Valve clearances
Valve clearances
Hi,
Am I right in thinking to get an accurate reading of the valve clearances on my V4 heads, the cam belt should be fitted and I should be turning the engine over to do so. Or can this be done purely with the cam's bolted down?.
Thanks for any help.
Am I right in thinking to get an accurate reading of the valve clearances on my V4 heads, the cam belt should be fitted and I should be turning the engine over to do so. Or can this be done purely with the cam's bolted down?.
Thanks for any help.
I normally bench set the clearances before fitting the heads but taking into consideration the clearances each side of the center 2 head bolts/studs will normally close down by approx 0.001".
You can simulate the 'pull of the cam belt' when setting the clearances by lifting up the back of the cam gently with a screwdriver through the half moon cut out's on the back of each head.
Mick
You can simulate the 'pull of the cam belt' when setting the clearances by lifting up the back of the cam gently with a screwdriver through the half moon cut out's on the back of each head.
Mick
Thanks Mick,
I've checked the clearances on both heads, and although on the inlet side there's one maybe 2 which a 0.20mm it would seem 3/4 on both heads are very tight on the exhaust side IE 0.15mm goes OK, 0.20mm won't so its tighter than the spec. Is there anything I could have done during the rebuild to make this happen?.
These are 100k mile heads, original valves, cams etc only the seals have changed. Would they have been this tight, I would have thought they would, if anything, loosen over time.
Should I expect these tolerances to change once the engine has run for a while?.
I've checked the clearances on both heads, and although on the inlet side there's one maybe 2 which a 0.20mm it would seem 3/4 on both heads are very tight on the exhaust side IE 0.15mm goes OK, 0.20mm won't so its tighter than the spec. Is there anything I could have done during the rebuild to make this happen?.
These are 100k mile heads, original valves, cams etc only the seals have changed. Would they have been this tight, I would have thought they would, if anything, loosen over time.
Should I expect these tolerances to change once the engine has run for a while?.
The exhaust clearances close up due to the pounding of the valve face against the seat over the thousands of miles the engine does during its life and causes the valve to stretch and distort, especially on the turbo engine.
As the clearance gets smaller the hot valve cannot transfer heat to the seat to cool itself so you get micro welding/hot spots forming on the seat and valve face - this further reduces the contact area/cooling eventually resulting in a burnt valve.
I''m suprised at your mileage that the exhaust valves and seats are in good condition with no hot spotting or distorsion on the valve heads.
If they are in good condition, just re-shim them (smaller shim needed) to get the correct clearance of 0.008"~0.010" ( 0.203mm~0.254mm ).
Mick
As the clearance gets smaller the hot valve cannot transfer heat to the seat to cool itself so you get micro welding/hot spots forming on the seat and valve face - this further reduces the contact area/cooling eventually resulting in a burnt valve.
I''m suprised at your mileage that the exhaust valves and seats are in good condition with no hot spotting or distorsion on the valve heads.
If they are in good condition, just re-shim them (smaller shim needed) to get the correct clearance of 0.008"~0.010" ( 0.203mm~0.254mm ).
Mick
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