Oil Pressure at idle

[bikertucker]

Have a 1975 CB750 (K5) Once I replaced all the intake boots I could tune engine to idle at 900 to 1000 rpm.Before boots where replaced 1800 rpm was the lowest idle speed it could hold. BUT once I went on a good ride the oil pressure lamp came on at idle, problem had been masked by orginal high idle speed. Connected an automotive mechanical pressure guage. Pressure is good above idle and at rpm's listed in several maint. manuals including Honda manual. Pressure on guage at approx. 1000 rpm is at the 15 to 18 psi range. Reading taken at operating temp. oil is 10W40 full synthetic. Have  inspected and measured pump clearances per Honda manual. All measurements are very good. Replaced all 4 o ring seals, same pressure. Had a spare oil pressure sensor, installed it and lamp remains off at same idle speed and pressure.  Can load engine till almost stalling and pressure dummy lamp now does not come on. Even though lamp seems to be operating normal now, and old unit was  too sensitive I would like to know proper pressure at idle. Want to have a happy engine and not just a happy sensor. Could not find idle pressure in any of the manuals. Have done a search on this site and could not find it either. One person stated 37psi but if I remember correctly
oil weight or idle speed was not given.

Thanks in advance

Tim

[shinyribs]

15-18 at idle does sound a little low,but not terribly low. I know both of mine idle at about 25 lbs. warm. But I also run 20-50w oil in mine. FSM calls for straight 30W ,which is hard to find,so i went with the 20-50. Easier to find neutral with the thicker oil it seems,too.

[Lucky 1]

FIRST replace the oil pressure gauge.

[bikertucker]

Your right, it could be the pressure guage I just bought. Just thought where I might find another sitting in a box. Wish a shop in the area could test the accuracy of guages and meters. Like back in the day when you could take in a tube from your TV and have it tested. Showing my age big time.....I know. If guage is ok
and I switch to 20W50 would allowing it to warm up longer before riding ensure oil circulating well during colder weather  be suggested.



Thanks Guys

Tim

[cdaiscool]

I would switch to a lower-rated oil during the cold months. 20W50 is THICK when cold, and takes a while to warm up. I run Rotella T6 10W40 and my bike really likes that. Also, I don't really wait for it to warm up, and it just doesn't care.

Do as you wish with the info.

[shinyribs]

Good point on a cold weather oil! My driveway is 1/2 a mile long. When I start the bike cold and let it run for a few seconds( 30-60) and then hop on it's still 3 or 4 minutes to get out the driveway. Plenty warm by then. I've also been using Valvoline motorcycle specific oil. It seems to pour really well cold( I havent actually looked up any hard info)and my oil pressure remains much more constant compared to using Rotella.Even when using comparable weights. It's pricey at $4.50/quart. I change my oil at 4-5k miles (since the bike runs so cool) so $36 per year for oil doesn't really bother me too much.

I figured if we're still talking about oil pressure than it's not hijacking!