Topic: Oil Cooler Suggestions for SOHC CB750

[754]

 Here is 3 major sizes , types of Lockhart,  there is also built in Thermostat  ones.
 The mid size  came in black or chrome and is most common.
 The narrow one I have seen in a Vertical configuration,  I think for Sportsters. Likely with hose barbs.
 The threaded port I prefer if you want to run real braided lines.. not the hose clamp type.

[PeWe]

Perfect with a complete kit, just bolt on.
I had thoughts about an oil cooler on my K6.
Purchased a Setrab cooler but did not collect all parts to complete.

I would like to use a thermostat that open after 100C.
I believe that oil must be hot enough to let condense water out.
Cooler to avoid 120C that a good oil can handle, but shorten life.

[KickstandDan]

Hey all,

I know this is an older thread, but I figured I’d add to it instead of creating a new one with the same info. I’ve been building up my CB750 with performance and reliability in mind, not going for style, just making sure the engine can handle the upgrades and higher RPMs I plan to run.

Here’s a quick overview of my build:

• Stock displacement with 10.5:1 compression pistons
• Head and crank work done by Ken at Cycle X (balanced crank, lightened rocker arms, new valves, springs, titanium retainers and jam nuts)
• CX-1 cam
• Stock airbox with a UNI foam filter
• Delkevic 4-into-1 header into a Cone Engineering 18” Quiet Core muffler
• Stock carbs (still dialing in jetting)

I’m using an Acewell 6502 gauge and reading oil temps through the sump via the oil drain plug sensor. After a typical 30-mile ride (mostly highway with some stop-and-go “city”), I saw oil temps hit 231°F.

I’m familiar with using a sandwich plate on the oil filter housing and how to hook up an oil cooler, but I’m unsure what size cooler and hose diameter would be best for this specific application. I’ve seen some mount them below the triple tree, and that seems like a good airflow spot.

Just wondering what others have done with similar setups, whether an oil cooler is worth it or if running a heavier oil like 20W50 on hot days is enough. Any thoughts or experience would be appreciated.

[newday777]

KsDan
These 750s run much better and cooler with good 20w50, even so an oil cooler is going to be helpful for the higher temps of a built engine and hot summer weather.
Back in the 70s when I went bigbore, cam, ported head and 3 angle valve cuts, I also put on a Lockheart oil cooler from recommendations of my motor builder(he built race motors) and the guys at the shop I worked at.
I would remove the cooler in the fall with cooler ambient temperatures staying below 65°F.

[KickstandDan]

Yeah I was reading about what you had done from your post in 2021 from back in the day. It seems like a simple oil cooler can really prolong the longevity of these engines. I’m more curious about the specs of the oil cooler itself. Some people are saying AN 10 fitting while others say AN 8. And how many rows/how big of an oil cooler? For starters it seems like I will go with 20W 50 on my next oil change as long as it is still hot outside. And good call removing it when it is too cold outside.

I appreciate the feedback.

[Don R]

 I've seen the lockhart coolers and vinyl covers on ebay, often the covers say Harley Davidson on them. I just missed a leather cover last year at a swap meet but I did get the lockhart cooler.
 There was an oil filter adapter made that has a thermostat built in, I have one, but ironically it spaces the filter housing out so far that it won't clear my RC header. It can go on my next build.

[HondaMan]

The 20w50 oil will also drop temps, and more than you might think.

[KickstandDan]

The 20w50 oil will also drop temps, and more than you might think.

Interesting, I didn’t know it would do that too. I think I am going to go with some generic eBay oil cooler, maybe 5-7 rows with either AN8 or AN10 fitting. If this works well I will upgrade to a better quality product.

Thanks for the help guys 

[KickstandDan]

Quick follow-up on my oil cooler setup. The sandwich plate I’m using is older, and I noticed the threads for the hose fittings seem a bit off from what’s typically available now. The threads on my plate are tapered, with a 1.5 mm pitch. The diameter at the base is about 14 mm and closer to 12.7 mm at the tip. Based on the measurements, I believe these are possibly a BSPT (British Standard Pipe Taper) or another older spec.

The inner diameter of the fitting that threads into the plate is only about 7.5 mm, which seems restrictive for this application—especially since I’m running higher RPM and temps.

I’m considering drilling and tapping the ports for a larger fitting size to improve flow. Has anyone here done this?

Also curious what size fittings or adapter threads others are using directly out of the sandwich plate. Trying to figure out if this is the main restriction point in my setup.

[seanbarney41]

The 20w50 oil will also drop temps, and more than you might think.

This is confirmed by the oil temp. gauge on the dash of my Suzuki GS1100E (which does not have an external cooler)  Another tip that I learned from that bike...for years I ran a Supertrapp full exhaust which fit very close to the oil pan   Just recently mounted a new pipe by Hindle that leaves much more space around the oil pan and I am seeing much lower temps for more miles and at higher speeds.  However, the Suzuki is not a semi dry sump system like the cb750...

As far as hose sizing goes, have a look at the hoses (and especially the fittings!...notice they are smaller id)that feed and return to the oil tank.