***This pictorial how-to takes a while to load on your PC but its worth it!***


I work on my own bikes and cars and have done for the last 25 years. Its saved me a shitload of money over the years and I know the job is done right.

If you're reading this then you want to change the primary oil yourself and its a really easy job you can do at home with a few basic tools. The service manual recommends changing the primary oil every 5000 miles (8000 kms) but I halve the intervals on my personal bikes. Every 2500 miles on the dot. I've found halving the service schedule for fluid and filter changes will let your bike live long and strong. There's an old saying that goes "Oil and filters are cheap, motors are not".

You'll need some primary oil too. The manual recommends 26oz (770ml) of primary chaincase lubricant. I've found that it is not enough, 32oz (1 litre) will fill the twincam primary to the proper level on my '05 softail. You can actually use almost any oil in the primary as long as it does not contain friction modifiers.

The oil is in there to pull heat from the primary drive chain and to lubricate the chain and clutch plates. I use an older grade of ATF (automatic transmission fluid) without the friction modifiers (type D or F). Dexron 3 is a no-no as it has the modifiers and will cause clutch slip under high load. I've talked to blokes who have over 100,000 miles on their primarys using nothing but ATF and have never had a failure.

I like ATF because car auto transmissions are full of wet clutch packs and chains as well. I get a great progressive clutch action with no slip using ATF but its entirely up to you what kind of oil you put in there and if there's any doubt in your mind whatsoever then get the harley recommended stuff.

You'll also need a new primary drain plug O-ring from the stealership (only a few bucks).

The tools you need are: Firstly a 3/16 allen key and secondly a T25 sized torx wrench. The Allen key sets are available from almost any tool outlet or car accessories place (you want an imperial size set). The Torx wrench sets are a little harder to find but are available from most electronic supplies outlets like Tandy's or Dick Smiths (where I bought mine). Look for the torx sets that have the small hole in the dead centre of the working face, they'll fit far more stuff. Both Allen and Torx sets are fairly cheap. A small 6" engineers steel ruler will be required for measuring and adjusting your primary drive chain deflection should you need to.

A small torque wrench is also very handy but don't worry if you haven't got one, its not mandatory for this How -To. The torque values we're dealing with are small and easily achievable by hand.

Once you've got your tools assembled, find a few clean rags and an oil drain pan (or any sort of old tray that'll hold at least 1 litre (32 oz). Find somewhere level, clean and clutter free to work on your bike. Today I put my bike in the driveway to get better lighting for photo's but I usually work on her in the garage.

Righto, time to get dirty.

First locate your primary oil drain plug. Its a little tricky to see at first and is recessed up into the underside of the primary casing.

The best bet is to plonk your ass on the deck and stick your head under the bike for a look.

When you do this is what you'll see.

Grab your 3/16" Allen key wrench and make sure its seated all the way up into the bolt head. Undo. If you cant budge it (Hercules probably did it up last time) then slip a small length of pipe over the end of the Allen key to make the handle longer. You can even use the ring part of a ring spanner in a pinch. Torque multipliers are a wonderful thing eh?

Once you've cracked the seal on the drain plug, slip your drain pan into place.

Find the drain plug again and wind that sucker out a few turns so you can grab it by hand but no so far that it'll drop clear and dump oil all over you and your tools... haha.. (ask me how I know that!!)

If your girl has got those disposable rubber gloves in the house then now is the time to pinch one and have a few shop rags on standby.

Reach under and finish unscrewing the drain plug by hand. Once its clear, dump it on a clean shop rag and clean the old oil off yourself.

This is what your drain plug should look like after it comes out of the bike. Note the rubber O-ring around the head of the plug and the magnet covered in a fine black fuzz on the tail. The fuzz is actually microscopic iron filings from normal wear between the primary chain and the crank and clutch sprockets. If you see big chips or shards of metal on your plug (this is very a abnormal occurrence) then you'd better investigate it further.

Clean up your drain plug on the rag, taking special care to get rid of as much magnet fuzz as possible. Don't forget to replace the O-ring, its cheap insurance against a leaking primary.

Go and have a cold beer while the last of the oil finishes draining into the pan.

Lightly smear some fresh oil around the O-ring on the plug and reinstall. The oil stops the rubber from binding on the alloy primary casing and allows you to screw it all the way home with ease. Insert your 3/16" Allen wrench and tighten to 6 foot pounds (which equates to "firmly snug" just using your hand on the Allen wrench). If you have no torque wrench then use about 70% of your total hand strength to tighten up the plug as a fairly accurate gauge. Don't swing on it with everything you've got as the plug is steel and the casing is alloy... you CAN strip it with enough force.

This is the primary inspection cover. We need to remove this to inspect / adjust the primary chain and to fill the primary chaincase with lubricant.

These bolts are the Torx ones.

Here is the Torx set I bought a little while back. They're made from aerospace alloy and are as tough as your Sargent at arms..... seriously ! I've had big ring spanners swinging off the larger ones trying to remove factory installed, locktighted bolts on my Harley and the Torx wrenches didn't even look like failing, even when giving them some serious curry !! Would you believe the whole set was 27 bucks at Dick Smiths electronics ? What a score !!

Notice the hole in the ends of the wrenches. This is what I was talking about earlier on... several of your Harley's Torx bolts will have the small protrusion right in the center of the bolt head rendering a standard Torx set useless. The ones like this are the ones to get.

Crack the bolts, outer 2 first. Then remove 3 of the bolts leaving the top one remaining. The cover is a loose fit and leaving any other bolt in place instead of the top one gives you a headache. Make sure you lay your bolts out on a clean shop rag in the same pattern that they came out of the bike. They're different lengths and you don't want them mixed up.

Its actually a really good habit to get into for pulling anything apart and if you have a complex casing to remove in the future with lots of bolts, grab a marker pen and draw the casing on the bottom of an upturned cardboard box. Use a Phillips screwdriver to punch holes in the box on your drawing where the bolts are. Every bolt you pull now has a hole in the box and getting mixed up with different bolt lengths is a thing of the past. I used this with great success the last time I pulled the outer primary off my Evo.

Here's how I laid them out on a rag.

Looking in through the Primary inspection port.

Grab the small steel rule and poke it upwards through the hole until you feel it contact the underside of the chain. It'll feel spongy and you'll be able to move it with the steel ruler.

Follow this procedure:

1. Push the ruler upwards into the chain and then let it slide slowly through your fingers (use a gentle touch here) until you JUST reach the point where the chain no longer pushes back.

2. Line up a ruler measurement with the top edge of the inspection port.

3. Push the ruler upwards fairly hard to take all the slack out of the chain.

4. Take another ruler measurement using the same part of the top edge.

5. Subtract the first measurement from the second and you have your chain deflection.

Factory Primary chain deflection specs are:

With the engine cold, upward (not total) free play in upper strand should be 5/8-7/8 in. (15.9-22.3 mm).

With the engine hot, upward (not total) free play in upper strand should be 3/8-5/8 in. (9.5-15.9 mm).

If your deflection falls outside the specs then you need to slacken off the tensioner shoe adjusting nut and slide the shoe carrier either up or down to tighten / loosen the chain. If you have some whiteout then now is a good time to clean off the metal on one side of the tensioner bracket and mark the backing plate and the movable bracket with a straight line. This will give you a solid reference point for your adjustments.

The adjusting nut torque spec is 29 foot pounds.

My primary chain deflection was perfect this time so now its time for the good oil !!

Some oil bottles have a really cool extendable pouring spout but alas... Valvoline were slack in that department!! If you have a normal type of bottle then turning it sideways to empty out is an ancient but still cool little trick. No glugging and no spills !!

They make those inspection ports just large enough to get enough angle on the bottle to empty it out. They're clever buggers those Harley engineers...

Clean off your bolts, the alloy inspection cover and carefully pat dry the gasket (or use a new one if the old one is R/S (ratshit). Reassemble and use the top bolt to hold it all in place while you start the other ones. Start all bolts before tightening any of them down. This will ensure gasket and inspection cover alignment, no pinched gaskets and no leaks.

Gently screw in all bolts until barely tight.

Tighten up bolts to 10 foot pounds, starting with the center 2 and then working outwards. No torque wrench? ... No problem..... just tighten them using only the Torx key in your hand and apply around 85% hand strength only. Don't use your whole arm for leverage, just your hand... it'll be really close to spec with no risk of stripping any threads.

Center to end torque sequencing stops component warpage and fluid leaks on just about any motor part you care to name, especially important as parts thermal cycle cold-hot-cold many thousands of times over in an engine.

Although its probably overkill on a small cover plate like this one, its still good practice to get into and attention to detail is the quality difference between you and the shitload of bike shop mechanics who often let quality slide for the sake of speed. You have the one thing they don't..... time.

Remember... to those guys your bike is just another job number in the workshop. To you, your bike is your pride and joy....


Extremely easy to do, your clutch hand will love you for it.

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