dominator 99 rebuild advise

A couple of things to think about:

1. You posted this in the wrong site.  A Domi is considered a heavy twin. The light twins are the Jubilee and Navigator. 

2. Is the bike running now?  If not, I would recommend that you get it running first so you have a good basis to work from.

Mike

Hello  Now here some Good advice  From 50 years of experience of Norton twins  Now you have a 62-year-old machine with limited  parts  So  you must follow  some rules  these machines do not like  to be  overstressed  in the engine department   So  do not overdo the mods now things you can do are  machine out the cam tunnel to take an S2 Cam profile  and RGM  pushrods they make in stainless  and flat type cam followers  and gas follow the head with atlas valves mean a valve seat recut to fit then Bronze  guilds with seals  and terry springs  and shims under the valve springs  as for the bore  Do not bore go over 40 oversize  the next its to go back to standard  as these barrels will not take big bores   as they tend to weaken the barrel,  next you need to check and large ends and main bearings  and not to forget the OIL PUMP  and the pressure release valve in the timing cover  and do check and clean all oilways and rocker spindles and there wear and tear,   and do get all the reciprocating parts  in Balance,   as for compression ratios goes 9:1 or  ( 9:45:1  is about fine  with lead subitues in the fuel,  carburettors   you need  a good pair of amal 376/288 and 376/289 chopped mono bloc  with a twin pull cables exhaust silencers  a pair of Dunstall replicers with baffels will be fine spark pugs  champoin N7BYC or N4  igntion spakrex D102    now go have fun   yours  Anna J       

Con rods can be obtained of a better design from Thunder Race, and I think they may be using ARP nuts and bolts. All those parts were available when the dealers closed their doors in the 1970's and I was there when Taylor Mattersons closed, and they had a huge amount of Norton  parts spread all over their main showroom floor.

The 99 I had was clocked at 115 over a 30 miles straight. Apart from 50 pounds lighter, it had high comp pistons, dunstall exhausts, single carb and everything polished and in good tune. Miss the time with no speed limits.

There are plenty of SH crankcases around if you blow up. The real difficulty is barrels .

If used sensibly they can be reliable, mine has not been properly to bits for 25 years, When built from bags of rusty bits and the seize sorted. The conrods are a bit like Russian Roulette, no idea what life they have led.And they do age too.

In reality Robert, my comment was based on the original request about tuning it. As you say, aluminium has a finite fatigue life and there are enough posts about it on here already.

As you said earlier, if you want to go fast, buy something more modern, or at least something where parts are plentiful/sensibly priced.

George 

hello  in days of old  when we were racing Nortons  Model 99SS  the cylinder head reworked so it breathed  better and oilways  opened that bit  so  oil can flow  around the rockers  and down the pushrod tunnels to the cam followers  and lube them and the cam  and good oil pump  is vital and main bearings  is to  along with vendervell  shells bearings  for the rods  our club as some for these at a very good price,  the camshaft  I said an S2 Cam  is a Dominator Road Cam   as S3 And S4  can be a bit hot for a Road Bike,  and a PW Cam is better for a Commando motor  then a Model 99    but  you will see over the ton  even in standard mode  its just the speed cams that will spoil things  a bit, When fitting twin carbs  you need new one as you never get them tuned right  and new set of cables as well,   to tune you start with left carb to right  get the left running something like on one pot  then move to right running something like on one pot then try both pots and then  tune so she ticks over on both  and revs with no blank spots,  then try her out on a good back road where there, not much traffic,  and give her a stort blast,  you love it,  have fun and stay safe   yours  anna j

You are right in that airflow in/ exh gas out with minimal restriction is important for power, as is in cylinder air motion(swirl) influenced by the throat/valve seat detail. However the bottom end is equally so. The cam profiles dictate torque curve shape and hence power, and the engine speed equally so as power = torque x speed.

This is where a '99' has an issue. 50 years ago the alloy rods were new/nearly new. Now they are 50 years older. The rod shape was always a compromise and nowadays as Robert says it is a bit of 'russian roulette' as to how good the rods are. They always suffer greatest stress as you close the throttle from high rpm (mininal gas to compress), and this is where and why original rods will let go near the small end.

With new (uprated) rods and pistons, together with a decent oil pump the 99 could become a reliable higher power bike, but the argument is really whether it is worth the cost to achieve that or not.

As you often say, have fun.

George.

I think the Dunstall was timed at 136.   If I was keen on building something really trick I would go for a 76degree  overbored 88 motor with very light valve gear and bathtub chambers fed by D shaped ports.

If you want to make a hot Norton twin engine, start with a 650 or 750 engine.  They are much stronger and have much more power potential, but vibrate.  500 engines are nice and smooth, but a '50s one is not a good basis for a fast engine.  The later engines look pretty similar, but the detail design is very different, for lots of good reasons.

Don't bother over-boring your 500.  They are not safe beyond +.040". 

The rods are marginal, so if you want to rev an old engine, buy some new Thunder Engineering rods.  They are well made and just go in.  (FWIW the rod bolts thread into the main rod, rather than having a nut below).  I bought a pair for my standard 500 - a previous owner bent the big end eyes by fitting -0.010" shells onto a standard un-ground crank (he confessed when I asked him how the rods got bent), and they got binned

Another good mod is a Commando oil pump, they have wider gears, so you get more oil pressure and faster scavenging. A hot early motor will have 0-5psi at idle, and maybe 40ish with some revs,so more is very good. Even standard, they wear well if the oil is kept clean and adequately fresh - I detected under 1/4 thou of wear on the drive side main on an engine with 80 or 90k miles on it.  Fit an oil filter.  But the 6-start pump gears on an early engine just cause trouble.  You have to re-engineer the whole system. 

The early inlet tract is restrictive, but don't go bonkers opening it out.  The 650ss was ported 1 1/8", but worked better with the standard 1 1/16" carburetors.  70% of that area makes 1", and the standard inlet tract in the head is 15/16".  The inlet valves are 1.4", big already, and there's no point in fitting 1.5" inlets intended for an Atlas. Those pots are 50% bigger.  Similarly, the hot cams you mention were developed for racing 750 engines.  A 500 will not make good use of them, and the high, rapid lift will just cause wear and drag.  Anything beyond the '60s Dominator SS cam (the Commando SS cam is different and unsuitable) is a waste of time, and just wears things out and spoils low-down power.

Port your head gently, give it a really good 3 angle valve seat cut (it really helps gas flow when the valve is just off the seat), and lighten the valve gear.  You can loose a lot of weight from the cam followers and rocker tips.  Don't forget the pushrod ends of the rockers

What I am saying is that development for efficiiency reduces stress on what is not a strong motor.  High tuning will make it go bang quickly.  When you really know the motor and how you use and want to use the bike, think about what will give results.  People have been there before.....

Paul