Valve Sizes

[frankfast]

I've read your posts completely and have a better understanding on the variety of combinations that may be employed on my 350. Thanks for the help. Once I get it back together I'll let you know the results.

[DewCatTea-Bob]

" Once I get it back together I'll let you know the results. "

____ Well, hope you keep us informed about which part-combos you decide to employ, before-hand !
In fact, it'd be fairly interesting to know what you're currently thinking, in that regard !


Fun-Cheers,
-Bob

[frankfast]

I'm not sure yet. I need rockers, a cam, guides at least and have priced those separately. It's beyond my budget even if I could find the proper green/white cam. I've been offered a complete reconditioned head (valves, guides and I'm not sure what else) done by a person very familiar with Ducatis at a fair price. However, he believes that the head originally came from a 250 Scrambler but is not sure that the cam is original to the head. Since it has screw type adjusters, I don't believe that they are original since I believe all Scramblers came with shim type. The cam has no paint marks on it. Unless the cam is removed and the lift is measured I won't be assured that the cam is a Scrambler cam. He's not willing to take it apart. I like the fact that the head is complete with a new valve job.

[DewCatTea-Bob]

" he believes that the head originally came from a 250 Scrambler but is not sure that the cam is original to the head. Since it has screw type adjusters,
Unless the cam is removed and the lift is measured I won't be assured that the cam is a Scrambler cam. "

____ Whenever ya find a cyl.head with screw-adjuster type rocker-arms, it should be suspected as being a Monza-head,, and to be sure, it should have a 26.5mm intake-port.
If that 250-cyl.head has (the previously expected) 28.5mm in.port, then one could expect that it would either include a 250SCR-cam, or a Monza-cam (which more likely came with those rockers).
There's actually very little difference between those two cam-models, so it shouldn't matter much which one it really is. _ And if the included camshaft happens to be some other cam-model, then it will be better suited to go with your open-meg.
__ It would be a good experience to install & run with that replacement-head (while you wait for the desired parts to come by your way, for your stock-head), until the day you're ready to reinstall your 350-head ! _ Especially if you can compare your DUKE's performance against another, before & after !
__ Then, you could sell your chosen-to-be-spare/extra cyl.head -(whichever one that turns-out to be), for likely more than you'll be paying now.

____ Did you ever check-into getting your rocker-arm's follower-faces redone?


DUKE-Cheers,
-Bob

[frankfast]

I did. Syds Cycle will reface rockers. Mine would have to be welded first because they are actually concave. I decided not to buy the 250 head because either the piston or the head would have to be machined. The 350 is a 76mm bore and the 250 is 74mm. I didn't want to make such permanent mods in case things have to be replaced in the future. I bought a set of screw type rockers (in good shape) for a reasonable price. Now I have to settle for a cam and have the opportunity to purchase a white cam out of a 250 Scrambler. If I'm not mistaken after our extensive discussion, the white cam is somewhere between the violet (Monza, Sebring) and the green/white of the 350 Scrambler. It probably will suit my purposes just fine.

[DewCatTea-Bob]

" I decided not to buy the 250 head because either the piston or the head would have to be machined. The 350 is a 76mm bore and the 250 is 74mm. "

____ So how did you come to believe that any machine-work would be needed? _ If that were true, then I certainly would've mentioned so !
While it's indeed quite true that there's a difference of 2mm between the stock bores of the 250 & 350, (and thus the squish-band width is 1mm less wide on the 250-head), ya must realize that whenever the installation of an oversize-piston requires cylinder-liner bore-increase machine-work, that any equivalent machine-work is never needed to be done to the cyl.head as well.
There have been many brands of oversize-pistons made for 250s up to .100" -(2.54mm) oversize, (and used in w-c 350s too). _ And you sure wouldn't be the first to use a 350-piston in combo with a 250-head !
The combo works, (and perhaps with a slight compression-ratio increase, due to the thinner squish-band's [reduced]- width).


" Now I have to settle for a cam and have the opportunity to purchase a white cam out of a 250 Scrambler. "

____ The 'White-cam' was first stock within (made for USA)- 1968 w-c 250-Scrambler models, and then also the 450-Jupiter/Scrambler models... But, as I've posted elsewhere, I have fairly-good reason to believe that the White-cam was originally designed (at least mainly) for the 350-Scramblers.
Until the White-cams were used, all 250Scrambler-type models always used camshafts marked with brown/tan color-codings !


" the white cam is somewhere between the violet (Monza, Sebring) and the green/white of the 350 Scrambler. "

____ It's a step* wilder/hotter than the 'Monza-cam', and more-or-less about the same as the other 2 or 3 (previous)- 250Scrambler-cams.
(* A "step" being a noteworthy-change in specs, yet nothing measureable by the seat-of-the-paints.)
__ The next wildest cam, (the Red/Mk3-cam) is 2-steps wilder than the White-cam, and the next wildest cam (the Grey/M1-cam) is another step wilder yet,, and depending on which of the two G&W-cams, (the 350Mk3-cam or the 250F1-cam), an additional 2 or 3 steps exist between them and the White-cam. - (That's a total-difference of 5 or 6 steps between the White-cam and whichever G&W-cam.)
Now while that comparison seems to belittle the White-cam, ya have to keep in mind that the difference in cam valve-timings is actually a trade-off - in that what ya GAIN in torque at higher-revs (with a wilder-cam), is also pretty-much LOST at low-revs.
Therefore, the wildest-cam would be best only for use in an engine which spends most of it's time at top-revs,, and the mildest-cam would be best for engines which spend most of their time accelerating from low-RPM.
__ So ya ought to ask yourself: 'What's funner, for me?' . _ Taking-off from a stop, or, being maxed-out, most the time??
So ya weigh your overall-ratio of the two extremes, and then go-for the cam that's best for your best overall-desire. _ (And not simply choose that which the common hot-rodder crowd drools-over.)


Dukaddy-DUKEs,
-Bob

[frankfast]

When we placed a stock 350 Scrambler piston into the combustion chamber of my 350 head, it fit perfectly as intended. But when I placed that same piston in the 250 Scrambler head the crown of the piston touched the top of the chamber rendering the squish band useless. It seems that the cylinder would have to be shimmed up, lowering the compression or the piston would have to be machined to match the 250 head. What am I missing?

[DewCatTea-Bob]

" But when I placed that same piston in the 250 Scrambler head the crown of the piston touched the top of the chamber rendering the squish band useless. "

____ Assuming that I'm understanding this (crazy)- issue correctly, then I have to say that I'd have to see that to believe it !
Cuz in any case, the squish-band on any stock 250/350 piston should contact the squish-band of any stock 250/350 cyl.head, before anything else could possibly make any contact within the combustion-chamber !
Also, all stock 250-piston models have higher domes/crowns than any stock 350-piston !
So perhaps that 250-head has been somehow modified (and made useless with any stock-piston?) ?
__ Got any pix?
____ I wonder if Eldert has ever heard of any such tale as that !?


Crazy-Cheers,
-Bob

[frankfast]

Sorry, i don't have any pix. Because of this issue I didn't buy the head and just purchased a set of rockers from the seller. I didn't use my Scrambler piston for the experiment but rather a brand new one from the sellers abundance of parts. I have only his word that it's the same. Perhaps a 350 Sebring piston (with a lower dome) would fit quite well.

[DewCatTea-Bob]

" I didn't use my Scrambler piston for the experiment but rather a brand new one from the sellers abundance of parts. I have only his word that it's the same. "

____ Perhaps that piston he had was not really a STOCK-type piston, but, it's still not understandable that ya could find any piston that would fit with a stock 350-head & not also equally fit with a stock 250-head !
__ Wish I could've been there to see the reason for that crazy/strange issue !


" Perhaps a 350 Sebring piston (with a lower dome) would fit quite well. "

____ The differences between a Sebring-piston & a w-c 350-piston is the dome-height of the crown, the size of the valve-reliefs, and the length of their skirts, (all of which are scaled-down on the Sebring-piston).
__ If a normal w-c 350-piston would not properly fit into a combustion-chamber, then any of the 4 types of stock 250-pistons, (which have even higher domes), wouldn't either !
But perhaps a Sebring-piston would fit with the mystery-issue of that 250-head, since it's dome is flat with the top-side of the squish-band.


Unfortunate-Cheers,
-Bob