valve stem oil seals

[martin418]

whats the latest thinking on valve stem seals , i had a fully rebuilt head with all new guides valves and unleaded seats inc the latter spring type stem seals on the guides on all 8 valves
i have got the head off after 2000 ish miles for an unrelated problem and just checking it over i found three exhaust valves to be tight and 2 have picked up in the guides + all 4 valves are badly worn on the stems , i am thinking i should i run the o ring seals on the exhaust so they get some oil any thoughts

[philthehill]

In my opinion and experience 'Top hat seals' should not be fitted to the exhaust valve guides.
Neither should the old type 'O' ring seals which are next to useless when fitted.
There is no lubrication in unleaded fuel and therefore leaving off the top hat oil seals (or 'O' ring seals) on the exhaust guides allows some engine oil to progress down the guide so reducing the possibility of the valve stem picking up on the valve guide.
The valve stem should be a loose fit in the valve guide.
The valve stem should drop through the guide without hinderance but not rock in the valve guide excessively.

https://www.calverst.com/technical-info ... and-usage/

[martin418]

i am going down your suggested route ,i have pressed in new guides and with new valves fitted all seams fine

[oliver90owner]

Do you have a valve seat cutting facility? Seats should be recut whenever fitting new guides.

[philthehill]

I agree that it is best to recut the valve seats to the valve guides (easy when you have a leaded head) but as you have unleaded hardened exhaust valve seats you will be unable to cut the valve seats with a valve seat cutter - you must have them ground with the correct shape stone. Get all eight done whilst you are at it.

I personally would give the valve a light grind with valve grinding paste and see what you find. You may be lucky and get away with just lapping the valves and valve seats.
You have nothing to loose and everything to gain.

Phil

[martin418]

all ground in fine , nice even seats