To me this sounds like leaky rings. https://forums.anandtech.com/threads/rebuilt-engine-with-low-compression.2456881/ seems to cover this and more.
You seem to have the head and valves covered but what was done on the block? Sometimes folk just pop in new rings and cylinders but it needs a bore job.
Hi, I own a chevrolet optra 2007 with 200.000 KM,
I did an engine rebuild & yesterday did a compression test to check the work done & found out it was low on compression on all cylinders.
- Cyl #1 135
- Cyl #2 75
- Cyl #3 135
- Cyl #4 65
We did a wet & dry test, after adding the oil I got:
- Cyl #2 100
- Cyl #4 90
What I bought:
- New Pistons & Rings
- 10 new valves (they were broken because timing belt went off). 5 intake valves & 5 exhaust valves. The other 6 were ok and were used again.
- 8 Guides for exhaust valves, mech told me only 4 exhaust guide valves were bad, but decided to change all of them instead because I got the set of 8 guides.
- Head Gasket
- Valve Seals
- Oil Pump
- Water Pump
- Timing Belt
The valves job were done by a professional, and I still I got these results.
Mech thinks theres a problem with the cam / valves, but from what I read it seems more likely the piston rings are at fault because of the results I got after the wet test.
Mech wants to take down the cam and have it checked again & mount it again to re-check the compression.
Mech says that it if were pistong rigs, the wet test results would be WAY higher.
I don´t really want to buy a new head gasket & valve seals & have the valves job done again....for nothing :/
If it doesn´t work, mech would have to take it all down again to check the piston rings & I would have to buy the head gasket & valve seals again....meaning more money....
With these wet and test results, what do you guys think? What would you ask the mech to do?
Any help will be really appreciated!!!