Melling Rocker Issues

[RemCharger]

452 heads with 78cc chambers?

 

[BSB67]

452 heads at 78 ccs
11.24 CR
Tiny cam

What fuel are you running? What is your cranking cylinder pressure?

There are things in this build that seem out of place. Not that it necessarily matters in the end, but it causes us to question more things

 

[The Flying Scot]

452 heads at 78 ccs
11.24 CR
Tiny cam

What fuel are you running? What is your cranking cylinder pressure?

There are things in this build that seem out of place. Not that it necessarily matters in the end, but it causes us to question more things

I’m using mainly Shell V Power unleaded. 99 Ron. Sometimes BP Ultimate 97. I don’t know what the cranking cylinder pressure is but I can ask the guy who built the engine.

 

[PRHeads]

Looks like a Comp 268H cam, which shouldn’t be enough lift(.454) to cause retainer to guide issues.
There are aftermarket retainers on the heads, which should increase the installed height.

 

[The Flying Scot]

What fuel are you using in this engine? I think you are lucky that the only problem so far seems to be pushrods punching holes in rocker arms. The cam, compression ratio and cylinderhead combination is.......uh.......politely........not optimal.

2.08/1.74 valves are factory stock sizes for that 452 cylinderhead.

Ok. I understood that the original valves were smaller than this and were increased in size to the dimensions you quoted. Here’s a description of the work done to the heads:

 

[The Flying Scot]

Here’s a few photos of the internal components used on the rebuild when they were first delivered.

 

[The Flying Scot]

As said coil bind, excess spring pressure, excessive cam lift.. I assume all 16 valves have the same springs. Any ideas on closed and open pressures? Were the guides new or knurled. I ave seen knurl jobs go bad and bind the valve stem.

Yes. The springs came with the Comp Cams kit shown in the photos I recently posted. I’ve no idea of the pressures. I believe the guides were knurled.

 

[Bee1971]

Like Turbine mentioned

What is the measured length of the pushrods installed ?
Check for lifter pre load

Section II on the bottom , non adjustable rocker arms
https://www.compcams.com/pub/media/productattach/c/o/comp4-116.pdf

Pull both sides , rocker arm shafts and all 16 rocker arms
Look for any wear on the bottom side of the rocker arms , and on top of the valve spring retainers , valve stem tips for center contact

I know the Edelbrock Heads and Spring Retainers are damn close using the Sealed Power Rocker Arms over the Chrysler Factory Rocker Arms

 

[The Flying Scot]

Like Turbine mentioned

What is the measured length of the pushrods installed ?
Check for lifter pre load

Section 2 on the bottom , non adjustable rocker arms
https://www.compcams.com/pub/media/productattach/c/o/comp4-116.pdf

Pull both sides , rocker arm shafts and all 16 rocker arms
Look for any wear on the bottom side of the rocker arms , and on top of the valve spring retainers , valve stem tips for center contact

I know the Edelbrock Heads and Spring Retainers are damn close using the Sealed Power Rocker Arms over the Chrysler Factory Rocker Arms

Thanks for your input. I understand the engineers fitted marginally longer pushrods after the first rocker popped. Not sure of the lengths. They assured me that all lengths, pre-loads etc were absolutely correct. Will check everything properly next week.

 

[The Flying Scot]

Spoke to a Mopar guy in Europe who doesn’t do social media. He reckons that it should never have been stroked, that the compression ratio is ridiculously high, the camshaft is too small for the job and that headers should’ve been fitted and that it won’t run properly on 99 RON fuel.
That’s not the issue with the rockers but just a general comment about the build. It’s appears to stuck between “street” and “race” and not in a good way! It has not been a balanced rebuild with mis-matched components. Keen to hear anybody’s views on this. Off topic slightly but still relevant I feel.

 

[The Flying Scot]

Looks like a Comp 268H cam, which shouldn’t be enough lift(.454) to cause retainer to guide issues.
There are aftermarket retainers on the heads, which should increase the installed height.

It’s a Comp Cams K21-227-4.

 

[BSB67]

Spoke to a Mopar guy in Europe who doesn’t do social media. He reckons that it should never have been stroked, that the compression ratio is ridiculously high, the camshaft is too small for the job and that headers should’ve been fitted and that it won’t run properly on 99 RON fuel.
That’s not the issue with the rockers but just a general comment about the build. It’s appears to stuck between “street” and “race” and not in a good way! It has not been a balanced rebuild with mis-matched components. Keen to hear anybody’s views on this. Off topic slightly but still relevant I feel.

Maybe not clear, but that was the point of my previous post. So yes, based on the info that has been given, it seems like it could be mismatched. Here, it is very hard to get 10:1 CR cast iron head with that small of a cam to run on 96 RON.

But as others have mentioned, the 78 cc for the heads also seems a little suspect. Not typical machining is needed just to put together a motor with that much milled from the heads. It can be done, but why in this case is the question. My first reaction is that the stated 78 ccs is a mistake and the actual number is 88 ccs.

But this is off track from your initial post. I would continue to focus on finding the root cause for the pushrod/rocker arm problem first.

 

[beanhead]

Sorry to see that happening...now that we know the camshaft in use IMO the build is pushing the limits of stamped rockers, especially with the inconsistent quality of the aftermarket units. If all the things the guys have mentioned check out okay (pushrod lengths, spring/retainer clearances, head machining etc) then it's probably time to look at some good roller-tip rockers, for the added durability. I have seen pushrods poke through the stampers on builds with less aggressive cams than yours, you're definitely not the first to have that happen...

 

[The Flying Scot]

For anyone curious as to the modification of the 452 heads please see the description in the photo and feel free to comment.

 

[PRHeads]

It’s a Comp Cams K21-227-4.

This is not a 268 cam.
It’s a XE275HL, .525/.525 lift.

It has not been a balanced rebuild with mis-matched components.

Not balanced?
Hopefully that’s not really the case.

A cranking compression test might shed some light on whether or not the claimed CR is accurate.

No one has mentioned it....... but since it appears the motor should have a fast rate cam in it(based on the part number), perhaps the Melling rockers just aren’t up to the job.

Edit- I see Beanhead touched on the rockers as being suspect.

 

[The Flying Scot]

This is not a 268 cam.
It’s a XE275HL, .525/.525 lift.



Not balanced?
Hopefully that’s not really the case.

A cranking compression test might shed some light on whether or not the claimed CR is accurate.

No one has mentioned it....... but since it appears the motor should have a fast rate cam in it(based on the part number), perhaps the Melling rockers just aren’t up to the job.

Edit- I see Beanhead touched on the rockers as being suspect.

Sorry. When I say “not balanced” I mean the components seem to be mis-matched for the intended build.
Everything requiring actual “balancing” in the mechanical sense has been done. Or so I was told….

 

[BSB67]

I didn’t bother checking cam part numbers, but the build write up has .454” and 268* and goes to the point that the info supplied raises more questions.

I agree the HL lobe rate and needed spring might be a little much for aftermarket stamped rockers.

 

[PRHeads]

I didn’t bother checking cam part numbers, but the build write up has .454” and 268* and goes to the point that the info supplied raises more questions.

Indeed.

If it basically runs fine, and the only main known issue is the the failing rockers......... I’d upgrade to better rocker gear and see if that ends the headaches.

 

[The Flying Scot]

Indeed.

If it basically runs fine, and the only main known issue is the the failing rockers......... I’d upgrade to better rocker gear and see if that ends the headaches.

Well I was gonna fit new roller rockers next week but if there’s something fundamentallly wrong with the build then I’m not sure what do do.
These are the ones: https://www.summitracing.com/parts/cca-1621-16

 

[PRHeads]

I don’t know about “fundamentally wrong”....... but my guess is if the rockers weren’t failing, you’d still be happily motoring along.