Oil Pressure Gauge reading

hillbone · Nov 30, 2015

Hi
I'm running an Old Britts Oil Gauge and the bikes pressure has dropped to around 30 lbs whilst under way and falls further to 10 lbs at idle.
From memory it ran into the 50's. I fitted a new sealing grommet on the oil pump when I rebuilt the engine recently.
I've drained the oil tank, fitted a new filter and checked the lines.
I'm running Penzoil 10w50 semi synthetic. Plan to pull the timing cover off and check the pump and seal......again!
What should be my target pressure?. The old Britts site says he's running 70 .
Thanks again.
Cheers Hillbone

gripper · Nov 30, 2015

That would tie in with what I have seen on a new bottom end once the oil is up to temperature. Starts off up around 50psi and once under way drops to about 25-30 at 3500rpm. If you are confident about your re-assembly I don't think you'll find anything amiss inside the timing cover. Don't worry about it.

concours · Nov 30, 2015

gripper said:
That would tie in with what I have seen on a new bottom end once the oil is up to temperature. Starts off up around 50psi and once under way drops to about 25-30 at 3500rpm. If you are confident about your re-assembly I don't think you'll find anything amiss inside the timing cover. Don't worry about it.

+1

My '74 850 has been at those numbers for 24,000 miles.

"Rebuilt the engine"
Reground crank and undersize rod bearings part of this rebuild?

toppy · Nov 30, 2015

I get the same reading with my fully rebuilt motor so I wouldn't be overly worried it seems the norm. On one really hotday after an hour at 70mph to 80mph on the motorway the pressure was 18 to 20psi but as we don't get much hot weather in England an I don't do much motorway mileage it doesn't worry me.

tomspro · Nov 30, 2015

I have the same setup on my 72 Combat and get similar readings when it is warmed up.
No worries.

JimC · Nov 30, 2015

I doubt there is any stock Commando engine with any grade oil that will hold over 10 psi at idle after the oil is hot. I used to run 80-90 mph on the freeway for about an 40 minute long trip to Daytona Speedway. When I exited the freeway and dropped to idle the oil pressure was alarming low, 5-6 psi. At startup with a stuck OPRV you will see extremely high pressures, well over 100 psi. If you can maintain 10 psi/1000 rpm with hot oil, consider everything good. I guess the rationale for those who insist on not running a pressure gauge is they don't want to see those very low pressures at idle.

Another troubling thing I've seen posted here, at times, is some thinking by shimming the OPRV the oil pressure at idle will increase. Only if the pump is delivering more oil pressure than what the OPRV is shimmed for. If the pump can only deliver 10 psi at idle you can shim the OPRV entirely closed and it won't change the pressure reading at idle one lick.

hillbone · Nov 30, 2015

Hi.
All good news there. Saves looking for a problem that's not there, cheers everyone. I'm in Australia so it gets hot here and that may explain also the lower readings. Cheers

pete.v · Nov 30, 2015

Remember, these gauges are not so much to tell you how much oil pressure you have, but to tell you that you actually have oil pressure.

JimNH · Dec 1, 2015

My oil pressure dramatically fell from around 55 to around 25 with about 5-10 at idle. The bike always pegs a 60PSI gauge at startup and will drop to 40 after an hour at 75mph on the highway. It generally runs 50-55 at easy back road cruise. 20-50 oil.

I found the pump to timing cover seal failed. I replaced it and it's back to normal.

Mine was a sudden change and there was no doubt in my mind something was wrong. I drive it easier now until the oil warms up enough to take the gauge off the peg. The over pressure valve is completely free and it does relieve at some very high pressure on a test gauge. I just don't remember what it was.

texasSlick · Dec 1, 2015

While the following is not likely the cause of the oil pressure drop, it is worth keeping in mind ..... the screen in the oil tank may become clogged with muck and starve the oil pump. It is easy to forget that it is in there and neglect to wash it in solvent every 10K miles or so.

Slick

gripper · Dec 1, 2015

The other thing in the feed to the pump may be a anti-wetsumping valve? That will reduce the flow a little IMHO

hillbone · Dec 2, 2015

Hmmm.
The bike always ran at 60psi. Maybe worth a check on that new seal. I did clean the gauze filter after the first observation of 30psi.

texasSlick · Dec 2, 2015

hillbone said:
Hmmm.
The bike always ran at 60psi. Maybe worth a check on that new seal. I did clean the gauze filter after the first observation of 30psi.

Perhaps you need a shim under the seal. Are you running a standard thickness timing cover gasket? A thicker than standard gasket will require a shim. From memory, a standard thickness gasket is about 0.015 inch.

The timing cover should stand off the seal about 0.010 inch when pushed on (with a gasket in place). Sometimes this is hard to judge. I would say, when in doubt, add a shim.

Slick

hillbone · Dec 10, 2015

Hi.
Will check and add a shim. It was a new gasket and seal. Thanks

htown16 · Dec 10, 2015

I would check the grommet out, it should have a bit of a witness mark if it was sealing okay. Good to to also take a look at the timing cover crank seal. While 30 psi at 3000 rpm might be okay on an engine with some rod bearing wear, the fact that it suddenly dropped 20 psi is concerning. Are you comparing measurements under the same conditions such as air temp and after say a 20 mile highway speed ride. Also, why are you using 10w50 and is it the automotive style SL or SM rated? I don't want to start an oil thread but you might try 20w/50 motorcycle specific oil that is rated SG/SJ JASO MA. I use Valvoline 4 Stroke dino but its also available in synthetic, along with Mobil1 Vtwin, and Castrol Vtwin. The vtwin products are designed to run in aircooled engines.

concours · Dec 11, 2015

htown16 said:
I would check the grommet out, it should have a bit of a witness mark if it was sealing okay. Good to to also take a look at the timing cover crank seal. While 30 psi at 3000 rpm might be okay on an engine with some rod bearing wear, the fact that it suddenly dropped 20 psi is concerning. Are you comparing measurements under the same conditions such as air temp and after say a 20 mile highway speed ride. Also, why are you using 10w50 and is it the automotive style SL or SM rated? I don't want to start an oil thread but you might try 20w/50 motorcycle specific oil that is rated SG/SJ JASO MA. I use Valvoline 4 Stroke dino but its also available in synthetic, along with Mobil1 Vtwin, and Castrol Vtwin. The vtwin products are designed to run in aircooled engines.

If the OP could answer the question I posed earlier, it MAY explain the markedly different reading.

" "Rebuilt the engine"
Reground crank and undersize rod bearings part of this rebuild?"

hillbone · Dec 16, 2015

Hi.
Went back to using the Penrite 50 Zinc. The oil pressure sits at about 25 to 30psi . Drops to 5 at idle. Today was 38 degrees centigrade on the open road. Very hot day but the psi doesn't get that much better on a cooler day.
The seal was not marked. In fact it still had a very fine raised ring still on it. I didn't have a fine enough shim at the time, so I just pet it back the way it was. The oil pressure reading was still not any better.

Oil Pressure Gauge reading

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