Saturday, September 27, 2014

Replaced the Head

Back in March this year I bought a spare engine (well two in fact) and I have been tinkering with them ever since. A lot of my tinkerings have been trying to get the head back to a usable state.

Having spent an age cleaning it, lapping the valves and even having a go at porting it, not to mention the time that went into refurbishing the rocker assembly, it seemed daft just having the thing sat on the shelf gathering rust.


The other main reason for changing the head is that the car seems very low on power and torque at the moment, especially going up hills. So I'm hoping changing the head over will sort it out.

Having never attempted anything like this before, I have to admit I was a bit nervous. The thought of taking the engine to bits and doing some real damage was certainly on my mind, but you can't let fear hold you back so I pressed on with the job and hoped for the best.

So after some research and planning, I decided on the following running order: First remove the carb and the manifold. Then moving onto the plumbing: remove the radiator, the heater valve, the thermostat housing and the bypass hose. Once that lot was off, remove the rocker cover and the rockers and finally undo the nuts that hold the head on in the 'special' backwards spiral order. Seems simple enough, so lets go...


Removing the carb and manifold.
Leaving everything still attached to the carb, I undid the two nuts that hold it in place and slid it back giving just enough space to get at the manifold nuts with a socket. The reason I wanted to get at them with a socket and not a spanner is twofold, Firstly, I don't have a spanner skinny enough to fit in the gap with the carb in place. Secondly, I want to be able to get my torque wrench on them to ensure they are set correctly when I come to reassemble everything.



Removing the Plumbing
I decided to remove the radiator also as part of this project as I thought it would give me better access to the pulley nut. My plan was to put a socket on and crank it, hopefully making it easy to turn the engine when I set the valve clearances. But after removing the radiator I discovered that the lower radiator bracket was still in the way, totally scuppering my idea.

Removing the radiator wasn't a total waste of time though as it was in need of a small repair that would be easier to fix with it out of the car, plus the coolant was brown and nasty and needed replacing anyway.



Once the radiator was out the other plumbing related items that needed to be removed were the heater valve, the thermostat housing and not forgetting the bypass hose. The spark plugs and coil also came off at this point and lastly the temperature sender wire was unplugged.


Rockers
Next to come off was the rocker cover and the rocker assembly.




The last job before the head would come free was to carefully remove the pushrods, giving them a wiggle as they were lifted to minimise the risk of pulling the cam followers out of their seats. I stored them in a piece of cardboard to keep them in order.


Head Removal
Now, finally I was in a position to remove the head. According the the Haynes Manual there is a specific order in which to undo the nuts. So carefully going round and around the spiral pattern in reverse, I undid each nut a little and a little more until they were all loose.

As I had chosen to leave the manifold in place, it left me with a slight problem. The two outermost manifold studs that stick out of the back of the head were still located in their respective holes in the manifold preventing me from simply lifting the head up.

In order to get around this I had to lever the manifold backwards far enough to clear the studs, while trying to lift the head at the same time. Although a little awkward it was manageable and also preferable to removing the manifold completely as I find the exhaust bracket a nightmare to get back on.



With the cylinder head off I pinched the vacuum pipe from the carb and used it to siphon the rest of the dirty coolant out of the block into a container.




Now the block was ready to be cleaned. I have read many differing views on how to clean the mating surfaces and I wanted to make sure I didn't do any damage.

Starting with a cloth dipped in a little diesel, I worked around the surface cleaning quite a lot of the muck off. For the more stubborn areas I used a nylon pan cleaner and carefully rubbed the carbon off where I could making sure not to damage the metal. Even after a thorough scrubbing though there were still lumps caked on here and there. So for these I had to resort to using a new Stanley knive blade to tease them off the surface. One all the lumps were dealt with, the whole surface was rubber over with a clean cloth to finish.

Before I started I placed kitchen roll down the cylinders to minimise the amount of debris that fell in. Obviously some bits still managed to fall in, so when I was done I used the vacuum cleaner hose and a small craft brush to clean out each of the cylinders.


On with it's Head!
Getting the new head out of storage, the first thing was to give the mating surface a wipe to get the grease off and then attach the new bypass hose.



One new gasket later and...



With the manifold levered back out of the way again, I aligned the 'new' head onto its studs and lowered it down in to position making sure the bypass hose connected properly.

Then with a fresh manifold gasket, I removed the lever which allowed the manifold to spring back to its original position among the rear studs. Before I could bolt the manifold back in place though, the cylinder head nuts needed torquing down.



But before I can do the cylinder head nuts, I need to reinsert the pushrods and remount the rocker assembly, torquing it to the required 32Nm. Now I can finally put the cylinder head nuts on their studs and get each one finger tight ready to torque them in sequence.

The Haynes Manual recommends following a spiral sequence shown below going around the cylinder head nuts turning each only a quarter of a turn. Going round and round the sequence until they are at the specified 68Nm.



With the cylinder head fully torqued down I was then able to attach the manifold, the carb, the heater valve, the coil, the thermostat housing and not forgetting the temperature sender.


Setting the Valve Clearances
The Haynes manual goes to great lengths stressing the importance of setting this gap correctly, so I didn't want to rush through this job. The topic is covered very well in the manual so there is no reason for me to go into great detail here. Except to say that the sequence given in the Haynes Manual is not named, but most people I have talked to on this subject call this sequence 'The Rule of 9',

There are a number of different methods available to open and close the valves during this process. As I still had the radiator out, I was able to get to the bottom pulley with my hands to turn the engine over.

Spending a good hour on this job I worked across the head using the sequence in the manual and set the gap to the specified 0.3mm for my engine with a feeler blade. Then checked it with a 0.4mm blade to make sure it wouldn't fit and finally a 0.25mm blade to make sure it fit too easily.

Once I had completed a first pass, I started the sequence again to check them, finally checking them a second time to be sure.



Radiator
Earlier on I mentioned that the radiator needed a slight fix. It seems that the small rivets that hold the inner part to the outer have come loose on one side.



One rivet had come away completely leaving me a hole where I could get a tiny nut and bolt in. So searching my stash, I managed to find a suitably minuscule item to do the job which also happened to conveniently have a nyloc nut.



With that fiddly repair done, the radiator was plumbed back in, remounted and refilled with coolant and with the addition of the spark plugs, it was now the moment of truth. Would the car start or just make a horrible noise and die!

Nervously I sat in the drivers seat and put the key in the ignition, pulling out the choke I ran through everything in my mind looking for any errors. Then  I went back round and looked in the engine bay again for anything I may have missed, but there was nothing.

I had to turn the key...
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wait for it...
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IT STARTED...
and without so much as a cough or a splutter.
Wow, I was very relieved.


The last job was to replace the rocker cover with a new gasket and some RTV.



And it was job done...



Test Drive
Taking it for a test drive, the improvement was instantly noticeable. Not only did the car accelerate better, it had more torque and idled better, so this is a really good result.

The mileage is currently at 78321 so I'm hoping that I can come back here in 100 or a 1000 miles time and still say all is well.


Old Head
A quick examination of the removed head revealed potential reasons for the cars' previous poor performance. There was a decent build up of crud in the combustion chambers which probably means the valves are not sealing as well as they should when they are closed. Nothing a good strip down and refurb cannot solve though.



Conclusions
Thinking back just a few years ago before I had the Mini, I could just about manage to change a wheel! So the fact I have been able to tackle this job leaves me feeling pretty chuffed with myself. It's a big achievement for me to be able to replace a major engine component and still have the car working afterwards.

Although I was very nervous about this when I started, worried that I might get out of my depth and make an expensive mistake, it turned out pretty well in the end. Yes, there were the occasional moments here and there when I wish I hadn't started, but I'm so glad I did as the whole experience has been an exceptionally positive one.


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