Rocker slipping

[bullzed]

Hey guys,

 

today dad and I took the Z out for a run to see if we could clear what seemed to be a semi-blocked jet in the SU's. It'd been coughing and losing power on and off and we didn't know what was the problem. This all occurred after dad plugged a pinhole in the gas tank and had to drain it, we think some debris got into the fuel line.

 

Anyways, just as we were coming home, something went badly wrong, the car sounded like it was running on 5 cylinders and there was a bad knock. We got home, pulled off the rocker cover and found out that one of the rockers had slipped off the valve stem and wasn't pushing it properly. We put it back on and checked the valve clearances and thought it was fixed, then we took it for a spin and it happened again. We're not sure what the problem could be, dad thinks the rocker itself may be rooted.

 

Have any of you guys had any experience with this problem or heard of it? Much thanks in advance

 

[Enzo]

Hello,

      Have a look at the lash pad that sits on top of the valve inside the spring retainer. If one of the sides has broken off the rocker can slide off.

David.

[bullzed]

I recall the lash pad being in perfect condition, the lash pad rotates and the rocker rides on-top of that. This means the valve never closes and it then opens further.

 

I have no idea how it jumps out of the retainer, with dual valve springs i don't see the valve sticking.

[Enzo]

Hello Bullzed,

                With the rocker arm in place the lash pad cannot rotate because the ears locate the rocker in position.

David.

[bullzed]

Hi David,

 

That's the thing, it DOES rotate. Somehow, the rocker comes out of the pad, the pad is given time to rotate and the rocker then comes down on it without seating. Any idea how this happens? I can take a picture of it tomorrow if you would like?

[Scoota G]

Photo good, he's right. No lash pad rotation is possible.

[PZG302]

From your description the lash pad is either broken or in the sump. The lash pad will retain the rocker and the two together won't let the lash pad spin. Sounds like you haven't got a lash pad there. One of my old race motors used to spit rockers out if I buzzed the engine over 7500rpm on a down change. It was generally number 5 exhaust and the lash pad would be spat out and drop down the back of the head into the sump. I used to keep half a dozen lash pads on the race kit for this problem.

[bullzed]

Okay, so I took the valve cover off again and this time, it was a different valve. The rocker had jumped up onto the right ear of the lash pad, all of the lash pads are undamaged and I really have no idea why or how the rockers are jumping on top of them.

 

This one occurred when we started the car, anyone have any ideas about what's wrong?

[bullzed]

Sure can

 

Sorry for the horrible quality, it's sitting in a dark garage at the moment 

 

 

 

 

 

[Enzo]

Hello Again,

              If you look at the second photo the rocker arm second from the right looks to be adjusted too low on the pivot post compared to the others. Maybe the locking nut has come loose. Check and adjust your clearances on all rockers.

David.

[bullzed]

what revs are you doing when this happens?

 

This has happened 3 times now, once at about 4k, once at start up and once at idle.

 

I'll have a look at the clearances when Dad gets home and I'll then give an update on how it runs.

 

Cheers all.

[bullzed]

These photos are pretty poor seeing as there's no room to get a side on photo. This is the best I could get

 

^ 2 cylinders closer to firewall

 

^ 2 cylinders closer to front

 

 

 

[bullzed]

Yeah I know, they're a mess. I bought this L28 from a guy who pulled it out of an MQ Patrol, he said it had been reco'd and totally setup, but now it seems that there are problems arising; right when we get it registered.

 

I guess the Z will be off the road for a while until I can get this all sorted out.

 

I'll be unbelievable taken aback if this whole motor is to the standard the head is.

[bullzed]

Thanks mate, definitely appreciate the help. 

 

I'll probably have to pull the head apart (and keep everything in order) just to see if the wipe and the lash pads are how they should be.

 

I can see the next month being fun 

 

 

[bullzed]

Maybe some history on the motor and what type of head it is may help more.

 

It's an N42 head with an F54 block. I've had this motor for about a year, it's only been in use for the past 2 weeks. Hardly any hooning, Dad never takes it over 6k.

[bullzed]

Just an update

 

We pulled the affected rocker off after this happened:

 

 

As you can see the rocker itself is off centre below.

 

 

Then we looked at the rocker

 

 

Huge groove along the middle and a chip in the side. I'm guessing this is the whole problem. The other one that has been jumping also has a small groove but not to this extent. I guess I need a whole new rocker set, yes?

 

 

 

[Scoota G]

Is that cam ground with thicker Lash Pads?

[bullzed]

I know the cam has been ground as the car sounds as lumpy as but I would have no idea about the lash pads. The guy before me did it all. I can check the lash pads tomorrow.

[peter mc]

the problem is not the rocker the pics tells the story the rockers are not adjusted properly ps the rockers do need resurfaced but they are not the problem pps the lash pads are to big as the adj posts are to low

[bullzed]

It's an N42 head with an F54 block. I've had this motor for about a year, it's only been in use for the past 2 weeks. Hardly any hooning, Dad never takes it over 6k.

[bullzed]

Cheers Steve, much appreciated 

 

I have checked the valves and they're all good, getting some new rockers on Saturday and then I'll have to see what happens after they're in.

 

I've got another Z mate trying to find out what's caused all this. I shall update as things happen.

 

Cheers

 

Zac

[bullzed]

Haha, I've been helped out quite a few times on this forum already. I need to find out how to adjust the pivot height. Is it simple? Would it be possible for you to give me a short run through?

 

[RB30X]

Those bolts with the round head on them that one side of the rocker sits on like a cup, those bolts can be lifted or lowered by screwing them in or out. The other nut on those bolts is to lock them in position once set. If you look back at your own pictures you can see that these bolts are all different heights which is what these gurus picked up on straight away. I believe you adjust the height according to your valve clearance. With both ends of the rocker touching the top of the valve and the top of the ball headed bolt, you wind the bolt up so the is X amount of clearance between the cam lobe and the lash pads.

 

How did you go with finding replacment rockers?  I've got two complete L28 heads which I'd prefer not to separate but I could remove the rockers for you if you're desperate.

[bullzed]

All the valve clearances were fine, what would you use to measure the distance between the cam lobe and the lash pad seeing as they're not directly under each other?

 

I've sourced replacement rockers from Paul in Brisbane, he has a Z graveyard which has helped me a lot in the past. So far I've only checked 2 rockers for their condition, hopefully they don't all have deep wipe patterns.

[RB30X]

Valve clearances are fine? How did you measure that.

 

The lash pads "should" be directly under the cam lobes and you use feeler gauges to measure the gap. Clearance specs are in the gregories manual.