Broke valve spring

[Faolan]

196cc, black mamba jr, 1.3 rockers 26# springs. Had lots of time on the springs.. like 100+ hours.. broke just being old? Broke because I put 1.3’s on after 100+hours on the springs? Pretty sure this setup floats the valves at ~7000. Even with brand new springs From 6800 and up it revs quite slow with about 7500 max. Just trying to figure out why it broke. Luckily it only destroyed the head and piston.
Should clarify that coil bind wasn’t an issue

 

[ole4]

BM JR with 1.3 ratio rockers need 37LB springs if you are going to rev it that high.

 

[Faolan]

BM JR with 1.3 ratio rockers need 37LB springs if you are going to rev it that high.

What about with 1:1 rockers? It doesn’t seem to rev any higher with stock ratio rockers

 

[ole4]

Big difference on valve springs then 26 would be ok If you set the install pressure correctly. The cam is not meant for 7500 RPM it is designed as a midrange cam with a 6000 rpm HP peak. It will certainly rev over that but will fall off after that. If you are floating the valves that will destroy the valve springs and could pull a valve thru the retainer or bend a pushrod if it comes off the rocker or tappet.

 

[Faolan]

Big difference on valve springs then 26 would be ok If you set the install pressure correctly. The cam is not meant for 7500 RPM it is designed as a midrange cam with a 6000 rpm HP peak. It will certainly rev over that but will fall off after that. If you are floating the valves that will destroy the valve springs and could pull a valve thru the retainer or bend a pushrod if it comes off the rocker or tappet.

alright, so new springs installed with included shims, not coil bound and factory style rockers should not float and pull until the cam runs out of steam? Just tying to not ruin the motor

 

[ole4]

No that is not correct, if you free rev the engine and hold the throrrle open it will destroy itself. The engine power will fall off after the peak, the peak itself depends on camshaft timing and breathing. If you decide to hold the throttle wide open for 10 miles it depends on your gearing how high it may rev and if it blows itself apart. If you are hitting 7500 RPM driving with a clutch then you are geared wrong for a power peak at 6-6500 RPM. You would need to add a tooth to clutch or remove some from rear wheel sprocket. Ideal would be to have the motor not be able to pull it much over 7K RPM. No when you add ratio rockers your power peak may increase. If you can't measure spring pressure then measure installed height and use the old arc chart for spring pressure @ your installed height. It is not the same as measuring but better than guessing. I hope this makes sense.

 

[ole4]

Rereading your post I see the engine lived a long life hitting hi rpms, so to be clear valvesprings do break. The original 26lb springs were very durable (White stripe) then came a batch that had a bunch of guys reporting early breakage. There were red stripe 37 LB springs and a lot of folks also had springs break and drop a valve. Now folks are using the outer of the dual green stripe springs that depending on install height give mid 30LB spring pressures and seem to hold up well. You may have not had anything wrong but the spring fatigued and broke. Floating the valves a lot will break parts also.

 

[Faolan]

Rereading your post I see the engine lived a long life hitting hi rpms, so to be clear valvesprings do break. The original 26lb springs were very durable (White stripe) then came a batch that had a bunch of guys reporting early breakage. There were red stripe 37 LB springs and a lot of folks also had springs break and drop a valve. Now folks are using the outer of the dual green stripe springs that depending on install height give mid 30LB spring pressures and seem to hold up well. You may have not had anything wrong but the spring fatigued and broke. Floating the valves a lot will break parts also.

I did try going from the 8 tooth clutch to 9 tooth today to try and keep the rpm’s down longer, haven’t had the chance to really wind it out to see a max but did see 6450. I am unsure if I did float the valves or not, I can’t tell??
Clutch setup is the juggernaut with 6 inch driven to a 53 tooth rear on 19” tires. I’ll look into those dual springs too, but on my head, other than ss valves and split retainers and being milled .060 it’s stock including rockers for now. I’m scared to put the 1.3’s back on for fear of breaking a spring.

guess I need to figure how to tell my valves are floating or not and order some spare springs

 

[ole4]

Valve float can show up in different ways. If your springs are too weak when they float the engine will get quieter. Sometimes they will float at a certain rpm but then stop and rpm can still increase because the float rpm excites the resonant frequency of the spring. These usually make a rattle sound.