Smoking and Overheating

July 18th 2016

These were the two main issues to come out of the shakedown trial.

Oil Burning

I hadn't looked at it in detail, but had convinced myself that the Imp Sport head doesn't like being used on an upright engine and the oil will pool around the valve guides instead of running away.
I was also guessing that it had double valve springs which meant it wouldn't have "top hat" spring seats and the valve stem oil seals. If you don't have the top hats you can't retain the oil seals on the valve stems. On the inlet valves this results in the oil being sucked into the combustion chamber by the manifold depression.
Research on t'internet showed that some people have fitted BMC "A" Series valve-stem oil seals to the guides with some success.

After speaking to someone (more of that later) I set about stripping it down to see where I stood.

Before removing the cam I checked the timing marks. Good job I did. With the engine at TDC the mark on the cam sprocket was not lined up. I lined it up and found it was miles away from Top Dead Centre.

Not only that but it was timed to fire on cylinder 4.
I thought I would be able to overcome all this, now that I was aware of the problem. So I marked the pulley against the timing mark on the block, in case I lost the position.
This was quite a possibility because I would have to turn the crank to get TDC for 1&4 and then 2&3 to enable be to use my special valve-holding tool I'd made, by using the piston crown as a fulcrum for holding the valves up.
(Special Tool. Who am I kidding? I bent an old screwdriver.)

Unbolting the carrier exposed the valve stems and spring caps

I went to lengths to keep the shims in the right order so that I didn't have to bother about clearances when I put it back on.



In this pic, below, you can see the oil is pooled around the springs. In an Imp, the engine is tilted towards the camera and the oil runs down to the edge and along to either the timing case at the front or the extra oil drain pipe at the back of the engine.

I has heard that you can take off the springs without removing the head and as I had 200 psi compression on all cylinders I thought it best not to disturb the head. Besides which it has Wills Rings instead of a head gasket and they are about £20 each to replace.

So I made a lever to engage in a bar I bolted to the head to compress each spring and also made a tool from an old screwdriver to hold the valve up whilst doing that.

Using my lever I could compress the spring cap to expose the collets and then remove them using a magnet. I stuffed rags around the area in case anything leapt up and fell inside the engine, especially down the timing chain case.

Incidentally a friend had suggested taking a suitable size socket which would just fit onto the valve cap and giving it a tap with a hammer to free the collets. I tried it both with and without doing this, and it certainly made it easier to compress the caps with my lever after a light tap with a hammer.

To tie all this together I'll mention now that I had spoken to Imp-engine-guru Reg Patten and he had agreed that fitting single valve springs would allow me to fit the top hats and stem oil seals. They only need to go on the inlets really as the exhausts just blows back into the cam cover and makes the engine breathe a bit more deeply. 

Luckily he had some top hat spring seats and oil seals and he also had a set of Terry's extra strong single valve springs so I bought those and had them ready to fit.

Very helpful bloke. I described the cam timing issue (I had already compared the lobe base circle and lift measurements and discovered it was the standard lift, not even the Imp Sport lift).

He knew the answer. It's a special high-torque cam. The overlap between exhaust and and inlet is all but non-existent. 

This prevents the engine from choking itself at low revs and helps with getting maximum charge into the cylinder, and not down the exhaust.

In doing this the nominal timing of the closed part of the cam travel is not necessarily at TDC. He suggested that someone may have scribed the sprocket wheel to show the true TDC on cylinder 1 and sure enough I found some spidery lines on the sprocket. You can just see them if you look back at the pic at the top.

So. Removing the cut down spring seat I could replace it with the top hat one. This shot shows the difference. The oil seal , which is just like a profiled O ring on this engine, sits on the valve stem and the top hat goes over it and holds it down.

This shows the top hat in place. The oil seal is beneath the top hat.

You can see how this will keep the oil away from the top of the valve guide and the seal will prevent oil going down the guide. The collets are in the foreground.

This is the spring in place.

It was then just a matter of boxing it up and double-checking I had got the cam timing right (it's an interference engine, so I didn't want to bend the valves). I also double checked I had timed the distributor to the correct cylinder. As the factory timing marks were now just a bit of fiction!

Being a bit cautious I whizzed it over with the plugs out first then put them back in and fired her up. 

Runs well and seems to be virtually smoke-free. 

This is a great moment. Just the cooling to sort and I think it may be ready for anything.

Tyre Trouble

Ah, well. I did get a front wheel puncture. Inspecting the tyres, they were worse than I had thought. I knew the rubber was a bit cracked, but when I took the tyre off it was about as strong as denim jeans. A thorn a bit like a rose thorn had gone through it and punctured the inner tube.

This is the best of the old tyres.

I got a new pair for about £20 each from a company called Feked.com. 

I was hoping the new tyres wouldn't  live up to their name, but they are great.

I looked through lots of Glenn Bennet's pics on the NPTCC website to see how many people, and who, used very knobbly tyres. It looked like the general trend was for ones very much like this, so that's what I got.

They just keep the front of the car off the ground really. Whilst aggressive treads might help with turn-in, I suppose you could say they may resist slithering when you are using your fiddles to get a sharper turn.

That's were we are for the moment. 

I do have an issue with the oil pressure gauge which seems very sluggish to both climb and to fall. It's a mechanical one and I know the pipe is clear, as I bled it. I have ordered a new gauge and I'm hoping that is the answer as the one that is giving bother is a Mini gauge, and will be pretty old.

The next Post will be about the Cooling System.