First time posting in a forum of any kind, but have used them for about 8-10 years. I feel like my situation is pretty abnormal and haven’t been able to find much of anything which helps me out. This is gonna be long as it’s a whole process, but gonna try to give as much detail as possible. ANY and ALL help is greatly appreciated.



Anyways, a few months ago I bought an LS swapped BMW. Engine had been torn down and rebuilt by previous owner. It’s an LM7 with 706 heads, BTR stage 4 turbo cam, BTR dual valve springs, rockers with bearing trunions. This is my first LS based car, coming from VW/Audi stuff, so it was running a little rough, but the guy said it just needed a tune because of the big cam. I know, I know, never trust the “just needs a tune”. Anyways I bought it for pretty cheap and knew I’d be getting into a project somewhat, but I was okay with that being a mid level mechanic and know how easy LS stuff is. So I took it to my tuner and he told me something was off with how it’s running, so I brought it home and began teardown. Took valve covers off and instantly found that pretty much every valve had one broken spring. Had about 3 of the main springs broken and the rest had broken inside springs. Took the heads off, inspected for any other damage or issues and everything else looks good. No bent valves or pushrods, no scoring on lifters, rocker arms, cam lobes. Suspected a few different things to be the culprit(s). Pushrods too long, incorrect installation(everything looked installed fine), ran it low on oil pressure, over-revved it, or he got sold fake parts(read a few things about that being common with BTR stuff). So I cleaned the heads and bought new titanium dual valve springs set directly from BTR(other guy cheaped out and went with steel instead). Lapped the valves and installed new springs and hardware. Last night I installed the heads with new head gaskets and ARP studs torqued to spec. Used an adjustable pushrod to check if the pushrods were good length or not. Found out that they were about 4mm or 0.15” too long. They are 7.4” BTR pushrods and BTR makes 7.25” pushrods, so went ahead and ordered them last night. BUT here’s where I’m getting confused, referring to coil bind. I was told by an LS builder to just subtract the cam lobe height from total spring height when installed without rockers. So coil bind is 1.07” as stated on the valve spring kit box, total spring installed height is 1.78”, and cam lobe height is 0.618”. So 1.78 - 0.618 = 1.162. 1.162 is more than 1.07, so according to this, I should be in the clear with the correct length pushrods. BUT then I’ve also seen that you’re supposed to take into account the rocker arm ratio, which is 1.7 in this case. Read that 0.618 is supposed to be multiplied by the 1.7 and that give how much the spring is actually compressed. This comes out to 1.0506, so 1.78 - 1.0506 = 0.7294, which is a lot less than the 1.07 coil bind, which means the spring should be compressing too much RIGHT??? Tested it out by putting the too long pushrod in just to see what happens with new springs and turned the engine over. Spring never bound up and had plenty of space between each coil on both the main spring and the inside spring. So now I’m stumped because based on the math including the rocker ratio, the spring should compress way too far, but it doesn’t. So am I overthinking it and shouldn’t be using the rocker ratio? If not, then why not? Is my math off somewhere?Any questions, feel free to ask.

 

Push rod length and coil bind are NOT related.

THIMK: the way a hydraulic lifter system works (doesn't matter if it's GM, BMW, Toyota, Lada, ...) is, the oil pressure forces the thing that the push rod sits on, up to the point where there's zero valve lash. I.e. takes up all the slack. So, as long as the push rod length or rocker adjustment puts the whole deal within the range where the oil pressure can do that, it all self-adjusts.

You're also REALLY confused about the relationship between lobe lift, valve lift, installed height, and coil bind. Valve lift is the rocker ratio times lobe lift; in these motors, valve lift is usually something in the .500" to 650" sort of range, give or take. Valve lift is rocker ratio times lobe lift. Real simple; the rocker is just a lever, so, just multiply the lobe lift by the ratio, you come up with the valve lift. Simple. Most cams give you the valve lift spec, so, expect a number somewhere between .500" and .650". (unless of course you're running with the Street Outlaw guys...)

Stock springs, and most common aftermarket, are set up at 1.800" installed height. IOW that's how tall the springs are at ZERO valve lift; like, when the heads are laying on your garage floor. Then you can subtract the valve lift, as calculated above, from that installed height, and that's how tall the spring is when it's fully moooshed down by the cam when the engine will be running. Coil bind MUST BE some lower number than that; that is, your cam can mooosh the valves down as far as it will, and it HAD BETTER NOT cause the height of the spring at that point, to be less than its coil bind spec. Otherwise you have metal trying to compress metal, which NEVER ends well except if you're in a forging foundry.

The cam lobe height IS NOT .618". That would give you a valve lift of .618" times the rocker ratio of 1.7, which would be 1.0506". Yeah ... NO. The .618" spec is right in line with the typical VALVE LIFT spec I gave you above, of .500" to .650". OK fine.

If your springs are set up at 1.800", then when the valves are fully opened, the springs are at 1.800" - .618", which is 1.182". Springs that bind at 1.107" SHOULD be OK, butt IF AND ONLY IF they're properly set up to begin with. Which requires a spring height mic such as https://www.summitracing.com/search?...g%20micrometer Get yourself one and verify that your springs are set up at the correct installed height (distance between whatever the spring sits on and the retainer). This can of course be done with the heads not yet installed on the motor; bolting them to a block doesn't change it. Nothing at all about the rest of the engine alters this setting.

The min valve spring height at full compression, minus the springs' max compression spec, is about .075" in your case. (1.182" - 1.107" = .075") PROPERLY SET UP, there shouldn't be a problem. "Properly set up" is the variable here. I'm pretty sure that your problem is RIGHT HERE. What is your springs' installed height?

Then, you select push rods based on the clearance between the top of the push rod cup in the lifter, when it's fully pushed up by either oil pressure in operating or by the lifter's own little internal spring while building, and the bottom of the push rod seat in the rocker, when it's just barely held against the valve stem tip. This has NOTHING WHATSOEVER to do with ANYTHING about the valve springs. It's all about setting the lifter so that its internal moving part is settled within its "desirable" range when the valve is at rest and the cam lobe is on its "zero lift" point. Some engines, with adjustable valve trains such as the old small block Chevy, you adjust that by the rocker position; with these, the rocker just bolts down, and then you set the lifter preload (how far down into the lifter body the push rod seat is pushed when everything is at "zero") by selecting the push rod length.

So: it's REALLY SIMPLE. You select springs that give you an appropriate safety margin between your cam's max valve lift, and the springs' coil bind height. Most people for most builds want as much of that as they can get. HOWEVER, in some situations, you can use coil bind to your advantage; to keep the spring from resonating and just "boioioioinging" around freely, you set everything up such that the difference as described, is some small butt adequate amount. Might often be in the .050" to .060" kind of range. Frankly, I'd guess that for someone coming on here and asking this question, the .075" you'd come up with WITH PROPER SPRING SETUP, is plenty close enough. So that's your first task: measure your springs' installed height, and set them up using shims, to get whatever the spring mfr recommends (usually 1.800", butt not always, READ the springs' spec sheet). Once that's done, move on. It doesn't affect anything else that follows, and nothing else that follows will invalidate it.

THEN, to select push rods, fully assemble the engine except for the push rods (heads, head gaskets, lifter, rockers would all be fully and properly installed at this point) and use an adjustable push rod such as https://www.summitracing.com/search/...ength-checkers ( personally I use the Comp 7702 butt lots of the others covering the same range would work fine too) and find the push rod length that just barely takes up all the VERTICAL slack in the lifter & rocker system; and add your desired lifter preload to that; and order that length of push rods. To do this you simply let the spring inside the lifter push the push rod seat fully upwards, and adjust the adj PR length to where there's no play anymore. Do this at all 4 corners of the engine (that being the usual way to capture the greatest variance), both intake and exhaust valves, on cyls 1 2 7 & 8. Don't EVEN think about "stock" or what somebody else used or what the cam mfr "recommends"; MEASURE what YOUR ENGINE wants. For example, stock(ish) LS7 lifters want about .075" - .100" of preload, so whatever you measure with your adj push rod, you simply add .080" or something to, and order. It's just not that hard. It's an American engine, and a GM one besides, which means that is EEEEEEEEZZZZZZZZZZZYYYY. Much eeeeeeeeezzzzzzzzyer than your typical engine from most other mfrs. It's SO EEEEEEEZZZZZZZZZYYYYYYY that lop-eared American kids out in the corn fields of the Midwest or wherever, with no education or "knowledge" whatsoever, can get it right, no problem. Hell it's SO EEZZZZZZZYYY that I can even manage it, and I don't even have a brain. It's REALLY EEEEEEEEEEZZZZZZZZZZZZY.

 

First off, always trust your math. Numbers don’t lie. Simply turning the engine over to verify by eye won’t work with a hydraulic lifter build. The valvespring is far stronger than the inner check spring in the lifter body, and with zero oil pressure present, the lifter cup won’t be pressed upward at all. The lifter will bleed down as you turn the engine….because of valvespring pressure against it….so you’re not seeing max valve lift with your eye. Trust the math.

 

So does that mean the 0.618” that the camshaft specifies is the VALVE LIFT and not the LOBE LIFT? It’s a BTR stage 4 turbo cam if you wanna look it up and verify. Because that’s what I’ve been using as my lobe lift number, and I believe that’s where I’ve been getting confused because I’ve been multiplying that number by the 1.7 rocker ratio and it comes out to 1.0506” which when subtracted from installed height is way past the coil bind spec of 1.07”

 

Yes. .618 is valve lift, not lobe. Lobe would be .363 with a 1.7 rocker. 1.05” lift numbers is NHRA ProStock territory….

 

Precisely.



A very popular spring combo for cams of that sort is the .660" capable dual springs available from several vendors. BTR themselves is one. Probably a good choice for what you're building. Call them and ask what they recommend, I'd almost bet that's the one, or at least among the ones, they'd point you toward.

 

If every spring was broken in some fashion, then something is mechanically off. I would verify the lift of the cam lobe with a dial gauge and verify the installed heights of the springs. I'd even take the cam out and make sure it is what the seller claimed. The seller could have fed a line of bullshit and just put in some junk cam kit from Amazon or eBay, or the camshaft could be legitimate and the springs are eBay junk. One or two springs I could see as a defect, but all of the springs? That's improper installation, improper spec, or counterfeit territory.

 

Right, just kinda hard to believe he would lie about the cam because everything else that’s in it is what he said it was from what I can tell. So I believe the problem would be the pushrods being too long. When I re-installed the old pushrods(7.4” long) when I torqued down the rocker, it compressed the spring a little just from torquing it to spec. I figure it’s either that or counterfeit parts. Now that I know that the 0.618 is the valve lift not the lobe lift, everything should be good. Going to be installing and finishing some stuff up on it this weekend and will keep yall posted.

 

it’s 100% not the pushrods. When pushrods get too long on a non-adjustable valvetrain engine such as the LS platform, it’s simply going to hold the valves open. Open valves mean no compression and at the very least, you’ll see backfiring out the intake and/or exhaust. From my vantage point on this side of the internet, you have a valvespring set up issue.

 

The spring will compress if you torque the rocker down when the lifter isn't on the cam lobe's base.

With all 16 springs being broken, you have a major mechanical issue that needs to be addressed, and it isn't the pushrod length. You either have springs with the metalurgy of a wicker basket or the springs were installed improperly. Either way, this is something that a visual check won't verify.

 

OK now, all of us have come on here and told you (a) your broken spring problem IS NOT caused by push rod length, and (b) you have a valve spring setup issue. We've all told you why and how these things are true.

Why are you STILL arguing about this? Do you want help, or just to argue? Which letter of the words "is not push rod length" and "valve spring setup" are you having trouble with?

Note also that we ARE NOT telling you that the PRs you have are the right length; they may or may not be; we HAVEN'T GOT THAT FAR YET. All we know so far is, you have a valve spring setup issue, which is what caused your springs to break. Gotta cover the valve spring setup issue FIRST before worrying about PRs. Your existing ones are most likely ruined anyway so it hardly matters anymore what they are/were.

Of course. Some of the valves are SUPPOSED TO BE open at any given location the engine happens to be turned to. A deeper question would be, why are you torquing rockers down to begin with, in an engine full of broken valve springs?

However all that may be, STOP ARGUING. Get the numbers off of your cam, call BTR, ask what springs they recommend and how they want them set up, and BUY THEM. Odds are, they'll call for the .660" duals that are extremely popular in applications like yours; butt whatever it is, just do it. Buy a spring height mic that's compatible with whatever springs you get: the difference among those is the height range that they cover (probably will be 1.800") and the diameter of the spring at the retainer end, butt whatever BTR tells you, BUY IT; and a set of shims and seals and whatnot (maybe retainers & keepers if yours are fornicated), and an adjustable push rod like the Comp 7702 that covers the range around 7.400". Many of the seals that you can get for these motors include a seat for the springs, which if you have that type and they caused your now-broken springs to be at less than 1.800" installed height, might be the root cause of your problem.

Then, when the heads are back on the engine, install the rockers one at a time with the adj PR, and find the push rod length that JUST BARELY takes up all the VERTICAL slack between the lifter PR seat and the rocker. DO NOT use the "twist the push rod" non-method; you want to take up VERTICAL FREE PLAY ONLY. Measure at least the 8 at the corners (both I & E on 1, 7, 2, & 8), and since by that time that's half the engine you might as well check the other 8 as well. Add the right preload for whatever lifters you have to whatever those measurements are. Buy that length (or those lengths, if they vary by too much). You MUST determine what lifters you have ACCURATELY, as different ones call for different preload values: might in fact be wise, with the heads off, to just go ahead and buy new ones and NEW GM plastic guide trays so you can be ABSOLUTELY SURE what you've got, and select PR length accordingly.

Once you MEASURE everything you'll know EXACTLY what you've got and what to do. Further arguing about it is USELESS.