Leak down test - position of piston?

[alanscottj]

Whilst doing a leak test where should the piston be? Bottom or top DC? I'm sure it should be bottom but I'm just checking!

Thanks

[Darrell Taylor]

rotate the crank during a test as can reveal a crank seal problem twisted crankissue etc .

[alanscottj]

rotate the crank during a test as can reveal a crank seal problem twisted crankissue etc .

Thanks Darrell, and as I do this, am I aiming to have no pressure drop whatsoever? How long should the engine hold pressure? Do I leave it pressurised, over night, an hour, ten minutes?

Many thanks

Scott

[Darrell Taylor]

you may see a slight change if air is distributed to where it was previously trapped but most gets past regardless of position as fuel/oil and running pressures form the seal when running so when static tested on bench the air distributes well after one rotation the pressure at that point remains the same if no leaks are present

[alanscottj]

you may see a slight change if air is distributed to where it was previously trapped but most gets past regardless of position as fuel/oil and running pressures form the seal when running so when static tested on bench the air distributes well after one rotation the pressure at that point remains the same if no leaks are present

Thanks Darrell, tested this afternoon. Pressurised up to 6psi, rotated the piston twice, needle twitched slightly as I turned but pressure remained at 6. Didn't do it a third time for fear of blowing a seal (no seal jokes please!).

Many thanks - another engine building lesson over for me

Scott