How can you tell if you have flat cam lobes?, Strange lash issue Options

[tornik550]

I am paranoid of developing flat can lobes on my recent engine rebuild. I am paranoid cause I have heard so much crap about the cam that I used- scat c45. I am asking this more for curiosity sake. I had a strange issue but I am certain it's unrelated. I set my valves on cyl 1 to 0 lash (chromoly pushrods). I did that at tdc for that cyl. Te intake and exhaust valves. Seem to lift normally. The issue is that at a different point in the cycle (other than tdc or full lift) the valves are very loose. The valves go back to zero lash at TDC. The compression is actually about 5 points better on that cylander. I think it's possible that the rocker shaft bolts may have loosened a bit, however I've already removed them. It doesn't sound like a flat lobe to me.

[yeahmag]

Sounds like you are setting it backwards. It sounds like you are setting the lash when you are on the nose of the cam (max lift) vs. the foot of the cam (no lift).

[tornik550]

Sounds like you are setting it backwards. It sounds like you are setting the lash when you are on the nose of the cam (max lift) vs. the foot of the cam (no lift).

Me...do something backwards? Haha

If its backwards why would it run so well?

The intake and exhaust valves are not loose at the same time.

[yeahmag]

If you aren't something is very wrong with the cam... It should only do what you are saying if you are *not* adjusting the lash at the foot of the cam.

[ChrisFoley]

It sounds like you are setting the lash when you are on the nose of the cam (max lift) vs. the foot of the cam (no lift).

How does one set valve lash when the cam lobe is holding the valve open?

If you have a cam lobe going flat, the lash adjustment will become excessive quickly.
More than likely, you're setting the lash in the wrong cam position.

[Dr Evil]

You are obviously not on the right part of the cam (IMG:style_emoticons/default/wink.gif) The cam will flatten on the nose thereby reducing your lift.

There are two spots on the cam that are like TDC, one is actually TDC.

Ex open/close --> Intake open/close --> piston at top = TDC

Intake open/close --> Ex open/Close --> Piston near TDC = NOT TDC (even though both valves are closed/ing)

You want piston at TDC on the compression/ignition stroke between intake closing and exhaust opening.

[tornik550]

If you aren't something is very wrong with the cam... It should only do what you are saying if you are *not* adjusting the lash at the foot of the cam.

By far most likely that I am tr problem and the cam is fine. I followed the valve adjustment instructions on pelican. Can the instructions differ with different cams?

[toolguy]

you're suppose to be adjusting the lash on the back side of the cam lobe, i.e. the lowest point or the base circle, when the piston is at the top of the compression cycle and the distributor is pointing to that cylinders wire. . . so start by looking where the rotor is pointing in relationship to the timing mark.

When a cam goes 'flat' it is from excessive wear on the top of the lobe or when a valve is fully open. . . you can't really feel or see that the lobe is going flat other than maybe noticing the valve doesn't open as far as the others. . / / / . . .

If the valve gets loser after you adjust it, then either your weren't positioned on the back of the cam in the first place. . OR the cam is not concentric on the base circle, meaning it was improperly ground in the first place. .

[tornik550]

Clearly I do not have a great understanding of this stuff so please help me out. I out and made sure that I adjusted the valves at TDC. I only did this with cylinder 1- just for experimenting. I verified that I as at TDC for cyl 1 by the mark on the fan, groove on the flywheel palpable in the window on the top of the transmission and the distributor was pointing to cylinder 1. Here is what I found-

-At TDC for cylinder 1 both intake and exhaust valves were set to zero lash
-I then started to turn the engine slightly and feel the valves at differnet points in the cycle.
-During the intake stroke (with intake valve wide open) the exhaust valve has .004 lash
-During the exhaust stroke (with exhaust wide open) the intake valve has .004 lash
- back at TDC the intake and exhaust again have zero lash.

Before my original post, I had significant lash on the intake and exhaust strokes. I think that my lash at TDC must have been incorrect. When I readjusted everything now it is greatly improved however are my results above normal?

[toolguy]

once again. look where the distributor rotor is pointing. . . Back to basics. . . . the cylinder has 2 top dead centers per 4 cycles. . . . . as there are 2 rotations for each four cycle cumbustion cycle.

It sounds like you are setting the valves at top dead center but 180 degrees of camshaft rotation out. . . that would be top alright , but of the exhaust stroke and beginning of the intake stroke, where the cam has overlap for scavenging effects. . you need to turn the engine one full rotation or
see if the valves on #3 are both loose since the firing order is 1-4-3-2
If 3 is both loose, then that's the cylinder that it at TDC and the one you should be adjusting. .

[tornik550]

once again. look where the distributor rotor is pointing. . . Back to basics. . . . the cylinder has 2 top dead centers per 4 cycles. . . . . as there are 2 rotations for each four cycle cumbustion cycle.

It sounds like you are setting the valves at top dead center but 180 degrees of camshaft rotation out. . . that would be top alright , but of the exhaust stroke and beginning of the intake stroke, where the cam has overlap for scavenging effects. . you need to turn the engine one full rotation or
see if the valves on #3 are both loose since the firing order is 1-4-3-2
If 3 is both loose, then that's the cylinder that it at TDC and the one you should be adjusting. .

I am not sure how I set it the first time however this time I made sure the distributor was pointing to cyl 1 wire. I checked to see what the valves were doing when cyl 1 was at tdc but 180 off- both valves were slightly engaged.

[toolguy]

that's correct at 180 out, the piston just came up and pushed out the exhaust, the exhaust valve is still closing [ it's open till a few degrees after tdc.] . . and the intake is starting to open just before the piston gets to top. because it's going to suck in the intake charge as the piston goes down. . . . .

[Dave_Darling]

My engine does the same thing as yours, toolguy.

I have been told that it is normal, and I have also been told that it means the rocker stands aren't torqued correctly.

The torque setting on the rocker stand nuts is very low, only 10 lb-ft. In fact, you need slack on both rocker arms or you won't even get the rocker stand down onto the head at the correct torque spec.

--DD

[76-914]

Once you get that down remember this. Setting chromolly @ 0 lash is a little trickier than adjusting w/ a feeler gage. When setting to .008 or .006 you are moving the rocker arm about while adjusting so the push rod ends up seating correctly while setting. But the first time I set my valves w/chromolly push rods I didn't wiggle the rocker as I adjusted to "0" so some didn't seat right and were loose after starting the engine. (IMG:style_emoticons/default/WTF.gif) Because a deaf man can hear them when they are loose. Took me a few times to realize that after I set them I need to spin the engine a few times then go back and check for any loose ones I might have missed. BTW, do a search to find Cap't Crusty's valve setting method. It will clear up all of your questions. (IMG:style_emoticons/default/beerchug.gif)

[ChrisFoley]

If you are really setting the valve lash at TDC for each cylinder, and the lash grows at another position, you may have gotten the cam index wrong during assembly.
It is better to set the lash when you see the opposite valve is open all the way, rather than using crankshaft position. (That wouldn't solve a cam index problem though.)

[tornik550]

If you are really setting the valve lash at TDC for each cylinder, and the lash grows at another position, you may have gotten the cam index wrong during assembly.
It is better to set the lash when you see the opposite valve is open all the way, rather than using crankshaft position. (That wouldn't solve a cam index problem though.)

I am pretty sure that I lined up the dots on the cam and crankshaft gears. Is there a way to check to see if they are lined up without taking apart the engine?

Assuming that I indexed the cam correctly- considering the issue that I am having- if I were to set the valves to zero lash when the opposite valve is fully open (this is also when the closed valve gets loose) wouldn't my valves be too tight during the compression cycle?

[ChrisFoley]

...
Assuming that I indexed the cam correctly- considering the issue that I am having- if I were to set the valves to zero lash when the opposite valve is fully open (this is also when the closed valve gets loose) wouldn't my valves be too tight during the compression cycle?

I don't mean the opposite valve in the same cylinder. I mean the valve on the opposite side of the engine which is moved by the same cam lobe.
Using this method to determine the correct position will result in the valve lash being set optimally.

Probably the easiest way to determine if the cam is indexed correctly is to see how the engine runs.

[tornik550]

...
Assuming that I indexed the cam correctly- considering the issue that I am having- if I were to set the valves to zero lash when the opposite valve is fully open (this is also when the closed valve gets loose) wouldn't my valves be too tight during the compression cycle?

I don't mean the opposite valve in the same cylinder. I mean the valve on the opposite side of the engine which is moved by the same cam lobe.
Using this method to determine the correct position will result in the valve lash being set optimally.

Probably the easiest way to determine if the cam is indexed correctly is to see how the engine runs.

Ok I see. That makes more sense. My engine runs great so I think I'll just put it bak together and drive.

[Dr Evil]

You most likely did not incorrectly index the cam. You are having a common issue with adjusting the valves. I had the same issue before I figured it out.

[Dave_Darling]

And what is it you figured out? Did you just change to the "opposite valve" method (AKA the Cap'n's method), or did you figure out something else?

--DD