402 and valve float at 6300
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TECH Apprentice
Joined: Aug 2009
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From: NB Canada
402 and valve float at 6300 i have a 402 with 236-242 cam with .650 lift with my 1.8 crane cam rockers adjustable kit, heads are patiot stage 3, 2.08int and 1.6ext valves, patriot dual gold springs. built 3 years ago and have about 20 000 miles on it, when dynoed new my graph took a dive after 6300 rpm. figured it was either my ls6 intake,t/b,maf or 3''exauste that was restricting me, but this year i changed to 102 fast intake and t/b, 100mafect and 4'' exaust, diferent tune and making more power but still dyno graph is taking a dive at 6300, feels like revlimiter, is it my rockers 1.8 to much with my cam for the springs, should i change the springs or the springs and back to 1.7 roler alum. rockers
Sounds like you've got a pretty heavy combo of valvetrain parts, and a relatively weak spring with some miles on it with that big lift. You could likely remedy it with a new/stronger spring, but you'd also benefit from lightening that valvetrain combo some too!
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Thread Starter
TECH Apprentice
Joined: Aug 2009
Posts: 389
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From: NB Canada
the cam is something like .614 lift with 1,7 rockers, i had my 1.8 crane rockers almost new when i built the 402, that is why i used them on that cam. gave me .650 lift. since dyno graph has been nose diving when the springs were new, what springs would i need and would bolt right in(other than mesuring inst. height , would like to keep the 1.8 rockers since i paid like 900 for the kit and my valve train is adjustable. thanks
you dont need the 1.8 rockers with that big of a cam its to aggressive and has to high of a ramp rate most likely causing your valve float problem if you want to keep the 1.8 rockers get a cam with less lift but i think you will be better off to just go to a set of 1.7 rockers
Springs with more load isnt the answer, the problem is your rockers are heavy.
1. Your on a lobe designed for 1.7 rockers, most likely fairly aggresive.
2. Your rocker arms have a roller tip = weight right where you do not want it = valve float
3. Crane rockers often come with "quick lift". When you start with a lobe thats aggresive for 1.7s, and add 1.8s it becomes more aggressive. Then if "quick lift" its the third strike.
How are your springs setup?
1. Your on a lobe designed for 1.7 rockers, most likely fairly aggresive.
2. Your rocker arms have a roller tip = weight right where you do not want it = valve float
3. Crane rockers often come with "quick lift". When you start with a lobe thats aggresive for 1.7s, and add 1.8s it becomes more aggressive. Then if "quick lift" its the third strike.
How are your springs setup?
Thread Starter
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Joined: Aug 2009
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From: NB Canada
you are right about the quick lift built in the rockers that i have, i was affraid that was the probleme, combined with my semi- agressve cam the springs could not handle it since new, my plans is t put 1.7 crane rockers to match the adjustable kit i have and a set of springs to handle them. any recomendation on a set of springs, would like to keep my retainers and locks.
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The 1.8 rockers are heavy as stated. The crane rockers are by far the worst on the market in this aspect. Also, there is no need for any 1.8 rockers on that large of a cam. They can have some added benefits on a stock...ish cam but nothing to justify the cost.
Do the basics first...
Remove the 1.8 rockers and sell.
Check and verify spring pressures.
Re assemble with stock upgraded rockers and go from there.
Do the basics first...
Remove the 1.8 rockers and sell.
Check and verify spring pressures.
Re assemble with stock upgraded rockers and go from there.
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TECH Apprentice
Joined: Aug 2009
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From: NB Canada
can i up grade my stock rockers (trunion kit)and use with my screw in studs, guide plates and push rods(not sure if they are the stock lenght only because of the kit, not that i ordered longer or shorter) that i have that came with the kit, since i am there i want to change the springs if good or not, they have 20000 miles on them anyway
Sell everything with the kit. Guide plates will be useless as the stock pedestals align the rockers, the screw in studs won't be needed, and the 7.5 push rods will be too long that come with the kit.
Upgrade your stock rockers, get the correct length push rods and change your springs if they already have 20k miles on them...let it eat
Upgrade your stock rockers, get the correct length push rods and change your springs if they already have 20k miles on them...let it eat
Thread Starter
TECH Apprentice
Joined: Aug 2009
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From: NB Canada
i would like to keep the adjustable valve train and not have to figure out the perfect lenght pushrods, will go with the 1.7 crane, any body have a sugestion on springs that will go right into place of my dual gold?
Don't go with stock rockers with trunion upgrade I have used several sets and they wear the trunion and bearings very fast at 8k the bearing came apart and the trunion had a .020 grove wore in it go with a good set of aftermarket 1.7 rockers I don't think u will have valve float problems I am running a set of harland sharp rockers pull to 6800 rev limiter with a cam very close to you lift and never had a float problem
Unless you have a solid roller, there is no reason to have adjustable rockers, barring a few rare setups. However, if your dead set on keeping it adjustable, spend the money and get a good set like t&d's or jessel. The crane rockers in any ratio are junk.
The stock trunion upgraded rockers are perfect for 95% of builds. Sounds like you just had some bad luck. There is absolutely nothing wrong with them.
The stock trunion upgraded rockers are perfect for 95% of builds. Sounds like you just had some bad luck. There is absolutely nothing wrong with them.
stock rocker are fine for most builds but i dare some on the people that have ran them for 10k miles to take the off and press out the trunion and inspect the bearings and the shaft i bet they aint holding up as well as everyone thinks, as far as springs dont trust that they will last more then 20k check them every year or 10k whatever comes first i had a set that i was told would last 40k with my cam two broke at 14k and the still had .075 lift left to be to what they were rated at
If you really want to keep the setup you have you can, but your going to need some very nice lifters and some big pressures. Probably at least 180 on the seat and close to 500 over the nose if not more.