B5254T2 and B5254T motor swap confusion?

[miner1no]

So a have a 2006 V70 200K plus miles (autopsy revealed burned an exhaust valve on number 4) vin 59 which reads B5254T on the block and B5254T2 on the timing cover. The serial on the timing cover matches the one on the block, but the motor family number does not. I have a donor motor from a 2009 s60 71k miles. Block and timing cover numbers match and its a B5254T sans the 2, In really sweet shape new turbo and wiring harness attached. I assume this will be fine, but Id like to use the new wiring harness as mine is coating with crud and crumbling wire insulation on the ignition wires, the heat has cracked and hardened the wire insulation.
Will I have issues by swapping out the motor and wiring harness, and why does the V70 engine family number differ on the block and the timing belt cover? Also as a root cause kind of guy, what causes burned valves? I noticed in the autopsy the exhaust cam had a hitch when rotated, felt like somthing in the vvt pulley? Cam not dammaged, burnt valve not bent, although I did not check all the valves. Timing was spot on before taking apart.
This is a great forum I wish I would have found it sooner for other issues. We are on our third volvo

[vtl]

No problems swapping one B5254T2 with another.

Detonation/pre-ignition is one of the major causes for burnt valves. Apparently a lot of reasons for that, but it happens often on simply neglected engines.

High calcium content in oil and high oil consumption is another one: oil burns away, ash resides in cylinders and forms cement-like deposits. They are hard, but brittle. Eventually some chunks chip off and get caught by a valve, between valve face and valve seat. Without cooling through its seat, valve pits and overheats in no matter of time and burns.

It does not help with this engines family that the valve stem seals job is a royal pain in neck, so barely anyone is doing it timely, like every 150k miles or so, before it's too late.

[miner1no]

Ha that makes total sense, it has been burning lots of oil. I assumed it was through the turbo, the throtte body and intake air system was coated with oil, have to check the stem seals to see how they look. Funny how these motors don't smoke much. I had major cement like deposits and on the underside of the valves. You could see how the hardened valve seat material held on for as long as it could while the inner material melted away. The valve had straitions where the melted metal erroded away. Thanks for the tip.

[SchalkwjkM4]

Hello, do this engines share same spec cylinder head gasket?