boogalou1 Posted March 12, 2009 Share Posted March 12, 2009 I'm in the process of rebuilding my heads and just ordered some Sealed Power valves and having my valve seats reground. I've read conflicting information on the internet concerning whether the new valves need to be lapped or not. Any ideas or advice would be appreciated. Quote Link to comment Share on other sites More sharing options...
Nismopowered Posted March 12, 2009 Share Posted March 12, 2009 I would say lap them. You are matching the new valve to the seat so they seal. Quote Link to comment Share on other sites More sharing options...
jasper Posted March 12, 2009 Share Posted March 12, 2009 I wouldn't jump to lapping. Some valves may be coated. Face or surface hardening could be an issue. I would do some research. Back in the 50's 60's70's, valves got laped. Things have changed CONSIDERABLY. Do some homework from reliable sources..not opinions.....I'm interested in the outcome. Quote Link to comment Share on other sites More sharing options...
MONGO510 Posted March 12, 2009 Share Posted March 12, 2009 Lap them! You can only improve the seal. Quote Link to comment Share on other sites More sharing options...
1 fast z Posted March 12, 2009 Share Posted March 12, 2009 I would Use Prussion Blue to see how wide the seat is on the valve, and where it is seating. Your machinest that did the valve job should not have done this without the valves. Quote Link to comment Share on other sites More sharing options...
Careless Posted March 16, 2009 Share Posted March 16, 2009 Nissan had their valve seats polished on the vg30 heads from factory, but they get pitted over time. I hand lapped them and was comfortable running them with the brushed/sanded look they leave... but I took it a step further and lapped again with polishing compound until I had a near mirror finish. just did a compression test yesterday, and on a 21 year old engine with no bottom end work (just did headgaskets and valve seals) she made 150psi across every cylinder, exactly. no more, no less, no leaking over 1 minute (not accurate for a leakdown test, i know). not bad for a motor with 223,000 km on it that's been sitting for 7 months. that was a cold test too. just something to think about. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted March 16, 2009 Share Posted March 16, 2009 Typically a shop will vacuum test the ports to see if the valves leak. If it leaks, then there is a problem. If the seats were cut right and the valve (new or not) is concentric and has the seat ground properly and concentric you should be fine. If it leaks I am not sure you have the means to check for concentricity of the valve or the seat but the home method would be to lap the valve IMO. Quote Link to comment Share on other sites More sharing options...
boogalou1 Posted March 17, 2009 Author Share Posted March 17, 2009 Thanks for everyone's comments. I'm going to hand lap the valves to make sure they seal correctly. Quote Link to comment Share on other sites More sharing options...
Careless Posted March 19, 2009 Share Posted March 19, 2009 Thanks for everyone's comments. I'm going to hand lap the valves to make sure they seal correctly. when u let the valve fall onto the seat, you should hear a "plock" sound rather than a "plink" sound, for lack of technical sound-pitch terms. some say to lap only in 1 inch palm/palm movements, but i went from edge to edge of my palms with the suction tool, and I often lifted and dropped the valve to re-distribute the lapping compound. what i did: 1st stage = lapping compound 2nd stage = lapping compound thinned down 50/50 with a good machine/cutting oil 3rd (and grossly unnecessary stage) = polishing compound and a lot of time and effort to make them shine. some have said that carefully locking the valve stem tip (where the retainer and locks go) in a cordless drill with an easy-to-modulate trigger button and pulling on the drill while using it to rotate the valve head at high speed onto the seat will produce excellent results. fentin_fury reinstated that method after i saw it on the internet but thought of it as too much of a risk. i think his motor builder did it that way and his engine was running great, last I read. I'd imagine you will need a lot more lapping compound to do that though, as the high speed will most definitely throw the compound everywhere. Quote Link to comment Share on other sites More sharing options...
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