serega

Here's a pickle - cylinders 3 and 4 show 30 and 50% loss at TDC respectively, but once we rotate the crank 45 degrees, both cylinders loss drops to around 10%, how is that possible ? I thought the valves are closed at TDC and either an intake or exhaust valve opens as the piston moves down, so how can my leak decrease as we rotate the crank 45 degrees ?

I know there is a case for wrong measurement, but it's the second time that i'am measuring my compression at two different shops and they arrive at similar results.

The shop has also told me that they hear hissing noise from the oil fillup area.

The block was split open a few months back to check for clearances and was given a clean bill of health, despite requiring about 500ml of oil every 1000 miles ( which was the cause for concern that made me measure my compression and do a leakdown which showed similar numbers to this later test)

As i was a little low on cash after splitting the block, i couldnt afford checking the heads for bent valves and since the block was fine i decided to put it back together and take it easy untill i had some cash. So recently i took it to a different shop to check for compression and do a leak test and after the same results were announced they proclaimed that it were either the piston rings or sleeves that needed new a re-bore and wouldnt hear anything about my bent valve idea, they keep insisting that the first shop just couldnt measure things properly and it's pointless to even open the heads.



Any ideas what i could do here to clear things up, or what do you think could be at fault here ? Help!

Graham1998

Are you sure you are checking leak down at TDC on the compression stroke on both cylinders.
At TDC on exhaust and intake stokes valves will be open so leakdownwill be high.

merlin24

iTrader: (1)

What marks/reference point are you using for finding TDC ?

Mick

serega

To be honest, I'm not exactly sure how they are measuring it, however, they managed to measure the leakage in first two cylinders the same way, which showed a normal leakage of 5-10%.

Iam unfamiliar with the exact procedure, despite reading a few notes of research, so I am unable to provide any exact information regarding their measurements. I would probably be sceptical about their numbers, if it werent for the fact that the resulting leakage is consistent with what the previous shop measured and both shops are very respectable.

So how can I, having very little mechanical knowledge and never having built an engine in my life, question and double check what they are doing and is there any point in it ?

WMS

iTrader: (2)

Get a compression test done, this tests cylinder pressures while cranking the engine over.