i did what mark suggested but in the opposite direction - put the head upside down on some pieces of 2x4 and filled the chambers up with some rubbing alcohol, then looked into the ports with a flashlight. this lets you do both valves at once, but mark's method is probably easier to spot the leak as it's right out in the open. 

 

cleaning & checking the valves, replacing the seals, head gasket and bolts and flushing out the block are all great things to get done without having to pull the engine. if you discover that the bores are worn, you're already most of the way to pulling the engine anyways...

rossiz, did you have much carbon build up on your valves? If so how did you clean it off?

yes, i had lots of carbon. best way to clean valves is to take 'em out. you'll need a spring compressor and an egg carton to keep your parts matched up. it's a very satisfying job - not particularly hard, just one that takes patience and a methodical approach. careful of the little retainer collets - if they've been on there for a while they can get stuck and fly off when you compress the springs.

 

i believe the build up on the back & stem of the valve are what will restrict flow, and the build up on the front face can increase compression and cause pinging. you will be happy when your head is all cleaned up, new valve guide seals, heck - while you're at it you can polish up the cover too. 

 

oh, and for the love of god - be sure to wedge your cam chain tensioner before you pull the cam sprocket!

and stuff the chain opening with rags or risk losing something down the hole of doom...

Blue had the best idea for cleaning valves to me, chuck them into a drill.  Low speed with a Scotch Brite pad and some cheap WD-40 knock off.  Shines up like new.  I did a few last night.  I'm working on a head that's been sitting under my bed for 3 years, they have a varnish like crud around the sealing edges.

 

Agreed! very satisfying process.

yup - simple way to get 'em nice and clean quickly. just to be safe, wrap some tape around the stem to protect the stem from the drill chuck.

Hmm....good info guys. 

Ha! yes I have learned my lesson about the "chain wedge". I really need to look at my timing chain wear too. I had to put it on the number "2" adjustment due to stretch. So if  I can get away with not replacing it I will. The only thing is, I just remembered, my front seal is leaking also.

 

Guess I have something else to consider now. 

heck, if your front seal is leaking, pull the timing cover and replace that seal - easy seal to replace, just a bit of a project getting the front cover on & off. radiator/fan come out first. since you're going to flush the system, pulling the radiator is less a deal because you will drain it anyways. timing chain kit is affordable and includes the seal, both sprockets, both guides and chain tensioner. 

Exactly what I was thinking.

 

I also have a broken water pump "long" bolt. Had to tap the front cover for a short bolt to get by. I can fix this issue as well.

 

Got some things to think about for sure.

Anyone know it the valve train components are interchangeable between the P79 and N47? I have the valves, springs, rockers etc. When I take my N47 head off to replace the HG, I figured I would go through the head and if I need anything I have parts available if they fit.