Postby DewCatTea-Bob » Thu Feb 25, 2010 10:37 am
" I will also run a 6x1.0mm blind tap down the threads of mine. Then put some 25mm long allen bolts in. "
____ I have completed this task on every DUKE-cyl.head that I ever really cared about. _ It can be done with 13 of the cyl.head's 17 6mm-holes! _ It should be done with care though.
" Why is it more common on the SCR? "
____ Well there's two consequential reasons for that.....
1_The Scrambler-models were far more apt to be exposed to & get covered with dirt & grime !
Now I suppose at this point, there are those who may think: "Big-Deal, Bob." _ But ya have to keep in mind that back in their day, most DUCATIs were considered by the vast-majority of their (ordinary) owners, to only be just mere 'cycles' -(or "bikes" as they say these days),, and not the 'true-jems' -(DUKEs) that WE know them to be, today! _ So thus the majority of those -(AHs) who worked on DUCATIs back then, didn't even give a second-thought (or even a FIRST thought!) about cleaning-off the dirt from the threads before reinserting the cover-screws back into the cyl.head. _ Believe me, I know how things went back in those days! _ As I've over-looked as many such owners (in more than one part of the country), would simply turn the screws back in and pay no mind at all to the faint sound of the grinding-grit as the cover-screws tightened !
Oh sure, once in a while a better-joe would say something like: "Seems like maybe a little dirt or sand got in there!?" , and perhaps then even go-ahead & take the screw back out and wipe it a bit,, but by then it's too late, and nobody's really caring enough to bother cleaning-out the internal threads with a grease-coated 6x1mm-tap, (as I'd always do!) ! - (I'd surely bet that there's nobody in the world who has wiped as much dirt-contaminated grease from the flutes of 6mm-taps [after each cleaning of those 6mm holes], than I myself have done !)
So I say that if you happen to have a DUKE-SCR cyl.head of which it's cover-screws have no sign of the feel of any grit as ya tighten them, then you're quite lucky to have found such !
2_Unlike the road-bike DUKE-models, the SCR-models were more likely not ridden for as long of time-periods, per ride (without any chance to cool-off), and so the SCR-engines were (also more likely) subjected to more heat-up_&_cool-down periods, which then puts the weak alloy-threads of SCR-cyl.heads through even more stress (against the screws) ! - (Due to the varying expansion-rates, [between those alloy-threads & those of the denser steel-screws] !)
After having performed well over 200 tune-ups on nearly 200 different DUKEs -(ohc-singles), I can well assure ya that the SCR-models were far more likely to have an alloy thread-coil wrapped-around a cover-screw, when removed !
__ So anyhow, when ya shop for 25mm allen-screws (or 18mm, which don't require deeper thread-tapping), do consider the more expensive aluminum type ! _ They now come in anodized black; gold; blue; & red, (besides the natural aluminum-color, of course) !
____ I have already posted (since Nov.21) at least one other post telling of other details which ought to be known about this subject concerning the cover-screws & thread-tapping of DUKE-cyl.heads. _ I believe I first touched on tapping the cyl.head holes in the thread on sand & glass blast-cleaning.
DUKE-Cheers,
DCT-Bob
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob