Topic: Low Oil Pressure at idle! Comments please

[RpBet]

O.k Boys,

I have an external oil pressure gauge (which I had tested and is accurate to 5lbs) and am running 20W 50. I have removed my oil pump and replaced all O-rings as per Hondaman's recommendation. Helped out oil pressure while revving! While the pump was out I also checked all clearances and pump is within spec. However, when she is warm and idling it drops down to 5 - 10 lbs. I believe it should be at 20. WTF?

Any suggestions?

[70CB750]

That typically means crankshaft bearings are worn out - sorry to break the bad news.

[MCRider]

That typically means crankshaft bearings are worn out - sorry to break the bad news.

Seems reasonable. Would you say if he has good pressure above 2000 rpm, no reason to panic?

[RpBet]

This is what I am wondering. As long as I don't let her sit for prolonged periods at idle.............................

[lrutt]

Damn, mine never went below 40lbs, 60 down the road, and 80+ when cold. Still to this day at 28k miles, and 20k miles on the K8. Both read the same.

You definately have some clearance issues. unless you have your oil filter installed incorrectly with the spring wrong. That could have an effect.

[grumpy]

That typically means crankshaft bearings are worn out

Really?
How would that cause the pressure to drop?

[MCRider]

That typically means crankshaft bearings are worn out

Really?
How would that cause the pressure to drop?

Engine oil pressure is pretty much determined and dominated by main bearing clearance.

PS: Assuming the oil pump is OK.

[RpBet]

That typically means crankshaft bearings are worn out

Really?
How would that cause the pressure to drop?

Engine oil pressure is pretty much determined and dominated by main bearing clearance.

PS: Assuming the oil pump is OK.

I have a 78K and a parts bike that is a 77k. I guess I should swap them and find out? One old part for another

[70CB750]

That typically means crankshaft bearings are worn out - sorry to break the bad news.

Seems reasonable. Would you say if he has good pressure above 2000 rpm, no reason to panic?

I would refer to manual for numbers - higher rpms bring higher pressure, but it may not be high enough.
For car engines 10psi per 1000 rpms are considered safe, but bike motor is different animal.
I would check the oil pump for clearances, get a new one since it is easier to replace then open low end.
And I would ask Hondaman for guidance at this very point.

[grumpy]

I still don't get it.
If the pump is what's, well, pumping the oil then how does the bearing come into play?

I'm missing something...

[nayto550]

I still don't get it.
If the pump is what's, well, pumping the oil then how does the bearing come into play?

I'm missing something...

The plain bearings on the crankshaft mains are nothing more than smooth metal to metal, using a thin film of oil pumped into the bearing to keep the journals from contacting each other.  If the clearances between the journals wears too wide, it begins bleeding oil out of the bearing at a much faster rate, lowering the pumping resistance, thus causing the oil pressure to drop.

[MCRider]

I still don't get it.
If the pump is what's, well, pumping the oil then how does the bearing come into play?

I'm missing something...

The plain bearings on the crankshaft mains are nothing more than smooth metal to metal, using a thin film of oil pumped into the bearing to keep the journals from contacting each other.  If the clearances between the journals wears too wide, it begins bleeding oil out of the bearing at a much faster rate, lowering the pumping resistance, thus causing the oil pressure to drop.

Yes and it is only plain (aka plane) bearing crankshafts (all Honda SOHC/4s, but not many other 4s) that serve the purpose of maintaining oil pressure. Or rather oil pressure must be maintained to serve their purpose. The thin film of oil keeping the bearing surfaces from touching must not fail. The more clearance there is the more likely the pressure will fail to keep the surfaces apart and they touch, resulting in a spun or seized bearing. Tragedy.

Roller bearing/ball bearing cranks do not maintain or need oil pressure. Like in most Honda twins, etc. That's why you can't put an oil pressure gauge on them.

[70CB750]

Thats also the reason I was able to bring the tiller back to life from the death by oil starvation.

You can imagine the oil leaking between the crankshaft and the bearing and the oil pump must keep up with the leak and pump more than that to hold the pressure high enough. If the leak is too big - ie clearance too big, the pump cant supply enough.

[steam-powered man]

according to my K6 manual the oil indicator light may come on at 800/900 rpms (engine warm), and that this does not indicate a problem.  does your oil indicator light come on at idle, confirming your pressure gauge reading?  what are the pressure readings at 3K and 4K rpms?

you may not have a problem. 

pressure gauges are most accurate at the middle of their range, and inaccurate at either end.  what is the range of your gauge?   

you may have a weak oil pump pressure relief valve spring (supposed to dump at 56psi / 4K rpms) or,
 
you my have a weak/missing spring in the oil filter. 

[grumpy]

Ah, now I understand

Thanks

[DH]

Seems like that little o ring behind the countershaft bearing holder
can allow some pressure loss if it's too old and hard? Thought I read that somewhere here?...

[HondaMan]

O.k Boys,

I have an external oil pressure gauge (which I had tested and is accurate to 5lbs) and am running 20W 50. I have removed my oil pump and replaced all O-rings as per Hondaman's recommendation. Helped out oil pressure while revving! While the pump was out I also checked all clearances and pump is within spec. However, when she is warm and idling it drops down to 5 - 10 lbs. I believe it should be at 20. WTF?

Any suggestions?

Did you also replace the seal on the shaft of the pump, in between the 2 rotors? If old, this will leak pressure from the high-pressure side to the lower pressure scavenge side, especially at idle when the flows are lower.

[MCRider]

Seems like that little o ring behind the countershaft bearing holder
can allow some pressure loss if it's too old and hard? Thought I read that somewhere here?...

Yes that's one of HondaMan's Tips and Tricks. As you say, It gets old and hard, and shrinks and allows oil pressure to leak out.

[Jerry Rxman Griffin aka MuthaF'er]

What's wrong with 10psi?! I don''t see what your idle rpm is set to? Mine would idle at 600 or less with a good cam even. Raise your idle some.

[andrewk]

I wouldn't worry about 10 psi at idle.  It's maybe a bit below normal, but it should be just fine, especially if it comes up (And stays up) when you're going down the road.

To follow the theory on the differences in oil pressure requirement between a car engine and a bike engine, I would say that if 10 psi per 1000 rpm is sufficient for a car, then it's sufficient for a bike- consider that the rotating assembly of a small block V8 is many times that of an SOHC 4, and the bearing surfaces are larger.  The biggest concern I would have of low oil pressure at idle is making sure that the top end is still getting oil at idle.

[RpBet]

Wow, thanks for all the replys.............were to start

I do not have a "dummy" light.

.

What's wrong with 10psi?! I don''t see what your idle rpm is set to? Mine would idle at 600 or less with a good cam even. Raise your idle some.

@ idle which is currently 1000rpm I have 5lbs pressure. I just assembled my head back together after bending some vavles. I wanted to contact you jerry before assembling cause I had this problem before I bent them. Time was pressing though.

Seems like that little o ring behind the countershaft bearing holder
can allow some pressure loss if it's too old and hard? Thought I read that somewhere here?...

Yes that's one of HondaMan's Tips and Tricks. As you say, It gets old and hard, and shrinks and allows oil pressure to leak out.

Not sure where this bearing is. Pic would relly help. However, as I just stated to Jerry I just re-assembled my entire head including new piston rings all seals and O-rings.

O.k Boys,

I have an external oil pressure gauge (which I had tested and is accurate to 5lbs) and am running 20W 50. I have removed my oil pump and replaced all O-rings as per Hondaman's recommendation. Helped out oil pressure while revving! While the pump was out I also checked all clearances and pump is within spec. However, when she is warm and idling it drops down to 5 - 10 lbs. I believe it should be at 20. WTF?

Any suggestions?

Did you also replace the seal on the shaft of the pump, in between the 2 rotors? If old, this will leak pressure from the high-pressure side to the lower pressure scavenge side, especially at idle when the flows are lower.

Hondaman. I cannot remember, but I am going to remove my pump again and re-check ALL clearances. I will have a double look at this seal again. Thanks for the help before and now.

Anyone know what a parameters of the spring on the oil filter are suppose to be?
Thanks to everyone thus far. I will keep you posted.

Ryan

[MCRider]

Its the countershaft bearing holder. It is behind the transmission cover on the lower left side of the engine. Onece the shift pedal and cover is removed its an obvious gadget held on by 4 flat head phillips screws. They are usually staked so it will take an impact driver to break them free.  You'll pull the cover away from the crankcase, the end of the CS will be hanging there, OK. The ORing in question maybe 1/4-3/8 diameter, likely stuck to the cover.

This is a nice thing to do but not likely to make a big singular improvement, just incremental.

[RpBet]

Its the countershaft bearing holder. It is behind the transmission cover on the lower left side of the engine. Onece the shift pedal and cover is removed its an obvious gadget held on by 4 flat head phillips screws. They are usually staked so it will take an impact driver to break them free.  You'll pull the cover away from the crankcase, the end of the CS will be hanging there, OK. The ORing in question maybe 1/4-3/8 diameter, likely stuck to the cover.

This is a nice thing to do but not likely to make a big singular improvement, just incremental.

%&#$, I had this all apart last year. Can't remember. I imagine I would have replaced but cant remember for sure. Oh well, gotta drain the oil anyways.
Thanks MC.

[MCRider]

Its the countershaft bearing holder. It is behind the transmission cover on the lower left side of the engine. Onece the shift pedal and cover is removed its an obvious gadget held on by 4 flat head phillips screws. They are usually staked so it will take an impact driver to break them free.  You'll pull the cover away from the crankcase, the end of the CS will be hanging there, OK. The ORing in question maybe 1/4-3/8 diameter, likely stuck to the cover.

This is a nice thing to do but not likely to make a big singular improvement, just incremental.

%&#$, I had this all apart last year. Can't remember. I imagine I would have replaced but cant remember for sure. Oh well, gotta drain the oil anyways.
Thanks MC.

It is a very un-obvious thing. If you've had it apart, there is the chance it stuck to the cover, fell off, and was never replaced! In which case, you would lose some oil pressure there.

[mrbreeze]

Hey Ron or Elan, is this what is mentioned in the oil pump kit as the full kit ? I only got the o-ring & spring kit. If this is something that could cause lower than normal oil pressure at idle then maybe I should change it while I'm in there. I haven't installed the kit yet. I'm gonna change my header bolts to studs and put in new donuts when I do the pump kit. I have around 20 lbs. at idle when warmed up but some people say they have 40 lbs. I'm not doing this because of a problem but it just makes sense due to the age of the parts in the environment they live in.