  Certainly overkill.

Regards, Tony
On 11/23/2019 9:11 PM, Phil Gott wrote:
Here are some photos:
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<image1.jpeg>

<image2.jpeg>

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On Nov 23, 2019, at 12:23 PM, Tony Drews <tony at tonydrews.com><mailto:tony at tonydrews.com> wrote:

I agree, that sounds like overkill.  Mine only requires the top of the cap to be machined flat, no other block mods.

Regards, Tony
On 11/23/2019 5:42 AM, Phil Gott wrote:
Thanks again, Tony:
The one we have, built by the late Bill  Throop, in addition to reinforcing the cap itself, has the block machined internally to accept the sides of a strap, then the strap  is cross bolted from the sides, through the block from outside.  I’m wondering if this is a bit of overkill. Based on your recommendation, it seems to be.
Maybe I can send some pictures later today, as we are pulling the engine today for other work.
Phil
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On Nov 22, 2019, at 10:56 PM, Tony Drews <tony at tonydrews.com><mailto:tony at tonydrews.com> wrote:

I run that setup, it was an uncle jack trick.  Here's what he wrote about that (on my engine building tips page):

"I also like to strap the center main to add rigidity to the bottom end.  To do this, mill off the cast face of the main flush with the surfaces for the head bolts. Get a front strap for a Chevy 400 block. You must enlarge the holes in the strap  and you must use longer bolts.  Some  builders feel that this is totally unnecessary, but since starting to do this, I have never had a main bearing deteriorate faster than a rod bearing, which is something that happens more frequently than you would expect."
Regards, Tony Drews

On 11/22/2019 3:58 PM, Phil Gott via Fot wrote:

Has anyone seen the need to add extra support to the center main on the TR wet sleeve engine? We have an engine that has a steel bridge cross-bolted underneath and supporting the center main cap. Is this needed? Just took 3 factory cranks to the machine shop and all three were bent about .002 in (.002 run out at center main when supported on first and last mains.) Two of these were raced, the third was removed from a tired street engine. note: None of these cranks came out of the engine with extra support at the center.

Curious as to the need for the extra support.

Thanks,

Phil Gott

114 TR4A

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