500 twin crank survey

I have two 500cc alternator cranks apart at present.

The internal oilways are:
Std Model 88:  1 inch
88SS:   5/8 inch.

Yes they are both alternator cranks as initially mentioned 

I could find a spare dynamo crank and check it as well if that helps.

No problem just take me a few days.

Drg dated 1951 says 1'' 

Hi Ashley - there must have been a drawing amendment for the 88SS and also for the alternator version of the crankshaft so was there an amendment for a 7/8 inch journal ?  Cheers, Howard

Its well known  that older cranks are more suseptible to fracture due to the larger core  hole together with an  internal stress raiser ,and genuine later  88 SS cranks are a better bet with a smaller core hole .  These are old motors and the fabled 88ss cranks are not easy to find . If looking for reliable performance I would think 650 SS.

Hello Pete,  As one of the contributors to assemble the Dominator Service Notes publication I have been looking for evidence of the mysterious 7/8 inch big-end journal hole on Dominator 500 and 600 crankshafts.  Only this morning I was reminded that all Nortons in the Bracebridge St era were virtually hand built and assembled as far as possible to  the customer's wishes.  Hence all manner of frame parts, gearbox ratios and engine-tune parts could be specified and Norton were keen to oblige.  When the factory closed the experimental department and the race shop many hitherto unseen components became available and crankshafts with all manner of different dimensions came to the market place particularly in the racing fraternity.  Crankshafts with 1/2 inch holes and 1.75 inch big-end journals (using Matchless big-end shells and con-rods).  Also 5/8 inch holes with 1.6 inch shells and - dare I say ?....Triumph rods were purchased.   So if a bike was intended as a private entry to Daytona, Sebring , Mosport or Thruxton all manner of different specifications were possible and likely.  Needless to say these modifications did not get included in revised Drawing sets or Parts books.  Some of you lucky readers will have owned a genuine 88SS.   These engines had a 5/8 inch hole in a 1.5 inch big-end but some of these crankshafts found their way into some of the later 88 Standard and De-Luxe models.  I personally had a 1962 88SS that had a semi-downdraught head with 28 mm inlet ports and no tin tube.  Most of these models had 1 1/8 inch inlet ports and a tin insert sleeve to reduce the port to 1 1/16 inch to match the 376 Amal Monobloc carburettor.   So, to me it is unsurprising that a rogue crankshaft may occasionally turn up ( from an ex-race engine) but searching for the evidence may be impossible.  My "head" too could have been a rogue but I hope it is still performing on an unsuspecting 88SS rider's steed.   Good Luck  Pete - buy an alternator crank with 5/8 inch hole.       Howard

It would make sense variations are out there, even back in the old days there would have been a MOQ for someone to machine and I suspect the race shop may have had an initial requirement of say 20 cranks, so ordered 20. However they may have only built 5 bikes and I doubt back then the extra cranks would have been wasted and used on road going models. Just like we often see Atlas crank drive ends on 750 Commando cranks. It no longer amazes me what turns up where, we see it all the time. 

Another thing I had no idea about ! Not having rebuilt a Norton motor before I have had pretty well , no, everything done on the bottom end and am waiting at the moment for the head to come back having had everything done to that. I did have the crank apart to check the `sludge trap` but didn`t measure it as up until now thought they were all the same . I was actually amazed at the size /volume of it and thought how much oil it would take to fill it up before the big end gets any lubrication . I dont really want to pull it all apart again just to check the size. Someone else had built the motor before I got it ( Badly ) so it unknown what crank he may have used . Am I in a fix ?Photo gives an idea of the crank . 

Hi Wayne ,interesting frame , i think it was orriginally a DL Dommy from around 1960? 

A few years ago I had all the gear for testing and properly servicing Norton twin oil pumps. This included being able to test flow output before and after a service. What surprised me was how long a 3 start/worm pump took to fill an early 500cc crankshaft.
With the Timing side big end taped up and the shaft at TDC it was up to 60 seconds for oil to reach the left crank pin.  This was using a 3 speed pump in good condition. These 3 speed pumps have a feed output of around 11.9 gallons per hour. Approx 1L per minute.

With a well-used oil pump and worn big ends on conrods fitted this time increased by roughly 50%.  Which possibly explains why the left side piston is often the one to show more wear and there are heaps of spare right side pistons on the market.

Back in the early 1950s Bracebridge advised that crankpins should not be reground below -20 thou. as it would weaken the pins. But I think that many of the reported broken crankshafts were more likely due to poor regrinding especially in the corners where a 90% finish is essential.  Possibly the advice was to scare owners into purchasing a new crankshaft because -30 thou big end shells were not available. A bit like +30 & +40 thou pistons were imitating hen's teeth in those times.
Remember that worn crankshafts can be hot metal sprayed and then ground back to standard by specialists and the cost is not bank breaking.

A few years ago I had all the gear for testing and properly servicing Norton twin oil pumps. This included being able to test flow output before and after a service. I still have 20 pumps to play with. What surprised me was how long a 3 start/worm pump took to fill an early 500cc crankshaft. 
With the Timing side big end taped up and the shaft at TDC it was up to 60 seconds for oil to reach the left crank pin.  This was using a 3 speed pump in good condition. These 3 speed pumps have a feed output of around 11.9 gallons per hour. Approx 1L per minute.

With a well-used oil pump and worn big ends on conrods fitted this time increased by roughly 50%.  Which possibly explains why the left side piston is often the one to show more wear and there are heaps of spare right side pistons on the market.

Back in the early 1950s Bracebridge advised that crankpins should not be reground below -20 thou. as it would weaken the pins. But I think that many of the reported broken crankshafts were more likely due to poor regrinding especially in the corners where a 90% finish is essential.  Possibly the advice was to scare owners into purchasing a new crankshaft because -30 thou big end shells were not available. A bit like +30 & +40 thou pistons were imitating hen's teeth in those times.
Remember that worn crankshafts can be hot metal sprayed and then ground back to standard by specialists and the cost is not bank breaking.