RB25 conversion Stage 4 - Dismantle the cylinder head and polish the ports

After dismantling the block last week (see last article here), I took the block to Elmsleigh Engineering in Benfleet, Essex for a rebore. The block needed to be bored from the standard 86mm width to 87mm to house my new forged pistons. Elmsleigh have seen a few Skyline lumps now as they do all the machining work for customers of RK Tuning, a local and well renowned Skyline tuning company. Here are some pictures of the pistons and the block with the pistons installed...

I still haven't ordered some of the bits I need to complete the rebuild (metal head gasket, big ends, main bearings...), so in the meantime I decided to take apart the cylinder head. I needed to get rid of the detonation damage from number 6 piston melting, and I also wanted to clean and polish the intake and exhaust ports, relap the valves and replace the valve stem oil seals.

The first step was to remove the detonation damage. I used a dremel and very carefully worked away at the pitted material in the combustion chamber of number 6 with the intention of smoothing off the damage. As I ground the pitted surface away, some of the pitted material broke off and left behind a nice clean area of cylinder head. Result! It seems that what appeared to be damage was in fact melted piston, and this could actually be carefully picked off. Some before and after pics will come later.

The next step was to remove the cams. The bolts have to be undone in a concentric pattern, working from the outsides towards the centre so as not to bend the cam. All the cam holders are numbered and marked for inlet and exhaust so there's no need to worry about marking them up as they come off. Once the cams are off, all the shims can be pulled out carefully with a pair of pliers. Before removing the shims, I used a permanent marker to label each one so that I know where to put them back...



On to the valves. I used a valve spring compressor and a small pick to remove the collets. The process is pretty self explanatory - put the compressor on the surface of the valve on one side of the head and on the spring retainer on the other side of the head. compress the spring, then pick off the 2 collets...






All of which leaves you with the valve stem oil seal one side, and the empty ports the other...




Release the compressor and put the valve, spring, retainer and collets in a bag and mark it with the port number. (I ran out of plastic bags so had to resort to coffee cups!)...



Make sure the head is marked with the ports too. I used permanent marker to start with, but I then used a spray cleaner to take swarf out of the ports and the marker came off - so I then used a crayon which resisted the cleaner much better...




Once the valves were removed I used a dremel with a sandpaper attachment to clean up the exhaust and inlet ports. The exhaust ports all had a small lump on them which I removed. I left the intake ports with a rough finish from the sander as It should help the fuel to atomize before entering the combustion chamber. The exhaust ports I rubbed with some wet and dry paper (wet) and finished with steel wool.

Here's 2 exhaust ports - one before and one after...



Another of 2 exhaust ports cleaned up...



And here's a cleaned up inlet port...



That was all the time I had this weekend. I need to get some new valve stem oil seals delivered and get all the valves lapped - Hopefully that'll be next weekend.