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 !
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.
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!
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.
There is a 99 around that's fitted with a decompressor.It can be done.
You'd need to be careful how far you lifted the valve or it might hit a piston...
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 are right Ian, but to start,you first have to get the motor turning!!.
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
Anna. I think you will find standard C.R. on a 650SS is 8.9:1; not 9.8:1.
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.
hello there the right numbers but they come out in the wrong order thanks yours anna j
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