Re: *Permanent* Oil Filter... Hmmm...

Posted by sgtslag on Mar 25, 2012; 2:23pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/Permanent-Oil-Filter-Hmmm-tp3851978p3855700.html

Well, oil coolers are few, these days.  The old Lockhart units are rare, but they were made for these bikes.  The most commonly available are radiators from CB900C's.  Please note that radiators must be rated/made for oil, not transmission fluid -- motor oil is thicker, and it will not flow through a transmission fluid radiator properly.

The challenge is to find the needed adapter to route the oil through the radiator -- almost no one makes them anymore.  Probably your best bet is to use the oil pump, and oil pan, with radiator, off of a CB900C.  If you visit the CB750C Custom Forum (http://www.cb750c.com/), search for the topic of "oil cooler".  You will likely find some good instructions on how-to-do-it over there.  It is very close to a direct, bolt-on, swap, but there may be some minor tricks to it.

This will pump some of the oil through the radiator (dual channel pump, dual oil flow circuits), all of the time -- no thermostat, just oil going through the radiator, being cooled all of the time, no matter what the oil temperature, which is how Honda set up the CB900C's. The radiator circuit draws oil from the pan/sump, pumps it up to the radiator, then dumps it directly back into the oil pan/sump.  It mixes the cooled oil, with the rest, which is not a terribly efficient method, but it works.  There was some concern, by the experts on the CB750C forum, about the 900C's radiator not being able to handle the 72 PSI pressure that my setup creates:  with my bike, 100% of the oil is pumped through the radiator, at full pressure, all of the time; in the 900C, the oil has supposedly no pressure in the radiator.  I've put over 7,000 miles on my engine since adding the oil cooler circuit, without issue.  I check the radiator, and hoses, periodically, for signs of a problem, but nothing yet.

If you can locate an adapter, you could do as I did, and install an oil thermostat, which will largely bypass the oil radiator until your oil temperature reaches 180 F.  Note, however, that this setup will still cool your oil well beyond the air fins, such that you may want to cover the radiator if riding in temperatures below 55 F, as your oil may never reach 180 F, the minimum operating temperature.

Here is a site that sells two types of oil cooling adapters/systems:

http://www.cyclexchange.net/Oil%20System%20Comp%20Page.htm

My setup is similar to the spin-on filter adapter they sell, only I have a different maker, now out of business.  I used a radiator off of a CB900C, cutting the hoses, inserting a thermostat, and additional hoses, to connect to the adapter.  Be sure to use T-bolt clamps!  The oil pressure will be 72 PSI, maximum, which will blow past worm drive hose clamps as if they didn't exist!  Only T-bolt hose clamps will work for this application, due to the high pressure of the system.  Any oil leaks will deposit oil directly in the path of your rear tire...  Think, "Bond, James Bond," for what the results will be.  

Here is an image of the thermostat I used:

http://www.wolfgangint.com/_images/parts/1115109.jpg

I used brass fittings, from a local plumbing shop.  As I said, avoid the shown worm drive clamps.  This thermostat will send 10% of the oil directly to the radiator, when fully closed, to avoid foaming, and thermal shock; when it opens fully (at 180 F), it will send 95% to the radiator, and 5% will go straight back to the engine.  I hope this helps.  Let me know if you have any questions.  Cheers!