Mick's 70 Lowlight

Made a start on the engine today. First order of business was to knock up a bench-top spring compressor. I've been meaning to pick one of these up for a while now as my manual one is a bit cumbersome to use. As I needed to do some head work today I decided that I couldn't wait any longer so decided to build one. A quick rummage through the scrap pile and a couple of hours later I had knocked one up. Works great. I will post up some more photos and a step-by-step to the garage group.

With the spring compressor done it was time to strip down one of the spare heads that I have. I wanted to use it to practice porting rather than just jump in on my good heads and potentially ruin them. These heads need new seats so it didn't matter if things didn't work out 100%

I started off with the exhaust valve. This exhaust port is very badly designed and has a massive ridge in the slow side of the port. It also has a lumpy valve guide boss which gets in the way a bit. The idea is to smooth out the ridge and the the lumps to the side of the boss whilst trying to retain as much of the boss as possible. Not going overboard on the boss is especially important on a forced induction engine as it tends to see higher port temperatures. If the thermal mass around the boss is removed the exhaust valve will run hotter which can potentially result in stretched or dropped valves.

With the ridge and lumps smoothed out the only thing left to do is to blend the seats into the port, match the outlet to the manifold and give it a light sand.

The intakes are much less work, all there is really to do here is blend the seats into the ports and match the intakes to the manifolds. There was a small amount of cleaning up to do around the guide boss but not much.

In both cases I removed the valve guides to get better access. I ended up using a tool I made 20 years ago when I changed the valve guides on my Triumph 13/60. It's been floating around in my toolbox ever since. Glad I kept it now.

With the ports done I turned to the chambers. I had already done a little un-shrouding on these heads before, but decided that they could do with a little more. Basically the shrouded area to the outside of the valves needs to be taken out to the inside of the cylinder boss and then blended back with the rest of the chamber opposite the spark plug. The area near to the plug is basically left alone.

It took about 4 hours to get one practice head mostly done. It still needs about another hour on it to sand and polish but I decided to skip this as I decided it would be better to spend the time on the actual heads. At some point I will return to those heads and attempt to do the valve seats at which point I will finish off the porting. I'm pretty happy with how they came out.

So with the practice under my belt I decided to move on to the engine. I got it up on the engine stand and started to strip it down. With the heads off I noticed that the inlets are substantially different to the heads that I just ported. There is a massive guide boss in the inlet ports. This means either the heads I practiced on were already ported (possible) or they have a different inlet port design (also possible as these are type 3 heads). I will strip the heads tomorrow and male a start.

One thing that I noted was that on the heads I ported the valve guide should ideally be about 10mm shorter. I will modify the guides on the other heads when I get them as I will be fitting new guides. I took a bunch of photos trying to get a good view of the port work but it was really hard to get a decent shot. It should be fairly easy to see the difference between the stock and modified exhaust port, however the one thing you cannot see is the ridge. You can only feel this with your finger as it is hidden in the depths of the port.

On my list of things to do is make a flow bench. It would be great to have this now as I could use it to test the heads. Will have to see if I can scavenge enough parts to make one. Anyone got a spare vacuum cleaner they don't need?