4jb1t rocker arm loose

[zacco]

G day all
Had a loud tapping noise coming from engine.Pulled rocker cover off and found the rocker arm closest to the firewall had approx 50 thou sideways play.How would this happen.Worked on plenty of engines and have never seen this before.
Any ideas.?
Cheers , zacco

[Roderunner]

The rocker arm is made of aluminium, while the shaft that supports it is a high grade steel, as the rocker arm wears (or gets starved of good quality oil) the aluminium wearing off the rocker builds up in the oil feed hole on the steel shaft, blocking oil flow down to near zero. It might pay to pull the shaft off, and slide the rockers and shims off (keep the rockers and shims in the correct order), so that the other oil feed holes can be inspected for aluminium/foreign body
build up.

[zacco]

Thanks roderunner, I had a look at the parts manual but couldnt see any shims.Have ordered a new one anyway (and circlip)
Cheers
Zacco

[Roderunner]

As far as I can tell, the shim is there for 2 reasons, one is to line up the rocker centrally in relation to the valve tip, the other is for the shim to act as a thrust surface. The rocker shouldn't have any appreciable sideways slop, and the rocker itself can be measured for wear with a set of calipers. The Isuzu workshop manual gives a wear limit on the rockers inner diameter, standard specs are19.036-19.060 m.m. Wear limit 19.100 m.m. Obviously you don't have to follow the workshop manual's wear limit, but don't overlook the inner surface of the rocker, because where the shaft oil feed hole rides in the rockers inner surface you should find a lump where there is no metal to metal contact (the lump should be on the bottom of the rockers inner surface) , and this lump blocks the oil flow as the rocker wears- you really need to check all of the rockers for this lump to ensure adequate rocker lubrication. along with an inspection of the oil feed hole for debris.
The lump can be removed with a file, something the size of a chainsaw file works ok, and the surface can be finished/polished with a plastic scouring pad. And while I'm on the soapbox, the steel wear pad of the rocker (the pad that rides on the valve tip) can be surface finished on a wet stone to remove the wear marks.
This link is part of an online workshop manual, rockers are covered on pages 9 and 10. http://www.bmhor.org/Isuzu%20Engine/p%2062-114.pdf

[zacco]

Thanks again for tech data
Cheers
Gaz

[Roderunner]

Here's a few pics of some rockers I've been working on
notice the lump that matches with the shaft's oil hole, as the bearing surface wears the lump gets bigger because it doesn't rub against anything, so ends up blocking oil flow to the rocker.

rockers 002.JPG

Lump filed off and bearing surface polished

rockers 005.JPG

Rocker pad after a (hand) surface grind on an oilstone, then polished

rockers 008.JPG

Finished and ready to go!

rockers 007.JPG

I'm thinking about changing the ratio on these rockers, they are only around 1.35 to 1 standard, so I might modify one and use it to check for possible clearance issues between the pushrod and head, and also valve to piston clearance....also spring bind/valve guide to collett clearance.

[superturbocompound]

done the rocker arm ratio...moved the adjustment nut 2mm closer to fulcrum...its been some years now and no complains from those cars with the rocker arms

[Roderunner]

Cool, I have been playing around with 1 rocker only so that I can check for piston to valve clearance (4jg2) once I get it finished. I remember reading one of your posts in the archives about how welding up the rocker can distort it, so I decided to fill the original hole with threaded alum. rod, and then weld it in before drilling a new hole, also the local aluminium welder wasn't confidant that he'd be able to fill the hole without any air cavities. I'm almost there, just have to drill the new hole (you can see the pilot hole if you look carefully amongst the air bubbles) when I can find a pedestal drill and the time. I'm going for a 1.5-1 ratio so the pilot hole is 2.5 m.m.'s closer to the pivot.
Sorry about the multiple photos, I had some trouble loading them, and can't seem to delete them without losing them all....bleh

3 feb 15 014.JPG

3 feb 15 014.JPG

3 feb 15 014.JPG