Lapping vs Cutting Valves

HondaDustR

Redline Racer

Join Date: Jan 2007

Posts: 2,444

Quote:

cvriv.charles

Originally Posted by

. .

Eh I would check the valves to see if they are worn first. If not then lap them. I would even lap new valves. Think of lapping as "fine tuning" or "fine fitting". .

Less than perfect seats and valves need the coarse paste so you're not lapping for 20 years, but finish with the fine grit if you do. You're looking for a smooth, even strip around the seat and valve that's free of surface defects. If there's deep pitting, the valve seat contact width or valve margin is out of spec, or you cannot obtain an even contact that seals, then you'll need to have the seats cut and most likely new valves installed. Carb cleaner or WD-40 works better for checking the seal since it will creep through smaller gaps than water.

This obviously will not work well with worn out guides, since they provide the stability needed for a precisely matched grind. Well, worn out guides suck even if you could get a good seal since the valve will just ratlle around and wear the seat out funny again. Check your guides, especially the exhaust. New guides require the valve seats to be re-cut.

Compression = power!

Couldn't agree more. It really rejuvinates the seal of used but good valvetrain pretty well and can remove minor pitting with patience. Just be very anal about keeping the grinding paste off the valve stem. Also, do not use the permatex water based paste that comes in a tube at auto stores. Too thin and too coarse. Get some good stuff like this Clover Lapping Compound - 120 Grit & 280 Grit - 2 oz Less than perfect seats and valves need the coarse paste so you're not lapping for 20 years, but finish with the fine grit if you do. You're looking for a smooth, even strip around the seat and valve that's free of surface defects. If there's deep pitting, the valve seat contact width or valve margin is out of spec, or you cannot obtain an even contact that seals, then you'll need to have the seats cut and most likely new valves installed. Carb cleaner or WD-40 works better for checking the seal since it will creep through smaller gaps than water.This obviously will not work well with worn out guides, since they provide the stability needed for a precisely matched grind. Well, worn out guides suck even if you could get a good seal since the valve will just ratlle around and wear the seat out funny again. Check your guides, especially the exhaust. New guides require the valve seats to be re-cut.Compression = power!

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Last edited by HondaDustR; 02-10-2010 at

10:02 AM

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