25-11-2019, 03:15 PM
Hi Roger,
On 2-bearing engines it is fairly common practice to ensure the piston crowns on cylinders 2 & 3 are 10 or 20 thou below the block face, this protects against the pistons touching the head in case of a missed gear / excessive rpm (crankshaft whip). I can't quite follow what has been done by you and what by others, but is it possible someone else has set the piston crown height for you with this in mind?
The normal way to correct is by skimming the piston crowns, they should tolerate 20 thou or so off, depending on what you are using for pistons of course.
Otherwise if a lot has been skimmed off the block a shim or spacer can be inserted under the block to bring it up to height again, some of our 'cherished suppliers' sell the necessary shims in 20 or 30 thou thickness.
I'm afraid I can only guess where your height disparity comes from, but it may be worth having a conversation with the person who did the work. I take it you have white metalled rods? Otherwise I cannot imagine the rod lengths centre to centre could differ unless something is badly adrift. Is the crankshaft straight?
At any rate, the pistons 'must' be arranged to lie below the deck at tdc under all ordinary circumstances.
p.s. you did check it with a gasket in place, didn't you?
On 2-bearing engines it is fairly common practice to ensure the piston crowns on cylinders 2 & 3 are 10 or 20 thou below the block face, this protects against the pistons touching the head in case of a missed gear / excessive rpm (crankshaft whip). I can't quite follow what has been done by you and what by others, but is it possible someone else has set the piston crown height for you with this in mind?
The normal way to correct is by skimming the piston crowns, they should tolerate 20 thou or so off, depending on what you are using for pistons of course.
Otherwise if a lot has been skimmed off the block a shim or spacer can be inserted under the block to bring it up to height again, some of our 'cherished suppliers' sell the necessary shims in 20 or 30 thou thickness.
I'm afraid I can only guess where your height disparity comes from, but it may be worth having a conversation with the person who did the work. I take it you have white metalled rods? Otherwise I cannot imagine the rod lengths centre to centre could differ unless something is badly adrift. Is the crankshaft straight?
At any rate, the pistons 'must' be arranged to lie below the deck at tdc under all ordinary circumstances.
p.s. you did check it with a gasket in place, didn't you?