Topic: Shot in the chest!

[camelman]

My engine just shot me!  I was reassembling when one of the crankshaft bolts failed. It launched out of the case and hit me a few feet away. Is this at all normal?  Should I replace crankshaft bolts, or can I reuse them?  This is on a 400f. The first time I pulled the engine apart the bolts were locked down pretty tightly. I wonder if I overstressed them on removal.

Camelman

[camelman]

Bueller?

What was so strange about the bolt failing is that I had not touched it for five minutes or so.  It just snapped and shot out.  So, just curious if there is an issue reusing crankshaft bolts.

Thanks,
Camelman

[nayto550]

Personally, I would normally reuse them.  But this doesn't seem to be normal circumstances.  If one failed in such a manner, it probably would be prudent to replace all of them.  Cheap insurance against failure further down (on) the road.

[Gaither]

Well, if it had to happen, the timing couldn't have been better.

If it had been me, it would have broken somewhere after the rebuild at around 5,000 rpm in heavy traffic on the road.

[bryanj]

What exactly do you mean by crankshaft bolts?

[crazypj]

I think he means con-rod bolts?
 You are using a torque wrench and not the 'German' method?
 (Gutentite) 
 Usually the bolts can be re-used several times, if you over torque them they will only stretch so far, break when they settle and try to unwind.
You did oil them before fitting?
 What was the temperature?
 If they were 'warm' from handling and tried to 'shrink' when they cooled down it will overstress and break something

[fire113]

...what is the "German" method ?

[bollingball]

(Gutentite) (good an tite) get it

[Gaucho]

I thought that that's how you said "virgin" in German.
Gaucho

[camelman]

I follow the book when I do these. Grease the threads, use a torque wrench, torque down in three or four steps and everything was at the same temp. The bolt must have just been overstressed during removal. I had three snap off and the others were tight. I looked at the fracture surface and a full quarter of a thread ring had snapped off with the remaining OD showing torsional yielding. It appears that a crack formed at some point that compromised that specific thread. Glad I had an extra set of bolts.

Thanks for the feedback.

[crazypj]

I thought that that's how you said "virgin" in German.
Gaucho

 Nope, thats titenairy

[paulages]

I think he's referring to the 12 bolts that hold the cases together at the crankshaft... I'd call these crankshaft bolts.

Anyway, I'd suspect your torque wrench. It seems unlikely that you'd have failure on several unless you are over-torquing due to an poorly calibrated torque wrench.

[camelman]

They failed when I removed them.  I snapped three off just below level with the threaded hole, and a couple on the top of the case failed too.  They were so corroded in there I couldn't even remove them!
I did learn a cool trick to extract the remains though.  First, i tried a mill with a wobbly head... bad idea.  Then I took them to a welder who ground the free part of the bolt to a somewhat pointy end and welded it onto the portion that was still in the hole.  The heat of welding helps loosen the remaining threads too.  Absolutely no damage to the aluminum, and the remainder of the bolt just unscrewed.  This guy's been doing it for decades with no adverse affects that he's noticed.  Pretty neat trick, although I imagine that if you put too much heat into the case, you could mess it up pretty quickly.

Camelman

[paulages]

I've freed many a frozen bolt by sticking the whole part in the oven for an hour at 200°F for an hour or so. Copious amounts of penetrant before and after the oven helps.