350 Scrambler Head on a 250 Monza

[gregwils]

I read that a Scrambler head and green cam would 'wake up' a Monza because of the larger inlet valve. I have a 250 Monza case and barrel, so was thinking about adding a later 350 Scrambler head. I think the 250 and 350 have interchangeable cases, but not sure about barrels and heads. Curious if I would encounter issues or require costly modifications.

Something tells me this probably won't work or at least work easily, but thought I would throw it out there for confirmation. Thanks.

[Jordan]

Check the parts manuals which cover all sizes of widecase engines.
You will see what parts are the same by the part numbers of the various items.

Parts lists are freely downloadable at ducatimeccanica.com

[gregwils]

Thanks Jordan. Interesting exercise. The Monza has a unique head, part number 0600.92.353. The Mach 1, Mark 3 and Scrambler (250 and 350) appear to share 0602.92.350. I say appear, because I could not find the detailed parts listing page for the 250 SCR, only the part drawing which showed the final three numbers as .350. I am assuming it's the same. The 350 SCR also uses 0602.92.350, so hard to imagine the 250 have a unique part number.

The 250 and 360 barrels are also different, so I am going to say "no", not compatible...at least without some machine work or other knowledge that I don't possess.

Thanks again.

[Duccout]

I can't see any reason why a 350 head will fit your 250 barrel? The 350 barrel is longer, but as the big valve 250 and 350 heads both have the same part numbers then they should both fit?

[ducwiz]

I have two scanned parts catalogs, from 1971? and 1974. The numbers for the heads are:

Monza 1974: 0600.92.353
Monza 1971: 0600.92.353

250SCR 1974: 0601.92.350
250SCR 1971: 0601.92.350

250Mk3 1974: 0603.92.350
250Mk3 1971: 0603.92.350

350 SCR 1974: 0603.92.350
350 SCR 1971: 0603.92.350

350 Mk3 1974: 0603.92.350
350 Mk3 1971: 0603.92.350


For the Monza a Dell'Orto UBF 24 carb is listed.
For the 250SCR it is a VHB26, for all others the VHB29.
Early models might have been equipped with SS1 carbs.

..

[Jon Pegler]

A 350 Scrambler head will fit onto a 250 Monza easily.
If it's a widecase head, you will have to fit the narrowcase 250 bevel driveshaft as the 350 widecase shaft will be too long for a 250 narrowcase motor.
Once fitted, you must check valve to piston clearance and squish clearance as a matter of course.

jon

[gregwils]

Okay, I appreciate the correct responses.

I have a related question, hopefully this doesn't seem like I am hijacking my own thread. The reason that I asked the first question is I bought a project bike a year or two ago and have not torn the motor down yet. I am trying to figure out what I have. I assumed the bike was a Monza with a 24mm port because it had Monza round body work and tank on it when I bought it. I just now measured the inlet port and discovered it is 28mm, not the 24mm that I was expecting. I thought the SCR head would be a fun modification, but now it seems unnecessary. I also have a Monza that definitely has a 24mm. I can't tell them apart except for the inlet size. Do I need to pull the head to see what size valves it has?

The serial number on the case from the project bike is 87495. Bevel Heaven lists 87494 as a '65 Diana, but I know there is no correlation between the number and what you have. I also realize the head could have been swapped previously or the tank could have been swapped. I guess there is no way to ever know what it was originally?

Would the inlet on the head be slightly smaller or larger than the carburetor if there was a variation?

Sorry for all the questions. I have decent skills to swap parts out, but I don't have a lot of experience to guide me in these instances. Thanks again for any input.

[Duccout]

I think that you will have to take off the head and see what you have got,

[DesmoDog]

A 350 Scrambler head will fit onto a 250 Monza easily.
If it's a widecase head, you will have to fit the narrowcase 250 bevel driveshaft as the 350 widecase shaft will be too long for a 250 narrowcase motor.
Once fitted, you must check valve to piston clearance and squish clearance as a matter of course.

I'm pretty sure it doesn't matter if it's a widecase or not, a narrowcase 350 shaft will be longer than a 250 shaft also as the cylinder is taller on the 350.

[Jon Pegler]

Narrowcase 350 bevel shaft is the same as widecase 250.
Narrowcase 250 is shorter than widecase 250
Widecase 350 is longer than narrowcase 350
To use a widcase 350 head on a narrowcase 250 the shorter narrowcase 250 bevel shaft would be needed.

Jon