This has got to be the Number 1 question on here by new Ironhead owners who are still waiting for their workshop manual to arrive. How do I change the oil, and is the transmission / primary / gearbox oil separate from the engine oil or the same?
So I thought I would put the basics and a few pics together for the newbs.
Others who have pics of other models etc, please add info as you see fit. This info is based on my 77 model. Earler tin primary covers are slightly different, and earlier/later models had different oil tanks.
TWO SEPARATE LUBRICATION SYSTEMS
An Ironhead has two separate oil sytems, engine and transmission, so needs two oil changes before you go ride anyplace on that new bike. Old oil that has been sitting for years can do damage right from jump street, so you should change that oil before firing up for the first time. See the sticky thread on “Dehibernating the Ironhead” for more details on first start up preparation.
THE ENGINE OIL
The engine oil is kept in the oil tank under the seat, filler cap on the right hand side, drain plug in the bottom of the tank. The oil pump, under the engine on the right, near the front, circulates the oil to and from the tank. The oil tank has a supply line from the bottom, a return line to the top, and a third, smaller vent line that runs from the top of the oil tank to the rear of the cam timing chest, in behind the timing chest, behind the rear cylinder.
Oil tank capacity is about 3 quarts. Only top it up after running the engine to clear any drained down oil from the sump first, or you will end up with an overfull oil tank and oil will puke out the engine breather, onto the floor on pre-79 models, into the air filter 79 and onwards.
THE TRANSMISSION OIL
This is separate from the engine oil. (There is a small crossover vent valve between the primary case and crankcase on earlier models but oil flow through there is normally negligible.) The transmission oil lubricates the primary chain, clutch and the gearbox.
It is checked and topped up at the primary chaincase cover.
Transmission oil capacity is 1.5 pints, or 24oz by the manual, but I have had mine take 28 oz to get it up to the level plug. More about that later.
HOW TO CHANGE YOUR ENGINE OIL
1. Start the engine and run it until the bike is good and hot, normal operating temperature. (If bike has sat for years unstarted, change oil cold before first start up, then change again after about 100 miles). Stop engine. Park bike on lawn where spilt oil is not a problem.
2. Take off oil tank cap. Put some wood under the side stand to get bike close to vertical Place a folded newspaper under oil tank, leading into oil drain tray. Remove oil tank drain plug and drain the oil.
Budget oil drain chute.
3. DO NOT take any drain plug out of the bottom of the sump of the engine, at the front, under the crankcase. These are notorious for stripping their threads. DO NOT TOUCH. There is so little oil in the sump it is not worth the risk of messing with. Repairing that thread properly can require splitting the crankcases and you don’t want to go there.
4. When all oil has drained out of the oil tank, put the oil tank drain plug back, with a new copper washer on it to seal it. I also put a smear of hard-setting gasket goo like Permatex on the threads, not so seal them but to stop the plug vibrating loose. The new copper washer is essential. Buy a bag of them at the local hardware or auto store cheap. Half inch is the size on mine. Don’t overtighten the drain plug.
5. If you have an aftermarket inline oil filter, screw the old one off, and screw on a new one. Hand tighten only. The filter should be in the return line, so no need to prime it.
5. Fill the oil tank up to the low mark on the dipstick, or about ¾ full by sight.
6. Start and run the engine for a bit. Then stop and top the oil up to the full mark, no further.
7. Put in a new drop-in oil filter if your model has one. XLH side mounted oil tank, pre-1979 has a filter that drops in the oil filler neck and filters the returning oil. I like the drop in filters from JP Cycles (JP part no 7400225) with the pleated automotive style element and spring loaded bypass valve. They work good. I had to cut my dipstick down to fit it, right on the low mark, so that is ok.
Drop in oil filter for pre-79 XLH sidemounted oil tank:
Cut down dip stick for JP oil filter. Oil level, if you have no dipstick, is about Full is about 2 inches below filler cap gasket surface. Low is about 4 inches below.
Now you are ready to change the transmission oil.
HOW TO CHANGE YOUR TRANSMISSION OIL
Tranny oil is often overlooked and seems to cause more headaches then engine oil. I change mine every time I change the engine oil. The manual says you can leave it longer, but I don’t like the idea of wear particles from the primary chain tensioner and clutch plates circulating through the delicate needle roller bearings in the gearbox.
1. Ride the bike to get transmission oil up to working temperature. Again, if the bike has not been ridden in years, change the oil cold before the first ride, then change again at 100 miles.
2. Put wood under the stand to hold bike near vertical.
3. Unscrew the primary chaincase upper inspection plug. Use the special tool to undo it, or make one from a piece of flat bar with curve ground on the end.
This plug here is removed to pour the new oil in:
The special tool will not scar up the plug:
4. Remove the primary drain plug. It is about 2 inches behind the side stand pivot, on the left, at the rear, under the clutch at the bottom of the primary cover. Drain oil into tray.
Tranny drain plug is this one here on the inner primary cover:
Tranny drain plug has a big hexagon but a small easily boogered thread:
5. BE VERY CAREFUL
putting the drain plug back in. It has a small thread, going into aluminum but a large hexagon on it. DO NOT overtighten it using the big wrench on that hexagon. Hold the wrench right next to the drain plug -- not way out on the end of the handle where you get too much leverage. Always put a new copper washer on the drain plug. This is what seals it. I also put a smear of hard-setting Permatex on the thread just as a mild threadlocker to stop the plug coming loose.
6. Remove the primary oil level phillips head screw, shown here in pic by IronMick.
7. Have an assistant hold the bike dead vertical and fill with transmission oil (more about what that is later) until it dribbles out the level screw hole. You pour the tranny oil in to the hole where you unscrewed that big primary inspection plug. When it stops dribbling out the small phillips head level screw hole, replace the screw, with a new copper or fibre washer to seal it. If you cant get that screw out, put in about 24 to 28 oz of transmission oil.
8. Replace the primary inspection plug. Put a new rubber o-ring on it. Mine takes a 1.5” o-ring with a cross-section of 3/32”, from the local hardware/auto store. Again, don’t overtighten it.
WHAT TYPE OF OIL?
I almost hesitate to mention this because it is always the topic of endless debate. So please guys let’s not turn this into yet another oil debate.
But to get the newb going, here is the minimum you need to know. If you want to know more, do a search for “oil” on this site and get ready to be overwhelmed.
ENGINE OIL CHOICE
I prefer Harley’s straight 50 engine oil. I live in a very hot place so it works for me.
Others swear by 20/50 multigrade engine oil. Any good quality straight 50 or 20/50 oil will get you going. You can sort out your final choice later, from other threads.
TRANSMISSION OIL CHOICE
Yes, the factory manual says you can use engine oil, but that was back in the bad old days when there was little other choice.
I use Harley Transmission Formula Plus. It works good for me and it does not let the clutch slip.
RyderRick has a list of other brand sport transmission oils that are made specifically for Sportsters, so he may post them if he happens along.
Again this topic has been and can be debated endlessly in other threads.
One thing not to use in your transmission is modern car engine oil. The friction modifiers might cause clutch slip in some cases.
90w gear oil is not a favourite either because it can make the clutch sticky sometimes.
My personal choice. Everyone has their own.
OIL PUKING OUT BREATHER:
If you start your bike up after a hot oil change and oil pukes out the engine breather, and continues to do so, you have probably overfilled the oil tank. Drain some off from the oil tank, ride the bike, then top up the level.
If the bike has not been run for a week or more, the oil can drain down into the sump and puke out the breather a bit on start up. Don’t worry bout it. They all do that, bless their oily little hearts.
OIL PRESSURE GAUGE:
Don't even bother to fit one. If your new bike already has one, ignore it. Rely on the oil pressure light.
Ironheads run on about 6psi of oil pressure, on a good day. Due to the roller bearing bottom end, they have a high-volume, low-pressure lubrication system. An oil pressure gauge will only scare the hell out of you by registering no pressure, or close to it. That is normal. The gauges fitted to rockerboxes are even worse. There is just no pressure there once the engine is warm. That too is normal.
ORDER A FACTORY WORKSHOP MANUAL. YOU CAN’T RUN ONE OF THESE OLD BIKES WITHOUT ONE. AND GET A PARTS BOOK TOO, THEY ARE ALSO INVALUABLE.