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Head stud positions
#1
Stripped down a block today, unscrewing the studs a number of them wobbles as they unscrewed initally I thought they had beem bent.However on cleaning the threads with a tap it was apparent some holes had not beeen retapped squarely, to compensate te studs had been bent to an upright position
Cleaning the block face revealed other bodges, 3 of the retapped holes are about half a hole out.
Is there an engineering drawing available that gives the correct position of the studholes so that this can be set up on the mill and the holes redone at the correct centres.
I know I could just measure the holes in a cylinder head, but a proper drawing would be better.
I could just get another block, but most seem to have issues of one sort or another.
Any help greatly appreciated.
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#2
If the block is that bad, you would have to go to 3/8" helicoils/ then make special studs which were 3/8" in the block and 5/16" for the head. Is there enough metal in the block to do this as the O/d is about 0.468" for a BSF threaded helicoil. Because the diameter is increased, you could go BSF instead of traditional BSW in cast iron. Slightly smaller than 3/8 inserts would be to choose 8 or 8.5 mm ones.
It sounds like even the good holes would benefit from being helicoiled back to 5/16" BSW if you are going to this sort of trouble.
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#3
(07-04-2018, 06:42 AM)bob46320 Wrote: If the block is that bad, you would have to go to 3/8" helicoils/ then make special studs which were 3/8" in the block and 5/16" for the head.  Is there enough metal in the block to do this as the O/d is about 0.468" for a BSF threaded helicoil. Because the diameter is increased, you could go BSF instead of traditional BSW in cast iron.  Slightly smaller than 3/8 inserts would be to choose 8 or 8.5 mm ones.
It sounds like even the good holes would benefit from being helicoiled back to 5/16" BSW if you are going to this sort of trouble.

Hi, thanks for comments.I have never seen BSW studs in an A7 block, they are always BSF.
Stepped studs are readily available from our cherished suppliers, 3/8 BSF X 5/16 BSF.

As the holes are off centre I may drill them out oversize off centre, locktite a short length of studding in the hole, then retap to 5/16 BSF in the correct position.

I have Helicoil kits for 1/4 and 5/16 BSF, and 1/4 UNC Timeserts which I use for 1/4 BSW holes.
Just being lazy in asking if a drawing exist, I can work out the position from a cylinder head.
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#4
If the holes are a 1/3rd out of position Gene you're going to struggle.They have probably been drilled by hand,the drill drifting from the tough stud to the softer cast iron.
Going one size larger will only take up 1/32" offset at best and then it will break out the side of your plug and probably move.
The holes between the cylinders are the most important as they can crack into the bores.
On one crankcase ,Sump thread,I had to tap it out to 7/16" Unf (most convenient) Plug it and to tap out 1/4" BSW.
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#5
What you could do, and I know it’s not ideal, is get the studs as close to position as possible using inserts as you suggest and take up the remainder by enlarging the stud holes in the head.
Alan Fairless
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#6
Hi all, I too found a number of bent head studs in my block when I stripped it down. I have no pillar drill etc to put things right so had to do a bodge. I replaced the straight studs and made su.re the head slid on and down them to sit nicely on the block. No gasket at this stage. I removed the head and replaced the first of the effected stud holes with a straight stud. Using the head as a guide I used a rubber hammer to bend the stud to a nice fit. Again checking with the head that it slipped down fully and easily onto the block. I repeated this until all the studs were replaced. I checked the points where the bent studs met the block to see the bent area caused any problems and rubbed each one with some coarse emery cloth. Cleaned it all up and re assembled with no problems.

John Mason
Would you believe it "Her who must be obeyed" refers to my Ruby as the toy.
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#7
(07-04-2018, 02:34 PM)John Mason Wrote: Hi all, I too found a number of bent head studs in my block when I stripped it down. I have no pillar drill etc to put things right so had to do a bodge. I replaced the straight studs and made su.re the head slid on and down them to sit nicely on the block. No gasket at this stage. I removed the head and replaced the first of the effected stud holes with a straight stud. Using the head as a guide I used a rubber hammer to bend the stud to a nice fit. Again checking with the head that it slipped down fully and easily onto the block. I repeated this until all the studs were replaced. I checked the points where the bent studs met the block to see the bent area caused any problems and rubbed each  one with some coarse emery cloth. Cleaned it all up and re assembled with no problems.

John Mason
Hi John, I think Iv’e got your block!
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#8
I woul find another block to use - the clues for impending disaster are all present.
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#9
(10-04-2018, 10:04 AM)Ruairidh Dunford Wrote: I woul find another block to use - the clues for impending disaster are all present.

Rorry, I am surprised at you! Too good to waste, standard size bores, no liners, what more could you want.
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#10
I would be looking for another block - if you don’t see the need, then you should use it.
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