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Author Topic: Rocker geometry questions  (Read 1602 times)
baz
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« on: June 04, 2017, 20:50:26 PM »

I've been getting my rockers set up over the weekend. I still haven't got my barrels back yet so I'm just working on centring each of the rockers on the valves for now.

I had to push everything left on head 1+2,  I'm left with no shims between the solid spacer on the shaft in one location, and again against one mounting block.

I was thinking I'd have the solid spacer trimmed down on that end to give clearance for shims and side play.

I'll have the block machined down also.

This is where I'm unsure which way to go, is it any advantage to have multiple shims in each location over a single shim?

If it is better I will have enough material removed to fit a stack of 3 shims instead of 1.

Hope I can get some advice on this, it's my first time ever working with rockers so my experience is zero Wink
« Last Edit: June 19, 2017, 11:33:34 AM by baz » Logged
baz
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« Reply #1 on: June 05, 2017, 09:49:47 AM »

How do these look?  I have all 4 rockers on head 1+2 centred the same as this. The more I read on this topic the more confused I get, I'm hearing centre the rocker and I'm hearing have it slightly off centre.


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Jim Ratto
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« Reply #2 on: June 05, 2017, 18:44:13 PM »

I try to align the rocker pad squarely over the lash cap, and get end play set to "feel". It takes a few attempts to get all four rockers' end play set where there is no perceptible end play, but still move freely on shaft. You need to have the head torqued down to check this, as the rocker stands "take a set" after the heads are torqued (so if you get everything set on the bench, then install heads and end up with tight rockers, this is why). I use a big piece of junk granite, WD40 and 400 wet dry and sand sides of rocker stands and end caps until everything is the way I want it. Sometimes the shims they send you have burrs or raised edges from stamping them out, so watch for this and dress any edges down.

Good luck and have fun

Jim
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baz
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« Reply #3 on: June 05, 2017, 19:33:13 PM »

I try to align the rocker pad squarely over the lash cap, and get end play set to "feel". It takes a few attempts to get all four rockers' end play set where there is no perceptible end play, but still move freely on shaft. You need to have the head torqued down to check this, as the rocker stands "take a set" after the heads are torqued (so if you get everything set on the bench, then install heads and end up with tight rockers, this is why). I use a big piece of junk granite, WD40 and 400 wet dry and sand sides of rocker stands and end caps until everything is the way I want it. Sometimes the shims they send you have burrs or raised edges from stamping them out, so watch for this and dress any edges down.

Good luck and have fun

Jim

Hi Jim thanks for that. So by square I want them centred on lash caps?  

I'm sorry for the dumb questions, I'm reading too much and thinking too much about these small details. I can't help it though, I spent my life reading but this is my first time doing!  Everything I read says make everything as good as you can,  that's what I'm trying to do,  it's easy to get things right now and not be crying later on Wink

Point noted on having the heads bolted down first. I was just trying to see where I may need machining so I can get those parts off to my machinist.

I've gone through the full stack of shims that came with the Scat rockers, they were all in or around. 030 before I sanded them flat, they're all in or around. 020 now and nice and flat.
« Last Edit: June 05, 2017, 19:38:34 PM by baz » Logged
Martin S.
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« Reply #4 on: June 05, 2017, 21:29:43 PM »

That tightness when bolted up is because the heads are not square to the crank. In a perfect world, that wouldn't happen. My engine didn't do that  Wink
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Martin S.
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« Reply #5 on: June 06, 2017, 01:24:07 AM »

Here's a video I made with Steve explaining the machine work that went into building my engine and why it is "worth it" to do so. https://m.youtube.com/watch?list=PLDI904iuOabMy11qRAy6WyvyA4akJdhcL&v=MoJFWVyYAt0
« Last Edit: June 06, 2017, 01:31:19 AM by Martin S. » Logged

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Fiatdude
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« Reply #6 on: June 06, 2017, 04:01:52 AM »

After talking to Mario at Pauter, I'm in the camp of not being centered over the valves....
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Clatter
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« Reply #7 on: June 13, 2017, 06:46:24 AM »

I was always taught to make sure to not be centered to promote valve rotation..

While a type 4 can have .002 or so side-play, and keep that for miles,
Not so with a type 1.
Because the pushrods are not square to the lifters and rockers on a type 1,
There is a lot of thrust-loading.
IME, the end-play on the shafts will open up after use.
Like Jim R, I have gone for 'tight as possible, but free' a.k.a. loose zero.
The more oil pressure you can build at the rocker shaft the better..

This must be right with everything torgued for sure.
When things get tight like that, you really see the numbers change..
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baz
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« Reply #8 on: June 15, 2017, 17:22:29 PM »

More rocker questions,  I'm trying to work out how to get this push rod and adjuster screw more in line at half lift.

I think I need to have the blocks machined down a millimetre or so to get a nice 90 degree angle between the rocker scuff and the lash cap. I'm not sure how this will effect the push rod / adjuster screw side.

Sorry it's not a great pic but this is where I'm at with half lift, I swapped a Scat lash cap for a taller Cb one and it helps get me closer to a good angle on the valve side,  still needs more hence needing the blocks trimmed





Edit. After reading my own post and looking at the pic I can see how the adjuster end will align better once the blocks have been trimmed as that will push the tip higher.

« Last Edit: June 15, 2017, 18:30:00 PM by baz » Logged
baz
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« Reply #9 on: June 15, 2017, 19:05:39 PM »

So I stuck 2mm worth of feeler gauges between the rocker and lash cap, if my valves were 2mm longer I'd have perfect geometry on both the valve and adjuster.  Would this equate to 2mm taken off the blocks? 

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richie
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« Reply #10 on: June 17, 2017, 08:08:03 AM »

More rocker questions,  I'm trying to work out how to get this push rod and adjuster screw more in line at half lift.

I think I need to have the blocks machined down a millimetre or so to get a nice 90 degree angle between the rocker scuff and the lash cap. I'm not sure how this will effect the push rod / adjuster screw side.

Sorry it's not a great pic but this is where I'm at with half lift, I swapped a Scat lash cap for a taller Cb one and it helps get me closer to a good angle on the valve side,  still needs more hence needing the blocks trimmed





Edit. After reading my own post and looking at the pic I can see how the adjuster end will align better once the blocks have been trimmed as that will push the tip higher.



Baz,

How are you measuring lift? I don't see a dial indicator there? and are you using adjustable pushrod? Also you need to wind the adjuster screw out about 3 turns before starting to get oil feed holes aligned and make sure you have some adjustment in future if needed. You seem to be focusing on rocker to valve instead of pushrod angle to adjuster screw?
If you cut blocks down then it will make adjuster to pushrod angle worse in my opinion.

A closer picture of pushrod to adjuster screw at half lift would help show how close or not you are

cheers Richie

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baz
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« Reply #11 on: June 17, 2017, 09:40:56 AM »

Hi richie that first pic I posted was taken after I started messing about with the adjuster screw just to see how it changed angles. In the second pic where I have the feeler gauges in there I have the adjuster screw 2.5  turns out and an adjustable push rod. Second pic seems to me to give good angles on the push rod side and the valve side

I'm at work but I'll be in the shed later today I'll get better pics then

Cheers
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baz
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« Reply #12 on: June 19, 2017, 11:33:11 AM »

Got some pics.

Zero lift,  adjuster 3 turns out.




Half lift



Full lift,  13.9mm



Now with 2.1mm of feeler gauges

Zero lift



Half lift



Full lift


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fish
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« Reply #13 on: June 19, 2017, 17:04:55 PM »


Like Ritchie said, make sure your oil holes are lined up irrespective of how many turns out, not all are created equal.

Before you start machining, install 2mm rocker block shims, try all scenarios including thicker lash caps, extended pushrod, etc.

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Dougy Dee
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« Reply #14 on: June 19, 2017, 17:22:19 PM »

What does your wipe pattern across the lash caps look like?
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Martin S.
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« Reply #15 on: June 19, 2017, 22:46:18 PM »

How do you check the wipe pattern Doug?
If the goal is to get the adjusting bolt inline with the pushrod at half lift, the second scenario clearly looks better.
What's the difference between shimming up the rocker vs. shortening the pushrod? Both of those would do the same thing, but how are they different?
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Jim Ratto
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« Reply #16 on: June 19, 2017, 23:29:30 PM »

you want to establish where the rocker assembly is on the head, without worrying about pushrod length. You can do this easily on the engine or on the bench. You need to dial what your real lift is before you do this, with the springs you're going to use. Light checking springs are needed, but not for checking real lift. You'll get weird numbers.

Let's say you dial indicate real lift @ approx. 0.560" (once you get your geometry set, it's going to change some, probably a minimal amount). Half of 0.560 = 0.280

Assemble a valve up with a light checking spring (again- you've already found actual lift)
Bolt your rocker assembly to the head with no shims, but with whatever lash caps you're going to use (make sure they're seated on valve stem and not held up on keepers)
Mount dial indicator with 0.040-.050" preload so it contacts retainer.
By hand, open valve with rocker arm to half lift (0.280" in our pretend world here)
Look at rocker arm pad. Ideally it will have center of curved pad, in center of lash cap. If it does, awesome. But not likely. You can take a felt tip marker or Dykem and color the lash cap and look for the pattern. I mark the side of the pad at zero lift, half lift and full lift and see where they are on the rocker pad contact.
Then, to get the contact points where you want them, you may have to raise the rocker off the head stands with shims, this depends on rocker brand, valve job, retainer, lash cap thickness and a combination of all of this. That's why you're probably going to have to shim rockers some, to get it right. The company making the rockers can't see the future and know where your seats are cut, what backside of valve is cut like, which retainers you're running, etc.
Once you've shimmed the rocker (if needed) off the head then put your adjusting screw where you want it. I like to leave a few threads for adjustment later, but not sink the screw towards the pushrod too much, or it can break at high rpm. I look for 2-3 threads above tightened lock nut. That's not a rule though.
Then, once you heads are torqued to spec, and rockers are torqued to heads, with lash caps on, you can use your adjustable pushrod tool to determine what needs to bridge the gulf between the lifter cup in the short block and the adjusting screw. Do not use the pushrod to determine or change your geometry.
BTW I do all of this before any of the motor goes together.

Good luck,
Jim R.
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Martin S.
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« Reply #17 on: June 20, 2017, 01:51:43 AM »

That's great, thanks Jim. Reminds me of the Berg writing / instructions.  Btw, do you know any source of those online? I have the book somewhere.  Roll Eyes
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Cal Look white 68 Bug with AJ Sims EFI Turbo 2332. 194hp 240tq @ 5500 rpm 3psi boost.
richie
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« Reply #18 on: June 20, 2017, 06:29:41 AM »

One I did last weekend, using Scat 1.4/1 Pro rockers, no shims, adjuster screw out 3 turns, 043 VW style head casting, FK8 cam, half lift[ total lift measured 0.535]
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richie
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« Reply #19 on: June 20, 2017, 06:38:30 AM »

What's the difference between shimming up the rocker vs. shortening the pushrod? Both of those would do the same thing, but how are they different?

No they don't do same thing, shimming up rocker away from head affects geometry, wipe pattern, lift and pushrod to adjuster screw angle as you change angle of pivot of rocker to valve.

Changing pushrod length does none of these things as relationship between rocker/ head and valve doesn't change, you just have to wind adjuster screw in or out to compensate, think of adjuster screw as extension of pushrod length
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baz
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« Reply #20 on: June 20, 2017, 09:50:46 AM »

Looking at how my adjuster screw to push rod alignment changes by stacking the top of valve by 2mm, it seems to me if I raised the rocker blocks I'd have worse alignment than in the pics without the 2mm of feeler gauges.

Ive read a few topics where folk had to loose some height off the blocks using Scat rockers. One guy used longer valves,  if he was using standard valves he needed trim 2.5mm from the blocks
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