Tony @ Mamo Motorsports

THIS ^^^^^

Im guessing you bought them used....if not you have likely owned them for over a decade. The stamped ratio on the left side of the rocker is the telltale sign these are the 1st generation rockers. YT has actually had TWO updates since them and the latest 3rd gen rockers have been extremely reliable. There are other factors that can cause them to break (tagging pistons at high RPM....a missed shift, etc.) but either way your dealing with a very old set of rocker arms and you should opt to replace them with a newer upgraded set of the same.

Don't even think about stock.....I would rather break a rocker arm than wear out my cylinder heads prematurely from all the sideloading an OEM rocker brings to the table. I have written volumes on this topic.....stick to what you have but upgrade to the newer version.

I will help you a bit on price.....just shoot me an email when you get a chance....mention this thread and we can go from there

You should consider a cylinder head upgrade at the same time....even a ported OEM casting has no place on a larger 427 CID engine....your leaving a ton of power on the table not running a much more efficient higher flowing aftermarket set of heads. We can talk about that as well if you have an interest.

mamomotorsports@yahoo.com

Cheers,
Tony

vettenuts

iTrader: (4)

You are running aftermarket springs with 5/16" pushrods, you really should consider 11/32" pushrods to stabilize the valve train.

JakeFusion

iTrader: (7)

Yep! The added stiffness from some 11/32nds would be great. Will fit with no problems either.

I spin an LSL lobe to 7000 with a PAC-1904 on the stock rocker with ease with no float using a short-travel lifter and stiff pushrod.

00pooterSS

iTrader: (40)

I've read that the side load is an issue at real high lift, I haven't seen what you've specifically said on the subject and I did a quick search and didn't see what you wrote on it.

Mind doing a little cliffnotes on it? Here to learn not to argue btw.

G Atsma

+1. I had always heard the side load issue was mainly over .600 (some would say more..) lift. Under that, and the nose of the rocker does not scrub. Or so I've heard. So I'm here to listen also!

big hammer

It also depends on your spring pressure

big hammer

Stock Ls rockers aren't a true 1.7 either.

vettenuts

iTrader: (4)

Side loads are generated by all rockers at all lift other than zero. As the wipe/scrub width increases, so will the side loads. As spring stiffness increases, so with the side loads. The stock valve guides will wear less for a given side load than a bronze guide.

Shinobi'sZ

I received my new GM HD Trunion Rockers. Installed them on the passenger side, car fired up felt like it might be missing at idle a bit but drove it around the block and it seemed fine. Decided to go ahead and swap out the YTs on the driver side, replaced them went to fire it up and is sounded like it was spinning with no compression and wouldn't start. Figured the new GM Rockers on the stand must have been a little shorter than the YTRs on the pedestal and were pushing too far down on the valve spring even torqued at 22lbs, keeping the valve from closing all the way. Reinstalled the YTRs on that side and it fired up again.

Strange that it the OEM Rockers worked on one side and then when installed on both sides didn't?? Must have had enough compression to start even with one side changed.

So assuming the push rods are too long for the OEM Rockers, can I still use the the OEM Rockers if I get shorter push rods? Thought about putting the shims that were under the YTR pedestal under the OEM Rocker stands to achieve the same height..but thought it would be better to get shorter pushrods if that is the answer.

Thoughts?

bbond105

If you are going to use those rocker arms you will most like need to readjust your wipe pattern and measure for new push rods.

Shinobi'sZ

OK was able to find some info on the engine build from some paper work.

LPE GT11 lift is 631/634
Lunati 72532 lifters (preload .045-050")
LS7 Performance MLS Head Gaskets for blow applications.
Comp 7.400 5/16" push rods

It had the first Gen 1 YT Rockers installed with a shim underneath the pedestal. As I mentioned the GM OEM Rockers kept the valve open when installed. So i need shorter push rods I believe in order to run the OEM rockers with this setup.

I'm assuming the YT rockers can be used as OEM replacements, I read the install instructions and it states to shim them if necessary. I measured the washer shims and they look to be about 1/16" thick which equate to about .0625".

I assuming the Lunati lifters are the same height as OEM GM also.

vettenuts

iTrader: (4)

Did you measure before installing? If the pushrods are too long and they are actually holding open the valves, the PTV will be reduced and there is potential to tag a piston. If the pushrods were measured for a shimmed YT rocker, than they are likely too long.

If you did tag a piston, you need to check compression and leak down to ensure your valves are OK. With the rockers off, are the valve stems all the same height?

If I recall correctly, the Lunati lifters are made by Morel and they are taller and require a shorter pushrod. YT can be used as stock replacement, but every installation I have done with them required some shimming to get a perfect wipe pattern.

Bottom line is you need to measure and check your valves, IMO.

Shinobi'sZ

Thanks i'm just being stubborn with not going and buying an adjustable push rod to determine the length.

I measured the shim that was under the YT pedestal and it is 1/16" which when I subtract from 7.400 push rod length equals 7.3375.

If all else is equal (same cam, pushrod length, lifters) and the YTs worked with shim, then the stock GM OEM rockers should work with either the same shim under the OEM rocker stand OR a pushrod length of about 7.325-7.350.

Appreciate the info and advice on this.

I think the motor is ok (PTV clearance) because the pistons have a -9cc dish and it starts and runs with the YT rockers re-installed. It wouldn't start with the OEMs installed on both sides, so even if it was close 1/16" more I don't think the valves would have hit the piston. It did however start with the OEM installed only on the passenger side, when I fired it up and to test.

gagliano7

With the stock rockers did you use the stock rocker stands?

kinglt-1

iTrader: (26)

Being stubborn is going to cost you a motor.

vettenuts

iTrader: (4)

Not necessarily. It also depends on how the rocker initially sits, it's design, etc. Not measuring could cost you big time depending on what the situation is.

Che70velle

iTrader: (6)

The YT’s require you to set them up. The shims under the pedestal are required to adjust pedestal height. Pedestal height is what sets the “wipe pattern” on the valve head. You have to determine this height by adding or subtracting shims to get your wipe pattern as narrow, and as centered as possible. Once you’ve determined that your wipe pattern is acceptable, THEN you measure pushrod length, factoring in lifter preload as you determine this of course.

Shinobi'sZ

Wanted to post my work around for the timing and want to express my appreciation for the advice offered. As mentioned my 427 has been running fine..no lifter noise for 3+ years and approximately 45K miles of daily driving and road course.

The first gen YTs let go just recently one after the other on different sides of the motor. Being that they have held up to the point of failure just recently. they have been fine. I'm assuming the push rod length, and lifter preload and overall valve train geometry has been fine.

Understanding that the YTs work on a stock engine, I understand that the shims for the YT pedestals are needed to set the wipe pattern, but they do change the overall height of the lifter as it makes contact with the pushrod and top of valve.

I decided for ***** and giggles to take the shims and place them under the OEM rocker stands to make up the difference since the OEM's weren't working by themselves.

I found TDC on one cylinder and followed the instructions on LS1Howto and got 3/4-1 turn on each, then torqued to 22lbs. The lunati lifter specs state 040-050" pre load. If each 1/4" is 010-012" then 3/4-1 turn is within spec.

I fired up the car and it is quiet, idles smooth, has vacuum, and road test good. So hopefully this will do it until I rebuild the engine at a later date. When that happens I will insure the pushrod length is correct...which should be the 7.325" using the OEM rockers.

If what I did screws up the motor it will give me and excuse to rebuild it sooner.

HappySalesman

iTrader: (3)

I would be very hesitant to run those shims under the stands. it's unlikely the shims are exactly the same thickness, so now you are adding a slight bend to the stand, which is probably going to cause side loading like crazy, since the stand not being flat will cause the rockers to sit at a slight angle.

Honestly, wouldn't it have made more sense to just buy the YTs and them use them in a rebuild rather than risk catastrophic damage to your motor? You're going to need to measure for pushrods when you rebuild anyway, and they aren't an expensive part.

There's a right way and a wrong way to do things. In this hobby, you can rarely (If ever) get away with doing it the wrong way. at least not for very long.

Shinobi'sZ

I'm assuming you read the last line in my update post. I also mentioned before that the best way would have been to have purchased shorter pushrods.I was part of all of the R&D for the first ATI D1 kit on a C5 and TTi kit for my Z....very aware of the wrong way and right way and what it costs.

My last setup made 660-1000bhp on my old Z06 and never had an issue with OEM rockers.

FYI-the shims are the exact same ones that were under the pedestals of the YT rockers. They are all the same and compress the metal between the boss on the head and bottom of the rocker stand..which really is no different than how the YT is connected per rocker set on each cylinder and no different than the bottom of the pedestal for the YT rocker.

I ran the car today hard and the drivetrain is still quieter than it was with the first gen YTs on it. The fact that the drivetrain is quieter and it is running great show that things are setup well.

Not saying you are incorrect just saying that the engine is quiet (no tick, tick, tick even with 1 7/8" LT headers), the swipe pattern was good when I checked it, the vacuum is good at idle....same as it was before, and the car doesn't miss a beat.

Appreciate you perspective though. Thanks.