Quick and dirty cam advance

[Ivan]

So, I was looking at my cam sprockets , well a spare set, today and trying to figure out how to machine a slot in them with out an indexing table.

Thats when I noticed if you flip one over, the teeth are staggered when the mounting holes line up.



As you can see, they don't split exactly in the middle. There are 34 teeth, for 10.5 degrees between teeth. That is 21 degrees advance. measured at the crank. Now the teeth don't split directly in the middle, so I am guessing by flipping the sprocket, it comes in at about 5 or 6 degrees of cam advance. I am not sure exactly, but the alignment holes both liked up exactly on my cams, when one was put in alignment. With the sprocket reversed, the mark is advanced probably .045 or so.

I did grind the front side of the sprockets flat, since there are bosses around the bolt holes, and I wanted the sprockets flat against the cam flange. I also stamped "front" on them for future reference. Also I only did the intake, since that seemed to be the one everyone did when I searched on the subject.

Ok, engine gurus, what do you think?

[TADracer]

Interesting. I bet this answers some of the questions on another thread where their cam pointers did not line up. Perhaps a gear is turned around?

But just turning a gear around might not give you what you are looking for. Advancing or retarding a cam can mess with your tune up and you still should set up a degree wheel and dial indicator to find your true lobe centers. also, if flipping the gear is retarding your cam then you really must check your piston/valve clearance, especially on the intake side where you could be getting dangerously close to a collision.

So if you are going through all that anyway, I recommend you slot your gears to give yourself real adjustment you can tune with.

[TADracer]

Sorry, I meant if the gear is advancing your cam you will get a better chance of a collision on the intake side.

[Ivan]

I suppose at some point I can degree it. I will have to bring my travel indicator home and pick up a degree wheel.

Here are a couple pics of what it turned out like. I don't think people would be flipping them mistakenly, since there are some bosses in the casting that makes it pretty obvious the flat side goes against the flange. I had to grind them off on my spare set. When I figured the trigonometry of this, the slot only needed to be elongated by about .085 to give ±10º. That isn't much. Most of the posts I read, one of which was yours, said advancing the intake by about 5º was what did the most good. This should have done pretty much that.

Ok, the pics:

Exhaust is lined up



Intake is advanced just a bit on the intake



It seems to run ok, definitely give the throttle a little more "Snap" and seems to have moved the power toward the higher RPM range. The low end torque seems to be the same, which is strange. Shouldn't the higher lobe separation increase the torque a bit? Anyway, it didn't bend the valves which I didn't think would happen, but could have. I was hoping for more top end, and I haven't had the chance to test that out yet.

Also, FWIW, to get the dots to line up with the sprocket in the stock configuration, the crank had to be just past the timing marks. I am guessing about three degrees. So, I ma guessing all told, the cam is slightly advanced and the exhaust is ever so slightly retarded, from chain wear, most likely.

[Ivan]

I got an e-mail saying that 81xsproject replied to this thread but I am not seeing it? Did it get removed?

[DiverRay]

Because he posted BEFORE the second cup of coffee!! His brain probably wasn't fully engaged at the time I know the feeling myself!
I like the results you have, but I'm going to try and have my gears slotted, as I chould be able to get access to a mill.

[Ivan]

After seeing Mashermotos results, it seems there may be three different possible advance positions by flipping the holes as well...

Hmmm...

Also I have access to a mill, but no indexing accessory. Maybe some day...

[aussixs11G]

I have paid to have my (spare set) cam sprockets slotted - and fitted them and "dialled" both camshafts away from each other......from the LHS of machine the exhaust anti clockwise and inlet clockwise - cant help with degrees ATM but the big picture result is

dyno in 2004 103hp
dyno in 2009 107hp

the cams are a hot grind that provided plenty of power across the rev range but lots above 6000rpm

Dialing as above brought this down but with a real kick in power at 5500rpm

the point of the exercise was to get more torque (hahaha too much is never enough) lower in the rev range.

Havent had much time to fiddle with the cam timing since but will re-visit and quantify and share results when I do.
Bryan

[TADracer]

Ivan, you might want to check your piston/valve clearances before you wind it up too much. All motors are different and you know alot of things like aftermarket cams, milling the head or even the head gasket can affect the piston/valve clearance. Many say .050" is the minimum and is probably a good rule of thumb.

After degreeing in my cams I check the clearance at 5 degree intervals from 20 degrees before and after TDC during the valve overlap event since the point at which the closest encounter occurs can change by moving the cam position as little as 1 or 2 degrees.

Just my suggestion, thats all.