Topic: Cam timing question cb500

[tennesseebreeze]

Setting the cam timing on this 73 cb500 and while it is at TDC on the 1 and 4 pistons, the notch on the end of the cam shaft lines up either fore or aft the middle position, depending on the chain being moved one tooth forward or back. I determined TDC by the notch on the timing plate and by the feel method with a screwdriver touching the top of the position. The plate appears to be aligned good. The center of the cam notch seems to be half a tooth difference from where the sprocket lands.

My question is, is this normal, and which position is the better one for the performance? With the cam shaft angled forward, so the cam lobe reaches the valve early; or the opposite, where it reaches the valve a little late. Or do I need to notch the sprocket mount holes to align it right in the center?

[tennesseebreeze]

Here are some pictures to aid my description.

[strynboen]

on mine 550, it fit perfekt.
.have you the cam hveel vrong on..can it be mirrored

[FunJimmy]

The ideal position will depend on the performance you prefer.
Advancing the cam will give a little more top end while retarding will help low end torque. Unless you've done some other engine mods like porting most would benefit from a little more low end torque.

[flatlander]

jimmy, it's the other way around:
advancing the cam puts peak hp more towards low and mid-range and increases torque a little. retarding it, you get more peak hp and get it later.

[bwaller]

In the top picture had you "tensioned" the camchain? If not a tighter chain will pull the cam backwards and align your mark. If it is tight is your chain well used or have you machined deck surfaces?

[FunJimmy]

jimmy, it's the other way around:
advancing the cam puts peak hp more towards low and mid-range and increases torque a little. retarding it, you get more peak hp and get it later.

No wonder I'm so slow. 

[tennesseebreeze]

Thanks for the replies. After re-installing the chain it looked a little more on point. Maybe the chain was a little bound up or there wasn't sufficient tension on it. I had a hell of a time putting it back together yesterday. Two valve cover bolts snapped and I had to pull them out and replace them. The old bolts must have been fatigued from being tightened so many times. She's running now, but definitely needs more tuning and things. More questions for the forum on those subjects soon!

[alacrity]

Setting the cam timing on this 73 cb500 and while it is at TDC on the 1 and 4 pistons, the notch on the end of the cam shaft lines up either fore or aft the middle position, depending on the chain being moved one tooth forward or back. I determined TDC by the notch on the timing plate and by the feel method with a screwdriver touching the top of the position. The plate appears to be aligned good. The center of the cam notch seems to be half a tooth difference from where the sprocket lands.

So is, is this normal, and which position is the better one for the performance? With the cam shaft angled forward, so the cam lobe reaches the valve early; or the opposite, where it reaches the valve a little late. Or do I need to notch the sprocket mount holes to align it right in the center?

You are asking the right questions... but the main one that stops the train, imho, is "IS THIS NORMAL?"  The answer is: sorry, it ain't.  It seems to me that unless your cam chain is terribly stretched or bound up in some way, and unless maybe you have it half-skipped on the lower sprocket and not on there with a each link having a tooth and vice versa, you ought to be looking at what is in the pic I attached here from my most recent top end job.  The notch should be centered when the mark is in the right position on the timing plate per the Honda shop manual instructions.  The amount you are showing is a couple degrees offset... so it's wrong as you correctly surmised. (Forgive me if any of this is obvious to you).  So if it was me I would search for why this is happening before closing everything up.  Like what you don't know is if this offset between crank and cam position is a result of chain stretch=slop/float or such badly worn upper or lower sprockets that the sloppy chain has skipped a link... or if it is gonna remain constant in this position.  Were the holes in the cam sprocket true and round and just big enough for the 7mm bolts to pass through and fastened to the camshaft "t-bar"?  Or had they become galled and stretched? If so, you could tighten it down to the wrong timing.  I don't think the amount you show is anywhere near enough to cause valve/piston interference but I couldn't promise that at redline - especially if it's all a bit loosey goosey in there.

[Frostyboy]

I have a theory on this, however before I embarrass myself, have you had the head & barrel off?

[tennesseebreeze]

I have a theory on this, however before I embarrass myself, have you had the head & barrel off?

I have. More recently had to lift them to install new o-rings in the oil ports to stop leaks. I learned my lesson. OEM rubber from now on.

As for the cam timing issue, I'm inclined to ignore the why, as it seemed to correct itself after pulling the sprocket off a couple times. The chain must not have been seating right on the lower sprocket or something. The top sprocket, to answer alacrity's question, is in good shape and the bolts holes are true. At any rate, the bike is running good with no more leaks or other engine issues.

My only problems now are with carburation. It needs a synch and a float adjustment I think. It rode strong all morning, but the idle is erratic and it tends to stall at lights.

[strynboen]

is the tensioner on place,,the rear (adjustable)one like to give problems" dovn under"..if it not is korrekt placed in the small groove...it dont give any tension at all...

[tennesseebreeze]

is the tensioner on place,,the rear (adjustable)one like to give problems" dovn under"..if it not is korrekt placed in the small groove...it dont give any tension at all...

I hope so. Because, frankly, I don't know that I can summon the energy to take this engine apart again. The tensioner adjuster bolt is very stiff and doesn't like to turn. But I believe it is working and I have no chain noise.

[Frostyboy]

is the tensioner on place,,the rear (adjustable)one like to give problems" dovn under"..if it not is korrekt placed in the small groove...it dont give any tension at all...

I hope so. Because, frankly, I don't know that I can summon the energy to take this engine apart again. The tensioner adjuster bolt is very stiff and doesn't like to turn. But I believe it is working and I have no chain noise.

strynboen has a point. If the tensioner isn't fitted correctly it could explain the adjuster screw being stiff. Have a read of this recent post. You could drop the pan to check it easy enough.
http://forums.sohc4.net/index.php/topic,156602.0.html

[tennesseebreeze]

is the tensioner on place,,the rear (adjustable)one like to give problems" dovn under"..if it not is korrekt placed in the small groove...it dont give any tension at all...

I hope so. Because, frankly, I don't know that I can summon the energy to take this engine apart again. The tensioner adjuster bolt is very stiff and doesn't like to turn. But I believe it is working and I have no chain noise.

You know, I did check under the pan at one point and did not see the end of the cam chain tensioner peeking out, so I figured I was in the clear. Maybe it needs another look-see.
strynboen has a point. If the tensioner isn't fitted correctly it could explain the adjuster screw being stiff. Have a read of this recent post. You could drop the pan to check it easy enough.
http://forums.sohc4.net/index.php/topic,156602.0.html

[strynboen]

you are use the( T) top marked... right....                .and not the f( fire) mark