Crankshaft resistance during cam timing
 

I have timed my cams and noticed that the force needed to turn the crankshaft went up as the cam started to lift the number 1 intake valve. That makes sense.

I also noted the force went up with the number 4 intake starting to lift the valve.

I then installed the rest of the rockers and adjusted the valve clearances

Now, when I rotate the crank, I only feel the force rise when I pass TDC and start to lift number 1 intake or number 4 intake.

Why am i not feeling the other cylinders, as each one starts to lift the intake valve like number 1??

Getting worried something else is wrong, but it is 100% related to crank position.

Maybe I can back off the number 1 intake and see what happens....

Any suggestions?

3.0l SC based engine
DRC DC-20/19 cam
DRC springs
JE 9.5:1 pistons

And: crankshaft nose was weld repaired due to a worn intermediate gear fit. Repaired by Armondo at CCR.

You feel resistance on #1 lift as it's the only one lifting
With all the rockers in place you have a constant lift all the time
Number one might feel more resistance but #4 is moving the valve at the time on Z1

Bruce

Well bad news is I loosened the #1 rockers so they did not touch the cam, and I still have resistance approaching TDC (Z1) every other rotation. Something is not right

Also, I replaced the intermediate shaft aluminum gear. Wonder if it not running true and binding once per revolution. (Binds every other TDC).

I checked for the presence of backlash during the assembly of the bottom end. But I did not check at multiple angular positions.

So with the crank approaching #1 cylinder TDC (valve should be open, but are not, due to backed off adjusters) I have resistance that is the same as before.

Something is resisting rotation. Crap.

Are you using glyco bearings by any chance? If so, read http://forums.pelicanparts.com/911-engine-rebuilding-forum/825748-rod-bearing-controversy.html]this thread

You'll probably want to pop them out and measure them.

Also did you triple check the dimensions of the rod journals?

No. That isn't the issue. GT3 rod bearings.

Removed all the rockers, tensioners. And checked the rotation. Everything seems to rotate cleanly. I think that's a good.

Found RHS cam was mistimed. Hmmmmm I was absolutely sure it was right.

Guess not.

But I did notice removing the #1 intake rocker significantly changed the resistance.

Time for a beer and sleep on it.

Cams binding? They rotate smoothly after the heads and carrier all torqued down?

glyco bearings
 

i used glyco bearings in my rebuild no problems at all.http://forums.pelicanparts.com/uploa...1430275465.jpg
http://forums.pelicanparts.com/uploa...1430275572.jpg

I am dubious that you have issues here (other than the fortuitous RH cam timing you found).

With each rocker added there is more resistance at some point. But when a lobe passes its TDC, it starts pushing the other way. Which is why at some point these start to sort of balance out. With just #1I installed, there are places on the crank circle where the crank won't stay in place without being held there.

Doesn't the intermediate shaft have a tooth count that means the teeth in contact changes continually to prevent wear of individual teeth so any problem with the shaft will be related to shaft bearings and not tooth contact?

I think the problem might be cam binding. LHS cam is harder to rotate than the RHS.

That will be my next step, pull the thrust plate, check the cam and retorque the head studs.

Does anyone have an optimum torque figure for cam rotation without the rockers fitted as this would be a relatively easy check to make on re-assembly.

I will make some measurements on the next engine we dismantle but this may take a few weeks.

Wouldn't this depend on the number of cam bearings, their diameter, and your assembly lube viscosity?

I have a different take on how important cam binding is. IMO mild cam binding is unimportant as is mild crankshaft binding. When the engine is running, the forces on the bearing surfaces are many times greater than the force on the bearing surface causing mild binding. Once you have oil pressure there will be no binding. As long as you can turn the cams by hand (not a wrench), they are fine.

-Andy

Checking the LHS for free rotation is my very next step. RHS was fine.

Just painted in the garage, so the check will happen tomorrow.

I'll try to measure the torque needed to turn the crank at various stages. I'd be interested in how it changes.


Ultimately, I lack experience. The pros are paid because they know what to expect and what is right and what feels wrong. I can only fumble through, learn by doing. I am undoing work to learn and fix.

The feel of the wrench, when it's right and when it's wrong is a valuable skill. Hopefully I'm getting better.

Most of the time a number of valves would be reacting to rising on the opening ramp as would be pushing the cam on the closing side that is why it get easier the faster you spin it, and why it seems to be harder a one point given there is no part that is out of whack. Which is also why needle bearing cam journal never really took hold. A 3.8 RSR two valve motor with racing springs and relatively low tension rings ( rings are a major source of frictional loss) requires 12 pound feet on a beam type torque wrench , after initial breakaway, 24 for a 4 valve cup engine.

regards

Many Workshop manuals used to give some basic torque to rotate figures as a guide to correct assembly/clearances. They were not meant to be definitive to but just to try to point the way. My manual for a Lotus Twin Cam gave torque to rotate the crank assembly with and without pistons as an example.

The number of bearings and the lube will make a small difference but how do we define 'mild' binding if we don't have any numbers?

A simple maximum figure may just be a guide that remover the need to worry.

I would tend to worry about cranks binding if there was a variation in torque around a revolution without pistons.

The figures I gave where for complete assembly spark plugs out and breakaway torque excluded.

Ok, found the issue.

LHS cam was tight in the cam housing.

Untorqued the head studs and resequenced the torque process. Now the cam turns nicely, like the RHS.

Retimed the cams, just now.

What a difference! Force needed to rotate crankshaft is down to a reasonable level.

Cam binding is very perceptible.

Details, details, details. These engines are tricky!