19 replies to this topic

[MRA]

it is caused by the pistons travel, ie. the vector angle caused by the force acting on the piston due to crank rotation............ draw it side on and plot the conrod and piston assembly at various crank angles and you will see a definate direction towards the bore wall, this is so for any engine.

However it is worse on some than others, for instance two identical A series engines but with different lengths of conrod, the engine with the longer conrods would see a lower vector force acting on the bore walls, therefore more power to the wheels

What you are seeing is the thrust of the piston on the power stroke, this is the early stages of "bedding in" or accelerated stages if it has been thrashed...... but either way this is where you will and are seeing the "initial wear" or bedding in of your engine.

the score marks, could be down to a bit of grit, did it have an air filter fitted at all times ?

it could be down to incorrectly fitted or damaged rings ok but these may now have bedded in and may never cause any other issues....

Offset boring has been done on thousands of 1275 blocks it's 10 thousandths of 1 inch about 0.25mm its going to have so little difference to your thrust forces.

5.75/0.010 = 575:1 ........... oh and 0.010 is the tolerance for the bore on an A series engine, so you could find it is already offset bored before you even start......

[Dan16v]

it is caused by the pistons travel, ie. the vector angle caused by the force acting on the piston due to crank rotation............ draw it side on and plot the conrod and piston assembly at various crank angles and you will see a definate direction towards the bore wall, this is so for any engine.

However it is worse on some than others, for instance two identical A series engines but with different lengths of conrod, the engine with the longer conrods would see a lower vector force acting on the bore walls, therefore more power to the wheels

What you are seeing is the thrust of the piston on the power stroke, this is the early stages of "bedding in" or accelerated stages if it has been thrashed...... but either way this is where you will and are seeing the "initial wear" or bedding in of your engine.

the score marks, could be down to a bit of grit, did it have an air filter fitted at all times ?

it could be down to incorrectly fitted or damaged rings ok but these may now have bedded in and may never cause any other issues....

Offset boring has been done on thousands of 1275 blocks it's 10 thousandths of 1 inch about 0.25mm its going to have so little difference to your thrust forces.

5.75/0.010 = 575:1 ........... oh and 0.010 is the tolerance for the bore on an A series engine, so you could find it is already offset bored before you even start......

Thanks mra-minis,

Yes I belive an airfilter has been fitted at all times, it could quite posibly be the rings as there are two similar lines that you can see but cant feel to the left and right of the score mark. Would damaged rings show up on a compression test? all the cylinders were within 5psi of each other.

I suspect if your not careful im sure its easy to get a little bit of grit in there that marks the bore on first start-up of the engine.

[MRA]

without seeing the damage, it's a little like groping in the dark...., If the compression test was 5psi maximum deviation then that is good.... especially as this about 2.5% deviation.

Ok list the cylinder pressure readings from cylinder to cylinder.... and if the lowest one is the same one with the scores then it may be an issue that is waiting to happen.

[Dan16v]

without seeing the damage, it's a little like groping in the dark...., If the compression test was 5psi maximum deviation then that is good.... especially as this about 2.5% deviation.

Ok list the cylinder pressure readings from cylinder to cylinder.... and if the lowest one is the same one with the scores then it may be an issue that is waiting to happen.

Stupidly I didnt write them down, but Im fairly certain the bore with the score mark was the 2nd highest figure.

I might try and negotiate on price and take a chance that it will run ok for a while, and posibly swap the block and rings at some point down the line.

Cheers for everyones help

[MRA]

Seems fair to me, good luck with your engine