This is what confused me slightly. When someone refers to nominal torque, they are usually referring to the rated torque at a given RPM range. You were asking if you think that it's possible that you reduced the nominal torque by an excess of oil. A couple months ago, I was pondering whether or not a higher compression ratio (given via the 351) would increase the torque values for the bolts in the head. A few members corrected my thinking and I found out that increasing the compression ratio does not effect the torque values.

I was saying that no, I don't think the torque is affected by an excess of fresh oil.

 

I thought he was talking about oil on the bolt shoulders resulting in reduced friction and therefore excess torque on the bolts, not torque of the motor. ???

Anyway, I once stripped out the oil drain bolt of a bike by using 60 N-m of torque on it - that's almost rear wheel axle torque! I was using the correct torque, but just on the wrong bolt. I thought I was on the *frame*/motor mount bolt that was right beside it. It was my mistake of course, right torque, wrong bolt, a case of not paying enough attention and mistaken identity, I mean, they were only an inch apart from each other down there, were the same size bolt head of course, and it was kind of dark. That ended up being a $1,200 mistake, by the time the cases were split, and the crack in the case made by stripping the drain bolt was expertly welded and repaired, and it was all put back together at $70/hour shop labor. Lesson learned the hard way.

Anyway, are you 100% positive you didn't have your torque wrench set for the higher torque value of the cylinder head bolts, and maybe just made a simple mistake and put it on the lower torque flange bolts without resetting it?

Otherwise, one might conclude it's the result of a casting flaw in your cylinder flange, but then, how was it torqued properly when it was first assembled without it doing the same thing?

Just a thought. Sorry for your trouble. Looks like welding might be the best option unless you can find a replacement cheap. At least you don't have to split the cases to repair the damage like I did.

 

I was talking about reduced friction.
About the resetting - I am positive that wrench was on Nm scale and had 12Nm for that bolt. I do mistakes but not like this coz I know the consequences quite well. There are few things that I can blame - wrench was on old batteries and I changed them without switching it off. I tried to repeat the experiment just opening/closing battery compartment but couldnt get wrong readings. Bolts and head were very oily. Could be the reason? I dont know. I must admit that it is a first time when I was working on partially opened engine. I done quite few rebuilds but all engines were completely stripped down and degreased. Never had this problem before. Flaw in casting - mmm even harder to check. I hope that head could be welded. If not - maybe I can just do not use this bolt at all hoping that its not gonna leak. One of the inmates from the forum said that he has spare head - its the best option. If nothing will work - I gonna spend my days googling the internet in search of the spare head

 

Sucks dude. I'm gonna say it was over-torqued before you took it apart, and the crack had already started... Or the head was improperly cast and there was an foreign inclusion in the alloy...

 

I would try to get it welded , and fixed right, BUT I think you could run it without that bolt. Definitely not the right way to do it, bu, to me, it doesn't look like that bolt holds too much. You would really have to keep an eye on it.
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Dan