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Rocker geometry and guide plates

7K views 22 replies 8 participants last post by  Richiehd 
#1 ·
My engine build is going slow but steady.
A few weeks ago I checked my push rods length and got a pretty centered line across my valves, today I wanted to bolt the rocker bolts and guide plates.
I could not get the rockers to center above the valves, they are centered if you look from left to right but are not centered if you look from front to back.


I've attached a couple of pictures of the no.1 cylinder valves and another picture that shows that the guide plate is pushed all the way to the right (back of the engine).
Push rod is touching the head but still turns freely by hand.



Is everything OK ?
Can I build the engine this way or do I have any wrong parts?



Block is stock sbc 350 bored +30
Heads are new DART SHP-180
Rockers are Summit SUM-141506 stamped steel roller tip
Guide plates are Dart's
 

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#2 ·
Need to make sure that the push rod is not rubbing on the head below the guidleplate - your one photo looks like it might be. The solution to your misalignment, from front to back is either adjustable guideplates or cutting the gideplate and rewelding into the proper location.

I had the same issue and ended up having to cut and weld two of the eight plates?????? The next time I will buy adjutable guideplates as I found it both annoying and time consuming.

FWIW, the rocker being not perfectly centered is not a deal breaker, but you need to make sure that the roller is not running off the edge of the valve stem surface and as what I mentioned initally.
 
#6 ·
This build did not start as a budget build, I bought all the parts new and according to my build plan.

I'm aiming at 400HP @ 5000rpm , Don't know if I will get there, but I hope.

Because I do not plan on raving it to more then 5000rpm (truck engine) I did not plan on buying roller tip rockers, but when I got to the stage when I placed the order on summit I saw that their roller tip rockers was getting good recommendation and I figured what the hack…


Replacing them with a new set of true rollers and spending couple of hundreds on something that I will never use (drive at high rpm) is not in my current budget.


If you guys think that this type of offset (as can be seen in the pic) will still run smooth at 5000rpm, than this is the answer I was hoping for.
 
#7 ·
This is pretty typical. You're seeing the sum of all the manufacturing tolerances between the lifter bore in the block to the valve stem in the head. This really shows up on engines running push rod guides to fix this is part of blue printing, that gets muy grande expensive quickly. For RPMs under 6000 without sustaining high RPMs for lengthy periods of time the variation you see is expected and fine to use.

You can conceal this with self guiding rockers which do not use guide plates. Where this type of tolerance build up exists it will be hidden at the valve as the guides will center the roller on the stem but then take up the dimensional variation by slightly leaning the push rod which is why you can't run push rod guides and self aligning rockers at the same time as that will put the valve train into a binding situation.

Full rollers will not correct this situation. This condition is a result of miss alignments between the location of the lifter, rocker stud and valve guide/stem. As I said earlier the correction of this situation is complicated and expensive machining which your neighborhood automotive machine shop is not capable of doing unless it's tooled to build NASCAR cup engines. It is common and unless you’re racing for big bucks is not necessary to correct. If, however, you just can’t live with it the least expensive solution is to remove the push rod guides and replace the rockers with a self guiding type. Keep in mind that if you do this the bosses for the rocker studs were cut to a height that assumes the push rod guide thickness would be there in its place will need to be a washer/shim that retains the original thickness of the removed guide.

Bogie
 
#9 ·
Ok, you all got me thinking again…

As much as I hate reordering parts (takes many weeks to arrive) I guess longer push rods are better.
I'm attaching 3 pictures of 3 sizes of push rods, stock length and then 1 turn longer and 2 turns longer.
The picture with the 1 turn longer push rod looks more centered than the stock length.
Stock length is what I have already ordered and that is was I was planning on putting in.


If you look at all 3 pictures none of them has narrower than 0.06" sweep path.
And all of them has about 0.03" offset from left (front engine) valve tip.
 

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#14 ·
Centered is not correct. If the sweep is wide across the tip of the valve you are loosing lift and wasting motion. Your also wearing out the valve guides quicker.

Just because someone has published something for 40 years doesnt' mean it is correct. Remember the old world was flat
 
#12 ·
It does because of where the radius of where the sweep begins. From 2 oclock to 4 oclock the sweep is small but from 4 o clock to 5 oclock the sweep is big.

Comp Cams and other simplify things too much and the info is poor.

Follow What Welcome to Straub Technologies. . .The Source of Custom Camshafts and Valvetrain says as it a way better way to get a narrow sweep the first time. I hope he doesn't mind a link....

Sometimes due to machining in accuracies a tolerance stack up exists that will prevent perfection. In this case just do the best you reasonably can and you'll still get good results. This kind of thing is important but not critical for you application.
 
#13 ·
rob_isr,
In the first picture you posted it looks as if the guideplates are holding the rockers away from the center of the cylinder, which implies that the guideplate is too wide. A wider angle picture from a top view would identify this.

EricNova has posted many times about cutting and welding the guide plates to eliminate your issue. Do a search to find some older threads identifying the exact issue you have. (I'm surprised that he hasn't posted a response to this already.)

I had the same issue with a set of Profiler heads that came with guide plates. I had to widen one and narrow two others. It was a weird process of tack welding them while the heads were installed on the block, but I did it. I wrapped everything to keep the splatter under control. As I mentioned previously, I'll be using adustable guideplates in the future to resolve this issue.

FWIW, I used Straub's method, that JohnsonGrass linked, on my most recent build and I was able to get my sweep pattern between .060 - .065" on every valve stem on the first try.

Good luck and keep us posted - Jim
 
#16 ·
I think that what the Comp Cams video was trying to get across but it was crappy and missed the point. Sometimes things get so dumbed down that the quality part of the discussion is completely lost entirely.

Centered provides the most metal to metal contact for strength but being narrow as possible is way more important.
 
#20 ·
The style of rocker won't matter as the main aobjective is too prevent the valve from being pushed away or pulled toward the rocker fulcrum in an effort to reduce wear, stability, and maximize the lift.

T@D makes a shaft system that is pretty much the shiz.
 
#21 · (Edited)
I decided to go with a 0.05" longer pushrods, and try to reduce the side misalignment by cutting and welding the guide plates.


Regarding the rocker arm type, there is a short video from Comp Cams that shows when to choose which


https://www.youtube.com/watch?v=fspvbmaWEAE


Definitely not bible type video, but supports my decision for roller stamp steel for Max of 5000 rpm build.
 

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#23 ·
Regarding the rocker arm type, there is a short video from Comp Cams that shows when to choose which


https://www.youtube.com/watch?v=fspvbmaWEAE


Definitely not bible type video, but supports my decision for roller stamp steel for Max of 5000 rpm build.
Its your decision. I ll say it again, I wouldnt use the roller tip rockers. They contribute to high oil temp and the roller tip really does nothing over a stock rocker. See my previous post of discolored rockers with very little time on them.
 
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