Broken spring

noseoil

Active Member
#1
Just curious, I'm running the Black Mamba cam, stock rockers (1:1 ratio) & all new SS valves, retainers, lash caps & 26 pound springs. Did a test pass today & at 6880 rpm it snapped a spring on the exhaust side. Fortunately, it didn't suck the valve & I've replaced the spring with an older one (another 26#), set the lash & buttoned it back up again. I'll put the engine back in tomorrow & fire it up again.

Question; does anyone know if there's a problem with these 26# springs that anyone knows of out there? I'm wondering about the intake side now, could be just a fluke, poor heat treat or a bad piece of wire it was wound from. Don't want to replicate this one, as I dodged the bullet again but sooner or later luck can run out & I could destroy the motor.
Spring.jpg
 

delray

Well-Known Member
#2
I would say check your spring height and make sure that is correct. if it is set wrong you could of been getting little coil bind and that could lead to a broken spring. 26 pounds with a black mamba should be good to 8500. I see gokart guys replace there springs every season or sometimes sooner. one thing that can help spring life is make sure the valves are close after running the engine. leaving a load or should say valve spring pressure when engine is hot, can lead to a weaker spring. i'm sure this was not the cause. more than likely it was something else that cause it to fail.
 
#3
Only springs with a breakage issue were the red stripe 37lb springs and it was still rare. It could just be a bad spring. Did it have much time on it?
 

noseoil

Active Member
#4
No, this was the "fresh" motor with a new bottom end, new SS valves, retainers, lash caps, & the new 26# springs (SS hemi kit from ARC). It has a little over an hour total now, but has run a couple of 8,000 rpm passes prior to this one. I'd changed gearing to keep it from winding up too tight & hitting 8500 rpms (was 72:1 & changed it to 6.46:1) so it won't rev as high with the 19" tire (70 mph tops now at 8,000 if it will pull that number). Thanks guys. Feedback will be posted again tomorrow after I run it.
 

noseoil

Active Member
#5
No, this was the "fresh" motor with a new bottom end, new SS valves, retainers, lash caps, & the new 26# springs (SS hemi kit from ARC). It has a little over an hour total now, but has run a couple of 8,000 rpm passes prior to this one. I'd changed gearing to keep it from winding up too tight & hitting 8500 rpms (was 72:1 & changed it to 6.46:1) so it won't rev as high with the 19" tire (70 mph tops now at 8,000 if it will pull that number). Thanks guys. Feedback will be posted again tomorrow after I run it.
Make that 7.2:1, not 72:1, sorry
 
#6
I see you just mentioned it’s a hemi, did you measure installed height between retainer bottom and spring pocket? Are the hemi 26lb springs different than the white stripe 26lb springs?
 

delray

Well-Known Member
#7
I see you just mentioned it’s a hemi, did you measure installed height between retainer bottom and spring pocket? Are the hemi 26lb springs different than the white stripe 26lb springs?
if that's the whole spring in the picture he posted,looks like a animal style spring(short)
 

noseoil

Active Member
#8
I'm going to check for coil bind this morning, but it's the "Hemi kit" from ARC Racing which has the SS valves, springs & retainers as a complete set, so I need to see if there's a problem with my setup. It's a stock head on top, but ported down below. Otherwise it's basically the factory head.
 
#9
Yes but you need to measure stock valve length vs ss valves. The si ss valves are usually a bit longer than the stock NH valves but im not sure of hemi stock length. Hate to nag but you should always check coil clearance at max lift and installed height.
 

delray

Well-Known Member
#10
also a hemi head is known to have just a little shorter spring height on the exhaust side. so definitely check your spring height. if indeed you find a problem with it. also check that push rod and make sure it did not bend.
 

noseoil

Active Member
#11
Checked pushrods (chromoly, glass & no click-click) & coil bind is non-issue. It's a good 0.06" between coils with valve fully lifted on the cam. Thinking a bad spring at this point.
 

delray

Well-Known Member
#12
yes, if it all looks good. it could of been a bad spring. good thing is no damage to anything else. just still need to check the actual spring height. you can still have good clearance between the coils with that cam,but to much spring pressure can still short live the spring. doesn't hurt to check double check that out.
 

noseoil

Active Member
#13
"You must have the correct spring height for proper spring pressure on the valve seat," I got that one, but what is it? Still looking for the correct spring height for a Hemi with 26# coils. It's different than the "normal" clone head height, due to the different casting & angled valves from what I understand. The Hemi has a shorter installed height & will coil-bind with regular clone springs. Got it. I'm still amazed that the stock valves ran so well with 26# springs & didn't snap at the keeper.

For now, .85" seems to be the correct installed height in the hemi, but it's hard finding that dimension in writing from anyone I know is a good engine builder. The regular gauge won't fit inside the coil seat to check height. A billet retainer is a bit tighter than a stock one, so there's another point in compression of the spring.

Going to run it for a test of valve spring height...

P.S. Just spoke with Jody at ARC about the setup & he mentioned coil bind at fully open valve & I told him what I was doing. Seems like it should run well enough, at least until I break something else. He said best guess when I hit the plug with the piston on the old setup was due to crank flex & not a stretched connecting rod as I thought, but the extra 50 grams of piston weight can't be helping things much with the Bullfrog piston. Spring gap.jpg
 
#14
.850 is the correct install height for a 26lb spring to be at around 26lbs seat pressure which is what you want. That is also around the non hemi install height. If you are at .850 you are fine.
 
#15
It's running again, but for how long? Ran 7,300 rpm & it was pulling well. Need to run it back up to 8,000 again & see what happens. Thinking the next motor should be a larger displacement, but down-tuned from this type of build for durability.
 

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