Lennie's Cam Sprocket Replacement 101

[pdonnell]

I don't pretend to be a very good wrench but I'm stupid enough to try anything once. And if involves girls maybe twice. With that bit of disclosure outta the way I contacted a BMW wrench whos given me a quick run-down on the cam sprocket replacement. Verbally, it took about 3 minutes to understand the process. . Below are some pic's of what I did last night. (in addition to a valve job) If something doesn't make sense lemme know offline. . The all powerful cam sprocket and chain taken from my '74 Schwinn bicycle and copied into our beloved bikes. . . After removing the valve covers on both sides and the cam sprocket covers you will need to address a few things. On the right side of the bike the chain tensioner screw is below the jug. However, on the left side will need to get the throttle bottle outta the way to get to the chain tensioner. Its no big deal just un-fasten the air tubes and slide it up into the air box. And then unscrew (two screws) the throttle bottle and move it outta the way. I used a bungie cord and moved up next to the air box. .

[pdonnell]

Then with the bike on the ground and in gear you will need to crack the torque on the sprockets with a 8mm hex socket. This babies on tight. It willrock your bike so I advise using a long torque wrench to loosen it.
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After loosening the sprockets (leave the fastener in) you then want to remove the cam tensioner bolt. This will give the chain a "slightly" looser feel to it. The one on the right is a no brainer it just drops out.

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The one on the left (behind the throttle body can be a ***** (without the right tools) I just cracked the torque on it and unscrewed it out by hand. (pushing down on it and unscrewing, as its spring tensioned)

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Removing the left side tensioner screw feels like pulling a snake outta your motor. But theres very little clearance. So just do it.

[pdonnell]

Now, you'll notice with the OEM sprockets and Lennies are guiding arrow stamped on the sprockets. The chain must be placed on the same guiding arrow on Lennies sprocket as it was on the OEM sprocket. What I did was spray some carb cleaner onto the OEM sprocket and removed all the oil and sheet. Then with wifies finger nail polish I painted the link that the new sprockets "arrow" should fit on. (be advised each sprocket has two arrows, one pointed to a female tooth and one to a male tooth. Look carefully at the sprocket and you'll see.)
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Once the nail is dry unscrew the 8mm bolt and brass washer securing the sprocket to the cam. The sprocket should stay on but keep your fingers in there anyway. We don't want anything dropping into the motor.
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With a screw driver gently pry the sprocket off the cam (with chain still on it) Once off fish the chain off the sprocket and slide the spocket out through the valves area.
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I did some playing around with the sprocket itself. Dry fitting it etc.... That's why I used a tie strip to secure the chain.
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[jclark]

So just what ex-aackly does this exercise do for you?

[pdonnell]

Re-installation is pretty much the reverse. In this lousy picture you can see the new sprocket with the chain on it ready to be fasten to the cam. You will need to thread the chain back onto the sprocket prior to securing the sprocket to the cam.

[pdonnell]

Other important notes about the installation.
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The sprockets have one pin on them which among other things serves to align the sprocket back onto the cam. When you have the new sprocket with the chain on you can look directly behind the sprocket to get an alignment of where the pin fits into cam. But since Lennies sprockets are advance the pin won't line up. It will be off to one side by a fraction of an inch (1/16). So, to get the sprocket pin to line up with the pin recess of the cam you need to have the bike in gear and put one hand on the rear wheel and move it forward/backward. This will move the sprocket back and forth against the cam. Before doing this I put the 8mm sprocket bolt through the sprocket and secured the sprocket very, very loosely again the cam. Basically, I didn't what the cam to move I wanted the orientation of the sprocket to move so that the pin would seat onto the cam. Moving the wheel just a bit gave me the alignment you need to then torque down the sprocket.
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I need to torque my sprocket down and haven't confirmed torques spec's but the tech said it was 60nm torque on the sprockets.
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I then (for frills) got the wife away from that flippen Entertainment Tonight show and out into the garage. I put the bike in 5th gear and turn the wheel and pistons a full rotation and guess what. That nail polish on that lonely link still lines up with that arrow embedded on the sprocket.
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Then you you re-insert the chain tensioner screws and put back everything as you removed it. The left tensioner screw you basically have to pull it slightly apart and feed it into the hole to re-install it. But no matter the spring and fitting go in as it came out.

[pdonnell]

Don't know what you mean Jeff.? Some folks in the past wanted to know the sequence of the install. The 9 degree sprockets are $130 (through CBT imports) but a shop will charge you about two hours. Why pay them?
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And besides whats the big deal about posting some pic's on the installation of this as yet to be tested performance mod.??
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Down the road I want to install a front Ohlins. Care to help with showing me how its done. (short cuts and all)

[jclark]

My question still stands –_what do these gizmos do?

[pdonnell]

Jeff,
As Lennie said in a prior thread. (lots of stuff said about this if you do a search) You really need to get rid of that Mac.
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Advancing the cam timing moves the power band to help the engine spin up more freely by increasing the midrange torque produced. This is what I have experienced in developing the sprocket.
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Cams, gears and things adjust timing??
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Jeff, My FIM chip is mapped for these sprockets too. So, to use the chip I gotta go for the sprockets.

[jclark]

Ahhh.... and are you using a PCRIII to advance your ignition timeing?
Or is the new timing burned in the FIM chip?

[pdonnell]

Jeff,
I'm just a redneck as you know. I just got the chip designed for the sprockets and the sprockets. Your question might be better for Lennie.
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That all I know about that underage girl officer.!
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[jclark]

K!

[Dave Hopkins]

Jeff
Here is how a 4 cycle engine works

We will start at zero degrees also called Top Dead Center (TDC), the spark plug just fired and we have what is called the power stroke. Due to inertia of fuel/air mixture and exhaust moving in the ports the valve functions are always a bit ahead of where they logically should be, same reason intake and exhaust valves are both open during “overlap”.
1st “cycle” is the “Power Stroke”:
This is degrees 0 thru 180, power is being exerted to the connecting rod, turns the crank etc etc. back to the wheel. As the piston approaches the bottom the exhaust valve starts opening and
2nd “cycle” is the “Exhaust Stroke”:
This is degrees 180 thru 360 and as the piston rises it pushes the hot/spent fuel out the exhaust. As the piston approaches the top (also TDC) the exhaust is closing and the intake starts to open shortly before the top. This is called “overlap” when both are slightly open as the piston passes the top and heads back down.
3rd “cycle” is the “Intake Stroke”:
This is degrees 360 thru 540 and just past TDC the exhaust closed, the piston is falling and creating a vacuum behind (above) it. As the intake port is open the vacuum sucks in a new air fuel mixture charge. As the piston is approaching the bottom the intake valve begins to close.
4th “cycle” is the “Compression Stroke”:
This is degrees 540 thru 720 and a bit past Bottom Dead Center (BDC), let visualize 25% of the way up, the intake valve closes! (We will come back to this point in a bit.) While the full stroke of the piston is called the “Compression Stroke” compression starts building when the intake valve closes! So part of the stroke is wasted.
Every tune up is a compromise of compression ratio (which is the area above the piston at BDC factored against the area above the piston at TDC) balanced against the point that the intake valve closes to start the building of compression, if it where 75% of the compression stroke as I suggested we visualize and we advance the cam we may now have 80% of the compression stroke.
What advancing the cam is, is a fine tuning of the engine, lets move that intake closing function forward a few degrees (9 in this case) and build pressure over more of the pistons stroke.
When the factory establishes there combination of compression ratio, intake closing point etc they are working with compromises including the likelihood that a customer will ride into Mexico and get some 75 octane gas, head up a mountain on a 100 degree day and lug the engine in a tall gear, the engine starts pre-igniting (pinging) and the rider ignores it and a piston destructs! The object of high octane gas is it burns slower, thus is more tolerant of the pre-ignition problem.
If you ran a compression test before and after advancing the cam it should read higher, maybe 10%? This is always going to produce more power, unless you pass that critical point of pre-ignition. The factory fearing the rider not alert enough to downshift or use more or less throttle when they do experience pinging always selects a conservative combination of compression and leaves room for tuners such as Lennie is providing us here. In one sense it is a crutch for too low of compression ratio, on the other hand it is a tuners tool to achieve several more horsepower thru fine tuning.
BTW I have just finished up this same project, except on my KTM dirt bike, its cam was a few degrees behind the factory spec so I advanced it slightly to spiff it up.
In a real race engine environment a sharp tuner with a good budget would typically advance the cam, then if the engine was happy, as opposed to pre-ignition, he would then raise the compression until he did get to pre-ignition, then move the cam back?
In all cases it is a fine tuning tool that can achieve several horsepower!

[Bails]

I have the sprockets installed. This is a great pictorial well done. I wish I hadn't paid the shop to do mine now.

[D Hammond]

Ditto, Good pics well explained.

I have Lennies sprockets in hand and after fitting the Induct and fiddling with the Staintune for a weekend I was going to get the shop to fit the sprockets in my upcoming 20k service.

I'll now give it a go myself, thanks Pat

David

[teamkbasa]

Don't forget that you need to have the cams aligned properly when you take them apart so you maintain the proper valve timing.

dave
team K

[pdonnell]

Dave,
I think you mean sprockets, not cams.
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But thats why I used the brake fluid cleaner (clean all oils) on the chain and OEM sprocket to apply finger nail polish to the link that the Lennie's sprockets get fitted back onto. (I believe I mentioned this in my install info)
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IT IS IMPERATIVE TO RE-INSTALL THE SAME LINK OF CHAIN ON THE SAME ARROW STAMPED ON THE SPROCKETS DOING THIS EXCHANGE OF SPROCKETS.
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One thing I didn't mention about the install (if you read it in its entirety) was that I felt the pin on the Lennie's sprockets was "way" longer than the pin on the OEM sprocket. So I took a file and reduced its height ever so slightly. May want to dry fit the sprocket itself first to see how well it seats to the cam. I just did it to make me feel better. (prolly didn't help any)
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But once you get the chain on the Lennie's sprocket the pin won't align onto the cam. (obvious I know) so play with the wheel while the chain is on the sprocket and get to line up prior to finalizing the fitting of the sprocket to the cam. Fingernail polish rocks. That sheet doesn't come off any clean surface.
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And I noted that using the nail polish I painted a female link on one side and male link on the other. So on one side the sprocket was being fitted onto the chain with its tooth and on the other side the depression in the sprocket. (something to think about while talking to my In-Laws next month)

[roger albert]

Nice Write-up Pat. Thanks.

[teamkbasa]

Originally posted by pdonnell
Dave,
I think you mean sprockets, not cams.
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Correct you are sir.



dave

[jclark]

>Jeff
>Here is how a 4 cycle engine works



Thanks, Dave! I know how they work ÐÊjust giving Pat some grief for ommiting backround info for his project. Not everyone ( me included! ) was aware of the 'Why' of the experience ÐÊjust trying to chide him a little..

Now here's a proper 4 stroke ( circa 1956 )



jeff
vroom, vroom...