Broken bolt for manifold mercruiser

[guuben]

.Yesterday, in curiosity wanted to check, before dissasamblying the manifold bolts for 3.0 Barr mercruiser with 27 ft lbs and result was one broken manifold pinbolt....the closest to riser. %@?#&*%#.
I am very confused: The service manual gives the same torque for all 5 bolts (25 ft lbs) but two of them are pinbolts with fine thread for the nut outside manifold and inside block goes 3 peices 3/8 UNC standard bolts.
Of course they will be much more load on the pinbolt if you use same torque amount on a fine thread than a "standard" thread.
Tried to get out the broken one from block...without succes...Now there is a drilled 7,5 mm 1 inch deep hole in the block and I am not shure how to continue the best way. Suggestions please.
I blaim the manual for the broken bolt and in my world its really stupid to mix fine thread and normal thread on the same item...or, do I been lost in the djungel? To have 2 pinbolts is smart but rest is not.

 

[alldodge]

What year is the motor?

 

[guuben]

I bought the Barr Gm 3.0 motor about 4 years ago but installed it 2 years ago. Its installed as an inboard engine
Into a Scandinavian wooden boat built 1934.
it was not so easy task to get it to fit in to a inboard motor as I thought

Before the "mercruiser" there was a BMW 50 hp diesel, very reliable, but to noisy.

 

[achris]

By 'pinbolts' I assume you mean the studs. If so, it's quite normal to have a mix of studs and screws. You know the mass of the manifold, imagine trying to hold that and a sgasket in place while trying to thread up a couple of screws...

So, on to the torques. The manual calls out different torques for the screws as the studs. I have cut and pasted the section of the manual.....

 

[guuben]

Thanks Acrish...again. interesting that measurement in your manual gives different numbers for outer and inner bolts/studs. My Barr torgue specs was not separated by that !!
Yes, the studs is really helpful to disconnect and reconnect the heavy exhaust manifold. When you have different torque for standard and fine tbreads all makes sense too.
I cant blaim myself for the the broken stud...good to have somebode to blaim on
What is yoir suggestion to go onward...there is now a 7,5 mm...0,3 inch drilled hole. Maybe best to try to make new threads for a 8 mm stud?? There is not so much of iron around that outer stud hole.

But...can you explain whats the idea to have different threads. Why not to have all bolts and studs on the manifold in both ends with UNC threads.

 

[achris]

Are you using a genuine factory manual or an aftermarket (seloc/clymer)?

As for the broken stud, I would try to remove it. Failing that, I guess the next option is an alternative, as you suggested.

Chris

 

[guuben]

For the torque: I used the instruction what came with the manifold from the dealer.
I feel like a fool to not use my own judgement about the torques for inner and outer bolts.By mistakes we learn....by some expenses too.
Matts