Valve Spring help
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Valve Spring help
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.
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.
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When installing valvesprings, ALWAYS use springs that the cam grinder specifies. Forget about the lobe height. You need the total valve lift with the rocker ratio you are using. Look for lobe lift, then multiply by.1.7 or 1.8 (2 most common LS ratios). This gives you the valve lift. Compare the lift to the coil bind spec. An easy, and common example would be, say, .600" valve lift. If the springs use an installed height of 1.800", subtract .600" from 1.800", which leaves you with a 1.200" spec. You should shoot for, maybe, a coil bind spec of 1.125-1.135. I also recommend PAC dual springs. Just an example, and hope this helps......
