Skip to main content
000000 000003 000006 000009 000012 000015 000018 000021 000024 000027 000030 000033 000036 000039 000042 000045 000048 000051 000054 000057 000060 000063 000066 000069 000072 000075 000078 000081 000084 000087 000090 000093 000096 000099 000102 000105 000108 000111 000114 000117 000120 000123 000126 000129 000132 000135 000138 000141 000144 000147 000150 000153 000156 000159 000162 000165 000168 000171 000174 000177 000180 000183 000186 000189 000192 000195 000198 000201 000204 000207 000210 000213 000216 000219 000222 000225 000228 000231 000234 000237 000240 000243 000246 000249 000252 000255 000258 000261 000264 000267 000270 000273 000276 000279 000282 000285 000288 000291 000294 000297 000300 000303 000306 000309 000312 000318 000321 000324 000327 000330 000333 000336 000339 000342 000345 000348 000351 000354 000357 000360 000363 000366 000369 000372 000375 000378 000381 000384 000387 000390 000393 000396 000399 000402 000405 000408 000411 000414 000417 000420 000423 000426 000429 000432 000435 000438 000441 000444 000447 000450 000453 000456 000459 000462 000465 000468 000471 000474 000477 000480 000483 000486 000489 000492 000495 000498 000501 000504 000507 000510 000513 000516 000519 000522 000525 000528 000531 000534 000537 000540 000543 000546 000549 000552 000555 000558 000561 000564 000567 000570 000573 000576 000579 000582 000585 000588 000591 000594 000597 000600 000603 000606 000609 000612 000615 000618 000621 000624 000627 000630 000633 000636 000639 000642 000645 000648 000651 000654 000657 000660 000663 000666 000669 000672 000675 000678 000681 000684 000687 000690 000693 000696 000699 000702 000705 000708 000711 000714 000717 000720 000723 000726 000729 000732 000735 000738 000741 000744 000747 000750 000753 000756 000759 000762 000765 000768 000771 000774 000777 000780 000783 000786 000789 000792 000795 000798 000801 000804 000807 000810 000813 000816 000819 000822 000825 000828 000831 000834 000837 000840 000843 000846 000849 000852 000855 000858 000861 000864 000867 000870 000873 000876 000879 000882
English French German Italian Spanish

Starting effort


Yesterday I had the opportunity to compare the starting effort of my 1956 Dominator 99 with my friends 1955 Dominator 88. The 88 which has a newly built engine started easily with just a gentle  to firm ‘ prod ‘. However my 99 , requires considerable effort to overcome the compression and I can stand on the kickstart for a while before it moves. The 88 was a joy to start compared to mine.

Whilst  I currently have no idea what pistons are in my 99 I am aware that the standard compression ratio on an 88 is 7.8:1 ( 9.0:1 optional ) and the 99 is 7.4:1 (8.2:1 optional). As the standard c/r on the 99 is lower than the 88 then all things being equal then the starting effort on my 99 should be just as easy as the 88 or even easier !

As my 99 is a fairly new acquisition I do not wish to partially strip the engine to measure the height of the pistons and I appreciate that in the past high compression piston may have been fitted. Is there anyway to check what pistons are currently fitted ?

Whilst I am new to Norton’s I would appreciate some advice if it is possible to fit a compression plate between the crankcase and the barrel to reduce the compression to standard ?  Perhaps I am on the wrong tack here but would welcome any advice from the wise out there.

When fired up the bike runs fine but at my time of life I need to emulate the 88 !




Hi George

If you have a compression tester you can work out the compression ratio. Standard atmospheric pressure at sea level is 14.7psi, so if you measure a compression of 140 psi, it is 10:1. For 7.4:1 it should be around 109-110 psi.

Can't help you on the compression plate though, but I'm sure there will be someone who can!




My 99 has std 650SS pistons fitted  and the CR is probably about 8.25 to one. It is nicely run in and goes well. I weigh 13stone plus and I can only just kick it over,if it did not start by the second kick I would be struggling.  You are not alone here. I ease it over compression before kicking and have a boosted coil ignition and a well set up carb. A compression plate is availiable , If the motor comes appart for any reason I will fit one. If you have a 60 onwards head then you could fit the earlier head which lowers the ratio by one ,it also has smaller valves.You could get a longer kickstart made ,but then you would struggle to get your leg up that far!!.

Thanks for your reply Kevin. I have a compression tester but have never I used it on a bike. I assume that to test for compression on a twin is to remove the plugs and connect the tester to one cylinder and open the throttle fully and use the kickstart several times. Repeat on the other cylinder.






Thanks Robert.

I would be interested to know if someone has standard pistons fitted to a 99 which should give a c/r less than an 88 according to the books. The starting effort should then be similar at least to an 88. Are the dimensions of the 650SS pistons similar to standard ?







Is the engine sprocket standard size ? Changes to primary gearing can make it harder to turn  the engine over.


I suspect Richard has the answer. A bigger engine sprocket will make it harder to turn the motor.  And the bigger engine bikes typically have bigger a sprocket on the engine. Incidentally, a compression tester does not give the ratio. The pressure multiplication is 30% or more greater than the volumetric ratio because the gases get hot (adiabatic compression). I can get 150 out of 8:1.

With a plate you should need longer push rods.


Doesn't a bigger engine sprocket makes it easier to kick?

That's right George, but see David Cooper's post- I was just working on a basic atmospheric pressure times the compression ratio!

I have a 650SS with Pazon electronic ignition, new Amal Premier concentrics, and full engine overhaul. Mine usually starts with ignition on, tickle both carbs until they overflow, full choke, kickstart to horizontal and it fires on the first kick. I do give it a fairly hefty kick though, not sure that a 'prod' would start it!

Good luck

I found the lengthened kickstart from RGM (part no.050179 I think) greatly eased the effort in starting my bikes. It looks a little alien, but folds neatly away when not in use.


Sorry Mikael... you are of course right that a larger engine sprocket gives more leverage to turn the motor over. Mine isn't all that hard to move... perhaps I didn't do as good a job as some others in assembling it! The crank stroke is longer on the bigger engines so with a slightly bigger bore the bigger force must combine with the bigger lever arm inside the engine to make the 99 and 650 harder to turn than an 88. And the short stroke of the 88 compared to an earlier Single also explains why they did not fit a decompression in 1949.

My Reliant......has a compression of about 200psi this means that its CR is 13.6:1 !? don't think so.

A very big factor in measuring CR with pressure gauges is of course the valve/piston ring leakage. So I think apart from stripping the engine and measuring.

Or could it be done by measuring the total piston travel by the 'lolly stick' method? But of course with this method you will need to know the volumes of the head/chamber as well.


I have just done a compression test cold and the gauge shows 11 bar ( 162psi ) each cylinder.



sounds Ok certainly not over high.  Today I got someone who is used to starting his Gold Stars,Boneville 120 and a  fully restored 61 Norton 99  to kick over my 99. He was surprised and asked if it had 10 to 1 pistons . It has not,just good ring seal and valves. Not been touched only used for the last 25 years.


Whilst a larger engine sprocket would ease the effort required on the kickstart, would not the knock-on effect be that the engine will turn over more slowly? 


You could increase the ring gaps! Sounds like yours might be a bit too close and maybe you are running the risk of them closing altogether.  It would be a cheap solution (if, of course, it works).


Go kick a few more before you decide yours is different to another 99. a fresh built 88 will be  easier to kick as the rings ands valves need to bed in and the chamber coke up a bit. besides the  motor being smaller,  gearing different the kick start lever is the same if i'm not mistaken. 

If the lever is too high for you, providing she is a decent starter and after setting position (just over TDC ), slip the clutch to bring the  lever to a height you can manage and kick away, its not a Velocette after all !  

 I have two dominators (99 & SS) both with good compression, neither take more than half a kick to fire up but i will confess, the iron head  88 I had would start by hand pressure on the lever....  super machines 88's 


My Velocette Venom Clubman is as easy to start as my 16H, first kick if done according to riders handbook. Much easier than the blasted ES2. The 99 I had when I was 20 and weighted 55kg was no problem to kick. I had high comp pistons in that.


hello now standard 650 pistons are 9:8:1  and flat topped ,and I did have a 99ss with 10:5:1 domed pistons fitted  end model 88ss you could get  9:5:1 hepolite pistons my other Norton is a model 88 of 54 vintage  this has 8:1  pistons fitted  and is about the same as My 650 the kick over  but the 88 sounds like a Manx when revving   its them tulp silencers  the 650 Norton manxman has music from her Manxman silencers  a deep mellow sound  unlike any other 650  I have  heard  but these silencers are like hens teeth Has they were only made in house by Norton at Bracebridge street shops     made by craftsmen no long with us any more,                                     yours   Anna J  


Hi George,

   I have a single with much the same symptoms. I don't think the different compression ratios make it very much harder to kick-over. I think the reason you have so much compression is oil getting past the rings and causing a hydraulic seal. This could be the piston rings, bore wear or inlet valve oil seals needing attention. To cure this will need at least a top-end strip for a de-coke and new rings or even a re-bore and pistons. I think Jon N. is right when he says your friend's 88 is not fully run-in, and also the rings will be running with the right amount of oil.

In reply to by mikael_ridderstad


Mikael, its not the starting of the Velo, mine also starts well once you follow the procedure,  whereas a Norton given a good kick with appropriate fuel air and spark will jump into life with no effort or  handbook  knowledge




Norton Owners Club Website by White-Hot Design

Privacy Policy