Is this correct information? I'm a DOHC-4 guy here, and I'm going on the premise that the oil filter bosses are the same between
SOHC-4 & DOHC-4, with the additional spacer, threaded 20x1.5 on the inner female end but something more like 25x1.5 or perhaps 26x1.5mm or more, on the outer male thread - which is what mates with the actual case itself.
Right? Or do the SOHC-4 750 engines lack that little adapter piece altogether?
Either which way, I've got to find the thread size on the DOHC-4 engine case. I've found an off-the-shelf TRUCK filter with the correct 4"-ish / 4&1/8" o-ring diameter, AND a male threaded pipe on the inside face - It seems to be about 1mm or less larger in diameter than the Honda bolt-adapter piece, but the thread pitch would seem identical, and that would seem to indicate there's a metric pitch of 1.25mm that's somehow very close or near exact to the IMPERIAL dimensions - well, that or perhaps this filter was intended for a Metric built truck? Bah! Tempting to just modify my crank-case to accept the new thread! Only REAL problem however, is the filter housing itself is something like eight or nine inches long! Whereas I'm looking for five inches, six inches max (ha-ha "that's what (S)HE said"!)
'Cause you see, I've got a very tight fitting hand-bent exhaust header, a "WOLFE" it's Canadian made, probably associated in some way with Kaz Yoshima's "OMT" Ontario Moto Tech, though of course they made their own exhausts - Well it's worth noting that Canadian outfits were pretty highly regarded throughout the DOHC-4 era, Ontario Motor Speedway being a place of much innovation and cutthroat competition for that matter.....
But yeah, this pipe doesn't give me ROOM for one of these adapter plates for a spin-on filter. If I want a spin-on filter, I've got to find something which approximates the dimensions of the OEM reusable cast alloy filter HOUSING, or as close to it as feasible - I could see myself using a very thin plate to extend the DIAMETER of the unit, for an O-ring size of something more like 6" size, but like I say it's the length/height of that filter which I've gotta look out for.
If I can't find the correct thread diameter & pitch in the actual filter itself, I'll have to grab some sort of pipe "nipple" type adapter, likely male/male as a reducer - Yanno you don't need the NUT in the middle, as it's entirely feasible to drill a hole through the very utmost tip of the threaded pipe, at either end, and so to insert a screwdriver or pen or other rod through the two holes and spin the pipe in & out without any sort of wrench at all! Used to do this a lot back when I was a hardcore aquarium geek, back in the '90s when recirculating systems with PVC hardline plumbing were all the rage......
But yeah, a threaded adapter - all the more sensible if it's just a simple pipe "nipple" of the same diameter on either end, or close to it, with the holes drilled at the tips ("Ju-uu-ust the tiiii-ips!" -Sausage Party)
THAT way, one could have a very large diameter pipe for the flow of oil itself, and a relatively much more common spin-on filter perhaps even multiple spin-on filter parts-#'s so as to make swapping on the fly, while touring, as easy as possible....
Personally, I'm excited about the possibility of a much larger overall filter housing diameter with the O-ring or glued-in-place round gasket with square cross-section etc, of a smaller diameter than the housing itself - You'll find a lot of the 4"-5" diameter spin-on filters have an O-ring diameter of more like 3" or less.
I'm ALSO open to the possibility of an extended narrow diameter tube running across the "BEAM" of the engine, much like the CAPELLINI filters for '60s twins such as the "Walrus-Head" like CB72/CB77 or the DOHC-twin CB450, etc etc. This way, the housing might function as a COOLER if it were covered in fins for higher surface area, and the long noodle of a filter could be accessed from the side without having to remove the whole damn header pipe with each and every oil change!
If nothing else, I should only hope this gives ya'll PAUSE as to that yen you have for HAND-BENT EXHAUSTS? You should be an informed consumer and just know wtf you'd be getting yourself into! Ha-ha.
-Sigh.
