Topic: Oil pressure light comes on below 2k rpms

[Frankenkit]

I think I know the answer here but I'm asking the hive mind anyway, partially for confirmation and partially so I don't epically screw up.

Bike- 1980 CB650c
Mileage- 30,000

Symptom-
When the engine/oil are warm, the oil light comes on whenever I'm under 2k rpms.  The problem is exacerbated as the bike warms, so when it's still cool, it idles with the light out.  As it warms, the light will come on very dimly and flicker, and once the engine's pretty hot it comes on much brighter, still flickering

Factors-
New oil (15w40, changed yesterday when the problem started, figuring it may have been old oil.  Oil registers as 'full' on dipstick.
I had a slow leak from the plate on the outside of the oil pump, so I took the plate off and replaced the o-ring.  The original o-ring had a crack in it I'm assuming the oil seeped through.  It is flat in cross section.  The new o-ring is round in cross-section and apparently very slightly thicker than the old o-ring.  The plate doesn't come down flush the way it did with the old o-ring but nothing leaks.

When I had the plate off, there was some wear in the side of the plate that was in contact with the pump's moving parts.  It appeared as though a small amount of metal was worn off (1/4 or 1/2 of a mm. Very little, just enough to make it shiny as opposed to the smooth matte surface of the pump plate)

I'm wondering if the small amount of additional internal capacity granted by the new o-ring is causing my pressure problem, because I didn't have the problem before I replaced the o-ring.

Additionally, should I put the old o-ring back in and use a dab of yamabond or something similar to seal that crack to prevent leakage?

Last-
When I took the pump plate off, obviously a bunch of oil came out.  The oil that came out had little chunks of what I think may have been carbon in it.  (When I tipped the pan back and forth, black trails leached out of the chunks, fwiw)  but I know the oil pickup screen is clean, I dropped the sump and cleaned it back when I did my last oil change.

Do I need to worry about my pump, or just replace that o-ring (or re-use the old one)? How can I accurately measure oil pressure on a cb650? Is is possible without drilling holes in the head/tapping/inserting a gauge etc, because I don't have the equipment to do that.

[simon#42]

i would think it was the o ring , the outer plate of the oil pump must fit flush with the housing . oil pumps work on pretty small tolerances, the extra space between the end plate and the pump rotor will stop it working , check the depth of the marks in the end plate again kit if they are as deep as half a mill throw the pump away [ double check though, and measure with something accurate , they are probably not as deep as you think or the pump would not have worked before you changed the o ring ]

[Frankenkit]

I do have a 2nd pump available.  I'll take its plate off just to see if it's worn as well.

[Hannibal Smith]

I don't know if you have the same setup as my CB550, but I also replaced all my oil pump o-rings.

The old one was very flat, and "square" in cross-section. The new o-ring looked awful "skinny", but it has to be compressed quite a bit to get the oil pump outer plate to bottom out (metal to metal). Perhaps your replacement ring width is too "fat"? and occupies too much room in the recess, and doesn't allow it to bottom out.

I took some pics. The top cover only gives me resistance a few millimeters before going all the way down, and my top cover "bottoms out" as designed, but is still sealed. You can see from the pics that the cross-section of the o-ring is pretty "skinny", and it fills the void nicely.
 

[Frankenkit]

yeah, same setup.  probably actually the same pump.  Any ideas on where I can get a replacement o-ring that'll work, or would it be better to, in the meantime, use the old one with a little yamabond (the semi-hardening stuff) inside the groove (just spread with a finger, not big glops) to prevent oil from going past the crack in the old ring?

[Hannibal Smith]

My rebuild kit didn't have one, and neither did Bikebandit. I went to a supply house (automotive shops should have them too) and just purchased it individually. I believe it was 1/16" cross section and it was from the Buna-N bin, so it is just your basic oil/gas resistant ring. The 3/32" cross section (next size up) was just too "fat" for the groove if I remember correctly.

I don't know about a "Yamabond" etc. type temporary fix.

[MickeyX]

According to the parts fiche, your 650 isn't compatible with the 550. All years of the 650 though, including the SC version, are the same.

I'm heading to the hardware store after I get the laundry started. Patience, patience. 

[Don R]

If the gears have worn into the end plate can the end plate be sanded or milled flat? that might restore a little more volume and pressure.

[simon#42]

yes , i normally lap them in on a sheet of glass with some valve grinding paste . if the scores are deep though it means the pump gears are also worn so it is better to replace the pump .

[cb650PK]

Exactly same story, new oil pump o-ring, but my oil light would flicker at low idle (800rpm or so). Switched to 10-40 ( from 10-30) have not seen the oil light since(2 years). I went through some 5 different thickness o-rings before I got this result. So, try another o-ring. I do wish I remembered the size of the one that worked. Actually it was more like 7 o-rings I tried.

[manjisann]

I bought a metric oring kit from Harbor Freight and had a fair amount of luck when I had to replace some leaking orings on the other side of the oil pump, so I can't say for sure the size you need will be in there.

You could always put the old ring back in and just see if the light flickering issue stops. If so then the slight size difference in orings is the cause.

Brandon

[cb650]

I just replaced the oring in my pump.  Found one at checkes in the assortment kit #80024.  So far working good.   I was at the races one day and my lite came on so I finished on another bike.  Turns out it was just a bad sending unit.

[Hannibal Smith]

I just replaced the oring in my pump.  Found one at checkes in the assortment kit #80024.  So far working good.   I was at the races one day and my lite came on so I finished on another bike.  Turns out it was just a bad sending unit.

That number is most likely store specific- Dash No. for that o-ring is prefixed with a "0" (zero) and would be in the 20's or 30's if AS568, and Metric rings are specified in diameter.

So, either inch or metric, that number doesn't cross-reference with my industry standard sheets. Is "Checkes" some sort of automotive chain store? They might have actual specs-

[Frankenkit]

Checkers = Schucks= O'Reilly.
http://www.oreillyauto.com/site/c/detail/DOR3/80024.oap?keyword=80024

[scunny]

if it's 13 in the fiche  46x3

[MickeyX]

Nope, I thought that was the one too. It's the one inside the front plate (3 screws). You could only get it with the whole pump assembly, not separate. 

[333]

No, on the Yamabond.  That will only add to the o-ring thickness and increase the clearance.  I had a similar issue with my 550 and solved it with 20W50 oil.

A tip.  About 100 miles before your next oil change, put in a couple oz's of SeaFoam in the oil.  If you think you have carbon building up, this is the best way to get it out.  You should be already running this in the gas of anything you own that is air cooled, especially any 2-stroke lawn equipment.

[Bodi]

This is the best O-ring sizing chart I've found. By measuring the groove width and depth you can find the O-ring cord size. Then measure the groove inner diameter and that will give you the size you need.
Then you have to find it, not always easy...
The oil pump is not a "service item" so no fiche available shows the internal parts, you have to get a whole new pump (as if that's available now) to get any of the parts.
Metric O-rings are a pain. The USA standardized O-ring sizes before or during WWII and there are about 400 standard sizes, most suppliers will stock every one, and almost every machine that uses inch size O-rings will be designed to use these standard sizes.
Metric stuff is not like that. There are many cord sizes, and many diameters. To stock all the common sizes would mean several thousand different ones. And there would still be thousands of others less common. Machine designers just make the groove whatever is good for the machine and production orders the size needed, no problem for a production run. Maybe a big problem for the guy who wants a replacement. Most suppliers have a minimum order - $50 or $100.00 is typical. There are some websites with no minimum but the cost is still high because of inflated per-unit and shipping costs.

[Frankenkit]

link?

[Frankenkit]

No, on the Yamabond.  That will only add to the o-ring thickness and increase the clearance.  I had a similar issue with my 550 and solved it with 20W50 oil.

A tip.  About 100 miles before your next oil change, put in a couple oz's of SeaFoam in the oil.  If you think you have carbon building up, this is the best way to get it out.  You should be already running this in the gas of anything you own that is air cooled, especially any 2-stroke lawn equipment.

I was going to use the yamabond to just beef up the old o-ring that's been crushed , and reinforce the areas that have been cracked.  After all this I realized last night that this wasn't the o-ring leaking, it's the ones behind the pump- which are still available.  

I used some valve lapping compound and a piece of glass to smooth out the bottom of the plate to the point where those contact marks are almost completely gone.  I don't have any really good way to measure something that small, but I could just barely feel them with my thumbnail to begin with.

I'm going to try to get the pump itself off for a cleanup, because of the black chunks that came out of it last time I drained it.  That means I need to do some fiddling, though- the phillips heads are all mangled... hopefully by the time I'm done it'll look like Hannibal's.

we'll also try the assortment suggested by cb650, because it bothers me, trying to re-use the old o-ring when there's a possibility I could replace the durn thing and be good for another 30 years.

[cb650]

I also replaced the phillips with some hex bolts.  I think its pretty jacked up honda doesnt offer the oring.  Has to fit other bikes or parts. 

[Frankenkit]

Ok.  Here's the news from tonight:

The 80024 kit o-ring worked like a charm.  On looking at the previous replacement attempt, that o-ring did it's very best to squish down, but just couldn't fit in the depression it was made for.  Oh well. The more you know.  That ought to be in the FAQ or Tips/Tricks somewhere...

Replaced the bolts on the cover with hex bolts, touched with a little anti-sieze and torqued down (but not stripped-out.) 

Once satisfied that I wasn't going to be leaking from there again, I pulled the pump off.  Those phillips bolts were in there TIGHT. Cleaned up the edges and o-ring grooves with acetone... replaced the o-ring around the oil pressure sender diffuser (that's what it looks like it is?  "thingamabob" is probably the technical term...)  and the dowel o-rings.  The big o-ring, still available from Honda, wasn't cracked, didn't appear too badly mangled, so I re-used it. The little dowel o-rings seemed the most likely leakers.  (and if I'm wrong, I'll just get a 46x3. )

The new bolts got a little anti-sieze on 'em, too.

Question now: Do I need to prime the oil pump in any way, or just refill the oil (replacing what puked out the side from the open pump)? 

and:
Is it really important for any reason that I pull the pressure release valve and replace that o-ring? It's not leaking, can I just assume it's doing its job? I mean, what's the realistic failure rate on those things?

Thanks again for all your help so far!

[scunny]

it's a trochoid pump so shouldn't need priming but do it if it makes you feel better. sorry can't help you on the other Q's

[Frankenkit]

that's ok. That was the important one.

[Hush]

So keep the bike above 2000 rpm ya throttle happy woman.