Questions about 79cc and 212cc valve springs

[FNTPuck]

A lot more than the the max rated pressure goes into changing a valve spring.

You need the correct installed height to prevent coil bind, the proper closed seat pressure to prevent valves from bouncing off the seat(too soft) or eating the cam lobes(too hard), and the proper open pressure to prevent high rpm valve float.

Before changing an unknown spring, you should first measure the installed height while the spring is still in the motor, use a feeler to measure the coil bind clearance while rotating the motor, measure the height when that valve is fully open, then remove the spring and measure the seat pressures both at installed height and compressed height. This will give you the numbers you need to make sure you do not hit coil bind, float the valves, or damage your seats - all of which would cause catastrophic engine damage.

In short: Never just blindly swap springs from one motor to the other. Just because the 212 is a bigger motor doesn't mean the springs are an improvement - if they are the wrong height or seat pressure you will ruin that 79cc.

 

[Will'smotobikes19]

They are shorter uncompressed than 212 don’t have a feeler yet. I believe scottsuki a guy that races 79/99cc said he used 18 lb springs on the other forum. That’s why I thought that.

 

[Will'smotobikes19]

https://motorbicycling.com/threads/79cc-predator-question.59889/

 

[youngchap]

this is the same thing i have been wondering im bought to just order new 18 pound springs maybe i need to know whitch gage to use

 

[5-7HEAVEN]

Google is your friend. Do your research.

You could also test the springs yourself.
It won’t be as accurate as a spring tester.

Firstly, remove the valve cover. Rotate the crankshaft until engine is at Top Dead Center (TDC).
Measure both springs’ height.

Spin the engine until each valve is completely open.
Measure each spring’s height.

Remove both springs.
Compare their thickness and length .
Usually, if there’s a difference, the larger ones have more spring pressure.
A simple “squeeze test” of all the springs between your thumb and forefinger also tells you which ones are stronger.

You could fab a makeshift spring tester.
Secure each spring on a flat surface, maybe with staples or nails
Place weightlifting steel plates onto the spring until it reaches the measured spring height.

If a 10-lb. weight squeezes the spring to the spring height, then that’s the spring rate.

LOL, it’s so much easier just to use the mechanic’s spring tester.

 

[5-7HEAVEN]

this is the same thing i have been wondering im bought to just order new 18 pound springs maybe i need to know whitch gage to use

Remember that if the 212 springs rated at 18lbs.are longer than the 79, they’ll be stronger at the shorter spring height.

It’ll be important to check visually and with a feeler gauge to ensure that the coils are not binding when compressed.

Some go kart vendors sell custom cams for 212 engines. They recommend using stock valve springs up to 6700rpm, and rate them as 10.5lbs.

 

[5-7HEAVEN]

When I installed 18lb. springs on my my 212 engine, I marveled how easy it was to compress the stock 10.5lb. springs, even the 18lb. ones.

This made me realize it’d be very easy to get an incorrect, tighter valve clearance when adjusting them.

I put my finger on the valve spring. Sure enough, when I slid a thicker feeler gauge between the valve and the rocker arm, I could feel the spring compress a tiny bit.

That tightened the valve lash.

So be very careful setting your valve clearance.

 

[Frogslayer]

you can not use the valve springs from a 212 in a 79cc. The size is not correct. You will bend a cam shaft or push rod period. The 79cc comes with 8 pound springs. Anything over 12lb anyhow would be so hard to pull start it would be moronic to even try it. You would be fixing strings every 10 starts. 212 springs 22 pound ones* yeah same deal that is why they start it with a butterfly starter! You can buy 12LB springs for a 79cc. They do make them cause I have a set in mine currently. Had to after I tore out my Governor cause of valve floating.


My past reply some place on this board:

• Mar 14, 2021
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• #18

Okay I'm kind of lost? Are we talking about a 212cc? or a 79cc? 212 comes with 10 pound springs. People put 18lb to stop valve float without a governor in. 22lb is more of a higher end know what your doing with the motor mods you did kind of thing and need them as a result. 78.5cc lifan, 79cc pred, 120cc honda all have 8lb springs. Honda springs are 4mm longer not useable in the other two, the 212cc springs are the same length as120cc engine wrong dia. 78.5/79cc engines. Lifan 78.5cc and 79cc are identical. 12 pound springs is the normal one used to stop valve float over 4500rpm. No other springs known to match these motors correctly on the mainstream market. Only 3 sellers that have them online. Hope that helps! If your springs are to strong they will eat into everything and wear stuff out faster. To soft they will slap around and stuff will wear as well pretty fast. Either way wrong length springs will cause even worse damage! Can bend cam and push rods easy to long with a binding effect from spring compression. To short the valve will slap and cause metal fatigue. This is not like everything else you see o youtube fixed by jb weld and an idiot with dermal lol. End result is if your running either at 5k rpm you got alot more worries then valve springs.

I can't believe all that work to turn 5k! Should have got a China Girl lol

 

[Street Ryderz]

Well I do have other builds..... Didn't want another 2 stroke. everyone talks like 5k is bad lol! You realize your transmission at 10,000rpm in your 2 stroke is 15 to 1 output. Your only putting 666rpm to your back wheel motor sprocket. From that point it goes to the wheel sprocket, then that is cut down even more. My build has a 1 to 3 trans and 1 to 3.2 to back sprocket ratio. Either way @ 3000 rpm you can cruse at 40mph with easy ride vs shaking your brains out full throttle on 2 stroke. end result is worth the time i guess if you actually try one. everyone knocks the 4 strokes but they do have a lot nicer ride then 2 stroke. don't get me wrong love my two strokes and after massive time they run very smooth now even full open little vibration. either way its a hobby!

Since when is the china girls 4:1 ratio considered as 15:1 and how do you explain the speeds we get if at 10k there is only 666 rpm available before the drive ratio? LOL I have 896 rpm at the wheel and 10k this guy is whack, A 79cc predator stock valve spring is 10.8 lbs NOT 8lbs and upgrades are 18 and 22 at the installed height, buy a spring gauge or have a shop check them and I've never seen a 12lb spring for any one of the engines you list!