Valve Clearances
Discussion
I replaced the head gaskets at the beginning of the year, so had to do the valve clearances
The car has done a fair few track miles since then, as well as several trips to and from Germany
So I decided to check the valve clearances at the weekend and found the weirdest thing
All inlets were 20 thou, and all outlets were 25 thou, except for two that were 20 and 15
I was not expecting that, seems very strange indeed
In both cases they shim came off the valve stem with the bucket, so it wasn't so tight that oil could have been trapped between the valve stem and shim giving a false reading earlier in the year
And anyway, that would have resulted in the clearance increasing, rather than decreasing as the oil escaped
The car has done a fair few track miles since then, as well as several trips to and from Germany
So I decided to check the valve clearances at the weekend and found the weirdest thing
All inlets were 20 thou, and all outlets were 25 thou, except for two that were 20 and 15
I was not expecting that, seems very strange indeed
In both cases they shim came off the valve stem with the bucket, so it wasn't so tight that oil could have been trapped between the valve stem and shim giving a false reading earlier in the year
And anyway, that would have resulted in the clearance increasing, rather than decreasing as the oil escaped
Edited by ukkid35 on Monday 31st July 08:15
gruffalo said:
Stretchy valve stems?
I seem to remember that this was a not uncommon issue with some of the original valves.
Heads were completely rebuilt in 2018, this included new valves/springs/guides/5 angle seatsI seem to remember that this was a not uncommon issue with some of the original valves.
I even re-shimmed the springs so that the spring pressures were equal, which is rarely done
Most engineers are suggesting that it's valve seat wear rather than stem stretch that closes up the shim clearance
ukkid35 said:
Heads were completely rebuilt in 2018, this included new valves/springs/guides/5 angle seats
I even re-shimmed the springs so that the spring pressures were equal, which is rarely done
Most engineers are suggesting that it's valve seat wear rather than stem stretch that closes up the shim clearance
Yeah, that is certainly a factor as well.I even re-shimmed the springs so that the spring pressures were equal, which is rarely done
Most engineers are suggesting that it's valve seat wear rather than stem stretch that closes up the shim clearance
Do you have enough in the shims to get it safely set right?
ususally the exhaust valves are typicall to get seated and hence clearance will be too low.
this rule of thumb is valid for old engines (which were constructed for leaded fuel), as well as for modern engines, which are constructed for unleaded petrol.
valve clearance becomming bigger is due to valve stretch (inlet & exhaust valves) or combustion residues ( exhaust valves).
this rule of thumb is valid for old engines (which were constructed for leaded fuel), as well as for modern engines, which are constructed for unleaded petrol.
valve clearance becomming bigger is due to valve stretch (inlet & exhaust valves) or combustion residues ( exhaust valves).
Gassing Station | Cerbera | Top of Page | What's New | My Stuff