ValveQuestion  By  f4milytime (Read 734 times)

Replace the head Leaky valves cause compression loss

absolutely, depending on his level of experience.It can be a trying experience for a novice to even remove and replacethe valve keepers, and lapping is a "learned" procedure. I figure it would probably be easier and less time consuming to replace the head. They're not that expensive. certainly cheaper than having a shop do it.

valves not sealing can be caused by the following:

1: the exhaust valve operates in a harsh environment due to High temperatures and corrosive fumes blowing across the sealing area of the valve and seat.
A lean mixture raises exhaust gas temps. making it drastically worse.
Long full throttle runs against a load will also push exhaust valve and seat temperatures up.
( both together will give you a you a non-sealing burned exhaust valve and seat in a hurry...)
The intake valve holds up far better due to the intake air helping to cooling it down.
Higher cylinder pressures increase corrosive NOX in the exhaust gases, temperatures and power.
( higher compression ratios and high octane gas at high rpm can add enough "WHEEE!!" factor from the additional power to make the shorter parts life a justifiable expense for some...)

2: worn valve guides allowing the valve head to rock back and forth slightly against the valve seat in the head every time the rocker arm pushes down on the valve stem. ( there's a small side force present also, normally it's taken up in the rocker arm sliding across the valve stem end. ) This can wear the seat oval shaped or cause the valve to wear deeper into the seat on opposite sides leaving the rest of the seat higher which then holds the valve off the worn areas after the rocker arm pressure is fully released.

3: lead in gasoline helps lubricate exhaust valve and seat reducing wear.
Installing hardened steel valve seats is required to run unleaded gas and not wear down the exhaust valve seat too rapidly.
Leaded gas is gone due to EPA requirements.
Adding the lead back with a leaded fuel additive will give longer valve life and create toxic lead pollution...

4. Exhaust valve depends on seating fully on the valve seat over time for cooling.
High rpm causes valve float and the valve may also bounce back open on closing,
both raise valve temp due to reduced time on seat,which can lead to a burned valve and seat.
( fixable with a stiffer valve spring, which will also allow engine to operate at a higher rpm,
but this is a compromise, it gives higher wear on cam lobes, lifters, rocker arms and valve stem tip. still worthwhile for some for more "WHEE!!!" factor...)

5. non-hydraulic lifter engine with too little valve lash clearance. if it even runs, the valves are not getting cooled enough by being fully seated.

Personally, I would say the worst factor leading to burned non-sealing exhaust valves is the factory jetting being slightly too lean at full throttle.
Next would be running a little engine for an extended time totally maxed out when a larger engine running nowhere near maxed out would be a better choice.
( both conditions together will give a burned exhaust valve quickly...)

well looks like ya got a lot of option.....or you could send it to my machine shop and i will give it the works..hate to bid for buisness lol.. any way millsc knows my work..good luck..thanks buford...