Medida

In the process of finishing my build on my LSJ engine and was checking the timining

It is a new cylinder head, supertech valve springs, comp cams stage II cams, new rollers, new lifters.

In my first set of measurements (after aligning the chain to the sprockets to the cam at TDC of #1), I found my intake duration @ .050 was very close to the cam spec on both open and close. My exhaust side had some variations from spec for the .050 valve timing and duration . Call this measurement #1. (I latter found out that I probably will need to have an adjustable cam gear if I want to meet the camshaft exhaust specs).

For an unrelated issue, I took the timing and sprockets off and started all over.

I then measured a 15 decrease in intake valve duration. I then measured the intake lift and found it to be .040 under spec. call this reading #2.

I then checked exhaust and got the same readings as in #1

Being somewhat paranoid, I then redid the whole assembly (that is, took out the chain tensioner, took off the cam sprockets and then redid the assembly). Lined up the dots on the chain to the marks on the sprockets and ensure that it was at TCD. After setting the chain tensioner, I then took measurements

I found the intake side to repeat as in #2 measurement (so it was showing the 15 decrease in valve duration from first measurement). I got the exhaust side to repeat (so no change across all the readings)

I am puzzled how the duration could have decreased on the intake side

I am very confident that the valves did not hit the pistons and that I was at TCD when setting the timing chain and that the camshafts and sprockets were properly aligned

In talking this over with someone else, they were wondering if the valve lash adjusters need to be purged of air. His experience was with SBF and he found that if he did not purge the lifters of air, he was get a lower valve lift and valve duration. He purged the air by immersing the lifter in oil and then pushing on the bottom end

I have the GM service manual for cobalts and it does not mentions anything about having to purge the valve lash adjuster. All it says is that you need to apply a GM lubricant to the valve lash adjuster, rocker, camshaft lobes etc (I used Torco engine assembly lube).

So wanted to see if anyone can weigh in on this. Does the valve lash adjuster need to be purged of air? If not, can you think of what my issues is that caused the decrease in intake valve duration (and the low intake valve height).

jdbaugh1

iTrader: (1)

I can't tell you what the lift should be without oil flowing to the lash adjusters, hopefully someone more knowledgeable will weigh in on what range the static lift should be within.



However I can fairly confidentially say that air should not affect your static lift. The only thing I can think about your buddy that would make sense to me is that the oil somehow hydraulically held the lash adjuster up higher and kept it from bottoming out which increased the lift compared to when it was fully seated. As far as I know the only way the lash adjuster will increase lift by raising the back side of the roller is with active oil flow. Otherwise the roller should be making contact with the surface of the lash adjuster, dry or coated with oil and the lash adjuster should be bottomed out in its seat.

mrbelvedere

iTrader: (3)

you need to check the cam events with checking springs so your not collasping the lash adjuster also stiffer then stock springs can reduce lift and duration (making the lash adj collapse) and also decking the block or head will retard cam timing

the ecotecs have a variable ratio follower also and can mess with degreeing the cams the only way to actually check is to use a solid lash adj

Medida

head and block are stock.

I do not have checking springs. I do have a set of old stock springs. Would this work (or would it still be to strong)?

thanks

mrbelvedere

iTrader: (3)

a couple checking springs from comp cams or summit is around 15.00 get a set and cut them to fit

you may want to get the head surface check to see if its warped 98% of the time they are

Henry3959

Do you know how much per .001"
I can't imaging chains stretched 1/4" or worn out guides and gears are doing it any good either if you're assuming the tensioner will always pull the chain negative.

jdbaugh1

iTrader: (1)

If someone knew the rise and run offset of the intake cam sprocket center with respect to the crank sprocket center as well as the effective diameter of each sprocket I could plot it out and let you know.

mrbelvedere

iTrader: (3)

its around a couple degrees per .010

Henry3959

Ever played with the Variable Camshaft tables?

mrbelvedere

iTrader: (3)

best thing to do with them is lock them out

Henry3959

Why do you suggest that?

mrbelvedere

iTrader: (3)

they don't work past 7k and are easy fouled