Topic: Oil Pressure cb750

[eschopper]

I recently acquired a 1972 cb750k.

I was wondering what the normal oil pressure for this engine is?  Also, I was wondering if I needed to purchase another oil pump?
My oil pressure gauge is brand new from drag specialties and I do not have an oil pressure light, tachometer, or speedometer.  The bike has been converted into a chopper.

Usually, when I start the bike up the oil pressure is between 40 to 60 psi.  Sometimes the needle will jump around from 0 to 60 psi.
As the motor warms up it drops down to around 15 to 20 psi. 
While riding the pressure is around 20 to 40 psi.
At stoplights the pressure can dip to around 5 to 12 psi.  If it goes below this the bike will stall out.

I am new to this type of engine and I greatly appreciate any help on this matter.

[Bob Wessner]

I'm not sure where you live, but the ambient air temp can have a lot to do with the start-up oil pressure. I live in Michigan and on a summer morning start with the temp. around 50F, and standard 10w40 oil, the pressure can jump to almost 80 lbs. Once the engine is hot and I'm riding, it seems to register 10 lbs per 1,000 r.p.m. on the pressure gauge. I have to admit I don't know what the optimal specs are, but this seems to be fine.

[johnny-from-bel]

10 lbs per 1,000 r.p.m. is the rule of thumb on most engines. The shop manual states 7.1 PSI as abolute minimum.

[andy750]

Oil pressure at speed (~60mph = 60 - 80psi). As mentioned by Bob on hot days pressure will be less and can drop to around 50psi. At idle should still be around 60psi (when I start up my K2 or K4 pressure goes up to 60+psi and stays there. Id check your gauge.

cheers
Andy

 

[lrutt]

my 76 with 28k miles will register 80+psi first start and will not drop below 50 psi even warm at idle. That is my only comparison point. I should move my gauge to my 78 and see what it runs.

[Bob Wessner]

Andy,

So what you are saying is when hot, if you pull up to a stop and idle, say around 900-1,000 r.p.m. you still show 50 psi on the pressure gauge?? Mine will drop to about 10 lbs and it's been that way since the mid-70's.

[andy750]

Ah good question Bob and I dont know as I dont recall the idle oil pressure when its hot - 85F+ (only when running on the highway/roads Ive looked down and sometimes have seen my psi lower than usual - like 50psi - and this is when its hot or riding through deserts etc - I cant say for idling in deserts). I was talking about idle oil pressure at regular temps - like 50 -65F (upon start up and then check oil pressure).

sorry for any confusion,
cheers
Andy

[Bob Wessner]

No problem, just wanted to make sure as to whether or not I had an issue.

[andy750]

Bob,
If you have been riding since the 70s like that then no I dont think you have an issue 

Issue is all mine,
cheers
Andy

[Dave K]

Bob, I have had an oil pressure guage on since new. It reads what yours does at both idle and highway speeds. I can't even say I have seen any change in oil pressures since it was new.

[Hockers Choppers]

Oil pressure at speed (~60mph = 60 - 80psi). As mentioned by Bob on hot days pressure will be less and can drop to around 50psi. At idle should still be around 60psi (when I start up my K2 or K4 pressure goes up to 60+psi and stays there. Id check your gauge.

cheers
Andy

 

Andy, you need to check YOUR gauge!!

[eschopper]

Thanks for all of the replies, all of your help is appreciated.  It helps me to figure out if my oil pressure is average or not.  Nobody around here has anything close to what I have, so this forum really helps me out!

[Bob Wessner]

How sure are you about the gauges accuracy? Does the oil pressure light ever come on at idle? Granted, it too might be off, particularly after all these years, but theoretically the threshold for the light is +/- 7 lbs.

[mrbreeze]

My gauge goes considerably lower at a warmed up idle. Once revving down the road,it comes back up. As far as I am concerned...this is normal.I've never seen one anywhere neer 50 lbs. at a warmed up idle. Some of you here may have a whacked out gauge but I'll say one thing.........You'll know real soon if you have a lack of oil pressure!!!

[chung]

I thought I replied to this???

Pressure is an indication to a resistance of flow. It is not an indication of flow. They call it an idiot light for a reason but likewise, the number on the gauge is just a number..... a reference point.

Pull a lash cap when the motor is smokin hot. The gauge may say 0 PSI but it can blister an eyeball from all the oil slinging about. Wear glasses boys and girls.

I have seen the oil light blinking so much @ idle on the 750s that I seized an engine once because I ignored the IDIOT LIGHT. (Rag in the tank) The oiling Syst on these bikes is NASA quality stuff. Pull the pump and measure it to spec if you are that scared or unplug the bulb.

It was normal for me to be riding with an ambient of 110F in the shade @ 5pm. That has gotta be 150 plus on the road, I have almost fallen off the bike from the heat. Almost 300 miles round trip EVERY DAY for 3 years. I ain't making this #$%* up. I typically used HONDA GN4 10w40 but CASTROL GTX is a fine oil as well, 20/50 or 10/40. The light only annoyed me, If it keeps going then it's all good right? Parts are parts. we break them and we replace them. (except for my lungs and liver)

I guess the point is that if you have oil flinging out of the lash caps on BOTH sides of the motor then it will probably live longer that you will. With a little maintenance?