Making A Little Progress (with pics)

[DewCatTea-Bob]

" Here's some better pictures of the piston we found inside the '63 Scrambler: "

____ Wish I could examine that piston in-hand...
It's dome doesn't appear as the same as a stock Motocross/Scr.piston, rather seemingly more like a 9.8:1 M1/Mk3-piston (with it's larger valve-reliefs).
__ Can you measure the actual max.width of those reliefs ?
I believe the 10:1 Mk-III piston has the same widths as the Monza & Scr (ex.=34.5mm ; in.=37.5 [+/- ,5mm] ), while the M1/Mk3 v.relief-widths are 37.5 & 41.5 (+/- .5mm). _ This last piston appears similar to a 9.5:1 WideCase-type 250-Scr.piston, except that it's dome seems to look more impressive/hotter.


" Also, is that little flat spot a relief for the spark plug? "

____ Not intentionally (as stock, anyhow) ! ...
It seems that someone once inserted an over-reach spark-plug.


" The archaelogical detective work is part of the fun for us. "

____ I really agree ! _ Whenever I acquired a used Duke, I always couldn't wait to explore/discover whatever changes it had within !


Fun-Cheers,
-Bob

[double diamond]

A stock scrambler piston would have four rings (including one oil ring at the bottom of the skirt) and be a casting. This piston is three ring and appears to be a forging. Also, the dome and valve pockets are clearly bigger than a stock scrambler piston. Wonder if it has a Mk3 cam as well? IF the cam lobes are symmetrical it's likely a stock cam but if they're asymmetrical it's something else. What are the valve sizes? Matt

[guzzijon]

I did some measuring tonight and here is what I came up with:

Engine in Scrambler:

Intake Valve: measured as 36.7 mm (36mm?)
Exhaust Valve: measured as 33.5mm (33mm?)

Do the valve sizes make this a Monza head? Or did the Scrambler and Monza share the same valve sizes?

Hairpin springs
Bad/stripped exhaust threads
Good bevel gears

Piston has Intake valve relief measuring 41.9mm
Piston has exhaust valve relief measuring 38mm

Piston is 74.5mm and bore is 75mm

Engine in 1964 Monza:

Intake valve: 40mm
Exhaust valve: 36mm

Do the valve sizes make this a Diana Mach 3 or Mach 1 head or a head that has been modified to accept Diana Mach or Mach 1 valve sizes?

Coil spring conversion
Good exhaust threads
Broken tooth on bevel gear

Monza piston valve reliefs are 40mm for both intake and exhaust.

Any insight is always more than appreciated!

[DewCatTea-Bob]

" Engine in Scrambler:
Intake Valve: measured as 36.7 mm (36mm?)
Exhaust Valve: measured as 33.5mm (33mm?) "

____ A little odd for valve-ODs but I have often noticed slightly oversized valve-heads in older n-c cyl.heads.


" Do the valve sizes make this a Monza head? Or did the Scrambler and Monza share the same valve sizes? "

____ Both those n-c.models used the same 36 & 33mm sizes, however the valves themselves were not the same.
Monza cyl.heads employ screw-adjuster type rocker-arms along with their slightly unique valves, so that should help confirm your cyl.head model-type. _ Also, a Motocross/Scr.head has a 28.5mm intake-port, whareas the Monza's port is only 26.5mm in diameter (at it's mouth).


" Hairpin springs "

____ These are the std.valve-springs for both models (and others which also employ the 36 & 33mm valves).


" Piston has Intake valve relief measuring 41.9mm
Piston has exhaust valve relief measuring 38mm "

____ Those figures seem right for a M1/Mk3 piston.
Does it have 'BORGO' stamped on it's flat top ?


" Piston is 74.5mm and bore is 75mm "

____ If that were actually true, then the engine would be quite noisy with piston-slap.
At exactly what points did you take your measurement-reading of the piston's diameter ?
I believe it should actually be measured across it's skirt just beneath the oil-ring and at front & back (90-degrees around away from the location of piston-pin holes),, you should try to find the piston's max.diameter reading, in order to determine it's true bore-size.



" Engine in 1964 Monza:
Intake valve: 40mm
Exhaust valve: 36mm
Do the valve sizes make this a Diana Mach 3 or Mach 1 head or a head that has been modified to accept Diana Mach or Mach 1 valve sizes? "

____ Those valve-sizes do indicate M1/Mk3-valves, and that the cyl.head is also likely the same model,, cuz there wouldn't be any benefit to installing the larger valves in a cyl.head which has the small-sized valve-seats. _ You ought to compare the two pairs of v.seats in both your cyl.heads to see if there's any difference in size.
A stock M1/Mk3-cyl.head has an intake-port dia.size of 29.5mm .


" Coil spring conversion "

____ This feature is not stock and a very good indicator of extensive cyl.head-modification throughout the head, as this rather radical-mod has probably never been done without also modding something-else as well, such as port-work.
What is the intake-port's dia.size on this cyl.head ?


" Monza piston valve reliefs are 40mm for both intake and exhaust. "

____ This must be of the MC-piston, which while certainly can be called 'valve-reliefs', are not really 'valve-pockets' or 'cut-aways' such as stock Duke-pistons actually have.
So while you may get-away with stating "Monza piston", it's actually certainly not a real 'Monza-piston' .
(Of-course you no-doubt had realized this already, I'm now just pointing-out the word-play for the sake of other readers' interpretation.)


" Any insight is always more than appreciated! "

____ Of-course I'm sure that we all feel that way.


Happy-Cheers,
-Bob

[guzzijon]

Also, a Motocross/Scr.head has a 28.5mm intake-port, whareas the Monza's port is only 26.5mm in diameter (at it's mouth).

Thanks, I'll measure that next.

Piston has Intake valve relief measuring 41.9mm
Piston has exhaust valve relief measuring 38mm

____ Those figures seem right for a M1/Mk3 piston.
Does it have 'BORGO' stamped on it's flat top ?

Not that I can see but there is a lot of carbon, I might be able to see after I clean off the carbon.

I believe it should actually be measured across it's skirt just beneath the oil-ring and at front & back (90-degrees around away from the location of piston-pin holes),, you should try to find the piston's max.diameter-reading, in order to determine it's true bore-size.

Thanks, I measured at the very top as all I have right now is a cheap Harbor Freight digital caliper. I need to remeasure with a micrometer or a caliper that will fit around the skirt.

[DewCatTea-Bob]

" Thanks, I'll measure that next. "

____ It should be noted that you posted your response-post before I got the second-part (on the "Engine in 1964 Monza") included within my-own response-post...
That's fine because from this point onward, the two separate engines can now each have their-own separate postings (so as to keep their info from being confused-together),, so keep-note of the post-titles (as you-yourself had instead included within your post-text).
(And BTW, it was myself that edited your last/previous post so as to straighten-out the 'quote' arrangement.)


" Not that I can see but there is a lot of carbon, I might be able to see after I clean off the carbon. "

____ Another (less likely) possibility is that it's an aftermarket-type piston, such as made by ASSO .


" Thanks, I measured at the very top as all I have right now is a cheap Harbor Freight digital caliper. "

____ If you already used it at near the crown-edge, then it seems like that same tool ought to be able to take a good-reading of the piston-skirt as well.
__ Anyhow, your "74.5" reading would indicate a brand of piston that produces over-sizes in .25mm increments (like brands such as ASSO has done), whereas BORGO goes by .2mm increments. _ So if it's a BORGO-piston, then it should be either 74.6 or 74.8 or 75.0mm,, hopefully the last, to match your measured cyl.bore.
Most piston-brands include the exact size of the piston, stamped near their brand-name.


Hopeful-Cheers,
-Bob

[guzzijon]

"
<Big snip>
A stock M1/Mk3-cyl.head has an intake-port dia.size of 29.5mm .
<Big snip>
What is the intake-port's dia.size on this cyl.head ?
<Big snip>
Happy-Cheers,
-Bob

Bob,

I measured the intake port of the cylinder head that came on the 1964 Monza and it measured as 29.5mm. So it has a 40mm intake valve, a 36mm exhaust valve, and a 29.5mm intake port. Is it safe to say that this is a M1/Mk3 cylinder head?

Thanks,

Jon

[DewCatTea-Bob]

" I measured the intake port of the cylinder head that came on the 1964 Monza and it measured as 29.5mm.
Is it safe to say that this is a M1/Mk3 cylinder head? "

____ Well due to the port's exact measurement, I'm pretty-sure that it probably likely is,, however to be sure, you should check & see that it's valve-seats are larger than those of your 250-Scr cyl.head, as that's the surest way to be the most certain of such a (desirable) Duke-head.
__ It now seems quite suspect that the engine of your Monza is no longer a Monza-motor. ...
Either the original top-end has been replaced with a M1/Mk3's top-end, or,
your entire motor (of your Monza) has been replaced with a complete M1/Mk3-motor.
Can you confirm the motor-number found on the motor-case of the motor in your "Monza" ?


____ BTW, thanks for giving your post a helpful heads-up & sensible re-title fairly-related to your specific post subject-material.
Too many of us neglect to properly alter the post-title when they've significantly wondered off-topic from the thread's original title-topic.


Happy-Cheers,
-Bob

[guzzijon]

The engine stamping is on the left side and is stamped "DM250" and the number on the right side is stamped "86472".

Tom Bailey's "Ducati Singles First Person" says that The 1964 Diana MK3 5 speeds have the engine stamping with just "DM250" and the later Diana MK3 5 speeds had the "...M1" added to the 'DM250".

I guess my question now is, with so little left of the bike, how do I know if it is a Monza or a Diana MK3? I guess it just might have one of the major things that make a Diana MK3 different from a Monza, the cylinder head...

[DewCatTea-Bob]

" the number on the right side is stamped "86472". "

____ The lack of either 'M1' or 'M3' leads me to think that your Monza's bottom-end is probably what's left of it's original (late-1964) motor.


Tom Bailey's "Ducati Singles First Person" says that The 1964 Diana MK3 5 speeds have the engine stamping with just "DM250" and the later Diana MK3 5 speeds had the "...M1" added to the 'DM250".

____ That ought to be a more authoritative source than myself BUT, it's always been my-own understanding that the 1965 version of the Mark-3 became the first of such models to then get the additional stamp-mark (which was actually: 'M3' ), because that was the first year for the Mach-I, and Ducati thus-then felt the need to distinguish between the two similar motors (of the Mark-3 & Mach-I), as THAT year Ducati chose to alter the then-past 'Mark-III' to employ the very-same top-end as the then-new 'Mach-I' .
__ Now since your Monza has the top-end of a Mach-I / 'Mark-3' (rather than that of the pre-1965 'Mark-III'), then your bottom-end (without any M-stamping) must thus-then be other than either of those then-new 1965-models (and-so thus likely still the original Monza bottom-end). _ In other words, it's quite likely not a Mark-III bottom-end because it has a 'Mark-3' top-end (and NOT a 'Mark-III' top-end).
__ Does anyone-else besides myself realize that Ducati altered their DianaMark(three)-name from "III" to "3" once the "Diana Mark III" model began employing the Mach-I model's top-end [for the 1965 model-year] ?


" I guess my question now is,
how do I know if it is a Monza or a Diana MK3? "

____ I believe I've (just above) given the logic to conclude that it's a Mark-3 top-end on a (likely) Monza bottom-end,, however to be more certain, let us know whether the bottom-end's alt.cable has two yellow (or perhaps one red & one black) wire-leads within it's black-conduit, OR instead, one yellow, one red, & one white wire-leads,, (as the Mark-III/Mark-3 models had three [rather than just two] wire-leads within their alt.cables).


DUCATIly,
-Bob