Rod knock/bent valves question

[nisileighty]

I’m not sure if this belongs in the small questions thread, but I’m at a dilemma.

I’m fixing a 2006 Altima QR25 which was ran with low oil and spun a bearing. Upon removing the cylinder head to see if it was salvageable, I did a pressure test to test the valves and it lost pressure/valves were leaking. There was no visible bent valves, but the air was definitely coming through.

Now my question, if a rod bearing is spun or he connecting rod it loose, is it possible that it could bend a valve? At first I thought yes, reason being that there’s now extra room for the rod/piston to move up and down while the crank is still in its normal position, but then I realized that the compression of the air would still be pushing the piston downwards away from the valves.

Feel free to say your opinion! I’m interested to see what’s up with this thing.

[Kingtal0n]

if you are sure it spun a bearing/has an oil related issue,

why are you looking under the head?

dude it sounds like a mess honestly if a next engine is like 50% of the cost of the car or less just go next

[nisileighty]

if you are sure it spun a bearing/has an oil related issue,

why are you looking under the head?

dude it sounds like a mess honestly if a next engine is like 50% of the cost of the car or less just go next



Would like to see if the head is still useable to sell or use for another motor

[mr.nismo.]

The only reason the valves and Pistons would hit would be if the motor went out of time (chain jump, break) , conrod/wrist pin break within the upper part of the cylinder, or a valve dropped/floated. Either way, you would very clearly see damage to the top of the Piston itself, and the bent valve. A spun bearing is just that, a spun bearing. Get the crank checked for clearance. If you're lucky, it will just need a micropolish. As for the head, the valve seat will need to be regrounded, and subsequent valve replaced. It won't be too bad if you get a decent machine shop priced.

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[kyral]

a little extra play in the rods wouldnt cause the pistons to contact the valves