Friday, May 2, 2014

Spare Engine - Lapping the valves

In the previous post, I was experimenting with various methods of lapping the valves into their respective seats. I found that lapping by hand worked very well if the seats were in good condition to begin with. The problem is though, the head I am working on has some bad pitting around the valve seats and lapping by hand was just not going to work

So I broke out my drill and bit of rubber hose to speed up the whole process of grinding past the pitting. Once into good metal, I switched to the more traditional lapping by hand to finish the job. As I completed each chamber, I tested for leaks by inserting the valves and filling the combustion area with fluid and left it overnight. The results were very promising, but I won't know for sure if it has worked until it sits back on the block and is used in anger.

Here's a quick reminder of what thinks looked like when the head first came off the block! (Numbering from the fan to the clutch 1,2,3,4)

Cylinder 1

Cylinder 2

Cylinder 3

Cylinder 4

Unfortunately most of the valves were quite badly pitted and no amount of grinding was going to salvage them. But luckily I had an identical spare head which was cracked and useless, but did have a very good set of valves to donate. But before they went in, I used the old valves to grind past the pitting on the seats as the grinding process grinds not only the seat, but also the valve mating surface. Once they were done with, I could see that the grinding had significantly altered the mating surface probably making them useless. Really glad I had that cracked head now with it's spare valves.

As the cylinders are numbered 1 to 4 (from radiator to clutch), I have numbered the valves in the same way. Here is the head after a bit of de-coaking with a wire brush.

Cylinders 1, 2 and 4
Cylinders 1, 2 and 4 were all in similar condition with some pitting visible on the seats as can be seen in the picture below. It took about an hour per valve seat with the drill constantly grinding on a low speed with the course compound, checking,  then grinding again making sure I got just past the pitting but no further. Here are some typical before and after shots...


And after

Cylinder 3 was different story. It was by far the worst of the lot and the exhaust seat was particularly bad. Here is a picture of the exhaust seat before I started.

and after an hour of faffing.

Eventually I got bored and left it for the night, coming back the next day for another go, I eventually struck a constant ring of metal...

The was still a small amount of pitting at about 10 o'clock on the seat, but I didn't want to grind any further.

The Final Lap
Once all the seats were down to a ring of unbroken shiny metal, I swapped the knackered valves over to the ones that were going to be used in this head and finished off lapping by hand with a fine compound. Once I was happy with them all. I dropped the valves back in and tested them for leaks.

To test for leaks, I sat some WD40 fluid in the combustion chamber and left it there overnight while also stuffing some kitchen roll inside the ports to catch any fluid that may have managed to find a gap and seep through. WD40 is designed to find a way through gaps so it seemed an excellent test fluid. The next day I removed the kitchen roll and examined it for signs of WD40 and to my surprise and delight, there were none! None at all.

Checking for leaks with WD40 fluid.

My guess is that if the valve seats were not too bad, lapping by hand would have probably been quick and easy. Like many thinks in life however, things are never that straight forward as they should be and the pitting on the valve seats did make the job really long and tedious in parts. That said though, I enjoyed the work a great deal and also achieved the results I wanted.

Glad I can now add valve lapping to my list of experiences.

<Next Post> - 'Spare Engine - Porting the Head'
<This Post> - 'Spare Engine - Lapping the valves'
<Previous Post> - 'Spare Engine - Valve Lapping Techniques'

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