general tech advice sought

[cyrusgsxr]

?

Hi all my queastion is very simple , when rebuilding an engine that is circa 20 years old , whilst replacing the valves is it advisable to lap the valves with grinding paste as i did , ive heard tales that this will destroy the special coatings on the valve seating surface and leads to premature wear

then again i was taught that it was necissary to do this to attain a good seal ?

would love to hear some proven technical accounts on this subject engine in question is a mere 350 sub 33hp so by no means high performance, thanks too all who can help

[ForsheeMS]

Lapping steel valves does not cause any problems. By lapping them all you are doing is matching the mating surfaces of the valve and the valve seat to each other creating a beter valve seal. If the valves in your engine are steel then you have done no harm.

Lapping titanium valves is definitely not a good idea as they have a coating that can be damaged by lapping thus greatly reducing the life of the valve.

[cyrusgsxr]

is there any easy way to determine whether the valves are titanium or steel ?

[ForsheeMS]

My guess is in a 20 year old engine they are steel. A magnet will not stick to titanium however that is also the case with some steel valves as well such as a low carbon stainless.

[cyrusgsxr]

Thanks for the help Forshee i still have the old valves in the garage will give that a try and see if its magnetic

[Fixitguy74]

It depends on the brand, but some manufactures say not to use lapping compound. Most steel valves for bikes have a stellite coating that is harder than steel and allows longer life between replacement. So lapping them in will wear this coating some and they will wear quicker. If you reface the valve seats properly with a cutter tool like Neway offers, then there is no need for lapping. http://www.newaymfg.com/frame.htm