Don Terrill’s Speed-Talk

One can apply this to any custom or factory vintage air cooled, oil-in-backbone design, it doesn't have to be focused solely on a Yamaha SR as pictured.

Two issues faced by someone putting an oil cooler on his moto are: 1) an oil cooler mounted up front on the downtubes is exposed to gravel rash and mud clogging, and 2) although oil coolers look cool and racy sometimes they also look clunky.

For someone building a custom scrambler for which both off pavement capability and aesthetic cleanliness are in the design brief the two above issues must be overcome at the same time. So how effective would the below idea be?

Instead of a traditional downtube mounted radiator type oil cooler, simply put an auxiliary oil tank under the seat, plumbed directly into the frame's backbone which is the main oil reservoir. The aux oil tank wouldn't be directly in the airstream, but it would be providing surface area for heat shedding and would also be providing anywhere from 1-2 additional quarts of oil.

A traditional cooler also adds volume of oil, it might not hold as much as the tank, but it will shed more heat.


One idea is to have the tank made out of a round automotive oil filter, using a remote mount for plumbing. The filter might even have a handy anti drainback valve.

The filters surface will shed heat like the tank, hold volume, and have the benefit of easy replacement when doing an oil change instead of disassembly and cleaning.

i cant imagine running hot oil through the frame right under the gas tank will do you any good for making power. the added volume, and the frame will acts as a heat sink, but is the down side worth it?

Years ago I worked on a Norton plumbed to use the frame as a cooler/reservoir; it was plagued with oiling problems from the get go. The remote filter idea from mini is a good one, there are also custom fined covers made for the street rod guys that are relatively tight fitting and would add surface area for cooling. Plumb it with braided lines to keep it clean; hose clamps and rubber on a road bike (or anything) are usually not a good plan.

Adding oil volume without airflow and surface area to transfer the heat will just take longer for the oil to reach the same temperature. BTDT.

Temperature differential is what cools the oil so, putting it somewhere in an active air-stream is where it is meant to be.

Cooling of engine oil is only required where the oils operating temperature is exceeded.
BSA and Triumph introduced oil in frame in the seventies utilizing the rear down tube as the reservoir, the singles used the top tube as well, a number of guys rearranged internal drillings to incorporate other tubes in the quest to aid cooling and volume. This was a dubious quest as the ones i saw were not any faster or more reliable than the ones that had a simple cooler mounted to the frame. De burring and pre cleaning before commissioning was also an issue.
Some years back i built a 100" Sportster with all the fruit, i used a vertical Jagg cooler with an inbuilt thermostat, i could count on one hand over years the amount of times that cooler was in circuit.

As Nicolas has pointed out, in a dirt off road application this would pick up volume and a cooling effect to a degree.

Cheers.

PackardV8 wrote: ↑Tue Aug 03, 2021 10:52 am Adding oil volume without airflow and surface area to transfer the heat will just take longer for the oil to reach the same temperature. BTDT.

Helpful, thanks!

hoodeng wrote: ↑Tue Aug 03, 2021 8:36 pm
Some years back i built a 100" Sportster with all the fruit, i used a vertical Jagg cooler with an inbuilt thermostat, i could count on one hand over years the amount of times that cooler was in circuit.

Very helpful, thank you.

The Honda XR400 oil cooler is a simple and durable cooler for adding a bit of heat shedding. Popular with dirt bike guys and I've seen it used on some street bikes. Made to go around the head tube, some have used it on the downtube as well.

That's neat. Is that -8 an?

In-Tech wrote: ↑Mon Aug 09, 2021 1:45 pmThat's neat. Is that -8 an?

Has Honda ever made anything with US inch dimensions?

Is why I asked, looks like AN hose end in the second pic and also looks like an adapter too. Is it bspp 45? I don't have a need for one, just curious.

AN and JIC will work together, they are both 37°[AN is the more accurate of the two]. Metric on the other hand [possibly JIS] is usually 30°[there are other tapers]. It would be pretty easy to work out if you had it in front of you and a pitch and taper gauge,,we haven't,, Can the op try a fitting on for us, or measure it?

Looks like a pretty useful and protected cooler in its given application.

Cheers,

And it wouldn't cook your crotch like the original layout might...