Chevy 350, stock bottom end, has a cam, heads milled .020. #5 spark plug plugged solid with burnt oil and puffs blue smoke after long idle. Replaced cyl 5 piston rings. Did compression check cyl 1 120 cyl 3 120 cyl 5 170 (new rings) cyl 7 120. 200 miles later #5 plug gummed with oil again and still blue smoke at idle. No smoke when driving down the road. What am I missing? If the rings were installed wrong wouldn't there be low compression in that cyl? Any help is great thanks.

 

Do a leak down test .
https://m.harborfreight.com/cylinder...ter-62595.html

 

120 psi IS low. Especially if the heads were milled down which should increase compression above stock.

My 150k 305 has 190 on every cylinder.

What has been done to the cylinders - you say stock, but has any honing or other work been done?

Valve guides and stem seals?

GD

 

 

Doesn't really tell you anything unless you also determine what is leaking. Rings, exhaust valves, etc.

120 psi is like 70 psi low for a milled head engine.

But regardless a leak down test won't really show if the valve guides are sucking oil and causing plug fouling. It doesn't really indicate ring oil control ability either. You can have excellent compression and have poor oil control from the oil control rings and secondary compression ring not doing their job.

Sounds like it needs a re-ring, valve guides, and stem seals. Regardless of the test results, an oil fouled plug isn't going to get better or be fixed with some mechanic in a bottle. It needs a machine shop for the heads and at least a ring slap. *I* wouldn't hone it - that tends to make the problems worse. If it's that bad it needs to be bored over.

GD

 

How much oil on too of the I take valve is to much oil?

 

I would try to compare the cylinder that is fouling to the others in that respect. You should see some carbon, but it shouldn't be a huge amount. It's hard to quantify "too little" and "too much" from the internet.

GD