Re: CB650 SC Oil Cooler for CB750's

Posted by sgtslag on Apr 15, 2012; 6:02am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/CB650-SC-Oil-Cooler-for-CB750-s-tp3909678p3911450.html

The spacer you refer to, is that the Oil Filter Boss?  The Oil Filter Boss is the hollow, threaded tube, which the filter housing Bolt screws into.  The Oil Filter Boss screws into the block.  For my adapter to fit, I had to cut off 1/4" of the Oil Filter Boss, to allow my adapter plate to snug up, and seal against, the block.  I used a cut-off wheel on my moto-tool to remove the 1/4", then I used a grinder to smooth the edges.

Here is a schematic showing the Oil Filter Boss on my 1979 CB750K:

http://www.bikebandit.com/houseofmotorcycles/1979-honda-cb750k/o/m2001#sch16784 (#14, the Bolt is #13)

The 1983 CB650 SC's oil cooler, and adapter plate, appears to be a direct bolt-on, which is why I recommend that over an after-market adapter made for the CB750's.  Besides that, some folks are currently selling the whole oil cooler unit, on e-Bay, for around $30 -- little, to no, modifications required.

Shiny, if your oil is that cool, then, No, you don't need a Cooler.  Mine read 250 F, at highway speeds, consistently, for 3 hours of riding, which is the thermal limit of dino oil, before it breaks down into carbon sludge.  Mine is a DOHC, which may run hotter, for whatever reason.  The best thing to do, is what you have done:  put a temperature gauge on it first, to check to see what temperatures your particular engine is running at.  If it is consistently at 240+ F, then a Cooler is a very good idea; if it is at, or below, 210 F, then you don't need a Cooler (mine consistently runs at 210 F, with the Cooler circuit running, in town, and on the highways).

Also, it depends on the air temperature:  if the air is cooler than 60 F, your engine oil will be much cooler; my oil won't reach minimum operating temperature of 180 F, if the air is cooler than 60 F (even with 90% of the oil bypassing the Cooler, due to the Thermostat, it still can't warm up).  In air temperatures of 80 F, or higher, my oil heats up to 250 F, without the Cooler; it only reaches 210 F, in air temperatures of 90 F, with the Cooler running.  Cheers!