Oil level questions as I'm getting ready to fire up

I bought the bike last year a low mile 1975 MK3 that was running last year. I left a petcock on and drained the fuel, I was concerned about oil contamination so I drained the crankcase and lost about a pint or less of oil. This year I wen to top off the tank and added about 1/2 to 2/3rds a quart of 20w50. One the center stand it barely touched the stick.

So I'm waiting on a new Mukini carb boot and will be firing her up soon. The oil had maybe 30 minutes of run time on it last year. I'm a bit in the dark with this oiling system and concerned as I don't want to burn up another bike (lost a Zuki on the Dyno last year!)

So I need some help and direction on adding oil, checking proper level etc. Seems simple to me but I'd rather look stupid here than in the drive with a bent valve or seized piston... Thanks for your help.

I got a pile of parts coming from Fred and Ella at Old Brits and looking forward to getting the girl on the road, new rubber front and rear and new brakes front and rear. The wooden shit had to go, 35 year old tires too!

Chances are that the engine has "wet sumped" if it has been sitting awhile. Not sure if you are familiar with the term but basically in old Brit bikes, if they sit for awhile the oil in the tank(sometimes about all of it) leaks past the oil pump and ends up in the sump.
First thing to do is drain the sump. That way when you fill the tank you won't have excess oil in the system. Once you get the oil out of the sump (okay to use again if you use a clean container) fill the tank so that it reads about halfway between add and full. Get the bike running and check for return of oil back into the top of the tank. Once warmed up, then check again while the engine is still hot and top off if necessary.
Checking the oil on these is kind of a two step process. Always check it right after a ride and top off if necessary. Then before you start it the next time check the level again. If its low, the oil is going to be in the engine sump and if you top it up with more oil, when you start it you will blow oil everywhere. Drain the sump if the level is below the bottom of the dip stick, otherwise the pump will clear it okay. Just don't add more oil.

Be careful with the term..."top off".... when it comes to oil. I know on mine, if I fill to the full line on the dip stick, it will just blow it all out within a very short time until it gets down to half way on the stick.

if I just leave it at half way on the stick it stays there. Does more harm than good to 'top it off' as it ends up all over the ass end of the bike.

I've heard this from others as well. Not sure if the MKIII has the same issue as the MK1s and MKIIs but it's worth a try.

Also, the MKIIIs had a change to the timing chest that helped prevent wet sumping. Will be interesting to see just how much oil you get out of the sump when you drain it. I know on my MKII the whole damn oil tank will drain to the sump in about a month or so.

My early bike seems to like it between L and H also, mostly on the L side or it blows out the breather, I don't think it's that much oil between the 2 marks anyhow. It's not like it's a quart, the bike only holds between 3 and 4 qt total anyhow and changing the oil only requires 2 qt, at least on mine and that's draining the sump and tank both.

Yep, mine likes it about half way between the two marks. Otherwise, I end up with oil on my boot.

Thanks to all for the advice!
I understand the wet summing business clearer now and will drain out the sump again before I start over.

Next on the list:
Install new master cylinder and U.S. Spec bars
Install new brake lines and rebuild calipers.
Add new rotors
Carb boot and throttle cable
And finally sort out the new avons on my tire machine.

My rear wheel offset is an abortion! At least two centimeters to the left! I don't know if I can pull it over with the spokes on there or not, maybe not enough nipple!

I hope to be on the road by the end of the month. Old Brits got my tractor money this month.

I'm struggling to understand how a higher oil tank level results in more oil up the breather, or on your boot, isn't the oil pressure created by the pump? or do you mean having higher head pressure in the tank causes more wet sumping, but the increased head would be tiny. Am I completly on the wrong line of thinking, I recently posted about my oil breather and return lines behaviour worrying me after starting up, but reducing oil level didn't come to mind, is it something that makes a difference? please enlighten my this Welsh hillbilly's mind,
Paul.

In my case with the central oil tank, it puts the oil in the tank higher and closer to the breather that goes into the air intake. I think it just blows out that breather and drips down on the gearbox, etc. until the level gets to a place where it doesn't blow out.

brxpb said:

I'm struggling to understand how a higher oil tank level results in more oil up the breather, or on your boot, isn't the oil pressure created by the pump? or do you mean having higher head pressure in the tank causes more wet sumping, but the increased head would be tiny. Am I completly on the wrong line of thinking, I recently posted about my oil breather and return lines behaviour worrying me after starting up, but reducing oil level didn't come to mind, is it something that makes a difference? please enlighten my this Welsh hillbilly's mind,
Paul.

Click to expand...

Oil tank breather, not engine breather.

Yeah, oil tank breather. Since I have a K+N airfliter, I have the tank breather coming out into a small breather filter at the base of the air cleaner plate. If I fill the tank completely after a hard run the breather filter will drip oil. Some ends up on my boot. Halfway between the marks doesn't seem to do it as bad.
Oil tank breather hose filter mounted to plate. Also, Mike's xs650 pvc valve on the engine breather line.

This photo shows the oil tank volume levels for one and two quarts.
Note that even one quart completely covers the oil supply fitting internal screen.
There are different level marked dipsticks also.

A good tip to remove and flush the oil tank after a long period of storage.

Makes sense now , as my tank breather isn't plumbed to the airbox I have a completely different mental picture to look at.

Another thing to check if the bike has wet-sumped is the primary chaincase level. I let my old girl sit for 2 years. She wet-sumped but I believe some of it leaked through the crank seal into the chaincase because the oil level in there was way high and got flung out the drive chain.

manxman