Cam lift/timing variation

[JHP]

cam timing lift is set at about 2.57mm on cyl #1 consistently .. but then when i check the cam timing on cyl #2, instead of it being the same, it is about 2.45mm lift consistently.

Furthermore, if i continue through the revolution, total valve lift on cyl 1 is 12.1mm. However, if i check cyl 2, total lift is about 11.95mm.



Is the variations normal? Cams were newly reground... could they have been done incorrectly or never gonna be perfect?

valve lash set as accurate as possible to each other. (maybe i should zero out the lash)
and rockers are new

I have not gone through the process of checking all the cylinder lobes.

Will this cause any ill effects when running?

thanks in advance

[Jeff Alton]

Couple of quick questions.

Have you tried to reset the timiing bank to bank to be closer to equal?

Show us your tools you are using to measure timing and total lift.

And, who reground the cams? Did you also get the rockers reground?


Cheers

[JHP]

sorry, maybe i wasnt clear. I am not talking bank to bank. I am talking cyl 1 and cyl 2.-left bank. I see most people only time 1 and 4 and move on.... but just out of curiosity i checked timing on cyl 2 expecting it to be identical to cyl 1 but it was not.. am i just going over board? wondering if its normal to have some slight variations between the lobes on the same bank/cam or is something wrong?

Rockers are new- ..just using z block and gauge

[stownsen914]

Years ago when I assembled a 2.7 race engine, I measured duration and lift on multiple cylinders because I was curious. I did the usual lift at overlap method and also had a degree wheel on the crank. Similar to you, I was finding different durations on different cylinders. It was repeatable. In my case, the durations were consistent from one cylinder to the next, but the intake/exhaust opening events were not. Basically, the cams had been ground with different lobe center values from one side to the other - I think it was several degrees. I spoke to a few people and decided it was acceptable to "spllit the difference" in setting the cam timing and move on.

Personally I wouldn't worry too much about a difference of .12 mm in cam timing measurement that you noted since it's within the typically recommended range.

I don't recall noticing significant differences in lift in my case. .15 mm difference across cylinders is a little more than I'd expect. Not sure if that's a big deal though.

It's worth noting that rockers sit between your cams and where you're measuring at the valve. You could measure lift and or duration at the lobe if you want to isolate the camshaft measurement. It would also give you some confidence in going back to your cam grinder if you decide to do that.

[dannobee]

I'd confirm my findings by using the same rocker arm on each lobe. If they are now equal, you know that the rocker is your variance. If the results are similar to before, it's the cam lobes that are off.

[JHP]

thanks guys.. yep i swapped rockers and still. I also checked cyl 3 and that one is the worse at about 2.35mm
So its:
cyl#1----2.55mm
cyl#2----2.45mm
cyl#3----2.35mm

So about .2mm variance. I wonder if this is normal but most people dont check.

[Neil Harvey]

You do not want to lose any lift. As low as 0.005" will make a difference.

This could be from several areas. Some her have touched on the most obvious you should be checking.

The two most important are as some have suggested. The rocker arms and the Camshaft. I assume the lash has been zero'ed out when checking.

Have the cam checked by someone with a Cam Pro or similar tool. They can measure all the lobes, give give you all the date to see if the cams are ok. It may look like what I have attached.

Have the rocker arms checked. Unfortunately, there are some places that will reface the rocker arms on a valve grinding machine with a rocker arm attachment. Steer clear of that process.

There is an absolute dimension for the radius the rocker arm to keep the geometry in place. You can check this by slowly compressing the valve and watch the motion of the rocker arm swivel foot. Often it stops lifting the valve and just slides across the face the the valve stem.