ES2 engine specifications

I would try to get hold of the Edgar Franks book - there are also several downloadable PDFs which would help eg http://www.pdfmotomanual.com/index.php?r=site/page&view=manuales&order=t&key=&make=1964&lang=ENG

But in answer to your specific question, piston clearance at bottom of skirt: .003" - .004" (acceptable wear around .005"), ring gap .012" - .016" compression, .005" scraper.

The gudgeon pin is 7/8" diameter from memory and should be a free sliding fit in the bush with no play.

HI Ian, Acceptable wear ? 5 thou clarance, or an additional 5thou.IE 8-9 thou total?.

Additional so getting up to around .010" in total. It might be a bit rattly at this.....

I must admit to always running my pistons / bores with "semi-worn" clearances as I don't want to spend the rest of my life running them in. I recently restored a 1931 Sunbeam which had obviously been rebored before I got it, and it used to tighten up on any longish climb. I had a couple more thou honed out of the barrel and it was much freer and ran much better. Didn't smoke either.

Just out of interest Richard, I did some quick sums. The book says you're comp ratio should be 7.1:1. Atmospheric pressure at 1100m is 12.88 psi (I prefer those units!) so your theoretical compression test should yield 7.1 x 12.88 = 91.45psi. So your 90psi is pretty spot on!

George

At an altitude of 1100m I take it you are not in the UK. Your next task will be to fit a supercharger to sort out a fuel mixture of 14:1

According to my (rough) calcs you'd be looking a ratio of 16:1 to compensate. So either a supercharger or a leaner mix?

Fair points Richard.

I was being theoretical!

G

Previously richard_salt wrote:

Previously George Phillips wrote:

Just out of interest Richard, I did some quick sums. The book says you're comp ratio should be 7.1:1. Atmospheric pressure at 1100m is 12.88 psi (I prefer those units!) so your theoretical compression test should yield 7.1 x 12.88 = 91.45psi. So your 90psi is pretty spot on!

George

Hi George,

Technically your calculation is correct,but not in practice.

You're assuming the piston starts moving up with the inlet valve closed. That's not the case, it only closes when the piston is partly up the barrel. So it's not the full 500cc which gets compressed.

The tappet clearance (I know the ES2 should be zero) will also make a difference - a small gap will keep the inlet valve open longer, so less compression indicated.

When running, the momentum of the air flowing passed the valve will result in more air being compressed.

Nothing is simple, is it?

Surely valve overlap occurs on the exhaust stroke not on the compression stroke

We've drifted off-topic a bit but to pursue the compression tack, when a manufacturer states "CR = 8:1" does that mean that the pressure to test for is 8bar (117.6 psi at sea level!) or is it something less?

George

Previously George Phillips wrote:

We've drifted off-topic a bit but to pursue the compression tack, when a manufacturer states "CR = 8:1" does that mean that the pressure to test for is 8bar (117.6 psi at sea level!) or is it something less?

George

The Compression ratio (or static compression ratio) is a theoretical number showing the ratio between the clearance volume above the piston at TDC and the piston swept volume plus the clearance volume. It is mainly used as an engine comparison.

In a dynamic situation when we compress the charge. we impart heat into it. The higher the compression ratio the more heat energy we get. The amount of heat we impart will depend upon the medium being compressed as well as the theoretical compression ratio. If we are compressing air only this will be less than for fuel/air mixture. By the gas laws this will change the compression psi figure (larger than your calculation). It has already been mentioned that the valve events will effect the final compression psi figure (lower than your calculation). Add to that gas inertia effects, simple things like throttle position, engine speed when testing etc. and you can see that things aren't so simple as it seems.

I think that your idea is a very good basic approximation of a ball park figure in the absence of any manufacturers specific service specifications which is the case with our old bikes! But remember, it is only a very basic approximation.

Reminds of Heat Generation days at College, Paul!

Probably easier to stand on the kickstart and see if ti will hold your weight!

G

Previously George Phillips wrote:

Reminds of Heat Generation days at College, Paul!

Probably easier to stand on the kickstart and see if ti will hold your weight!

G

I always thought it was the best way but you started it!

Colin