Plastic bit behind cam gear adapter?

#1

I’m going through the process of getting stuff out of the way so that I can slide my rocker shaft out the front of the head in order to change a broken rocker. Never done it before, but following a writeup that ctbimmer did, and it seems straightforward.

It looks like I need to pull of the cam gear adapter in order to get the plastic bit behind it out of the way, so that the shaft can slide through the spaces in the cam sprocket.

Question is, do I need to put that plastic bit back when I’m done? Does it serve any purpose? Seems like if I ever have to do this in the paddock, it would be nice for it to just not be there.

Here’s what I’m talking about:

#2

I’ve heard:
Keeps electrical interference from the distributor cap.
Keeps random sparks relegated to distributor cap.
Helps protect timing belt from debris.
Helps protect distributor cap from debris.
Personally I think the last one is correct but it’s enough for me just to leave it in. It’s no big deal to r/r.

#3

[quote=“bedmonds” post=82490]I’ve heard:
Keeps electrical interference from the distributor cap.
Keeps random sparks relegated to distributor cap.
Helps protect timing belt from debris.
Helps protect distributor cap from debris.
Personally I think the last one is correct but it’s enough for me just to leave it in. It’s no big deal to r/r.[/quote]

Cool, thanks Brian!

#4

Bust it out with a hammer and don’t look back.
Not needed. You can get things to line up and the rocker shaft will slide through your newly created passageway.

RP

#5

[quote=“Patton” post=82494]Bust it out with a hammer and don’t look back.
Not needed. You can get things to line up and the rocker shaft will slide through your newly created passageway.

RP[/quote]

I like this answer, as I can’t find my Torx sockets right now anyway.

#6

You’ll need to purchase Chuck Taylor a beer or two for the write-up that will save you sooooo much time and money.

RP

#7

[quote=“Patton” post=82503]You’ll need to purchase Chuck Taylor a beer or two for the write-up that will save you sooooo much time and money.

RP[/quote]

Gladly!

#8

Julian, add to your list:

After you perfect the R/R, you’ll need to teach the next guy how-to.

Tip: rotate the cam, as best you can, off of the valves that you are removing. Call people if you need help.

#9

[quote=“Patton” post=82506]Julian, add to your list:

After you perfect the R/R, you’ll need to teach the next guy how-to.

Tip: rotate the cam, as best you can, off of the valves that you are removing. Call people if you need help.[/quote]

Yeah, I think I’m going to need some help. I’ve got everything torn down and ready, and conceptually I get it. What I’m not clear on is where to actually park the rockers. There just doesn’t seem to be any room. I’m not sure where this “neutral zone” is supposed to be, as the intake and exhaust cam lobes are so close together. I’ll take another look at it tonight. I’m sure I’m just being an idiot.

#10

There isn’t a totally neutral zone. Just loosen all the eccentric nuts and scoot the rockers on the exiting shaft to-and-fro off the cam lobes as best you can.

Go slow and watch everything carefully. What you want to avoid is binding up the edge of a rocker foot and the side of a cam lobe.

Good. “Hey, that rocker is going to try to bind up on the lobe the next couple of times I bonk on this retaining shaft.”

Bad. “Damn. This rocker is all kinds of bound up on this lobe. Shit.”

See the problem coming.

#11

I think the size of the parking lots may vary a bit from valve to valve, or perhaps from intake side to exhaust. The fastest I ever did it, with 2 excellent helpers (actually I might have been more of a helper than the brains) was 30 minutes on a hot motor between races. And, it was a middle (3-4) rocker that broke.

However at Nats last September I was trying to help my neighbor, and my boasts of “it’s easy”, with me as brains, took quite a bit longer, we could not completely remove all the rocker pressure on the shaft, but we did get it done. Still better than pulling a head or knocking a hole in firewall to go backwards.

#12

OK, so I finally figured out the parked rocker thing after getting some sleep and then staring at it for a while. It helped that I could move the intake rockers over a bit to make room to get the exhaust rocker off the valve. Here I parked the #2 and #4 exhaust rockers:

Although, I tried everything I could to get some leverage on the rocker shaft, and could only manage to move it about 1/8". I wound up “cheating” and just putting a small hole in the firewall. I’ve got everything removed in the interior anyway, so this was really no big deal. Bonus is that I can go either way with the shaft now, depending on which rocker gets broken.

The bad news is that I’ve got not one but two broken rockers. The #1 and #5 exhaust rockers had broken pads:

So, I’m guessing this was probably the result of an over-rev. (I remember having a small one a few races back, but didn’t seem like there were any resulting issues at the time.) I guess next step is to pull the head and see what the valves look like?

#13

I’d go for hope for the best mode. Maybe your valves are still straight. You can replace the rockers and do a compression test. If that turns out ok, you dodged the bullet and your valves are probably straight. I don’t have a lot of experience with over-revs, but it’s easier for me to imagine a scenario where the left rocker failed months ago and the right rocker failed recently, then it is an over-rev cause your valves to hit pistons. Just because your engine goes a bit high on rpms, doesn’t change the basic timing of valves pull up and away before pistons go up. An over rev puts a lot of stress on rockers and they can break. My perception is that the rocker breaking from the additional stress of the over rev is more likely then the valve being slow to lift because of float, and getting whacked by a piston and therefore bending the valve.

Also, when a good rocker breaks, it usually breaks by the eccentric. Pads coming off like that isn’t an obvious symptom of rpms going too high.

Rich Bratton needs to weigh in on this. He’s got more experience with this than I do. I’ll give him a holler. Robert Patton and Chuck Taylor might have good input also.

#14

On the black plastic thing you have two easy options.

  1. Take Robert’s approach and just bust it out. It has an outer ring that will break off smoothly and allow enough room for the rocker shafts to come out. I’ve never dyno tested with and without, but don’t believe you’ll see any performance impacts. I think it’s really just a dust and water shield.

  2. Remove the cam gear bolt, remove the black plastic piece, install the cam gear bolt without the plastic piece and do your work. Replace the plastic piece as you complete the job and torque the bolt to 55 ftlbs (I think). The cam gear will not come accidently come off with removal of the bolt, but you should at least hand tighten the bolt before turning the engine just to be safe.

I have never seen OEM or Febi rocker arms fail in that fashion. Like Scott said,rocker arms normally break at the fork on the eccentric side. Most failures are a result of over revving the engine or weak valve springs. Either condition can create a situation where the rocker arm doesn’t follow the cam as it should, the valve to stay open too long, the valve to impact a piston then impact the rocker arm, and cause a failure.

The rocker arm pad failing makes me suspect you have an oiling issue in your cylinder head. After you replace the rocker arms, and before you install the valve cover, start your engine and make sure there is oil dripping from the spray bar at low engine speeds. Pay attention to orientation during the installation of the rocker shafts too; the oiling holes must be lined up.

Is there any visible cam wear on the cylinders that failed? Cams that show any wear on the lobe tips need to be replaced.

For good measure, you should check all over your valve springs and pay particular attention to the cylinders that fail. Check visually for corrosion, pitting, cracking or fracture; any with visible issues should be replaced. Also check for weak springs. This is easy to do with a large screw driver by just pressing down on spring hat. With the valve fully seated (closed), it should take 68lbs of pressure to crack the valve open. If you have a weak spring, you’ll be able to feel it in comparison to the others.

Like Scott said, I would not pull the head unless you need to replace springs or you have low compression on one or more cylinders.

#15

Thanks, Rich! The black plastic piece is long gone now. (Wish I could rename the thread!)

I’ll do as you suggest and after inspecting the cam lobes and springs, I’ll replace the rockers and idle the engine with the valve cover still removed. Never done this, so not sure how much oil I should expect to see, but presume that a steady drip at idle speed is sufficient?

I’m hoping not to pull the head, but depending on the results of the dyno testing I’m planning to do, a head refresh might not be a bad idea anyway. I know this engine has had the bottom end refreshed by the PO, but nothing in the head has been refreshed.

Thanks!

#16

What do you want the thread title to be?

#17

Something more useful to people who may be searching later. Maybe something like “Questions about replacing broken rocker arms” or something like that. Thanks Ranger.

#18

Muahahahaha…

https://www.youtube.com/watch?v=amzp5MPfuyc