TR2/3/3A Crankshaft crank bolt head[108498]

[HJR]

The bolt head on the crankshaft bolt is so worn on my TR3A that the crank will not engage enough to spin the engine. The crank tries to work itself out of engagement when torque is applied to the bolt head. The bolt is NLA at the American big three. A used bolt may be worn worse than mine. Is there available somewhere the engineering drawing of the bolt head design so that I may rework the head to the original design or better yet a source unknown to me that has this bolt for sale in original design at a reasonable price. I can guess but I do not want to fix the head so it can easily break my arm if the engine should backfire on cranking.
HJR

 

[Geo Hahn]

I have never had to source one -- but I would think most used crank bolts would be in pretty decent shape since few people really use the hand crank for starts (though I do).

Since you're mainly looking for sharp, undamaged edges, a good photo of the part may be enough to gauge it's suitability.

There's one an ebay at the moment -- reasonable I suppose though it included the extension.

TR3 Crank Bolt

I assume you have examined the tip of the hand crank and it looks good.

 

[Crankshaft]

If you're careful to only pull on the compression stroke on starting, and to keep your thumb on the same side of the crank as your fingers, there is not much chance of broken arms, wrists or thumbs.

 

[TR3driver]

Is the guide in place, and the fat part of the crank matches the guide? I'm having a hard time imagining how that bolt could get so badly worn, unless the crank is twisting sideways (which is what the guide should prevent). You're not trying to use something that grabs the flats, are you?

As Geo said, I'd look for a used bolt. I've never seen one with any significant wear. But the surface in question is just a flat cut, should be easy to clean it up. The fore-aft axis is in line with the bolt; the radial axis is offset just enough to match the pins on the hand crank (so the pins rest flat against the flat of the bolt head). Not rocket science here

 

[TexasKnucklehead]

Not to rob the thread, but I failed to initially set my dog bolt orientation properly. While I was repairing the radiator, I remembered to shim it properly -but my shims were not helping as I expected. A club member had a few spare dog bolts -four or five of them. I tried them all, and tightening them, each provided the exact same (wrong) dog orientation. The shims sold come in .015", and (I forget the TPI) but doing the math, one shim would change the orientation by 90 degrees. Two shims would put it back exactly where it started. So, we were confused as to why such a size was chosen. Each of the shims we had from other cars, were .015". So my good friend took some different thickness shim stock and made me some to provide the proper dog bolt angle.

Some of those spare bolts did not have as sharp engagement edges, but any could have been used.

I have yet to hand crank my TR3, but the day is coming...

 

[HJR]

I ordered the bolt on ebay. It looks like it is a little rusty and the head looks much better than mine. I will look on ebay next time first. I do use the hand crank quite a lot and I do not know what buggered up the bolt head so bad. It is very handy for valve clearance adjusting and timing.
Thanks Geo.
HJR

 

[HJR]

Yes, I have adjusted the guide and engine and radiator so it is a straight shot to the bolt head which was not an easy task. The crank is the orighinal crank and is a little rounded on the grips but I think I can fix that without much difficulty.
I guess that some people never use the hand crank since they make a radiator without the hole. Maybe the bolt I am buying from ebay is one of those.
HJR

 

[HJR]

I will try to shim the bolt so the crank is at the right angle on compression. Thanks to all!
HJR

 

[GerryL]

What was the thickness of the shim that was needed to provide the proper orientation? This would be useful, since several different dog bolts had the same orientation? After reading these posts, I realized that the dog bolt was not in proper position. It will have to wait. I recently replaced the radiater and apron. I wish that this post would have appeared prior to the reassembly.

 

[CJD]

It varies with the machining tolerances of the bolt and nose piece. Mine has .010" of shims...but that is meaningless to anyone else...

 

[TR3driver]

but doing the math, one shim would change the orientation by 90 degrees.

I think there might be a mistake in your math. The bolt is 18 tpi, so .0555.. is one full turn, making 90 degrees a bit less than .014". Two .015" shims should effectively move the head by about 14 degrees (194.4).

The shims used to position the timing gear will also affect the shims required for the dog bolt. And I'm guessing that there is some variation in crankshafts as well (hence the need to shim the timing gear).