valve train pressure

#1
A roller-tip billet arm next to a new billet arm.
The other side of the roller-tip is slightly pooched-out
from the pushrod being that close! 275 lift 1.3 rocker cro-mo pusher 6000rpm 26lb springs IMG_20190104_134216757.jpg
 

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#5
I agree friend. I went to #37's and didn't have any more problems.
Also I suffered from pushrods that were too long. New motor has
364 lift, it gets 37's. The head is milled 075 so I shortened up the
rods accordingly.
 
#7
Well in to the "builder vs assembler" range of cams.

Rocker adjuster nut is .5mm/turn so you can extrapolate the ratio and distance to utilize what I call "negative lash" technique to check coil bind, confirm piston/valve clearance after changing timing, etc. It's a little less math on my bike stuff since the adjuster is at one end of the rocker, but you can get it pretty close.

Or, at least, roll it to max lift and put a big thumb on it to make sure the spring isn't bottomed.
 
#9
Well in to the "builder vs assembler" range of cams.

Rocker adjuster nut is .5mm/turn so you can extrapolate the ratio and distance to utilize what I call "negative lash" technique to check coil bind, confirm piston/valve clearance after changing timing, etc. It's a little less math on my bike stuff since the adjuster is at one end of the rocker, but you can get it pretty close.

Or, at least, roll it to max lift and put a big thumb on it to make sure the spring isn't bottomed.
That is some solid advice right there! I'll have to try that next time.
 
#11
Usually engine builders get the cam at max lift and measure between the coils with feelers. Some clearance is not the same as enough clearance.

"Some" builders use feeler gauges. Others know that at .020/turn, they can squash the sucker flat and know what the actual stack height is.
Of course, they bench checked the spring pressure at the height between retainer and spring seat, that they also measured and adjusted to make seat pressure enough without being wastefully excessive, right? That way the histrionics post-final-assembly are just a double redundant act. And, as an OCD sort, on the bench, check baby check baby one two three four, and $h!t/ LOL
 

delray

Well-Known Member
#12
I agree friend. I went to #37's and didn't have any more problems.
Also I suffered from pushrods that were too long. New motor has
364 lift, it gets 37's. The head is milled 075 so I shortened up the
rods accordingly.
now you say you went with 37 pounds springs? are they a dual springs. most applications if not all when you get into a 364 lift you need a dual spring with the correct retainers and the seat may need cutting too. all this will allow you to have the correct spring height because of all the extra valve travel your now getting with the 1.3 ratio rockers(assuming your using 1.3's) and for most applications you will need about .060 clearance for coil bind. some app's I have seen little less .040 . but .060 seems to be the magic number. that's coming from dyno,arc...etc...
.050 is about the max on milling most heads and anything more you need to start double checking the push rod length. I see you said .075 so that's good your checking that out. also you can start to get into valve to piston clearance problems. that all depends on other things you may have done to it. might be something you will want to double check first...…..
 
#13
Hey delray ,thanks, I've been hanging on every word you and others are
good enough to share and as a result I just might build a strong
and durable motor. It's when I assume I am making the right decision
that gets me in trouble, for example ordering single 37 red stripes
instead of the duals. I'll gladly eat the $8.00 and go with the duals.
Where exactly do I need the .060 clearance? I have calipers now which
I see are essential.

As far as the geometry goes, if the rocker is contacting the lash cap centrally
when half open, is that a good index? Also isn't there something about
a 90* angle?
 

delray

Well-Known Member
#18
coil bind is check with a feeler gauge. now for your geometry goes that can be a loaded question and you could run into couple different problems so you need to check this out. with the mod's you say your doing you could run into the guide plate issues,so you will need a aftermarket plate.
you will need a good rocker arm. you will need to find out if you rocker is traveling correct. if the rocker is not center correct it could bend a push rod and also run into where the rocker could bottom out on travel and breaker a stud. are you going back to the roller tip style rockers again? you don't really want the stock style stamp 1.3 rockers with a 280 cam. you can run them,but you take a chance too with breaking them too. for starters you will want to check your rocker angle and see if the rocker tip(spring side) is just so slightly higher then the push rod end when installed without a load on it. for example a bad angle could come from milling the head and now the head sets closer to the deck and the stock push rod is now trying to push the tip(spring side) of the rocker down.
I think ole4 can also elaborate little more on this...…..
 
#20
To answer you both, I'm going with the billet arms that are not roller-tipped. I
assumed the NR 280/220 was 104 since my Isky 260/220 was 104 LSA. There's
an assumption again.
I don't see that info on NRR, so let's say you are correct here.
I have the billet guide plate and feeler guage, again, exactly where to test for the .060?
Thank-you both for hanging in there with all my questions!
 

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