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Discussion Starter · #1 ·
My '94 has Combination Motorsports 612 valve springs, and the one on the #8 exhaust valve broke. The specs on those valves are:
--145 lbs seat
--345 lbs open
--Good up to .570 lift, 6300rpm

The cam is a GM Performance Parts grind number 12370845. Specs:
--488 intake valve lift (assuming 1.5 rockers; car has 1.6)
--509 exhaust valve lift (assuming 1.5 rockers; car has 1.6)
--214 degrees intake valve duration
--222 degrees exhaust valve duration

As far as I can tell, CM is out of business, so I'm not sure if there's any way I can get a replacement for just the broken spring. Cost is an object, so are there valve springs from any other manufacturers that are close enough in specs that I could just buy one spring to replace the broken one?

My mechanic has a set of new Comp Cams 918 springs. Would it be a good idea to just have him replace all of the CM springs with the 918s?

Thanks!
 

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the CM springs may have just aged and one finally failed. yeah you could replace with a single spring close to those specs but I would just replace all the springs at this point.

918's will work fine but there are other options most likely for less.

Alex makes a set, Howards are another option for not much $.

Obviously anything from Comp or Crane also
 

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First of all, don't feel bad. Almost all of the popular 1.25" "upgrade" springs for iron head LT1's have broken with the kind of lift you're running on the exhaust. The springs that come with the popular Crane 10309 kit have broken for me and several others running that kind of lift.
I'd replace at least all of the exhaust springs; I'll guarantee you they're all on borrowed time after a few thousand miles running that lift on top of that seat pressure.
There are plenty of cheap springs that are just as good, maybe better than those CM 612's. Alexsparts.com and Howards cams are two that come to mind. Summit carries the Howards springs.
Running a couple of ZZ3 cams (similar exhaust lift) in Vortec motors, I've seen no performance debit running 1.5 rockers on the exhaust even with non-ported heads which are acknowledged to have a weak exhaust port (same ports as our iron LT1 heads). So that's one thing I'd recommend if you're sticking with those same springs and you have access to some 1.5 rockers.
Or, check out those Howards micropolished springs that Dan Fahey raves about. I'd trust them over any of the other 1.25" springs to hold up to that valve lift.
 

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Discussion Starter · #4 ·
Thanks for the responses, guys. I forgot to add that the heads were sourced from a Corvette, so they're aluminum, and were ported, polished, etc, by Lloyd Elliot back in '06 or so. The engine has about 20k on it since the work. Is that enough time for springs to become worn out?

The 918s that my mechanic has are the single spring version, and he says they are a "couple years old". Looks like the current 918s are a double spring version. I've asked him to verify the batch number--as it looks like the 918s were very failure-prone back in '06-'07 according to some threads I've read.

The benefit of the 918s is that he's got them in hand and wants to work on the car today. But if you guys think that the Howard or Alex springs are cheaper and better, I'll look into them.
 

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My bad. I assumed iron heads and the springs CM used to sell for those.
If you run those 918's (those are the beehives, right?), don't set them up to 145 on the seat. About 125 with beehives will control that cam just fine, and will better your odds against breaking one.
 

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I don't think the 918's "bee hives" are now a double spring. Mine are single.

they spec a installed height of 1.800" so your LE heads most likely had the spring pockets machined down slightly as most aftermarket springs are 1.800" vs 1.70-1.75" the stock springs are.

918's are around $180 new for a set. I believe the Alex springs are around $110ish. Both will work fine.

Your mechanics 918's being a few years old are not a problem but if they are used might want to just get "new" something.

valve stem seals are something you should replace if they are old since they are cheap. FelPro viton ones.
 

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Discussion Starter · #7 ·
The 918s my mechanic has are the 26918-16 kit. In the pic, they appear to be single-spring. http://www.summitracing.com/parts/cca-26918-16/overview/

I've never installed valve springs before (leaving that up to my mechanic), but how does one change the seat pressure? I assume that if the lash was set properly, the seat pressure would be whatever the spec is, and the 918s list a seat pressure spec of 125lbs.

I'm browsing through the Howard Cams parts on Summit Racing, but there are literally 148 items and not being well versed on these things, I have no idea what to pick.
 

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Discussion Starter · #8 ·
918's are around $180 new for a set. I believe the Alex springs are around $110ish. Both will work fine.

Your mechanics 918's being a few years old are not a problem but if they are used might want to just get "new" something.

valve stem seals are something you should replace if they are old since they are cheap. FelPro viton ones.
If he didn't already have a set, I'd probably opt for the $110 set if they were of comparable quality, but if you guys feel comfortable recommending the 918s, then I'll go with them. I'm pretty sure they are new (will confirm).

I'll mention the valve stem seals to him too. Thanks!
 

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Discussion Starter · #9 ·
One more thing--when left in D and given WOT, the car shifts at around 6300-6400 on the tach (it has a Z28 gauge cluster). Should the 26918s be good up to 6500rpm or so? I haven't been able to find the float RPM.
 

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918's are good springs. you should use the correct spring locator and retainers with them. If they are the 7 degree retainers you can re-use the stock 7 degree locks. Comp also makes a 10 degree retainer and locks for them also.

valve stem seals require removing the spring so often people do replace those seals if they are original or old when doing a spring swap. I would not use teflon "white" ones though. Just a viton full jacketed seal like stock. FelPro makes them.
 

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yes so if a spring is spec at 1.800" installed height than installing them on stock heads that have not had spring pockets machined down yet making them 1.7xx" will increase the seat & open pressure some. Not anything to worry about unless you have a very high lift cam

you can buy a shim set for a few $ that has a variety of shim thickness and use a valve spring height tool to set up your springs at a specific desired height.
 

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Discussion Starter · #13 ·
My mechanic called Lloyd Elliot and he said that Lloyd recommended against using beehive springs for my application.

Instead, Lloyd recommended the Lunati
73925K2 spring and retainer kit. http://www.jegs.com/i/Lunati/638/73925K2/10002/-1

The guy is apparently pretty experienced with this sort of thing so I'm inclined to take his recommendation, but I figured it couldn't hurt to see if you guys have any comments.
 
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