Shinobi'sZ

I have a broken valve spring..REV 1116. REV has since changed the part number and claimed that they didn't have the correct installed height originally and that a shim would be need..which subsequently means a longer valve is needed. I don't know why it broke though..didn't really over rev the motor. Even at the wrong installed height they have worked for sometime now. I am wondering if I should just replace them all? Probably huh.

Is the best way to measure Piston to Valve clearance by the installed height?

Why would a valve spring break without excessive rpm?
I only went up to 6000rpms.

Thanks

cyphur

iTrader: (10)

well the incorrect installed height is prolly the root cause. that'll throw your **** off a lot more than you think. swap them all out for some springs you can install CORRECTLY and not worry about it. ****.....looking at your list of toys a set of springs shouldn't be a huge expense for ya

zo6vetteman2003

iTrader: (1)

The shims are needed to give you the proper valvetrain geometry. There are so many different vendors out there that have their own specifications on valvesprings, plus their customers are milling heads and other modifications to throw of standard valvespring heights. So, shims are used to raise the spring height incrementally, so that the rockers and valvesprings are within manufacturer's tolerances. I don't think that is the reason for a broken valvespring, but gives you something to think about when you are doing the reinstallation.
Using pladoh between a piston and valves, turning the motor over by hand, removing the head and measuring the distance of the valves and the piston impregnated on the playdoh is a way to check the clearence. You might want to use a micrometer to measure with to be very accurate.

PREDATOR-Z

yeap, replace all of them.

pdd

iTrader: (3)

id replace all of them too

mrr23

iTrader: (3)

just because shims are needed doesn't mean you need longer valves. don't know who told you that one.

shims aren't use to raise height or to set valvetrain geometry. they are used to lower spring height and to get proper spring seat pressure. valvetrain geometry has to do with pushrod length and valve stem length. putting a shim under the valve spring and head shortens the overall installed height of the valve spring. installed height is measure from the spring seat pocket in the head to the bottom of the retainer when attached to the valve.

for instance, spring calls for 1.750" installed height. now, you put the valve in the head and attach a retainer to it with the valve locks. with various tools you can measure the distance from the spring pocket to the bottom of the retainer. say this is 1.800" you subract 1.800" - 1.750" = .050". that will be the amount of shim needed to get the proper spring height. which should get you the proper spring seat.

this does not change the height of the valve stem retainer. because of the length of the valve. so, shimming doesn't change valvetrain geometry. what changes that is length of valve, milling of heads, decking the block, pushrod length and lifter height.

Shinobi'sZ

Well this is whats got me concerned. I had the heads cleaned up and it is the second time I have had work done. So they have a combined (re-worked 2x) milling of .010" (.005" per re-condition). When I had my short block built up, the block was decked and with 6.125" rods and 3.905" Diamond Pistons, my deck height ends up being .014 (vs stock .007"). However, my pistions have -2cc Valve Reliefs in them, and my cam is only a .581 lift, so I don't think there is a piston to valve clearance problem. But with the deck height at .014 and my heads milled .010" what installed height should the new springs be?

Thanks

mrr23

iTrader: (3)

ok you must have missed what i said. all the milling and decking has absolutely ZERO to do with installed height of the spring. look at what the cam needs for seat and open pressure. then you buy a spring with that parameter and set them up according to what the spring manufacturer tells you. i prefer to use the springs that the cam manufacturer says to use. if you have a comp cam, use comp springs. if you have a crane cam, use crane springs. that way there is no issues with spring rates, harmonics and everything else that goes with it. they designed it, they know what to put with it.

all that decking and milling has to do with what pushrod length you'll end up needing to get the rocker to sit in the middle of the valve stem and no fall off of it during movement through full lift. basically, you want the pushrod to intersect with the rocker at a 90* angle. same with the valve stem and rocker. then turn one full revolution to make sure the tip stays on the valve stem and no run off the edge. to make sure of correct length you assemble the motor and use an adjustable pushrod to get the correct length. then buy those.

Shinobi'sZ

Yes I missed it, I am just getting over the flu and am not comprehending everything as well yet. So afer reading your last response, I thought about one more thing. I went with a .065" Cometic head gasket vs. the stock .054" GM MLS gasket. I am using Comp Pushrods in stock length...will the extra .011" thickness of the cometic, should I have got longer pushrods??

mrr23

iTrader: (3)

considering there was .010" taken off the heads, no.

.054" + stock head deck = .054"

.065" - .010" taken off heads = .055"

cyphur

iTrader: (10)

no....generally you switch pushrods after ~.030 of millwork or more. even with .010 of cleanup work, you should be alright.

Shinobi'sZ

I know this isn't related to pushrod length but it maybe to something else critical I need to know. My deck height is .014" out of the hole. This was due to using 6.125" rods, Diamond 3.905" pistons (-2cc) valve reliefs, and a .005" clean up on the block. I think stock LSx deck height ranges from .007"-.010" out of the hole.

Thanks again.

mrr23

iTrader: (3)

this will have to do with compression and piston to valve clearance issues.

this is what you have for quench area: .065" - .014" = .051" quench area. most area saying to look for .035" - .041" area. this helps to prevent detonation. in doing the heads on the wife's car, we used a .042" mr gasket head gasket. so, i have .042" - .007" = .035" quench area.

but you may need the added thickness if you are looking for a certain compression ratio. what did diamond say the compression ratio with those pistons would be with certain chamber sizes and gasket thickness?

Shinobi'sZ

For FI it was my understanding that having a little more quench would not hurt.
Here are my specs though
bore size 3.905
stroke 3.622
cc 77
pistons -2cc
deck .014 out
head gas .065

Hell a stock LSx has .047" quench area if you subtract the deck height from the head gasket thickness. I didn't have any detonation with 15* of timing and 12lbs of boost.

I calc'd my CR at about 8.8:1. If I used the stock MLS gaskets it would be about 9.2:1

mrr23

iTrader: (3)

well you want to end up with whatever compression ratio you need to accomplish your goals with. with you running 2 turbos, i wouldn't go past 9:1 personally. but again, the thicker the head gasket, the more prone to detonation you can have. most engine builders would use a thinner gasket and bigger cc chambers in the heads. or small chambers, thin gasket and deeper dished pistons, to me, would be the best case scenario. you want the fuel mixture as close to the piston as possible. that way the time spent burning the fuel mixture isn't wasted in the head area. the closer to the piston it is, the more it'll start pushing the piston down on the power stroke.

remember this is just my opinion. i'd consult your engine builder or some other well known FI guys, like lingenfelter, to make sure you get this done right the first time.