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PostPosted: Sat May 03, 2014 3:00 pm 
Racing ECU (!!)
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Joined: Sun Mar 23, 2014 9:21 pm
Posts: 535
Location: Parksville, BC, Canada
Several times it's occurred to me just how useful it is to have a sacrificial clutch. In fact, I've made use of them many times over the last year.

Depending on what repairs you are doing this also plays a part on deciding when you should install a new clutch. Take for instance my engine rebuild. I'm going through the entire engine and replacing all the bearings and installing a new performance camshaft. I'm also going to be installing a new clutch...

Should I install the new clutch during the engine overhaul?

No. The reason for this is that the engine is chalk full of assembly lube. The bearings are coated in it, the camshaft will be filled with it, the oil pump was stripped down, cleaned and filled with, you guessed it, assembly lube.

What the heck does that have to do with installing a new clutch?

Assembly lube is full of friction-modifiers. In other words, it's designed to be as slippery as all get out to prevent as much initial start-up engine wear as possible. The one area that is particularly important in initial startup on a new engine build is if you are installing a new camshaft. It is absolutely essential that the camshaft be given as much assembly lube as possible to facilitate initial startup and break-in. You want that thing coated in oil/assembly lube right off the bat. To that end, I use a syringe/needle to inject and fill the cam (literally) with assembly lube so that in the first few seconds of running engine oil from the oil pump will push all the assembly lube onto the camshaft.

In that light you can see that the engine oil is going to have a pretty healthy dose of assembly lube in it. That very oil is used to lubricate your clutch. In fact, your clutch is saturated in it at all times. It is literally soaked right into the very pores of your clutch. Because assembly lube is designed to make your engine as slippery as possible it makes for a very poor clutch lubricant because those very properties are in direct contrast to what your clutch is designed to do - which is clamp at high pressure and not slip....assembly lube, on the other hand, is designed to make everything slip as much as possible....

Once you slip a clutch, even once, it's already on it's way out. Each time you slip that clutch it will become progressively easier for it to slip next time. You're on a declining curve and your returns will steadily diminish. This is why our HD clutch springs are so important. The more pressure you can apply to that clutch, the less it will be inclined to slip and the further you stave off clutch replacement. Not to mention the performance increase you experience when all of your engine's RPM's are put use to turning the rear wheel - instead of loosing some of them at the clutch....

So, in my case, doing a ground-up engine overhaul, I'm going to re-install the old clutch and use that for the first few hundred K - if it lasts that long with all the assembly lube in the oil. I'm also going to be using a conventional motorcycle rated 'dinosaur' oil. It's better to break the engine in with decent cheap stuff as opposed to contaminating a nice new batch of synthetic oil with a friction modifier such as assembly lube.

Mind you, if you're already prepared to sacrifice your sacrificial clutch then do you even need the more expensive motorcycle rated dinosaur oil or can you put regular car oil in the bike? That's a good question!

Once the engine has got some good time on it I'll do a HOT oil change and tilt the bike on a sharp angle to get as much oil out as possible. At that point, once the engine is feeling it's oats, the clutch cover will come off, a minor inspection will take place, and then the new clutch goes in - along with the proper synthetic oil.

Knowing when to install a new clutch is important any time you've introduced a friction modifier to the engine. In my case, a ground-up rebuild means the engine is full of it. For most riders though, this is the case when changing out the camshaft.

Earlier this year I beta-tested several Thailand camshafts with miserable results. In each case I took steps to ensure that I protected the clutch. The 'good' clutch was removed, a 'bad' clutch was installed, and conventional oil was used each time. The idea being that you save yourself from destroying your clutch and also expensive synthetic oil in the event something goes wrong.

Anyway, just a TekTip that I thought I would share seeing it's at the front of mind today and it's something I was meaning to put down 'on paper' at some point as it's quite important if you're re-building or if you're installing a camshaft. :top:

Best & Thanks!
Marvin Miller
cbr125world Store

...because every day is MotoGP day when you own a CBR 125r...

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