Fitting an alternator crank to dynamo cases

Hi Pete, you could fit the crankshaft from a later 88SS engine. It has the stronger, thicker big-end that you may need.  If you wish to keep the dynamo type primary cases you will need the shorten the drive-side crankcheek to suit. Lots of people have done this modification,  The shaft portion that holds the alternator rotor will have to be machined and a new thread applied to the part immediately after the wide tapered portion.  You will need a thick spacer/washer to keep the sprocket in position.  Make sure everything will suit before you cut the crank.... Cheersm Howard

Why not just go for an alternator bottom end? All relatively simple.

Gordon is right, the chances of finding a gen 88SS crank? And how would you recognise it as being correct ?. Only a strip and measure. Alt cases are cheap and plentifull .

Gordon/Bob - It's only the 88SS crankcheeks that have the stronger big-end journal and they are stamped 88SS. The flywheel is also different.  (See the DSMs) .  An alternator crankshaft will not necessarily give a stronger big-end journal so why would it be worthwhile converting to an alternator set-up ? The logic evades me at the moment.  If Pete needs a stronger crankshaft for his needs and piece of mind then let's help him to so do.  If he can get hold of a genuine 88SS bottom half,  then the added modifications to an alternator set-up can be discussed. Cheers howard

Pete - So if your Model 88 does have a Model 7 crankshaft then you are quite correct in wanting to replace it with a later Dommie one.  A dynamo crankshaft up to 1956 will be fine for most peoples' needs.  A later alternator crank will fit your cases without any problems but I would stress that you should fit the later 88 con-rods as well.  If you wish to utilise your Model 7 rods I should get them crack-tested and polished to relieve any weakness areas first.  If you're building an 88 Track bike or Roadburner then look for an 88SS crank (5/8 inch journal inside diameter).  You don't mention it but if your donk also has the Model 7 cylinder head, camshaft and low compression pistons then you will be better buying an 88 engine complete and parting company with the Model 7.  Good luck, Howard 

Pete.....check the numbers on your camshaft.  It looks to me that it is displaying T2219@3 on the side in which case it is probably a Q.R. or SS camshaft. Look for extra letters such as Q.R. or X1 or X2 stamped on it.
The cylinder head probably has 22707 next to the inlet rocker cover which would make it an early spigoted 650 or possibly 88SS version. If the head has 23166 on the underside this also is an SS head.
If your barrels have lost their spigots then any of the SS heads will fit, including any 650 version with 25139 stamped on the underside. Note the 750 head has the same numbers but will not fit.
The best twin carb set-up for a 500cc engine to give acceptable riding in town and on open roads is the 376 Monobloc type.
If you opt for a belt drive primary conversion, then you might escape having to mess around with the alternator crankshaft end.  RGM sell a tidy looking alloy primary cover to go with their belt drive kits.

Those ports look big for a road bike 500, port sleeves are available which should (if they fit) help keep you a decent mid range .

I have raced an 88 with a standard head and single 1" carb quite successfully (first in class at National level). My gut feeling is that you can try and get too much out of an old 500cc motor. They went well enough when they came out of the factory. Would you actually use the potential performance bearing in mind that it is likely to kick in above 5,000 rpm?
These days keeping things fairly standard and going for reliablity has a strong appeal.    

I am firmly with Gordon on this one , a well set up 88 will be happy all day at 70/ 80 and feel happy too . A 650 SS / Atlas with more power and speed will tire you out with its vibration and make you settle for a slower speed . Concentrate on smooth and efficient with reliability  and peace of mind.A Daytona cam with flat followers would be my choice.

The Daytona camshaft (T2219 @ 2) appeared in 1956 on Norton Heavy Twin road bikes.
The Q.R. (T2219 @ 2) in late 1958 and the SS (T2219 @ 3) in 1960.
 

Hello again Pete - Further to what Phil has written please note that the Daytona and the QR cams have the same profiles. The QR stands for Quietening Ramps.  Flat followers are fine for those three types of cams. The SS cam gives more power - if it's needed ?  Don't use a Model 7 or early 88 cam.  The 88SS used 9.45:1 compression ratio pistons.  Use a pair of 1 1/16 inch AMAL Monoblocs or 28mm AMAL Concentrics on your downdraught head or a single carb manifold with an 1 1/8 inch Monobloc.  Cheers, howard     
 

Yes . Sorry , the Daytona cam with the quieting ramps . Standard cam for many years fitted to 88/99 ,  from late 1950,s up to early 1960,s , very similar profile to the SS cam of the 650 and Atlas but with slightly less duration and lift cheap to find s/h and does not need the stronger valve springs or barrel pushrods that the SS had. Less valve clearances too so a bit less clatter. Good enough to power a 99 to the Ton ., and the  std 88 to 90 mph 

Look like std rods suitable for a Daytona cam , I would also use with an SS cam , but I am unlikely to be exceeding 6000 revs !