Topic: Oil Cooler Suggestions for SOHC CB750

[Finnigan]

Anyone have an external oil cooler setup, specifically hoses and radiator, that mount up and look good?  Cursory searches have come up with some pretty random equipment.

[johno]

Hi Finny,
Yeh there's lots out there, so what's the priority,..... style or temp reduction or combo ?
If temp reduction from sustained racing RPM obviously bigger is better but if occasional road use then a smaller cooler would be more beneficial due to quicker rise to operating temp when stopping / starting but still capable of reducing max temp at high speed touring.
 Different requirements demand different sizes ( number of tubes etc) but bigger is not always best.  Sounds like style is important to you Finny so the two styles, one will be a base plate under filter with two short lines up to small medium cooler , the other is bigger cooler with bigger lines running back to the oil tank line area.

So quick anecdote on my bike, dead stock K2, I used to run a small Lockhart type just to take the edge off temp on long trips across OZ, usually several thousand mile trips and in the summer with 80 to 100 deg F temps, I had one of those temp gauges in the oil tank lid with a red line at 250 deg F, riding hard ( 70 to 90mph) even in summer heat it usually hovered around 200F with the Lockhart cooler on. Only once did I ever get the temp up to the redline, mid 1970's, was stinking hot day ( 110f) two up with my girlfriend on the back on a flat straight road through the outback ( desert) and a bloke in a new 911 Porsche passed me. I hate being passed, would happily risk death than let some ponce past me so held the bike flat for over 70 miles non stop on the gas and managed to cling behind him at 110mph for about 50miles before the bike started to misfire from fuel evaporation and the ol girl dropped back to 90 to 100, I just kept it flat until we got to the next town (Hawker) where I was embarrassed to say a car beat me.   Point being when refuelling at the pump I shed the temp and it was over 250 F in the red.  I changed the oil when I got home and its still running fine 40 years later.         I think the cooler saved my butt that day Finny but in the winter riding around town it took about 5 minutes longer to reach operating temp on the way to work.
cheers

[newday777]

I have 2 of the Lockhart coolers for my 75 and the 76. Both were bought in the 1970s.

Lockhart used to offer a cover for winter riding to help warm the bike up faster. It was nauga-hide with a draw string to hold it on. I've thought of making one out of leather.

[754]

Lockhart with Hose barbs ? the 700 Lockhart comes with threaded ports , , and is bigger . Better if you want to run Real braided lines... unfortunately  the ports  are on top when mounted the conventional  way, fine for Kawi and Suzi, not so good for Honda 4.

[Sam Green Racing]

OK Finnigan, fill us in with more details, I see you're in So Cal and it gets quite hot there, is your bike a race bike or a tourer ?
We can't help if we don't know what your problem is,

Sam.

[Finnigan]

Planning to run an 836 kit with cam and ported head.  Want to run a cooler for stop and go traffic in the summer, not planning on sustained high RPM.

[Alan F.]

Lockhart with Hose barbs ? the 700 Lockhart comes with threaded ports , , and is bigger . Better if you want to run Real braided lines... unfortunately  the ports  are on top when mounted the conventional  way, fine for Kawi and Suzi, not so good for Honda 4.

I think the Lockhart sandwich plate I've got had brass 90 degree barbs on it. I took it off a K0 in a junkyard back in 04, spent 1/2 hour digging down in the dirt to even reach it. Some moron had placed a fire engine frame on top of a row of bikes and pushed them into the mud over the years. If I hadn't spotted the rusted out cooler with the Lockhart logo I'd never have known it was there.

No pics though, it'd take forever to find it.

[Sam Green Racing]

You shouldn't need a big one then as long as it is in the right place.
Place it up high on the down tubes so that it get a good blast of cool air and is not obstructed by the forks and front wheel.
 See where it is in this picture.

[KasperK/Denmark]

Is the oil cooler connected to the oil tank and return hose?

[Sam Green Racing]

Is the oil cooler connected to the oil tank and return hose?

Something like that.
Just to the rear and behind the clutch cover you can see two oil lines.
One takes oil from the tank and it is pumped around the engine where it is needed.
The second line takes the hot oil back to the tank but instead of doing it this way, you take the second line via the oil cooler before returning it to the oil tank.
Here's a picture of a bike I built, OK it's not stock but you can see the return oil line coming out of the engine, running up under the gas tank to the cooler just under the head stock.
Oil is returned along a line running under the gas tank and back to the oil tank. I hope this helps Kasper.

[CB750R]

Lockhart isn’t around anymore are they? No suggestions for new oil coolers? From what I’ve read the oil cooler fittings are close to a 10an hose size? So would a small Earl’s trans cooler or a Derale cooler with a custom fabricated mount?

Anyone doing the old oil filter adapter like Terry used to make? Hopefully this doesn’t turn into another 39 page pissing contest, let’s just assume the poster has decided he want needs an oil cooler and we don’t need a dissertation on why anyone considering this is an idiot and that Honda made a perfect machine and that it doesn’t need modifications etc... I’m too tired to hear it again.

[slikwilli420]

Setrab oil coolers are top quality and I've had one on my race bike for 4 seasons now with no issues at all. Get their adapters based on what you need. I run -10AN on my race bike since its a perfect match to the oil fittings on the engine, but you could run -8AN with the sandwich plate setup. Mine is mounted right under the head stock isolated with rubber dampers.

[CB750R]

Setrab oil coolers are top quality and I've had one on my race bike for 4 seasons now with no issues at all. Get their adapters based on what you need. I run -10AN on my race bike since its a perfect match to the oil fittings on the engine, but you could run -8AN with the sandwich plate setup. Mine is mounted right under the head stock isolated with rubber dampers.

Hey Awesome info thanks for sharing!

Looks like this is one of the top recommended ways to route the oil lines?
http://forums.sohc4.net/index.php/topic,66026.msg1255550.html#msg1255550

[754]

There should be no shortage of used coolers out there, and adaptors.. a lot are good brands like Lockhart.
A lot of them are sold as for Harley or other makes, but coolers are the same.
 The Setrab are  quite wide. And can easily look akward or hit things.
 UP AND over with the lines robs a bit of space under tank, and can get in the way.  180 degree fittings and going back to sandwich plate should work well . I will use - 8 fittings on mine... no point in going larger than other holes in the oiling system..

[Don R]

 Yamiya has a Rockhart oil cooler listed. 

[Finnigan]

I searched on Yamiya and didn't see one, can you post the link?  I hope its not the 800 dollar one...

[754]

YamYamaha 800 bux ? That seems to fit..
 Serious I checked eBay last few days , Lockhart s are running mostly from 25 to 100 bux .. a few are higher.
 Black, chrome , several sizes. . You will need  the adaptor plate and nut if you want to run up front. .

[bear]

I will be needing a cooler for my Auto as well. Because it will have to deal with the heat generated by it's torque converter and the extra weight of the a sidecar combination I will be using a cooler designed for a 4x4 truck.
I have the room so I might as well use it.
As far as I can tell my only option will  be an oil filter adapter.
Hopefully there is an adapter hidden in amongst my spares.
If not I may have to go "cap in hand" to Uncle Terry

[andy750]

Here is one TTR400 (Kevin in SA) made for my CB750. Lines not attached.

[andy750]

These guys in the UK also make an oil cooler kit

http://d-mengineering.co.uk/cart/index.php?rt=product/product&path=79&product_id=2789

Andy

[Finnigan]

These guys in the UK also make an oil cooler kit

http://d-mengineering.co.uk/cart/index.php?rt=product/product&path=79&product_id=2789

Andy

Exactly what I was looking for, thank you!

[754]

It looks good , not the cheapest thing to buy, but if Lockhart was making them today  price would be right up there.
 Mounting  looks  good , I think lines could run straight down.
 
 Here is the typical adapter  you find on ebay, if you look a while .

[Finnigan]

Yep, found something jsut like that with my parts, its seen better days though and I still would need to source a radiator that fits up well

[754]

Well if you have that part, you can run many different coolers.

[newday777]

Yep, found something jsut like that with my parts, its seen better days though and I still would need to source a radiator that fits up well

PM sent with a link for a cooler

[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.