Author Topic: cb750 which oilto use  (Read 1467 times)

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Offline D DIAMOND

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cb750 which oilto use
« on: June 24, 2021, 02:00:59 am »
i have been led to believe that honda recommend to use 10/40 oil but some people say to use 20/50 if so which 20/50 do i use DD

Offline Kevnz

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Re: cb750 which oilto use
« Reply #1 on: June 24, 2021, 02:17:28 am »
You'll probably get a different opinion from everyone who responds, but I have been using cheap 10\30 car oil in my 500 for over 10 years with not the slightest issue, plus I get to change it more often, which , in my view is a GOOD thing. That said , my bike doesn't get a hard time, so that may be something to take into consideration. Bear in mind that cheap modern oils are probably far better than the best of oils used back when these bikes were new. Mention is often made of friction modifiers ( whatever they are) and their effect on wet clutches, but, as mentioned, it's never caused me any trouble.
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Offline lash

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Re: cb750 which oilto use
« Reply #2 on: June 24, 2021, 04:04:03 am »
 :o
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Offline Nurse Julie

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Re: cb750 which oilto use
« Reply #3 on: June 24, 2021, 04:06:33 am »
As you are in UK 10w/40 is just fine.
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Offline CaptFatCat

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Re: cb750 which oilto use
« Reply #4 on: June 24, 2021, 04:20:40 am »
Castrol GTX 20-50 with a shot of zinc additive on my K2.
I read about the Zinc additive here,  it does make the shift much smoother.
Resurrecting a Herman Munster CB750 from a few old baskets of K2 and K7 parts.

Offline TwoTired

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Re: cb750 which oilto use
« Reply #5 on: June 24, 2021, 06:36:15 am »
Just about everyone is certain that Honda doesn’t know what is best for the engine they designed.  And with their degrees in metallurgy, chemistry, and most importantly personal anecdotal experience on a single machine example, will do their best to convince you that their favorite oil is the elixir to all metal based friction machines, because they said so.  (Without ever having an oil analysis performed or actually inspecting engine internals, mind you).  Like me, their only qualification to offer a preferred opinion, is to have access to a computer keyboard and current payment for internet access.  As I have both these qualifications in addition to owning a motorcycle or two, I’ll offer my recommendation for the best oil you should use in your bike in which I have zero dollars invested in.

Oil that Honda currently recommends for bike. (Assuming you can’t actually get what’s recommended in the original owners manual.)  Or, any oil that has the same specs on the label as what you find at the Honda dealer.  And that would be JASO endorsed and 10w40.

Also, I’ve even been known to buy actual Honda brand oil, though not the cheapest you can find,  it is WAY cheaper than replacing parts inside your engine cases, not to mention the time and effort lost to such repairs.  And the most convincing argument most will offer;  “It’s worked well for me so far”.

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Offline Bodi

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Re: cb750 which oilto use
« Reply #6 on: June 24, 2021, 06:48:07 am »
Well, enjoy the worms from the can you opened.
Anyway, my probably crazy oil rant:
The zinc thing seems important. As car makers have been "encouraged" to improve efficiency - use less fuel - their engine design goals have changed. Internal friction, using fuel without producing motive power, has been reduced a lot. So valvegear like what's in our engines with flat followers rubbing against a cam ... nope. Lots of frictional losses, that has to go. So basically all modern engines have roller cam followers with lots less friction so less power wasted. And since oil no longer needs the additives like zinc that stick to the cam and followers to help them not gall, additives that are not free, most available car oil today doesn't have them - or a lot less of them.
Some motorcycle specific oils have more zinc compounds because shim in bucket cam followers are still fairly common, using roller followers takes up a lot more room and increases the follower weight (the rev limit is directly related to valvegear weight) which would make the engine larger and less powerful due to the lowered rev limit. A typical R1 rider doesn't care about fuel economy much, and the government regulations focus on emissions and noise rather than efficiency.

What oil viscosity rating you should use depends on the temperature it's expected to run at. When these bikes were made, multigrade oils with really wide ranges were not available - there was no 10W50 oil in existence.
Multigrade oils are made with long chain molecules that stretch out as they heat up, that makes the oil "thicker". But these get smashed into smaller bits in an engine so the oil thins out after being in use. In the engine that takes a while because the bearings don't shear the molecules a lot and their oil film is decently thick even at high throttle. But our engines also use the oil in the wet clutch and transmission which does put lot of shear force and pressure on the oil in the clutch and at the gear faces, ripping the molecules apart. Zinc helps with the gears as well but can't eliminate the oil degradation.

Many of us use diesel oil, it's just normal oil with friction additives like zinc because diesel engines still need them. Or you can get zinc additives to put in car oils.

As to viscosity, the owners manuals usually have a recommendation something like SAE 30 for air temperatures below 20C/70F and SAE 40 above that (this info may be cast into the engine case by the dipstick/filler). The different viscosities are because an aircooled engine's running temperature varies relative to the the ambient air temperature, water cooled engines don't have that problem except in extremes.
I use a multigrade diesel oil that covers the recommended range, like 20W50 - the "thin" cold rating of 20wt is not going to cause trouble during the time the engine heats up. The 50wt hot viscosity is OK because parts of the air cooled engine will run hotter than anything in a water cooled engine ever will. And I change it fairly often, knowing the clutch and gears are messing with the high temperature viscosity. I also use synthetic oil. No brilliant arguments on why it's better, I've just found that my engine ran quieter and happier the first time I tried synthetic at least 30 years ago and decided to go with it from then on. I've had none of the problems that synthetics are supposed to cause, that doesn't mean I don't believe they exist.

But we all have oil opinions, some of us have oil opinions that must be defended vehemently.

Yes you can use the cheapest oil you can find, use the latest high efficiency car oil on the Walmart shelf, whatever - change it regularly and probably have no issues.
Some oil should be avoided because their anti-friction additives work too well: our wet clutches do need friction after all. And never use molybdenum ("Moly") oil additives unless you really want your clutch to slip until you flush it all out and replace the clutch friction discs - consider any oil additive that's black as taboo.

Offline 71 V12

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Re: cb750 which oilto use
« Reply #7 on: June 24, 2021, 06:50:00 am »
Just read you post about oil pressure woes.

I use Shell Rimula R4 X 15W-40 (Formerly RT4 X) Heavy Duty Diesel Engine Oil, recommended to me by oil technology expert and my 750 runs great on it.

Offline 70CB750

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Re: cb750 which oilto use
« Reply #8 on: June 24, 2021, 07:47:24 am »
Valvoline 20W50 year around - I never park my bikes. 

Offline goodtryer

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Re: cb750 which oilto use
« Reply #9 on: June 24, 2021, 08:08:10 am »
Valvoline VR1 20W50 works for me.

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Online Deltarider

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Re: cb750 which oilto use
« Reply #10 on: June 24, 2021, 08:15:32 am »
I suppose Honda oil is American Honda oil. Maybe it is also sold in Canada, but not in Europe that I know or any other market, which make me suspect it's mere branding. I have not seen BMW motoroil, Ducati motor oil, VW oil or Porsche oil.
Does Honda always knows best? Should you just follow the Owner's Manual and stop thinking? I'm afraid not. An example: in the CB500-550K3 Owner's Manual it's advised to do the camchain adjusting with the engine running. Mecs in Honda dealer workshops know better.
In America Shell Rotella (Rimula) seems to be a popular choice. The package states it is JASO approved. The package in Europe lacks that particular info. In Europe Shell has an extensive line of motorcycle oils (whatever that maybe) the company wants to sell.
Also Castrol has a line of motorcycle oils. Does that imply other oils are not as good? No (link below).
I remember the years Castrol's GTX2 was first choice in all dealer motorcycle workshops. GTX2 was not marketed as a specific motorcycle oil (again: whatever that maybe).
In Holland for years we have had a tribologist that regularly published about oil not only in a magazine for professionals in the automotive branch but also in a motorcycle mag. I've learned a lot from him. He owned a CB550K3 and his preferred viscosity was 15W-40 as he never rode his bike in temperatures below 0o Celsius.
Here's what I've found: http://forums.sohc4.net/index.php/topic,186850.msg2168655.html#msg2168655
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Online PeWe

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Re: cb750 which oilto use
« Reply #11 on: June 24, 2021, 11:34:08 am »
There is other viscosity recommendation  for  CB500/550 than CB750?
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline bryanj

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Re: cb750 which oilto use
« Reply #12 on: June 25, 2021, 02:35:11 am »
Honda oil in UK back in the 70's was made by Shell
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

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Offline jlh3rd

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Re: cb750 which oilto use
« Reply #13 on: June 25, 2021, 04:08:53 am »
Just about everyone is certain that Honda doesn’t know what is best for the engine they designed.  And with their degrees in metallurgy, chemistry, and most importantly personal anecdotal experience on a single machine example, will do their best to convince you that their favorite oil is the elixir to all metal based friction machines, because they said so.  (Without ever having an oil analysis performed or actually inspecting engine internals, mind you).  Like me, their only qualification to offer a preferred opinion, is to have access to a computer keyboard and current payment for internet access.  As I have both these qualifications in addition to owning a motorcycle or two, I’ll offer my recommendation for the best oil you should use in your bike in which I have zero dollars invested in.

Oil that Honda currently recommends for bike. (Assuming you can’t actually get what’s recommended in the original owners manual.)  Or, any oil that has the same specs on the label as what you find at the Honda dealer.  And that would be JASO endorsed and 10w40.

Also, I’ve even been known to buy actual Honda brand oil, though not the cheapest you can find,  it is WAY cheaper than replacing parts inside your engine cases, not to mention the time and effort lost to such repairs.  And the most convincing argument most will offer;  “It’s worked well for me so far”.

Cheers!

+1

Offline jlh3rd

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Re: cb750 which oilto use
« Reply #14 on: June 25, 2021, 04:10:56 am »
I suppose Honda oil is American Honda oil. Maybe it is also sold in Canada, but not in Europe that I know or any other market, which make me suspect it's mere branding. I have not seen BMW motoroil, Ducati motor oil, VW oil or Porsche oil.
Does Honda always knows best? Should you just follow the Owner's Manual and stop thinking? I'm afraid not. An example: in the CB500-550K3 Owner's Manual it's advised to do the camchain adjusting with the engine running. Mecs in Honda dealer workshops know better.
In America Shell Rotella (Rimula) seems to be a popular choice. The package states it is JASO approved. The package in Europe lacks that particular info. In Europe Shell has an extensive line of motorcycle oils (whatever that maybe) the company wants to sell.
Also Castrol has a line of motorcycle oils. Does that imply other oils are not as good? No (link below).
I remember the years Castrol's GTX2 was first choice in all dealer motorcycle workshops. GTX2 was not marketed as a specific motorcycle oil (again: whatever that maybe).
In Holland for years we have had a tribologist that regularly published about oil not only in a magazine for professionals in the automotive branch but also in a motorcycle mag. I've learned a lot from him. He owned a CB550K3 and his preferred viscosity was 15W-40 as he never rode his bike in temperatures below 0o Celsius.
Here's what I've found: http://forums.sohc4.net/index.php/topic,186850.msg2168655.html#msg2168655

I guess they changed that procedure for '75 550F's ?

Online PeWe

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Re: cb750 which oilto use
« Reply #15 on: June 25, 2021, 04:12:13 am »
Castrol GTX 20W-50 the old recommendation here for CB750. GTX2 when no longer available in middle of the 80's.
Almost no cathalysts back then reducing important additives.
Late 80 when I used the "best" oil I could find, Mobil 1 which ended up in clutch slip when slamming in 5th gear at WOT, around 190kmh.

Edit: CB750 cam chain adjustment at 15 degrees, when spring tower is visible.
« Last Edit: June 25, 2021, 04:14:37 am by PeWe »
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Christian85

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Re: cb750 which oilto use
« Reply #16 on: June 25, 2021, 04:27:11 am »
I'm currently using the mineral based Spectro 4 20W-50.

This is the best oil I've had in my bike when it comes to clutch operation, smooth shifting and finding neutral when hot.
I've been using MOTUL the last years, both 10W-40 and 20W-50, but the Spectro is remarkably better.


Online PeWe

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Re: cb750 which oilto use
« Reply #17 on: June 25, 2021, 04:45:03 am »
+3 for Spectro.
Spectro Heavy Duty mineral 20W-50 recommended on this forum before. I ordered and found gearbox to shift smoother.
There is a Spectro Semi synth too.

I'll order some more Spectro.
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline MJL

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Re: cb750 which oilto use
« Reply #18 on: June 25, 2021, 04:58:54 am »
I used to use Honda oil, until I read on here that Rotella has the needed zinc and is suitable for our bikes, and is cheaper. If there is a newer option I'm all ears.
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Offline ekpent

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Re: cb750 which oilto use
« Reply #19 on: June 25, 2021, 05:36:58 am »
Honda oil in UK back in the 70's was made by Shell
I've read a little chatter that over here it was formulated by Mobil. Some of the current mc oil may be formulated to conform better with catalytic converters which a lot of bikes have now. Not sure what that would mean for zinc.

Online PeWe

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Re: cb750 which oilto use
« Reply #20 on: June 25, 2021, 06:27:59 am »
I read on another site that Shell Rotella had got reduced amount of zinc and phosporous which is important to be aware of.

 "About 1200 ppm zinc and 1100 ppm phosphorous" which is as many other newer oils.
Spectro HD  has around double that.

Not this site that mention it too. There is a small difference of the name.
https://www.dieselplace.com/threads/rotella-15-40-no-zinc-huh.234328/

Oil for cathalytic converters has less amount.
Quicker wear on cam, rockers and guides not welcome on these old designs.
« Last Edit: June 25, 2021, 06:49:23 am by PeWe »
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Online Deltarider

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Re: cb750 which oilto use
« Reply #21 on: June 25, 2021, 07:21:39 am »
I guess they changed that procedure for '75 550F's ?
It was the other way around actually. The K3/4s were the last developed in the CB500/550 serie.
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Offline ekpent

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Re: cb750 which oilto use
« Reply #22 on: June 25, 2021, 10:35:54 am »
 I've seen that also Per.  I bought an old big jug cheap of Rotella 15x40 never opened in an estate sale and thought to myself "Oh the good stuff".

Online PeWe

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Re: cb750 which oilto use
« Reply #23 on: June 25, 2021, 11:02:44 am »
It must be  a barrel or 2 for your garage, Eric!
I tried to search for old oil that our bikes got for many years ago.
Not cheap, it seems to have become collectors items.
https://www.ebay.com/c/1710368904

I hoped to find a barrel with Castrol GTX 20W50 for my garage.
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline D DIAMOND

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Re: cb750 which oilto use
« Reply #24 on: June 25, 2021, 12:27:25 pm »
thanks body those can of worms they were very nice i have ordered 5 ltrs of semi/synthetic 20/50 oil with jaso spec thanks for  all the replies DD