Sunday, April 6, 2014

Spare Engine - Head Inspection

As the strip down of the engines continues, my attention now turns to inspecting the heads. The better engine came with complete head and rocker assembly, whereas the 'not so good' engine's head came minus the rockers. Looking at the casting numbers, both the heads are of identical spec and designed for a 99H engine.

Two heads really are better than one. Having a 'spare', 'spare' head is exceptionally useful, even though it's not in the best condition. As I have no experience what so ever in this area, working on the 'spare', 'spare' first, allows me to get away with mistakes while gaining valuable knowledge that I can use when working on the 'good' head.

Removing the Head
Removing the head from the block seemed like a simple 'nuts and bolts' task. To be fair it was, except I made the mistake of removing the head with the rocker assembly still attached, which pulled all the pushrods out. Although not a huge problem, it would have been far easier to remove the rockers first, then the pushrods and finally the head. Oh well, you live and learn.

Once on the bench, I unbolted the rockers and removed the pushrods and stuck them in some cardboard to keep them in order and stored them away.





Combustion Area
Working with what I considered the better head, I could see that the combustion chamber area around the valves was a total mess. This is what it looked like.






Gasket Surface
After a quick clean up I examined the gasket surface and noticed that some of the holes were blocked with a crusty plug. Really not sure what it was, but I was sure that it was not supposed to be there, so I poked them out and cleaned up the holes. The rest of the gasket surface looked sound.





Valve Extraction
Next job is to get the valves out, for which I needed a valve spring compressor. I didn't have one, but discovered that they were pretty easy to make with a few hand tools and a spare G clamp, check out how here.

With my newly made valve spring compressor, I was able to remove the valves with ease and stored each one in a labeled bag along with the spring, retainer, collets and oil seal. The last part of the stripdown was to remove the manifold studs.



With both heads stripped, it was wire brush time. Switching to the 'not so good head', I used a de-coaking brush in a drill and cleaned out the combustion area. I reinserted the valves for this so I didn't scratch the valve seat surface. Removing all the crud revealed a very pleasant looking surface.



Valve Seats
The valve seats in both heads were for unleaded petrol, however they were quite pitted in the head I was working on.


Valves Guide Clearance
One area for concern was the amount of wear on the valve guides. There was slight valve movement on both heads, but how much is too much? The only solution was to measure everything and check it against the specification at the start of Chapter 2 (Part B) of the Haynes Manual. (See, it is useful for something!)

I measured each valve stem 3 times: towards the top, in the middle and towards the bottom and calculated the average. Then I measured the diameter of each of the valve guides three times and again took the average. From these two averages, I was able to calculate the clearance of the valve in the guide and compare it to the spec. The calipers I have are accurate to 100th of a mm. The results (below) showed that two of the clearance numbers were 1000th of a mm below spec. I can live with that if the alternative is changing the valve guides.

Here are the results in Excel...



Spark Plug Holes
The last thing I was concerned with was the state of the spark plug threads. I wasn't too bothered about the 'not so good' head as I wasn't planning to use it but the 'better' head showed some surface corrosion. They really could have done with running a tap through, but as I didn't have one. I managed to clean them up with the wire de-coaking brush and used some old spark plugs as a makeshift tap. Three of the holes were okay, but one was particularly concerning.



The picture above shows the problem and I was worried that I would cross thread the thing while trying to get the spark plug in. It was very tight at first, and I didn't like how much force was needed to turn the spark plug, but after a good clean out and plenty of WD-40, it was fine.



Overall
All in all, the 'better' head looks like it will do what I need it to do. The valve seats look good, the gasket surfaces look okay, there are no visible cracks, the spark plug threads are sound and the bypass pipe looks intact. The only slight concern is the valve guides being a little under spec, but as I am not looking for perfection, I can live with this.

The overall plan is to make a good spare engine out of the two, swap it over with my current engine and then go to town making that engine perfect and eventually swap them back. Doing it this way, I gain experience making the swap engine and still get to drive the car.



What's Next...
Next on the agenda is to investigate porting the head to get better flow, for that I will need the help of David Vizard and his Bible: So plenty of reading to get through.





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