Bugout4x4

I have a technical question that might be affecting us all when it comes to oil pressure in these and it has to do with the rocker arm oil hole location. When I first tore mine down I noticed that it had been worked on before because one of the rockers was different than the rest. Obviously one was misplaced and someone substituted it with one that was slightly different. The difference is this... It is the correct ratio and everything but all the rest have the oil hole right on very top and the replaced one has it off towards the side.

So what I noticed is that when not being pushed the rockers with the hole on top were passing a lot of oil flow from the pushrod. But the one with the hole on the side was blocking this flow until it was actually pushed. Maybe I'm wrong... but it seems like the ones allowing this constant flow when at rest (which is most of the time) could result in a substantial loss of overall pressure. I also noticed that this one rocker was quiet and the rest were rattling so this may even be affecting how the lifters are doing their job.

My question would be from an engineering point of view, make and model aside, which design would truly be better? Almost all other makes and models use the off center oil hole type that blocks the flow until pushed. Thoughts?

Tbone289

I would think that flow would be more important in the top end than pressure. Pressure is more important where clearances are tight.

Bugout4x4

I would think that too, But at some point especially after some normal wear, I'm thinking this issue could be affecting overall pressure and most importantly how efficient the lifters are working. There sure are a lot of lifter/rocker rattle problems with these and it very well could be just as simple as this difference. It was an observation I was able to make because one was different than the others and seemed to be working much better than the rest. And like I say most other makers use the offset hole rockers as a universal standard for some reason?

Bugout4x4

I really would like to get some expert guru thoughts on this, from Dave and Cruiser maybe if they could find the time. As soon as the wind and dust slows down I am throwing my engine back together and would like to investigate this possibility a bit before I bolt the rockers in and throw the cover on.

cruiser54

Lubrication is more important than pressure.

Bugout4x4

I screwed up and was off in my thinking here anyways Cruiser. Both hole configurations go directly to the small pocket in the middle and flow continuously anyhow. But I did notice that the hole is smaller in the one with the offset hole. I just can't help thinking there is a design issue with these being prevalent to run loose and rattle. Most other engines with hydraulic lifters never do this, even when well worn. There is something unique about these that ain't right, this should not be such a universal problem.

The wheel needs to be reinvented here and it warrants more investigation.

cruiser54

I have never seen any rocker issues. Lifter issues, yes.

Bugout4x4

Yes... The lifters of course would be the cause, but I wonder why? What is different with these compared to other engines that don't have such a problem as this? For some reason they are not pumping tight and staying tight like most others. Lifter design? Too light of a spring inside? Oil port size? Are they built like the Rhoads variable lift design that always have a little slack? Something is different...

cruiser54

I believe they are the same lifters as small block chevy.

Bugout4x4

That is what I was curious about and the direction I was heading Cruiser... I just can't help but wonder if there might be an alternative mix and match part number that might cure this issue that plagues this particular engine.

So if they are a Chevy lifter the only difference would be that the Chevy is adjustable as where these are bolt down and static. Could it be that these are just not pushing into the lifter far enough to make it pump tight and stay tight as it should like a Chevy?

'90Cherokee

It would be interesting to know if the restricted ones are a later or earlier model thing. Restricting the flow would indeed keep more pressure in the lifter and the rest of the system. With no other knowledge I'd put my trust in whichever is the latest design.

Bugout4x4

This is my thought too. It seems we are just treating the symptoms rather than curing the true root disease with this issue. There is a design issue somewhere in this mess that might be remedied, there always is, just got to find it. I have been poking around and this is a common problem even in the AMC forums, so it is a long standing common engineering issue that probably should have been investigated many years ago with this engine/parts design.

'90Cherokee

My first thought is to check OE part numbers throughout the years and see if there was a change(s) and then see what changed on them. It might just be that the one different rocker is aftermarket and the change might be an engineering improvement or just the way they decided to make it. If that rocker isn't OE and the change wasn't a smartly engineered decision what seems to be an improvement may be a disaster. At the very least you now have an unbalanced system. Might be no big deal, but it's still unbalanced and would bug me some.

'90Cherokee

There are few places where clearances are tighter than the pushrod to rocker interface. Bearings & such have a fairly constant clearance and the parts are 'floating' on a layer of oil where the rocker is under pressure between the surfaces.

Tbone289

The holes in the rocker that are the subject of this thread are not there to lubricate the pushrod to rocker interface. They are there for splash lubrication, thus my statement about flow vs. pressure. I have doubts that reducing the size of those holes will have a significant impact on the oil pressure in the hydraulic lash adjusters. The orifices in the HLAs themselves should provide proper pressure, rather than a hole downstream of the HLAs.