So I decided to check compression on the engine since it should be broken in by now(400 miles). first one=110psi, second=85psi and so on...

The motor has shaved LS1 heads on it and should be 200psi+. The motor doesnt smoke at all and the plugs look good, not black at all so I figure the rings are good. So I pulled the valve covers off and what do I find??? The valves dont shut all the way. The heads are shaved .025 so it made since to me to buy push rods that are .025 shorter than factory. Is this a mistake or did the machine shop cut more than I asked them to? I also installed ls6 valve springs when I put it together. Could the spring height be that far off that there isnt enough spring pressure to go agains the lifters? What is the spring height suposed to be?

Thanks

 

#1- Judging your pushrod length based off of how much the head was milled is a 100% incorrect way to measure pushrod length.
#2- If the valves aren't shutting, you're not going to have any compression on that cylinder.

 

fair enough... the valves are def not shutting, but it is building up some compression, just not full compression. I loosened up the rockers and it has 210psi compression. So, can you assist me on how to measure for the right length push rods? I know you can cut one in half and put nut on it to adjust the length, but I'm not sure about the hyd lifters.

 

what cam are you running? i know someone that has milled heads .025 and 7.375 pushrods with no problems!!

 

How do you know the valves don't close?

The pushrods aren't going to keep your valves from closing. The spring in the lifter is much weaker than the LS6 valvespring, so you would just have more preload if the pushrods are too long.

 

I've got a GM hotcam

 

Incorrect. Pushrods that are too long will cause the valves to hang open.

Also, not TQ'ing the rockers while the lifter is on the base circle of the cam can also cause this problem.

 

I did find this which is pretty helpful:

"1) The only way to properly check (and know where you are in the travel) is
to use a special checking lifter or completely compress a stock lifter.
a) Checking lifter consists of a lifter that has been disassembled
to install shims that lock the plunger at the top of travel in the lifter body.
If using this method you would add length to the checking pushrod to put the
final pushrods into the middle of travel of the plunger.
b) Using a stock lifter, you must make certain that you have pumped
all the oil out of the lifter. To do this leave it at valve full open (highest
spring load) for a while with an indicator on the pushrod side of the
rocker. Watch to see when the indicator stops moving (when the plunger is
fully compressed in the lifter body). Once you have compressed the lifter
rotate the engine to close the valve, extend your checking pushrod to full
length. Using this method you will subtract length from your checking
pushrod to put the final pushrods into the middle of travel of the plunger.

2) Typical plunger travel on Gen 3/4 lifters is 0.150 - 0.200 depending on
the manufacturer, year, etc. We recommend 0.075-0.100" from the bottom of
travel (using method 'b' described above) or 0.075 from the top of travel
(using method 'a' described above). That will generally put you close to
the middle of travel. While there are many different strategies for where
to put the plunger, for street use we strongly suggest that near the middle
of travel is the safest for durability.
3) The more precise method of checking is 'a' because you are not guessing
that you got all the oil out."

I will look into this over the weekend
Also, I'll ask again, do I need to be concerned with spring hight when changinf from ls1 to ls6 springs?

 

The valves could be hung open if the pushrod was long enough to take up all of the preload in the lifter, essentially making it a mechanical lifter. However, common sense should tell you that is not going on here.

Like I said, the pushrods aren't going to hang the valve open.

 

He said he loosen up the rockers and the compression came back up to 210

 

Try this method. Courtesy of Shane at Thunder Racing.

The TDC method is NOT always accurate. Try the EO/IC method to check pushrod length. I have posted directions on this forum numerous times... Here it is again:

FWIW, EVERY cam install I have done using the LS7 lifter with a cam with greater than .600" lift (read smaller base circle) AND stock heads w/GM MLS gaskets has taken 7.425" pushrods for ~.050"-.060" preload. We measure lifter preload on each and every cam install we do. I have never had a lifter failure nor do we end up with the dreaded "sewing machine" noise.

Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.

I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.

Here it is again in a nutshell:

1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.

For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...

I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.

If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
For a given cylinder as the Exhaust valve is Opening, the intake lifter will be on the base circle of the cam and lash/preload should be checked for that intake valve.
For a given cylinder as the Intake valve is Closing, the exhaust lifter will be on the base circle of the cam and lash/preload should be checked for that exhaust valve.

THIS METHOD ALWAYS WORKS!!!

Check it using the above method and see where you are.

 

I am confused on your exact setup, this is an LS1 with a hot cam and LS6 springs and the heads have been milled 0.025", is that correct?

The pushrods in use are what length?

Stock rockers and rocker stand?

As for the springs, they will develop plenty of force to shut the valve on a non-running motor (checking compression) so the seat value will be more of a question at high RPM.

 

Don't listen to this guy.

You need to reread this below.Then read it again. Then go MEASURE for your new pushrod length. Buy a $20 checker from Summit, JEGS, etc.

 

Hmm....maybe he ordered 4.475" on accident, lol.

 

that is all correct, the pushrods are 7.375 and I have checked them... they are 7.375. Stock rockers. I will try the advice of 69lt1bird tomorrow... I assume you check it after makking sure the lifters are compressed

 

Read what I posted and follow those instructions. Shane, who wrote them, is very good at what he does. Zero lash does not mean compressing the lifters.

 

something else i noticed when i was messing with the rockers is that as I loosened the rockers and re-tightened them they would open the valve different every time... The lifter was at the cams base circle, is this becasue it was compressing the lifter plunger differently? Thats why I asked if i should have the lifter compressed(all the oil out) to get the same mesurement everytime.

thanks

 

Im just confused, ahahaha

 

The amount of oil in the lifter doesn't matter right now. If the pushrod length is causing the valves to hang open, the oil has already been pushed out of the lifter and the plunger is bottomed out. It should open the valve at the same point everytime.

Is there anyway you can post a picture?

 

well, I just checked my pushrod length using 69lt1bird's suggestion and the first time I come up with 1 1/2 turns to 22lb/ft of torque, but it pushed the valve open while I was doing it. I loosened it up and made a video the second time. You can clearly see in the video that the valve spring compresses and opens the valve as I am torqueing the bolt. After the video i did it again, this time it only took 1 turn to torque it. So I them made a second video, this time it took less than 1/4 turn fron zero lash to torque the bolt and the valve didnt move this time. Its hard to come up with a answer when things change everytime I do it.

Video #1: 1 1/2 turns from zero last, valve opens
http://s12.photobucket.com/albums/a2...ULY2010001.mp4

Video#2: 1/4 turn from zero lash, valve stays shut
http://s12.photobucket.com/albums/a2...ULY2010002.mp4

I appreciate the help guys and hopefully someone can tell me what I'm doing wrong here.