I have been reading some conflicting information about testing for piston to valve clearance on the LSx. I have never had to test PTV with an engine running a hydraulic lifter before now, and I have read myself into a bind. I would really be interested ina video or nicely detailed explanation of the two more common methods: Clay (Solid lifter with clay) and Dial (Dial indicator and checker springs). I have used the clay method on SBC's running solid lifters and a given lash. Here are the things I am confusing myself on...

1) A hydraulic lifter has a given preload distance (around 60 mils is what I am seeing for a stock LS1 lifter). The writeups I have read tend to focus on a solid lifter (usually an old one filled with washers) and a pushrod of the final length. This would mean that the valve is opening to far by whatever the pre-load is. I have seen one thread on the internet that mentioned using a shorter pushrod to compensate, but that could get pricey quickly. Most agree that a checker pushrod will not be happy when used to open a dual spring.

2) Everyone mentions the gasket compression thickness, but what are people using to get there, head gaskets are pretty expensive, and i don't want to crush one for the test and then pitch it. We bought Gm MLS gaskets, can they be used for the test and still be used when we are ready to bolt the heads on for good?

3) In the dial indicator method, it appears that you go to a very light checker spring that will not compress the plunger in the hydraulic lifter. This again gives me concern with the lifter pre-load. That value is not taken into consideration.... It would seem that checking every 2 degrees from 15* before to 15* after is in order.

I am sure that I am working all this up too much in my mind, but I really do want this to work, and I would like to feel confident in my measurement. A video showing how to do it on an LSx (in vehicle in this case!) would be great! Any help out there?

 

For the clay method, the follwing should answer your concerns...

Install checker springs (by doing this, you don't have to worry about lifter preload as the lifter spring is MUCH stiffer than a checker and it will act like a solid for the test as long as you don't go crazy with the clay on this piston)... or you can shim up a lifter, tack weld an old lifter etc...

Lay the MLS on and torque it to 20lbs or so around the hole you're testing. The very slight compressed difference between 20lbs and 80 is going to be so little that it won't affect your test results.

Be sure to oil the clay and turn the motor over 4-5 times

I don't use the dial indicator method anymore... Takes too damn long.

 

Thanks. WHat length on the pushrod for the test? Since you took the pre-load out, if you used the full length (say 7.4), you would be opening the valve a little more than normal, is this intentional? I could make a case for wanting to check every possibility of PTV contact....

 

Sorry, I've been running adjustable rockers forever. If this is a previous combo (ie: just a cam install), just assemble it with what you've got if the combo is known to be good and the cam is the same base circle. If not, an adjustable push rod (or 2) will get you the rest of the way as this is ALSO a good time to go ahead and check your rocker geometry and check the wipe on the valve tip.

 

He wants to know if the lifter preload is going to be a factor in PTV. If he uses check springs then the preload is eliminated. Do you therefor add the preload onto your clay measurement for ptv or no is the question he is asking.

 

Detroit, you are correct. No methods I have read seem to take this distanc einto account. It is a significant distance.

As for the combo, VRX3 Cam with Stage II 59cc (milled) LS6 heads with 2.055 intake valves. GM MLS head gaskets, LS7 lifters, Crane Dual springs. Stock LS1 bottom end. We have a set of 7.400 hardened pushrods on hand, and may need to swap them for a shorter rod, we will see...

 

This is one more small benefit of running an LG series camshaft. They do all the legwork and all that is needed to be checked is valve drop. This still leaves a bit of trust in the fact the cam was ground correctly by Comp. I've had 2 LG sticks in my motor used the valve drop method using figures LG furnished me and spun both to over 7K without issue.

 

With flat top pistons, milled heads, and larger valves? Explain your method please, and include what ifo they gave you to test with....

 

Stock flat top pistons,my heads are milled .020 and I run a 2.08 intake valve (5.3 head). After a motor has had the correct PTV clearance determined lets say .080 for arguements sake, the piston gets brought to TDC and the head is placed on the block with a gasket and snugged down. The valve is already in place with a test spring if desired and a dial indicator placed on the valve stem. You simply measure the distance from the valve on the seat to piston contact AKA valve drop. Assuming you have correct PTV clearance this measurement will be constant.

LG does the legwork of attaining proper PTV clearance and cut that portion out for you. They give you a minumum valve drop figure according to your cam,combustion chamber volume,head type,etc. If you fall short on your valve drop figure flycutting is needed. I called and spoke with a tech at LG he told me the minumum I could get away with was 120 thous I flycut .060 into my stock pistons (see thread here= https://ls1tech.com/forums/10975575-post71.html ) and wound up with 190. Almost seemed like a waste to even have to flycut them but I have plenty of clearance and will never have any issues. Obviously cam grind/type will alter the needed valve drop figures. The guys at LG are awesome and always take time to answer questions and get your details worked out.

 

Ah, but did you subtract the lash of the hydraulic lifter?

 

When you say lash are you referring to preload?

 

Yes, what did you do with the pre-load. Once you have 0 lashed using the adjustable, you need about 60mils more to pre-load the plunger. Thisis the value I am confused about. When doing the PTV, how do I acount for this distance? Do I subtract it and smoosh my clay using the checker springs and the 0 lashed adjustable pushrods, or do I use my full length pushrods with the checker springs and not account for that distance. If that is the case, I will actually wing up with considerably more clearance, unless it is common for the pre-load to dissapear when the exhaust is closin and the intake is opening. This non-adjustable, hydraulic valvetrain has me a bit confused. With a mechanical solid lifter, you would lash it and rotate the engine. No worries. With the hydraulic, there is a bit more to it.... what happens to this 60-80 mils of pre-load???

 

That additional preload is taken up with pushrod length. This is why there are ALOT of different pushrod lengths available for these motors. So think of it this way a modified lifter with a solid washer in conjunction with an adjustable pushrod adjusted to zero lash will keep the valvetrain in the same postions as a lifter with lets use .080 preload and the correct length pushrod.

 

THAT is what I have been trying to find out! Thanks, I will use light checker springs, and 0 lash the adjustables, cycle a few times, and pull the head.