Topic: Silly but Serious Oil Change Question

[Rosinante]

The bike is hot right now and the oil is dripping out of the sump.  I plan to also do a compression check.  Will this drain the oil from the tank?

The filter housing is still on.  My plan is to do the compression check then remove the filter housing.  Will this run at least some oil out of that housing?  I do not know where the filter sits in the oil pressure system. 

If the filter housing is off the bike during compression testing, will this spew oil out where the housing was?

I figure that running the starter with the plugs out will help remove as much oil from the system as possible.  Right?

My plan also includes putting fresh oil in the tank and then running the starter until the oil pressure light goes off.  Is this a good idea?

[denward17]

The bike is hot right now and the oil is dripping out of the sump.  I plan to also do a compression check.  Will this drain the oil from the tank?

The filter housing is still on.  My plan is to do the compression check then remove the filter housing.  Will this run at least some oil out of that housing?  I do not know where the filter sits in the oil pressure system. 

If the filter housing is off the bike during compression testing, will this spew oil out where the housing was?

I figure that running the starter with the plugs out will help remove as much oil from the system as possible.  Right?

My plan also includes putting fresh oil in the tank and then running the starter until the oil pressure light goes off.  Is this a good idea?

Lots of questions here, but I would not spin the engine to perform a compression check unless the oil system was buttoned up, meaning oil in the system as you would ride it.

[Rosinante]

I've got a whale of a lot of respect for you Dennis but I don't think this damages engines.  The forces are not nearly the same against rod bearings and the engine speed of a starter burst is nowhere near idle speed.  1200 RPM is twenty revs per second, and 150 psi is not a match for the pressures inside an exploding cylinder.  Also, the only cylinder with pressure during a compression test is the cylinder being tested.  All other cylinders are making no compression at all.  A thin film of oil stays on the important surfaces, at least for the few revolutions it takes to check compression.  My opinion.  But I'm certainly listening.

[denward17]

You are probably right, I have a tendency to be overly cautious.

[Rosinante]

And I have a tendency to be overly reckless. 

[HondaMan]

I have 2 CB750 engines in the garage, one waiting over 7 years now for a new crankshaft.
It started out as "I fully drained the engine oil and then decided to do a compression test."
Crankshafts for these engines are really hard to find.

[bryanj]

Its not always the load but the dryness as well, been an engineer/mechanic all myblife and would never spin an endine withoit oil

[PeWe]

Oil pump will be dry and take very long time to pump the new oil. Crankshaft will run dry.

[bustech51]

If anyone is looking for a crankshaft I  have some. 
Drop me a line if one is needed.

Sent from my SM-G950W using Tapatalk

[dave500]

fill it with oil,you might draw air into the pumps,even just spinning with no oil pressure the clearances at the plain bearings aint floating on a film of oil.

[Rosinante]

... waiting over 7 years now for a new crankshaft.
It started out as "I fully drained the engine oil and then decided to do a compression test."
....

There has to be more to this story.

[Rosinante]

Its not always the load but the dryness as well, been an engineer/mechanic all myblife and would never spin an endine withoit oil

You do it every time you change oil.  The oil pump feeds the filter, and then the pressurized oil goes to the crankshaft galley.  In the time it takes to fill the filter, your main and rod bearing have zero oil pressure.  You can almost always hear the rods knocking when you start the engine, and this noise stops when the oil pressure light goes off.  I've watched this several hundred times including a Ford Fiesta oil change exactly one week ago.  During that time of zero pressure to the oil galley, cylinders are making pressure against the rod bearings in the neighborhood of 700-1000 psi at a rate of 15-50 times per second.  For two or three seconds.

That is far greater punishment than rotating a crank a few turns slowly with pistons that are not even making compression (except of course, the one being tested at 150 psi or less).

[Rosinante]

And in that explanation is an answer to one of my questions.  Yes, oil would spew from the oil filter area if I ran the starter.  As it turns out, as I had suspected and just mentioned, oil goes from the pump to the filter to the crank galley.  Right now, the filter housing is still on and filled with old oil.  The tank is filled with oil.  And so.....right now, if I pulled the plugs and did a compression test, the entire engine would have oil and pressure. 

Heck, if you think about it, then when the tank has fresh oil but the filter is DRY and the sump is EMPTY, the kindest procedure would be to run the starter with plugs removed until the filter is filled and the oil light goes out.  And THEN start the engine and subject the rod bearing to the pressures and speeds mentioned above.

[PeWe]

It runs quick with no plugs. Pressure OK quicker too.

Check plugs is good to do now and then.
I take photos of plugs so I can compare later if they look different.

[MauiK3]

safety and caution are #1

[TwoTired]

Unless I had  some serious oil contamination, I would rather have some used oil in the galleys and bearing journals than air, which would allow metal to metal friction contact.  I would never consider doing a compression check, purposely starving the oil system and allowing the cylinder walls to dry completely.

While you may not get full oil pressure during the filter fill, you still get some flow to the bearings during that time, just not full flow.  Light goes off at 5-7 PSI.  But, even low PSI indicates flow and oiling.

Many spin on oil filters have an anti drain back valve, the purpose of which is to keep oil in the oil system for the next start.  It would appear that engine designers and manufacturers think oiling when the engine turns is important for longevity of the motor.  Anyway, When this ADB valve is faulty, the hydraulic tappets collapse making the valve train clatter during initial start.  You are advised to change your canister filter brand if this occurs.  You can’t check this valve operation without cutting the canister, and one of the reasons why I don’t use spin on filters on my bikes.

[Rosinante]

Understood.  Dry sump systems have certain advantages over wet sump.  One of those is oil pressure at the pump input during starting.  The oil tank on our bikes sits above the pump, and feeds that pump directly.  This means there is positive (gravity) oil pressure to the pump input.  Wet sump systems do not have this.  I have a car with this kind of oil system, and oil pressure is IMMEDIATE during starting.  Basically, the oil galley is pressurized BEFORE the engine fires.  Before the first crank rotation is completed.

[Don R]

 I don't see an upside to cranking an engine without oil. You may lose prime in the pump and have to crank a lot more to prime the pump again.

[PeWe]

I have done oil change when I drained a little more by the starter splashing out old black oil where the filter should sit. Just a few sec...2-3...

Not fun to whitness the much longer time red light was shining at the start when new oil was filled and dry filter.

[RAFster122s]

Rosinante, it sounds like you are going to argue that it is fine to do it. Go ahead and do it and find out down the road if it is or is not OK to do.
Many have said it isn't not a good idea but you continue to argue it will be fine.

An old 50 year old motorcycle engine is not like a modern car engine, so not a good comparison.

Personally, I would never buy a vehicle or motorcycle subjected to this treatment if it were revealed that is how it was treated.

Just like rebuilding a motor, if you are reassembling fairly quickly and restarting soon after finished you can get away using oil on moving parts, otherwise you are better off using assembly paste for increased protection.
Not all parts of the SOHC4 motor will have the same film of oil protecting it. Tight tolerance areas like cranks and rods film may last longer than the camshaft and rocker arm or the pushrod and rocker arm. Then piston rings and cylinders will have a different oil film strength too.

You are playing with a hand grenade to do it with no oil in the system. Do you plan on checking each cylinder or just one this way.

There is an expression in use today that comes to mind...
F___ around and Find Out!

[Tracksnblades1]

Rosinante, it sounds like you are going to argue that it is fine to do it. Go ahead and do it and find out down the road if it is or is not OK to do.
Many have said it isn't not a good idea but you continue to argue it will be fine.

An old 50 year old motorcycle engine is not like a modern car engine, so not a good comparison.

Personally, I would never buy a vehicle or motorcycle subjected to this treatment if it were revealed that is how it was treated.

Just like rebuilding a motor, if you are reassembling fairly quickly and restarting soon after finished you can get away using oil on moving parts, otherwise you are better off using assembly paste for increased protection.
Not all parts of the SOHC4 motor will have the same film of oil protecting it. Tight tolerance areas like cranks and rods film may last longer than the camshaft and rocker arm or the pushrod and rocker arm. Then piston rings and cylinders will have a different oil film strength too.

You are playing with a hand grenade to do it with no oil in the system. Do you plan on checking each cylinder or just one this way.

There is an expression in use today that comes to mind...
F___ around and Find Out!

👍 Well Said😁

Down on the Farm, the expression was “F*+^ with the Bull, you’ll get the Horn”. Similar to the sleeping dog…Sometimes learning it  first hand is the only way 🙄. I still can’t believe someone would post it with the amount of information available at one’s fingertips 🤔

[ekpent]

I have done oil change when I drained a little more by the starter splashing out old black oil where the filter should sit. Just a few sec...2-3...

Not fun to whitness the much longer time red light was shining at the start when new oil was filled and dry filter.

If you really want to get more oil out try tipping the bike way over to the side till the foot peg almost hits the ground especially when tipping to the left. You will be surprised at how much more oil will come out the drain plug when you put it back upright. I do this on my 750's when changing oil.

[BenelliSEI]

I just changed the oil on the K1, Sunday. Came back from a long run and let it sit for 1/2 hour. Drained the tank, drained the sump, and pulled the filter. Not a speck of anything on my magnetic drain plugs, which always makes me smile.

Filter housing goes in the cleaning tank for a good scrub and dries in the sunshine while the last few drops come out of every where. New filter, with the spring and washer in the right way. Lube the big “0” ring with a drop of oil. Three litres in the tank and run it for a few minutes. Takes a bit more to get it just below the full mark, and then check it after the next run.

I never vary the procedure and would not run it with the system open. I don’t spin it when draining because it already takes long enough to fill the filter housing and “off” the oil light on first start. +50 years old and still runs great.

Spinning the motor with the plugs out until you get oil pressure is an excellent idea. I always do it on a fresh motor, but truthfully on a warm engine pulling the plugs is a pain. As someone said earlier, my oil is never that contaminated so I don’t worry too much about leaving some in there which of course does happen.

One of my good buddies, that has several beautifully maintained old Hondas, only changes the filters on alternate oil changes. He swears we are all excessive! He may be right, but for the cost of a filter I’m not playing that game…..Oil and filters are the cheapest insurance you can buy and the only Honda engines I’ve seen totally destroyed were from lack of oil.

[Rosinante]

Knowing that new engines are assembled at factories with oil instead of assembly lube, and knowing they must turn many times before oil galleys become pressurized (probably by starting the engine but let's assume those engines are rotated another way to fill oil galleys) and knowing that we all fire up engines and wait several seconds before oil lights go out each time we change oil (at between 15 and 50 revolutions per second with a thousand psi of explosive pressure beating those rod bearings every two revs), and knowing there is a film of oil in rod and main bearings after an oil change and that a compression test is mighty gentle compared to all this, I do not wish to argue with people here or beat this dead horse further.

I also do not want to give anyone PTSD here, so here is what I did:  With oil in the tank and the oil filter, I did the compression test.  I found that a GREAT many revolutions would be needed to empty the oil tank.  Oil pumps can develop some good pressures, but they do not pump a fast volume of oil, which is what I expected.  The test procedure probably reduced the volume of oil in the tank by about 1/4 quart.  There was still oil there when I removed the oil filter.  Nobody suggests avoiding compression tests to protect bearings, and those bearings were always under pressure.  Except of course, for the ten or fifteen seconds it took the oil light to go off during the testing of compression on #1, and the several seconds it took for the light to go off testing the others.  The oil filter housing is off now and, after installing a new filter and draining the rest of the oil from the tank, I will fill the tank and probably run the starter with the plugs removed until oil pressure is re-established before installing plugs.  That will probably take thirty seconds or more.  Probably enough to do the compression test I already did. 

I hope someone will find this information useful.  Thanks to all for contributing.

[scottly]

So what were your compression readings?