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1956 Dominator 99 compression

Submitted by george_arber on Fri, 21/08/2020
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Heavy Twins

A while ago I queried the difficulty I had getting the engine over compression prior to starting the bike. Since then I have rebuilt the top end ( a long story) with new liners and bored back to size and new standard pistons etc. I am really enjoying the bike and nearing 500 miles so far since the rebuild .

However, getting the engine over compression prior to starting is a real effort. Once over the Initial compression I have no problem in starting the bike. I have fitted a longer kickstart lever but I still have to dance on the lever to ease it over compression. Is this normal for a 99 ? 
I have fitted a belt drive and as far as I am aware the belt drive engine sprocket / clutch ratio is standard.
George

 

Submitted by Xanna_jeannett… on Fri, 21/08/2020

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hello  well no its not normal you should able to kick a model 99 over with ease like I do with my 650 Norton Manxman so some one has fitted 10.1 domed pistons  but you can over come this with not much trouble try fitting a compression plate  under the bottom of the barrels this will take the compression down a bit  and make it that more easy to start   yours anna j

Hi Robert,

Perhaps I am missing a trick here but as the gearbox is in neutral when swinging on the kickstart I cannot see how a variation in the ratio between the engine sprocket and the gearbox sprocket has any meaningful effect on the starting compression. Maybe I am having a senior moment though !

George

Submitted by george_arber on Fri, 21/08/2020

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Hello Anna,

The pistons are standard I.e flat topped. No domes in sight.

George

Submitted by george_farenden on Fri, 21/08/2020

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The clutch basket to engine ratio thst is important here, not the gearbox to rear wheel. Taller primary ratio means harder to turn engine but more turns per kick.

Regards, George 

Submitted by george_arber on Sat, 22/08/2020

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I have to admit that I had got my thoughts the wrong way round. The ‘ driver ‘ is the clutch sprocket and the ‘ driven ‘ is the engine sprocket. 

George

Submitted by george_arber on Sat, 22/08/2020

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Thanks Robert, I feel better now . I guess the time to worry Is  when there are no more gaps !
 

 

Submitted by steve_marshall1 on Fri, 18/09/2020

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If the engine is running well, there can't be much wrong, so it looks like your valve are seating perfectly and your rings/bores/pistons are in great shape.

I remember how you could stand on the kickstart of my mate's 250 Starfire forever.

Submitted by russ_payne on Fri, 18/09/2020

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My '60 Model 99 is easy to kick over compression on standard pistons.  I agree with the other reviews, but if you're sure the pistons are correct for the factory compression ratio, it can only be the belt timing ratio, or there's some major friction somewhere. 

Submitted by robert_tuck on Sat, 19/09/2020

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Hi George,  My 99 has flat top pistons  from a std 650.  I think the ratio is about the same as the late 99  .Now fully run in the compression is a bit more than I find  comfy to kick over. So I allow the compression to leak away for a few seconds before giving it my best shot.It is set up to fire first kick when warm.Cold is another matter, I bump start it!. Sadly leg strength has faded with advancing age and  arthritus.  I may be shamefully reduced to riding  a mere 900 bevel drive OHC Ducati with electric start and Brembo disc brakes.There is one  somewhere about . Not the same as a NORTON tho.

Submitted by philip_hannam1 on Sat, 19/09/2020

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Robert.  Why get a Ducati when 961s are being almost given away at the moment?

The Bevel Duc is old tech,  there is nothing I can't fix , It has lots of class,  It has a relaxed way of doing things, Its not too powerfull, I can service it no probs. No depreciation (already worth 3 times what I paid for it.), No road tax, Cheap Insurance. Everyone will look at it and ignore the 961  close by.  Just like my 99 !! Just got to get those Norton slimline tank badges to stick on the Duc tank.  99.9% of the worlds population will think its an old Norton. Very few will know that with a working electric start and proper brakes , it can't be.  

 



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