Poor guide support on ported head.

[Bevel bob]

My mark3 head was ported for racing at some time, Good for breathing , the motor shoots up to 10000 in a blink, however this is not much use as its bad for the big end and i don't ride that hard anyway.the lack of the guide boss is known to provoke guide movement. Has anyone had a boss welded back in ? is there another solution?.

[Jordan]

Yes, I have another solution: Use a desmo head without valve springs, or with lighter springs.
That relieves the guides of much of the pressure that would act on them.
Also easier on everything in the valve-driving train - cams, rockers, valve stems, shims, spindles, bushes, gears.
That's my theory, anyway!

Jordan

[DewCatTea-Bob]

By: Bevel bob...
" the lack of the guide boss is known to provoke guide movement. "

____ Of-course that's fairly true and stands to reason, as there's even less material left-behind to help support & hold-tight the v.guide, after Ducati's largest (std.production)*intake-port has been further 'ported' -(enlarged).
__ * Ducati had three obviously different intake-port type/sizes in their std.production 250/350 cyl.heads... 26.5mm for the Monza/GT/Sebring; 28.5mm for the 250-Scr./Motocross/Mark-III; 29.5mm for the 250M1/M3 & most-all wc-350 models. _ The 26.5-port is the only port-type which has an obviously obtrusive/(somewhat obstructive) v.guide support-boss, while the other two port-types leave the bare v.guide 'sticking-out' from the intake-port's port-wall/ceiling,, although later model wide-case heads did have their port-roof/ceiling's height notably reduced near the v.guide area, but it's relatively too settle to be considered as a clearly-obvious v.guide "boss" (like the Monza-port more certainly has).


" Has anyone had a boss welded back in ? "

____ Well probably-not actually merely-just a "boss" for the v.guide only...
What others (who think that port-SHAPE makes a worthwhile-difference, [I-myself don't] ), have done, is have pretty-much the ENTIRE intake port-way welded-up within, (not just the guide-support area),, and then bore-out a new intake-port (with an expected superior shaped air-flow path-way, for improved 'breathing', [and hopefully also still sufficient v.guide-support] ).
But rather than go to such an extravagant expense (for relatively next to no really useful beneficial-return), it would serve you better to simply trade your 'ported' cyl.head (for another unmodified one), to someone-else who would prefer your already ported-out cyl.head, (likely for their intended race-engine).


" is there another solution?. "

____ Yes... What I did, (way-back when I was thinking that bigger-is-better), was after porting-out the intake-port too large (to leave much meat left for supporting a stock-type v.guide), I then next threaded the v.guide-hole, and also threaded a replacement-v.guide, so that then the v.guide would be 'threaded-in' rather than merely 'pressed-in'.
The special-v.guide was turned on a lathe and made to have it's threads somewhat over-sized (compared to std.threaded-fittings), so that the cyl.head needed to be heated-up in order to get the v.guide fully screwed-down into place. _ And besides that extra measure, a tiny-hole also had to be drilled-through the (pre-tightened down) threads (of both head & guide 's top 2-threads), so that a short pin/peg could then be pressed-through in-between, so as to then lock-in the v.guide (to the head, to KEEP it fully threaded-in).
All this extra added-work done just to make-SURE that the v.guide REMAINS stayed-put, (as well as keep the guide solidly positioned so it couldn't ever be wobbled-loose, [like a merely pressed-in std.guide eventually becomes], of-course).
___ However to the dismay of the racer-types among us, it's been my-own experience that such enlarged intake-port modifications are not really worth the relatively rather small resulted-gains in power-production,, since rider-weight differences of just-merely 5 to 10 pounds can make a roughly equal/cancelling difference in acceleration. _ (So-thus it's probably easier/cheaper to just loose 10-lbs some way.)


Duke-Cheers,
DCT-Bob