Valve lash curiousity

[cwdaniel]

I'm working on my new engine getting it tuned, adjusted and broken in. While adjusting the valves I noticed that the when finishing on #2, The #1 exhaust valve is looser than when I adjusted it at the start. If I crank it back to TDC for #1 all is well. While turning and watching I can see it unload a little somewhere in the revolutions.

The cam is a Engle TCS 10, Is there some sort of cam overlap I need to account for?

[Bugfuel]

I'm working on my new engine getting it tuned, adjusted and broken in. While adjusting the valves I noticed that the when finishing on #2, The #1 exhaust valve is looser than when I adjusted it at the start. If I crank it back to TDC for #1 all is well. While turning and watching I can see it unload a little somewhere in the revolutions.

The cam is a Engle TCS 10, Is there some sort of cam overlap I need to account for?

No. Adjust them at TDC as usual. For some reason many cams today are ground like that, I don't know why. Sloppy machinework?

Make sure your TDC mark is correct. Many aftermarket pulleys are marked incorrectly.

Jan

[Marc]

...I can see it unload a little somewhere in the revolutions....

that sounds like you either haven't got the crank at the correct position for adjusting those valves, or the cam isn't indexed to the crank properly (either off by several teeth or the gear's not bolted on correctly).

Or am I reading too much in and we're only talking about a few thousandths?
When you follow the normal adjustment procedure the lifters aren't on the heel of the lobe but they are still on the base circle, so it shouldn't make much difference. If you want to see just how much, check the lash again when the opposite (other side of the engine) valve is wide open.
Also remember that the cam has a little clearance in its bearings (~.002" or so is typical) and that it can move from side to side when pushed by the valvesprings.

[rcb78]

The cams I've used in the my last few engines had the same 'issue'. It's what Marc said about TDC not being a the heal of the lobe, rather the base of the ramp. The worst one I've seen opened up about .008" (an old Engle w110), my current cam only opens an extra .002-.003". The measurements I took were when degree'ing the cam with no springs so bearing play is out. I went a little more in-depth during my last build and set an indicator on the lobe itself. What I found is that there virtually is no base circle at all, it's all ramp, all the way to the heal. Granted we're talking a very minute range of lift here. It's that .002"-.003" from TDC to the heal and then back up to the BDC location. I asked CB about it because it's their cam (Eagle). Actually I talked to the guy that grinds the cams last time I was there and he said it's in the master that the cams are ground from and there's really no reason to be concerned with it. It does in fact tend to serve a purpose, rather than just dropping the valve on the seat, the ramp rate slow dramatically and 'sets' the valve on the seat. Supposedly helps with the life of your valve job. --Ryan

[cwdaniel]

So if there's no real "bottom" to a lobe, what's the optimal point to shoot for when making adjustments?

The cams I've used in the my last few engines had the same 'issue'. It's what Marc said about TDC not being a the heal of the lobe, rather the base of the ramp. The worst one I've seen opened up about .008" (an old Engle w110), my current cam only opens an extra .002-.003". The measurements I took were when degree'ing the cam with no springs so bearing play is out. I went a little more in-depth during my last build and set an indicator on the lobe itself. What I found is that there virtually is no base circle at all, it's all ramp, all the way to the heal. Granted we're talking a very minute range of lift here. It's that .002"-.003" from TDC to the heal and then back up to the BDC location. I asked CB about it because it's their cam (Eagle). Actually I talked to the guy that grinds the cams last time I was there and he said it's in the master that the cams are ground from and there's really no reason to be concerned with it. It does in fact tend to serve a purpose, rather than just dropping the valve on the seat, the ramp rate slow dramatically and 'sets' the valve on the seat. Supposedly helps with the life of your valve job. --Ryan

[Marc]

Again, are you only talking about a few thousandths' difference?
You can adjust each valve when its opposite is wide open - that puts the lifter on the lobe heel and ensures that the lobe is pushed towards the lifter by the opposite valve spring. Then compare the lash at the "normal" valve adjustment position (TDC ready-to-fire).
For example, you might set the lash to .004" on the heel and find that it's .006" elsewhere. If all 4 lobes act about the same I'd say there's nothing to worry about.

[rcb78]

As Jan said, TDC just like normal. If you were to try and set the valves at the lowest point on the heal, then you risk the valve being open at TDC. It's good that you noticed it because it means you're paying attention. But unless we're talking about a significant amount of clearance here, it's nothing to worry about. --Ryan

[cwdaniel]

I guess you'll never really be rid of that clatter with a solid lifter engine
It's not unusually noisy anyhow.

I'm not sure how much additional clearance is there, just visibly more. I didn't try to measure it, but I'm sure it's a few thousandths.
I guess I'll check for sure and let it ride if it's not excessive.

Thanks for all of the input.

[jrandy]

Huh?
I just put a shortblock together with a 110 and I don't think it has enough degrees of rotation to be on the ramp at the valve adjustment points on either lobe.
If the lash is adjusted with the crank/cam turned to another postion it will do strange things like changing lash clearance at the actual TDC.
If I saw the rocker bobbing up and down instead of smoothly rising and falling up one side, across the tip, and then down the other ramp I would be thinking I need a new cam or maybe some cam gear teeth were missing or damaged.

[Tom in PA]

Interesting, I just logged on to search this exact problem.

I'm using a webcam split lift/duration cam and when I set the intake valve at tdc it is significantly looser when the exhaust is near full lift and vice versa. I just measured and most are 0.004 to .005. One exhaust is 0.006. I was wondering if the split cam profile was the issue and if I had to do something different with setting up the clearances. Looks like this may be the nature of the beast

I currently have the cam retarded 4 degrees to make sure I have enough valve/piston clearance should I want/need to change it in the future. I'm using billet straight cuts from CE.

I'm 99.99 percent positive the timing marks are correctly aligned but I'll triple check when I split the case to start parts cleanup.

BTW, this is with rockers in place on just one side of the engine currently (mock up) so some of this is definitely oil clearance from the cam bearings. looks like with your help, I've answered most of my question already Any other thoughts, please feel free...

Thanks,

Tom

[Marc]

...when I set the intake valve at tdc it is significantly looser when the exhaust is near full lift and vice versa. BTW, this is with rockers in place on just one side of the engine...

Don't give this much weight until there's a rocker assembly on the other side, right now the cam's being pushed over by the "open" valve.

[Tom in PA]

Yea, I went back to the garage and set up the other side and the readings dropped by a bit. They're in the 3-4 thousandths range now. Bit of a bummer though since that gap will only increase with these chromo pushrods

I just never noticed it before today. I learned something new.

Tom

[volksbugly]

So my engine is doing this. The valve lash grows .008 I have the split duration tcs-20 cam. I'm not sure what to do or if I should run it like it is.

[volksbugly]

Ok so after thinking and deliberating over this for the past several weeks, and using physical mockups I think I figured this out.

Since my cam is split duration that means the exhaust and intake valves are putting pressure on the cam at different times which causes it to move. it will actually cause it to move like a teater totter from side to side, while around cylinder 1 and 3 it will push one way, then around 2 and 4 it will push another way, and keep going back and forth.

[Marc]

Doesn't need to be "split duration" to have that happen, all cams will do it.