Topic: Quick and dirty advancing F cam

[MRieck]

Sure you want a Webcam? There's another live thread going that says stock, unless you're making a drag bike motor.

I have to say that is an exaggeration....plenty of bikes on the street with stronger cams that run very well. If all you want is torque put some compression in it and use the mildest cam (stock in general) and you will have instant torque but basically stock upper RPM power. For example...on a CB750...put a set of Wiseco 836 pistons and put in a CB750 Automatic cam. It should idle well and have good torque but nothing special on top.

[Kickstart]

You have to have some springs in there.  I did it with just the inner springs when I was searching for a good cam advance. 

You don't have to take the head off.  I'm doing my final assembly, and I am able to pry the intake valves to do final clearance check using a tire iron with both springs in there (HD from APE actually).

Something to note: If you had your head or deck milled, using the factory cam sprocket will now cause your cam timing to be delayed slightly (depending on how much you had milled off).

Here's a thread I started a while back when I was having some troubles:
http://forums.sohc4.net/index.php?topic=117206

Here (In the same thread) is where I finally got the hang of it:
http://forums.sohc4.net/index.php?topic=117206.msg1327897#msg1327897

I used 0.04" lift to determine "official" valve opening - I believe this is what Honda used, but some cam manufacturers use a different lift measurement.

Also, remember that advancing your cam to open 5 degrees earlier, is 5 degrees earlier on the crank... so the cam is only 2.5 degrees ahead from stock. (I think someone mentioned that earlier above).

[70CB750]

Thank you, Chris.  It is a learning curve, I had two major "duh" moments:

- when I realized which way to move sprocket against camshaft to advance and which way to retard.

- that the opening starts at 0.04" and not at 0.004"  - that accounts for some big difference in numbers, let me tell you 

[70CB750]

I measured all valves, the intake opens at 1 and closes at 40, exhaust opens at 4 and closes at 35.

These are average values from cylinders 1 to 4 as close to original setup as I could get based on the wintesa mark on the cam sprocket.

[Kickstart]

I measured all valves, the intake opens at 1 and closes at 40...

I assume that's 1 degree before or after TDC, and closed at 40 after BDC

That sounds about right for stock (I think) - at least that's what my F0 was.  I think the F3 was similar.  So it sounds like you've got it close to stock.

... exhaust opens at 4 and closes at 35. ...

That sounds like you swapped the open/closed numbers.. what is that in relation to After/Before TDC/BDC?
But if you got the intake set right then the exhaust is set correctly by default.

[70CB750]

Sure I did, lol.

No, just checking if somebody pays attention )

Thank you, Chris, now I will go for clearance and advance. Will be able to run the hed tightening sequence in my sleep pretty soon. But this is one of the coolest things I ever worked on.

[Kickstart]

Funny... I've got the torquing sequence memorized as well now. 
I lost count how many times I bolted the head on and then took it back off (fooling around with clay on the pistons and measuring clearances).

Did you leave the inner springs on for measuring the clearance?  I thought about buying some weaker springs at the hardware store - but ended up just using the inner springs.

I was able to get a clearance measurement with both springs installed during my final assembly (as mentioned above), but that was only for the intakes, as it was easier get the tire iron in there at a good angle.  I was too nervous to try and pry up the lifters for the exhaust with both springs in, as it seemed like it could crack the towers.  It worked fine with only one spring... just scared me too much to try it with both springs in there.

I found that my intake valves had the least amount of clearance around 5-8 degrees ATDC.  And the exhaust around 5 degrees BTDC - but your engine may be different.

Good luck!

[70CB750]

I am sure your valves have the least amount of clearance at TDC, I verified it by experiment last night 

Brain fart made me do few full cycles with playdoh on top of the piston and after taking it apart, I started fretting about literally 0 clearance on the valve.

Luckily at that moment I dropped and lost my 10mm socket and I decided to quit - makes no sense to work on CB750 head without 10mm socket.

The full truth and related self evaluation hit me by 3AM, I will try again, this time the leverage method from the top. 

Unless I will be building wind tunnel for my oldest - high school science project.

[Kickstart]

I've lost countless minutes (well, probably hours), looking for the 10mm socket I keep on misplacing.

That's interesting that your least amount of clearance is at TDC.  I measured mine at a lot of different degrees to determine the exact spot with the least amount of clearance.  It was between 5-8 degrees ATDC for the intake (depending on how much I advanced the cam), and pretty consistently at 5 degrees BTDC for the exhaust.  I guess that's not too far from TDC.

Hmm... I've got everything set-up right now... maybe I'll double check

[70CB750]

Well of course it is at TDC, but that does not count, the valve is fully recessed in the valve seat - I guess my joke was not that transparent, sorry.  I meant to say I squished the clay/playdoh, because I pushed it through the compression cycle where valves and piston come closest but completely safe.

Made some progress, see my built.

[Kickstart]

Ahh... sorry I did miss that... I'm not the quickest

But, you should be able to cycle the crank a couple times and still get valve clearance impressions... at least I did that when I was fooling around with the clay.  Where the valve "sticks out" (or comes closest to the piston) should be a couple mm from the edge of the piston, so the valve will squish the clay more than the dome of the head/chamber at that spot.

I'll check out your thread.