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ES2 compression


Can someone tell me what the compression pressure should be for a newly rebuilt 1961 ES2 with rebore, new rings, etc.?

Mine is reading 90 psi (at 1000m asl).

Is it about right - the bike doesn't have much power?


1/ Are you  using full throttle, and

2/ How many times and how fast are you kicking it over?

3/ Is this hot or cold engine?

All of the above will affect the result you get.

You can check sealing of rings by squirting a bit of oil down the plug hole before fitting the comp gauge.  If compression goes up, then ring sealing is poor.  

You say newly rebuilt, so has it done enough miles for the rings to bed-in? Also, are the pushrods still free to turn (ie is a valve being held off its seat a tiny amount.)?

Normally, compression figures are quoted for a hot engine, WOT and at a reasonable cranking speed (say 200-300rpm).

Hope this helps, George 


Thank you.

Full throttle, yes;   Kicking it 4 or five times as fast as I can; Cold engine;   

It has done only about 30 miles.  Pushrods are free.

It is definitely low on power, something is wrong. Need to change down for even the mildest of hills.  Has also nipped up twice on hills, frees again after a minute. Have not had a real seizure.

Has a 376 carb, 3-1/2 slide, 106 needle and jet, needle in middle groove. Main jet is 230 but hasn't been used yet.                                              

Ignition is at 38 d fully advanced. Plug is slightly sooty, but not too bad

Can you give me an idea of what the compression pressure should be, in your opinion?



Richard, check your valve timing, by which I mean the actual valve events, with a degree disc, the timing marks cannot be trusted on any of these engines.

Good Luck!



I had a problem with compression on my 1955 ES2 and eventually found that the exhaust valve lifter cable was sticking, so may be worth checking yours is allowing the valve to close fully.  This became more of a problem when the engine was hot.


.. for your help and advice.

I certainly will do these tests tomorrow.

(I removed the valve lifter, I found I did not need it!)




My 1956 ES2 took ages (700 miles) to run in and nipped up a couple of times when very new with a JP piston and rings. On a number of occasions it would loose compression when cold and needed a squirt of oil down the spark plug hole to get compression back. It would blow a lot of smoke until it warmed up as well.

I eventually got sick of it and bought a GMP piston ( and blocked off the oil feed at the back of the barrel but that is another good news story) and haven't looked back. 

It goes very well now but I wouldn't know what the compression pressure is.

Don. Fro m Melbourne. 


Don't need a valve lifter?  That doesn't sound right.  Can you get it past compression that easily?  To start mine, I retard the ignition a bit, slightly tickle the carb, move the kickstart just past compression using the valve lifter, just the tiniest bit of throttle, then give a long, slow push on the kickstart and advance the ignition as soon as she fires.  I couldn't get past compression without the lifter.  How do you do it?


I checked the compression again (cold, throttle open, kicking hard 4-5 times.). It was about 90 psi again (I'm at 1050m asl, so that's about 102 psi at sea level). I put a few teaspoons of oil into the plug hole, the compression was then about 109psi (124 at sea level)

I checked the valve timing by measuring the valve lift at TDC.  They were roughly the same, about 1.5 mm open (inlet opening, exhaust closing).  I think that means it is correct, the gear marks are all in line. If it was out, a correction of 1 tooth would change the timing by 9 deg. That would be a large change, one valve would be way more open than the other.

To start it, I simply get it up to compression, throttle half open, jump down with my weight on the kickstart and away it goes. I weigh about 70kg. It always starts second kick after tickling until a few drops drip out of the carb.

In the next few days I'll look at the auto advance again.

BTW, there is no sign of oil inside the rocker box when looking into the valve adjusting opening. It's dry. Is this usual?

Thank you for your comments and help.



30 miles is not much at all to bed rings in, run it for a few hundred more and then check it. In the meantime open the throttle fully for a few seconds every now and again to get the combustion gases behind the rings so they wear against the honing and bed in and not glaze the bore. If you have JP rings then they may never bed in, just too hard a ring to wear in against the honing.


It never hurts to put a (gloved) finger over the oil return pipe by the oil tank filler cap to force some oil up into the rocker box, sometimes after a rebuild or a long sleep it can be a bit reluctant. 

The figures you report should be plenty, but not needing the lifter sounds wrong, my Model 50 will hold my weight for 2-3 minutes (only a 350 and I really did eat all the pies ) and I always need to use the valve lifter, when I didn't the performance  was very flat, so I checked the timing properly and found that the exhaust cam needed advancing a tooth from the marks, which made a massive improvement. I also tried different sets of cams, all standard and they varied quite a bit, as do the crank pinions..

Since you are at quite an altitude, is your mixture right?


...of the bike was so poor that I really think something basic is wrong. I'm going to check that the valve timing is exactly as it should be using a degree wheel and that the advance is working properly. I did of course check these things in putting it together but I'll check them all again. Thanks again.



.,,,is in order before anything else. Find out if and where compression is being lost.


Hi Richard,

   If you have the standard flat top piston, 38 degrees fully advanced sounds too retarded. This figure would normally be used with a 9 to 1 compression ratio. You could try 45 degrees and see if there is an improvement. Different fuels and altitude can make a difference so this is just a ballpark figure.


... the bike certainly "sounds" too far retarded - flat dull sound, no crack to it. And feels it going up hills. I got the 38 d from the Bacon book. I'll certainly try it but maybe in smaller steps. (I'll leave the primary case cover off!)


The valve timing is exactly as the Bacon book states. Checked this time with a proper degree wheel and pointer needle.

I will set the timing to 40 deg and then 45 after testing.



The 9th Editon of Haycroft's "Book of the Norton" covering '55 - '62 ES2's gives the advance as 17/32" btdc for'59 -'62 coil ignition models.  Someone else can work that out in degrees!



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