It’s all in the head

“The goal towards which the pleasure principle impels us – of becoming happy – is not attainable: yet we may not – nay, cannot – give up the efforts to come nearer to realization of it by some means or other.”

So said Sigmund Freud.   I think that what he was saying was that we don’t have any choice but to keep on trying and reach that point whereby satisfaction is reached even though it isn’t likely to happen.    Ether that or he was really keen on electronic rock music and had heard that Gary Numan was about to bring out a solo album.

Freud spent his life working out what was going on inside the head of people and is considered the founding father of psychoanalysis.   It would have been far more convenient for the Little Project story if he’d spent a lot of time working out what went on in the cylinder head and had been the founding father of cycleanalysis.  Still, at least he’s helped me invent a new word!

“Why haven’t you update the blog for two weeks?” a number of people have said to me.   I’ve been doing my proper job during the week and last weekend I was having a marvelous time helping out at a (not quite summer) fete.   You’ll find details of what I got up to on The Verbal Hedge if it is of any interest.  You’ll have to dig through to find “The old lady smell” page.

This weekend I have been a little like Dr Frankenstein in that I’ve taken off one head and put on another.    I thought to myself “This will be a doddle, I’ve done this loads of times”.   As I was thinking this I should have nudged myself and said “Yeah, but only on two stroke engines and not on four stroke engines that haven’t been taken apart for three decades”.

Just a little bit of background on two stroke/four stroke engines.    They both work very roughly by making an explosion in a chamber.  The explosion forces a piston down onto a crankshaft which in turn spins and pushes the piston back up.  The spinning crank is connected to the gearbox and this in turn is connected to the wheel and so everything spins and goes forward merrily.

With a two stroke engine, the fuel comes in, the piston goes up and explodes the fuel against a spark and then the gases are expelled on the way down (remember, this is a very rough description!).   With a four stroke engine. a valve opens to let the fuel in, the piston pops up and explodes it, then it pops down again and another valve opens and on the pistons next visit up the chamber a different valve opens and the exhaust gases are pushed out.   Then the cycle repeats itself.

So the obvious difference to me between two stroke and four stroke are these valve thingies.  They have to open and close in the correct sequence and at the correct times to allow stuff to come in and get burned and then go out again.   This is managed (on Little Project at least, things have moved on since the late 70’s) by something called a camshaft.    It’s a bit like a stick with lumps on it.   When the stick turns, the lumps press on the valves and pop them open, so you can imagine that on Little Project, the two lumps on the stick are in different places, one to open the innie valve and one to open the outie valve.

When you think about this a bit more, with two stroke engines, the spark that makes the fuel go boom has to happen when the piston gets to the top of the chamber.   Every time.   Simple.   With the four stroke engine, the spark happens every other time the piston gets to the top of the chamber, and it has to happen when the valves are closed or the energy goes wherever the valve leads to rather than in pushing the piston back down the chamber.

I hope that you are still with me and you haven’t died of boredom during that.   It is only a very rough description, so any mechanics who are shaking their heads with dismay should just remember that I’m a computer programmer and I can easily bugger up your payroll if you make harsh comments.

So, changing heads.   Simple.   Nope.

The camshafts (on Little Project they are “Overhead Cams” which mean they are at the top of the engine) are driven by a camchain which connects to a cam sprocket (I may have made that word up, it’s a cog that has a relationship with the camshafts).  So to take the cyinder head off you have to disconnect the cam chain and all sort of things.  None of this is difficult if you are in possession of lots of spanners and sockets and a sense of adventure.

So I took the cylinder head off the engine that has a defunct gearbox and I took the cylinder head off the engine that has a good gearbox but some broken bits on the cylinder head and put the cylinder head off the duff gearbox engine onto the engine that previously had the broken bits on the cylinder head.   Still with me?

Then I thought “I’ll just take a quick look at the manual now I’m feeling all smug”.

Oh my word (as the young people say a lot around here these days).

It said (I’m paraphrasing a bit here), “Make sure that the “o” mark on the cam sprocket is lined up with the engraved V on the casing and at the same time the “T” mark on the alternator is at TDC and ONLY TURN THE CRANK IN AN ANTI CLOCKWISE DIRECTION or serious engine damage may occur”.

Blimey, I hadn’t done any of these things!   I went back to look.  There’s an “o” on the cam sprocket…


Can you see it?   I think that it is definitely lined up with the (impossible to see) v that is engraved on the casing.  However…


If you look closely, the “T” is definitely not at the top (TDC stands for Top Dead Centre I think).  It’s sort of at just before 6 o clock.  What’s worrying me though is that there’s a little mark on the alternator (the yellow plastic looking bits) that almost lines up with the “T”.   So I’m thinking that this might need to be at the top and then everything will line up and then when the piston gets to the top and the spark goes off and there will be a massive explosion and I’ll find bits of my leg splattered all over the A316.

My simple solution was to take the cam sprocket off, turn the crank (in an anticlockwise direction of course) until the “T” was at the top and then put the cam sprocket back on again.   I can’t for the life of me see how this makes any difference but at least it is all how the manual says.

If you find a bit of leg in a few weeks time, it is possible that it is mine.   Can you return it to somewhere near Twickenham Stadium please.

Thanks for taking the time to visit.


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