Two things to watch out for:
Make sure the valves are not going to hit the tops of the pistons
especially if you have put in a 1.5 ratio rocker arm, if they do you
will need to relieve the pistons which will drop your CR slightly.
Also if the line boring raised the crankshaft in the block you may end
up with a slack timing chain and have to modify a tensioner from an A+
block to take up the slack (I have not done this but have heard about
it), or install one of the belt drive conversions.
Good luck,
Peter.
>From: GuyWeller@aol.com
>Let me share this with you !
>I set out to discover the compression ratio of my 1275 engine by
measurement
>so that I could decide by how much to skim the head to raise the
compression a
>bit.
>Started with a standard engine, though re-bored to +0.030
>
>The plasticine idea for measuring the cylinder head capacity works well
and is
>easy to do. I reckon it gives an accurate measurement to within at
least
>0.25cc
>Then did all the sums for the extra capacity in the piston tops, gasket
>thickness, etc and to my surprise the ratio works out at 10.5 : 1
Certainly
>as high as I would want to go, possibly even a bit too high. I may
need to
>enlarge the cylinder head capacity a bit just to get it down. I had
planned
>on 9.5 or 10.0 at most.
>
>I was puzzled by this as standard should be 8.8 : 1 I have "cleaned
up" the
>head chambersa bit, which if anything should reduce the ratio. After
some
>thought and checking I realised that the reason it is so high is that
the
>pistons are coming right to the top of the block at TDC, or at least
within
>0.007 of it. I think that in a standard engine they would be perhaps
0.050
>down at TDC.
>
>One of two things has caused this. Either the new pistons are taller
between
>the gudgeon pin and crown (unlikely) , or, and I think this is it, I
had the
>crank journals line bored, and this has effectively raised the center
line of
>the crank nearer to the top of the block.
>
>Anyone "got the T shirt" who can confirm this ? Also with the pistons
that
>close to the top of the block am I likely to get problems ?
>
>Guy
>
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