Sunday 7 December 2014

Engine Work Begins

Hi all

Well after getting my bikes back it didn’t take long to start fiddling, and was only a matter of days before the engine was sat proudly on my bench.

Before removing it from the frame I did a compression test on the cylinders, as this may help determine where the missing horse power has gone.

As with the dyno, it wasn’t great news as it showed that I had between 90 and 110 psi whereas I should be getting a minimum of 100 and up to between 160 and 170 psi.

Loss of compression can be caused by two things, either the valves are not closing properly, usually due to a build up of carbon on the seats or the shims that open the valves are wrong, or the piston rings are worn.

To check which is happening at this stage I poured a small amount of oil into the cylinder, if the compression goes up it means the rings are worn as the oil acts as a sealant, if it stays the same then the valves need attention as this would not be affected by the oil.

The compression went up to 160, so this means either the rings or the bores of the cylinder have worn, I’m hoping it’s the rings. Just goes to show worn rings are usually spotted by blue smoke from the exhaust as oil is burnt with the fuel, but on mine there was no sign of blue smoke.

Still this is only theory at this stage as the engine needs to be stripped and then I can measure the rings and bore to see which is worn. 

This one I call engine on the bench.

It didn't take long to strip the engine, far too much practice, sadly.

The bores showed signs of wear so I have choosen to use another set of barrels which I had as spares. I also measured all the bearings on the crank and con rods, and ordered new ones.

I've also bought a new cylinder head which has been tuned, so await that with baited breath to see if it is any good.   

With the head off I checked to see if any of the vavles were leaking. I did this by putting a small amount of parafin down each valve and left it over night. When I checked the next day I could see the head was wet meaning the valves were not seating correctly.

From this I can see that I need to grind the vavles to fit the face they sit in, this is called lapping the valves in. I will also check to see if the springs are still strong enough to close the valves properly, this is simply done by measuring them.

So now I'm just waiting on bits to be delivered, and postie is quite busy at this time of year, so am having to wait longer which is really frustrating as I am so keen to see if I've improved my engine at all.

I'll give you an update just as soon as I have a progress report.


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