Author Topic: What is the heaviest oil to use for CB750K1? Desert heat 110-120 in the summer  (Read 2160 times)

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Offline DesertKyorugi

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I live in the SoCal desert where summer temperatures are north of 110 degrees for a month with moderate summer temps in the high 100s. What oil weight/viscosity would you guys recommend? For example, the current temperature now is in the high 70s and low 80s.

I have always mixed my own oil for my vintage cars and my other bikes(all liquid-cooled). Currently, I am running 5w-30 synthetic(auto oil) mix with 70 Plus Lucas Racing Oil on 60/40. When the weather gets warmer I go to 50/50 ratio. Since I now own 2 air-cooled CB750K1s(one to be running soon), I would like to get a headstart before the temperature goes over 100 in 2+ months.

Thanks
US '71 CB750K1 Stored for 39 years, currently running
US '71 CB750K1 Currently running
JDM '71 CB750K1 Stored for 21 years, currently running
US '70 CB750K0 Stored for 28 years, currently in restoration
US '70 CB750K0 Stored for 43 years, currently in restoration
US '70 CB750K0 Currently waiting to be restored
US '73 CB500K2 Stored for 40 years, currently running

Offline PeWe

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5w-30 really? Way too thin for a CB750, sure metal contact when viscosity will not keep the pressure.  Use an oil pressure gauge and you'll see.

Maybe in the arctic with plenty of minus. Modern cars with tighter clearances use that thin oil.  If comparing a CB750 with car engine, look oil recommendations for race engines. Audi R8  is recommended 10W-60.

20W-50 is minimum in my CB750's, motorcycle oil.
My K6 that is modified with 1000cc etc get Red Line 20W-50 motorcycle oil.
2018 was very hot here with +30C so I did a quick oil change adding 2 bottles of 20W-60 of same oil. Much better pressure at lower rpms when cruising around

My stock K2 get a mix of Spectro mineral oil and synthetic oils. Also 20W-50.

Gearboxes feels hard and clunky with 20W-40.

If I were you, 20W-60 summertime in that heat. At least a mix of Red Line 20W-50 and 20W-60.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
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 DesertKyorugi

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5w-30 really?

As stated in my post, I am running  50/50 and sometimes 60/40  mix of 5w-30 with SAE 70 racing oil. It is a a single viscosity oil with higher level of zinc - Lucas 70 Plus Racing Oil is what it is called.

From what you are saying, I probably can run the straight SAE 70 during the summer and it wouldn't be too heavy. The current 50/50 mix in my K1 is shifting fine with the new clutch.
US '71 CB750K1 Stored for 39 years, currently running
US '71 CB750K1 Currently running
JDM '71 CB750K1 Stored for 21 years, currently running
US '70 CB750K0 Stored for 28 years, currently in restoration
US '70 CB750K0 Stored for 43 years, currently in restoration
US '70 CB750K0 Currently waiting to be restored
US '73 CB500K2 Stored for 40 years, currently running

Offline Tracksnblades1

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5w-30 really?

As stated in my post, I am running  50/50 and sometimes 60/40  mix of 5w-30 with SAE 70 racing oil. It is a a single viscosity oil with higher level of zinc - Lucas 70 Plus Racing Oil is what it is called.

From what you are saying, I probably can run the straight SAE 70 during the summer and it wouldn't be too heavy. The current 50/50 mix in my K1 is shifting fine with the new clutch.

DK,

Just curious, do you know the oil temp as per your mix of oils?  Newer dyno comparisons with heavier weight oils vs 5w-30 oils are showing increases in oil temps and oil pump parasitic losses with heavier oils.

I don't know anyone running straight 70 weight oil nowadays excepting the NitroMethane guys.

My son's 2014 Honda CB1100, aircooled W/oil cooler, has the same recommended oil clearances as the old 750s. But Honda now recommends 10w-30 oil.

The attached is a long read, but it brings clarity to viscosity and load ratings. It becomes apparent why car manufacturers have moved on...

https://540ratblog.wordpress.com/2013/06/20/motor-oil-wear-test-ranking/
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Offline PeWe

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Too thick in cold engine is not good either, it will not lube the bearings properly.
20-50 or 20-60. These multi grades also available as 15-50, 15-60 (Motul).

Old English bikes used straight 50. The clearances in need of thick oil.

I should use Red Line motorcycle oil 20W-60 in ambiemt tenps over 30C (Oil temp in tank +240F). It has high levels of zinc.
Start with a 50/50 mix 20W-50 included and use oil  pressure gauge.
 Spectro another brand with high levels.

I do not know how a mix between single grade and multi grade will end up. I guess you can google and find threads wirh it.
« Last Edit: March 10, 2020, 10:17:02 PM by PeWe »
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
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 DesertKyorugi

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DK,

Just curious, do you know the oil temp as per your mix of oils?  Newer dyno comparisons with heavier weight oils vs 5w-30 oils are showing increases in oil temps and oil pump parasitic losses with heavier oils.

I don't know anyone running straight 70 weight oil nowadays excepting the NitroMethane guys.

My son's 2014 Honda CB1100, aircooled W/oil cooler, has the same recommended oil clearances as the old 750s. But Honda now recommends 10w-30 oil.

The attached is a long read, but it brings clarity to viscosity and load ratings. It becomes apparent why car manufacturers have moved on...

https://540ratblog.wordpress.com/2013/06/20/motor-oil-wear-test-ranking/

I don't know what the oil temperature is because I don't have an oil temperature gauge on the bikes yet but it kept my oil temperature stable under 200 in my 80s turbocharged cars with oil coolers. I have been mixing my own oils since the 2000s when I started noticing low oil pressure and overheating during summer. Also, my 06 Subaru Outback XT runs happier and cooler with 70/30 mix even though Subaru recommends 5W-30.

FYI, the nighttime low temperature in July and August is over 100 degrees. Coldest lowest nightime temperature in the winter is in the high 40s.
US '71 CB750K1 Stored for 39 years, currently running
US '71 CB750K1 Currently running
JDM '71 CB750K1 Stored for 21 years, currently running
US '70 CB750K0 Stored for 28 years, currently in restoration
US '70 CB750K0 Stored for 43 years, currently in restoration
US '70 CB750K0 Currently waiting to be restored
US '73 CB500K2 Stored for 40 years, currently running

Offline jlh3rd

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The owner's manual  states the correct viscosity of oil to use. Arguably, the 750 engine is one of the best built engines ever as evidenced by current examples of these 50 year old engines still pulling strong. Id say the engineers knew what they were doing.
using "auto" oils , if they are energy conserving, is not recommended for wet clutch motorcycles....

Offline PeWe

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Oils have changed since the 60-70s and 80s. Zinc content almost removed due to catalyst equipped cars and bikes.

CB750 has 10-40 as recommendation up to 15C, the 20-50 next
My own finding is over 30C is next, using thicker oil 10/15-60.

Its up to the owner to verify oil.
Oil temp cap on oil tank and oil pressure gauge is one way to see what happen.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
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 Tracksnblades1

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DK,

Just curious, do you know the oil temp as per your mix of oils?  Newer dyno comparisons with heavier weight oils vs 5w-30 oils are showing increases in oil temps and oil pump parasitic losses with heavier oils.

I don't know anyone running straight 70 weight oil nowadays excepting the NitroMethane guys.

My son's 2014 Honda CB1100, aircooled W/oil cooler, has the same recommended oil clearances as the old 750s. But Honda now recommends 10w-30 oil.

The attached is a long read, but it brings clarity to viscosity and load ratings. It becomes apparent why car manufacturers have moved on...

https://540ratblog.wordpress.com/2013/06/20/motor-oil-wear-test-ranking/

I don't know what the oil temperature is because I don't have an oil temperature gauge on the bikes yet but it kept my oil temperature stable under 200 in my 80s turbocharged cars with oil coolers. I have been mixing my own oils since the 2000s when I started noticing low oil pressure and overheating during summer. Also, my 06 Subaru Outback XT runs happier and cooler with 70/30 mix even though Subaru recommends 5W-30.

FYI, the nighttime low temperature in July and August is over 100 degrees. Coldest lowest nightime temperature in the winter is in the high 40s.

It's good to read your doing well with your oil mix. Cooler oil temperatures are all of our goals..
Lately some  dyno operators have been testing lighter oils vs heavier oils temperatures and parisitic losses. The dyno tests with lighter oils are indicating lower oil temps, lower oil pump and rotational resistance parasitic horsepower losses. Some operators testing dry sump gear pump systems have reported of temperature rises of 25 degrees when comparing oil pump inlet temperature to discharge temperature with just 50w oil.

I know NitroMethane guys use heavier racing weight oils including 70 weight. Some racing oils are specifically and specially formulated for methanol and NitroMethane crankcase dilution, commonly experienced in maximum effort mechanical injected engines.

With today's modern engine management systems many temps can be continuously displayed or accessed through connected displays. Years past, I liked temperature strips to provide a tell tale indicator of max temperature reached. I see todays temp strips are somewhat different and don't provide the tell tale max temp. While I would only recommend a quality temperature gauge, the strips could provide a economical directional reference.
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Online scottly

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I live in the SoCal desert where summer temperatures are north of 110 degrees for a month with moderate summer temps in the high 100s.
Do you actually ride when it's 110 degrees?? :o :o
Don't fix it if it ain't broke!
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Offline ekpent

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 A friend of mine moved from Michigan to Scottsdale and took his old Yammie 650 with him. He said trying to ride in the summer was like sitting in a blast furnace and the heat coming off the road was incredible. Guess we all have our riding seasons.

Offline DesertKyorugi

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I live in the SoCal desert where summer temperatures are north of 110 degrees for a month with moderate summer temps in the high 100s.
Do you actually ride when it's 110 degrees?? :o :o

I don't ride when it is over 115 degrees

A friend of mine moved from Michigan to Scottsdale and took his old Yammie 650 with him. He said trying to ride in the summer was like sitting in a blast furnace and the heat coming off the road was incredible. Guess we all have our riding seasons.

Yeah, you pretty much need to be born and raised in the desert or you will never be able to get used to the dry smoldering heat. The heat off the tarmac is much higher than the ambient heat so there is not much air-cooling when you ride. The CBs are my first air-cooled bikes, I am pretty sure straight SAE 70 oil will be fine for running in the summer here. Not sure I would ride during the day though.
US '71 CB750K1 Stored for 39 years, currently running
US '71 CB750K1 Currently running
JDM '71 CB750K1 Stored for 21 years, currently running
US '70 CB750K0 Stored for 28 years, currently in restoration
US '70 CB750K0 Stored for 43 years, currently in restoration
US '70 CB750K0 Currently waiting to be restored
US '73 CB500K2 Stored for 40 years, currently running

Offline PeWe

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I remember first time I visited Greece,  in July, an island called Rhodes.
We rent a buggy and found the hot day became hotter faster we drove the car, like a heat gun in the face.

Another year riding my bike in Italy, really hot,  leather jacket zipper opened half way down,  ok temperature after 100mph ;) Italian highway.
 Side adventure was using sunglasses inside helmet, flimsy visor locked with 2 buttons (Jebs Clay Regazzoni helmet), suddenly a tunnel thrown into my face in around 100mph (160-170 kmh) . I had to remember how road curved in tunnel at the entrance and wish for luck when I did not see anything for 2-3 sec.

My helmet today has built-in sun visor, quick to open/close. A really good feature!!

A few years earlier my CB750 engine was really hot. I could not have my boots close to engine covers too hot for my skin despite jeans inside leathers. Italian race boots 69-70 style not thick.

Following winter tear down found the rods little ends bluish, wrist pins not nice either.
Probably the oil that lost it in heat. Hours of rather high speed cruising.
836cc with rather high CR  for street, pinging if twisting on 5th gear from 100kmh (4000 rpm), pinging at 120kmh (5000 rpm).

If I have known then in 1984 what I have learned now thanks to Internet and my own findings,  different oil. ;)
That hot holiday may have needed an oil cooler on the bike ;) ;) Most likely!
« Last Edit: March 11, 2020, 09:50:25 AM by PeWe »
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
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 Deltarider

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Summer 1973 during a heatwave, we crossed the desert in the south (California, Arizona, New Mexico) riding freighttrains like hobos. My buddy and I were under a trailer on a piggyback wagon. Temperature must have been around 45 degrees Celsius. We discovered that in a lying position it was better to endure the heat. Whenever I got up, the heat became unbearable because of the riding wind. First time I experienced the opposite of the chill factor. :) Oh... and another thing I learned then: you can drink warm water no prob, but you can not drink hot coke. It was awful. Haven't touched the stuff ever again.
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Offline Pat_at_APE

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I work in Rosamond, CA in the high desert and ride often in high temps.   I've been running 20-50W 4T oil for 30,000 miles and now that I'm rebuilding everything looks great.   I change oil at 1500 miles and the filter every other oil change. 

Pat

Offline PeWe

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I work in Rosamond, CA in the high desert and ride often in high temps.   I've been running 20-50W 4T oil for 30,000 miles and now that I'm rebuilding everything looks great.   I change oil at 1500 miles and the filter every other oil change. 

Pat
Changing oil that often means fresh oil even if its lifetime is decimated by the heat ;)
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
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 PeWe

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Deltarider,  have you tried to dilute Coke with vodka? It work fine! ;)

I had an episode with orange juice when I was a young teenager. It took many years to let the alcohol taste out of the normal orange juice so I could drink juice again ;)
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
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 carnivorous chicken

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Lived in Phoenix for 20 years, rode all year including 110+ during the summers, although not really long trips -- just around or across town. Staying out of stop and go traffic was key, but my bikes -- either SOHC fours from 350-750 or Honda twins -- did fine. Pouring water on my shirt and jacket and inside my helmet helped.

Offline PeWe

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32C (90F) is enough for me to enjoy the ride.
Here we have a period we can't use bikes due to the cold, Nov- March.
It's the opposite with you guys living south, too hot for a period of time?
« Last Edit: March 12, 2020, 01:21:36 AM by PeWe »
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
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 ekpent

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I work in Rosamond, CA in the high desert and ride often in high temps.   I've been running 20-50W 4T oil for 30,000 miles and now that I'm rebuilding everything looks great.   I change oil at 1500 miles and the filter every other oil change. 

Pat
  That sounds like a very solid testimonial from someone who knows these bikes well.

Offline Tracksnblades1

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I work in Rosamond, CA in the high desert and ride often in high temps.   I've been running 20-50W 4T oil for 30,000 miles and now that I'm rebuilding everything looks great.   I change oil at 1500 miles and the filter every other oil change. 

Pat
  That sounds like a very solid testimonial from someone who knows these bikes well.

???  🤔🤔  Rebuilding after 30,000 miles?  Or everything looks great?  🤔
Age Quod Agis

Offline Pat_at_APE

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I took the motor down because the base gasket blew out and I was tired of an oily foot...   Decided to upgrade to 836cc, ported head with oversize valves, lightened crankshaft, and more aggressive cam.... 

Motor had more than 30,000 miles.  That's just I put on it personally, and I flogged it for most of that chasing newer bikes through the excellent canyon roads we have locally.

Pat


Online scottly

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The CBs are my first air-cooled bikes, I am pretty sure straight SAE 70 oil will be fine for running in the summer here.
No, do not run straight 70 weight oil in your CB. If you are worried about the oil temp, which is normally well over 200* F, consider installing an oil cooler.
Don't fix it if it ain't broke!
Helmets save brains. Always wear one and ride like everyone is trying to kill you....

Offline HondaMan

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20w50 until the temp falls below 30 degrees, then [maybe] consider 15w40 or 15w50. Never use a base-weight of less than 15w in these engines.  The [in]famous mistranslation of Japanese-English (Jinglish) in the 1973-4 750 Owner's Manuals by someone in American Honda/California caused the sudden "switch" from 20w50 requirement to 10w40: the latter was supposed to be used only below 30 degrees F. The engines had not changed: only the Owner's Manual had...
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline senyah750

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Love this stuff! 20w50

Bel-Ray EXL Mineral 4T Engine Oil... https://www.amazon.com/dp/B0045LCCKG?ref=ppx_pop_mob_ap_share

« Last Edit: March 13, 2020, 06:05:36 PM by senyah750 »
'77 cb750F2

Offline PeWe

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Interesting read about oil viscosity, film strenght and pressure.
https://rennlist.com/forums/928-forum/1041459-engine-oil-and-last-century-porsche-road-engines-some-light-reading.html
It is the post 12-31-2017, 11:38 PM #1  by JET951 that is interesting

The details about film strenght on moving parts that have no oil pressure, only splashes of oil is like an old CB750 and other old CB's.

I start to understand why the K6 head I bought on eBay USA had such worn ex guides/valves when inlet looked like very low mile.
 Head in general in good shape, no bad threads.
Probably got too low viscosity oil like 10W-40, warm days and very hot rides. Lower quality oil loose it quicker, shorter change intervals.
It is the viscosity that is the point here, not synthetic vs mineral.
Synth withstand high temperature better and longer, though.

But, a better synth oil with lower viscosity can not replace a correct viscosity simple mineral oil which the thread was about. Experienced race shops write-up.
« Last Edit: March 14, 2020, 02:31:07 AM by PeWe »
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
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 Tracksnblades1

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Oil has evolved a lot faster than engine internal clearances have.

It's important to remember the old Honda air cooled engines have the same recommended clearances as the newer air/water cooled Honda's do.

While some lighter weight automotive oils formulated for stock (catalytic converter)  performing roller lifters may not contain the required additives for flat tappet engines, there are many light weight oils available that are more than adequate for all performance levels and temperatures. Some low viscosity diesel oil still offer sulfur and phosphorous additives for more extreme pressure ratings. 

For instance current Pro Stock technology from Vavoline Racing oil is their new 0w offering. 0 being *winter* temp J300 test temperature not weight. It pours like water.

Current NASCAR oil is Mobile 1, 5uperSynthetic 0W-30. Some racers are using both lower and higher viscousity oils too. Below the link indicates current oils may be 5w-20 for the roundy roundy guys.

And then the NitroMethane 70w racing oils. Formulated for the 8000+ Horsepower, restricted cubic inch engines, sporting internal components sizes of OEM offerings of 400 horsepower more/or less. The best explanation why 70w oil is required that I've heard is: Imagine an engine originally designed for around 350hp, bore it out to 500 cu in. Pump as much PSI the largest supercharger can make and pump that through the best flowing intake port you can make. Add one part of NitroMethane to one part air and you'll have nearly a 1000hp controlled explosion per cylinder slamming down on the stock size crankshaft journals, sending harmonics, vibrations, resonances, and torsional twists that can destroy the best crankshaft in seconds. Image all 8 hitting now on the same crank and 8 pistons and cylinder heads trying to comtain it all. Hell, he said, the whole d*m thing, cylinders , block, crankshaft bores, are huff and puffing, vibrating and resonating like a 16 year olds 15inch subwoofers hitting bass notes on a rap cd. If we could run tighter clearances without spinning bearings we would, our oil pumps require more horsepower than some cars have. We have to change oil after every pass...

Below are but a few of modern oils articles explaining important aspects of the same, furthering why modern manufacturers and racers have moved on...and 540Rat has been testing and publishing the results for years....

https://www.enginelabs.com/tech-stories/racing-oil-vs-street-oil-know-the-differences/

https://www.machinerylubrication.com/Read/30835/lubricant-film-strength

https://540ratblog.wordpress.com/2013/06/20/motor-oil-wear-test-ranking/
« Last Edit: March 14, 2020, 10:29:03 PM by Tracksnblades1 »
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Offline Keith

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Its important to understand how multi grade oil works. A 10w30 oil is a 10 weight when cold. This allows oil to get to critical wear areas quickly. As the oil heats up, long chains of molecules form, causing the oil to thicken. As it cools, the molecules go back to their original state. The oil is not simply a mix of 10 weight oil and 30 weight oil. Mixing oils will defeat the way the oil is supposed to work.

Offline PeWe

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Maybe those thin oiled racer teams  do everything to win, teardown and repair after each race not a problem, right? Bearings are still shells in need of good pressure, not ballbearings?
Or the later design the Porsche thread post described, lower oil pressure needed to lubricate the rods. Still film strenght for surfaces that get splashes of oil.

The Porche post also notified the multigrade oil's base oil which the oil will end up in when additives have given up, a process that start very soon. Too thin base oil not good for those engines.  Also different engine designs of oil distribution to rods, later need lower oil pressure and therefore possible to use the modern 5-40 oils.

I' m convinced that same ideas are valid for a CB four too.

I have seen how quick a 0W-40 synth oil becomes much thinner when cold.

My car's oil feel bad after 9000km. 1.8 L engine with turbo, only 3.7 L oil. Not as good oil as my CB750 get  that get fresh oil more frequent ;) I think the hot running turbo kills the small amount of oil quickly.

Multigrade oils that loose it also a reason for more modern car engines like BMW get expensive repairs when cam chain tensioner stop work due to the low viscocity and too low oil pressure. Chain can jump or snap. Audi engines similar expensive repairs. Sludge involved too.

I start to understand the very short oil change intervals Honda recommended, multigrade oil viscosity degradation.
Oil pressure gauge feels as a must where this process can be supervised. Pressure when really warm.
« Last Edit: March 15, 2020, 12:32:52 AM by PeWe »
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
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 ckahleer

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There was a guy on the KLR650 forum that had his oil analyzed at regular intervals between 2 oil changes. Oil degraded very fast during the first couple hundred miles, then more slowly after that. The oil change interval was 2,000 miles, but after only 200 miles the 10-40 oil was down to 10-30.

Offline PeWe

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He changed oil brand after that?

I'm sure that there are better or worse brands when it come to viscosity, how to fulfill specified values and how fast it will degrade.

If the gearbox feels smooth to shift and easy to find neutral when warm seems to be one way to verify the oil on a CB750 together with a pressure gauge.

I tried several oils on my K6 in the hunt for the right one. Both my CB750 have now relatively smooth gearboxes and no dragging clutches.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
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