nc gearboxes

[Jon Pegler]

The Mototrans models do not have their own exclusive parts numbering system.
Prior to about 1970 they used a mixture of the old and the new system as used by the Italians.
When Bologna stopped using the old numbering system in the early 1960s, using both numbers and letters, they changed to a system only using numbers.
An example would be the clutch inspection cover 175.KA 53 in the old system, 0400.49.020 in the new system.
The Spanish did not do this but used both the old and the new system,seemingly in a rather random fashion.
After 1970 they seem to have gone over to the fully numerical system, although interspersed with plenty of their own exclusively Spanish parts.
Quite often when looking up parts in a Mototrans parts book it is necessary to cross reference the old numbers with the newer system using a number conversion book.
Number conversion books were available at one time from Domiracer or Steve Allen at Bevel Heaven, but whether they are still obtainable I am not sure.
This does not help very much if you own a 125 Scrambler.
I have never seen a parts book for that model, although there may have been one published in the past.
There was a parts book for the early Spanish 4-speed 125, but that is little use for a 5-speed Scrambler.
The 125 5-speed motor is more like a 24 horas or late n/c Road or De Luxe model, so some of the parts from those models will be the same.
The top end will be almost the same as an Italian or Spanish 160 model, so a parts list for one of those models will help.
The 125 Scrambler chassis is quite different from almost anything else, although fairly straight forward.

Jon

[Jordan]

Thanks.
Did Ducati Italy give a new set of part numbers for the older models? (2 sets of numbers for the same bike?)
Or, did they just change their numbering system, and only applied it to subsequent models?

Jordan

[bodge]

anyone know if a widecase 250 clutch will fit a nc 250 4 or 5 speed box?

[Eldert]

yes it will fit .

but the machining tolerences at the Ducati factory where not that good . so Ducati made the front primary gear in a couple of undersizes .

Eldert

[bodge]

having serious problems fitting my narrowcase 5 speed gearbox (as stated by ebay seller) into my narrowcase 5 speed cases (as i assume they are from oft repeated statement that nc 5 speeds cases have the dm stamp on the left hand case) anyone give me any clues as to how to identify the parts ?

[Eldert]

one of our members made a nice drawing of a narrowcase 5 speed gearbox ( i forgot who , sorry )

here it is :

[bodge]

thanks eldert just checked all the same except my main shaft 5th only has 30t any ideas what it is? also does anyone know if which case the engine prefix is stamped on is definitive cos the two 250 cases i have with the prefix on alternate sides appear identical?

20150712_195620[1].jpg

upper pair have dm250 on left hand case when sat on bike (5 speed ?)
lower pair have dm250 on rhs
only visible differance is on the upper pair the left hand case appears to have the layshaft bearing missing or the centre knocked out ,there is a steel sleve in the hole which i thought was the outer race of a broken bearing but on inspection when i tried to remove its solidly in the case and there is no track in it for a ball to run that you would usually see if someone had just knocked the centre out of a ball race.

[Jon Pegler]

Your upper pair of cases appear to be 5-speed Spanish case.
The cast in boss you have identified takes a needle roller bearing to support the shaft.
You will not get a 5-speed Italian set of gears to fit into that case.
If you tell me what the engine number is, I can confirm which Spanish model the cases came from.
The lower set of cases in your photo look to be 4-speed.

Jon

[bodge]

thanks john the number is 858** im not sure of the origin of the gearbox now, according to walkers book it is a narrowcase 5 speed due to having a 17 tooth fixed first gear but mine has a 30 tooth mainshaft 5th with a 30 tooth layshaft 5th according to the manual and elderts drawing it should be 31/30 could it be a spanish gearbox too?

[double diamond]

The lower case set is an early NC 4-speed, distinguished by a ball bearing in the left side case supporting the driven 1st gear. This case should have DM250 stamped on the right side case half. The upper set appears to be the later 4-speed version, distinguished by a roller bearing supporting the driven 1st gear. This design uses a race machined into the driven 1st gear as the inner race for the roller bearing and employs loose rollers for the bearing element. Similar to a 5-speed driven 1st gear arrangement but not identical. The upper set should have DM250 stamped on the left side case. I don’t know what a Spanish 5-speed case looks like, but all aspects of the upper set appear to be identical to the lower set except for the countershaft bearing. If they are both Italian cases, they’re both 4-speed. I’ll defer to Jon if the upper set is of Spanish origin. Matt