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MP purple cam and lifter recommended preload?

uk-maxie

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Hi all,

Firstly, yes I have searched on here and I've seen there is already quite a bit of preload info, but I couldn't see any that relates specifically to the cam and lifters we have.

Koffel built us a 440 stroker a few years ago and the build sheet says it's a P5007698 cam. Googling only gives info on the P5007698AE and suggests it's a 292/509 cam but Koffel's dyno sheet says it's the 484 version.
I don't know if this affects how much preload we should set the lifters to but Koffel told us their procedure:
"The way i set the rockers is when ex rocker just starts to open you set the int.I get just a little drag on .0015 feeler guage then turn down adjuster 5/8 turn and tighten lock nut.Then to set ex you wait till int valve has just finished closed. This method will give you about .040-.050 preload which is what cam people want on the lifters".

We did this at the weekend, and mentioned it to someone here in the UK I've known for years and trust him as a mechanic and racer, and he said he'd go with Hughes' recommendation of 0.120-0.140" !! He says most people agree that lifters now need more preload than they used to, as new lifters start off from used cores which are refurbished.

If I had a Hughes cam I'd probably go with that but from what I've read on here, 40-50 thou seems more common, so I wanted to ask if anyone has any info on what MP recommend for their cam and lifters?

The reason I ask is that we've now had 2 occasions when a pushrod has jumped out from its location under the rocker. This could be down to faulty lifters but our trusted UK adviser mentioned above suggests, using only 40 thou could be the reason they are jumping out and that we need more preload.

Any advice gratefully received :thumbsup:
 
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The rule of thumb is 1 turn past zero lash.
 
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The rule of thumb is 1/2 turn past zero lash.
Thanks.
But if (roughly speaking) 1/4 turn = 15 thou and your 1/2 turn = 30 thou, then Hughes' recommended 120 thou = 2 full turns, so something doesn't add up!
That's why I'm trying to find some info specific to Mopar Performance.
 
Run .090" preload. Mopar tappets have about .210" of plunger travel which seems to be very generous. I prefer the plunger to be somewhere close to mid travel. Pretty sure Hugh's says .090". Factory with stock rockers is about .110". I never was satisfied with the .060" or less but you can always experiment if you have adjustable rockers.
 
Thanks.
But if (roughly speaking) 1/4 turn = 15 thou and your 1/2 turn = 30 thou, then Hughes' recommended 120 thou = 2 full turns, so something doesn't add up!
That's why I'm trying to find some info specific to Mopar Performance.
Wow, I have never seen 2 turns. It seems excessive. I guess if you go a half turn and they rattle you can always go more.
 
I just poked around and read 1 turn to 2 1/2 turns. Not a clue. Recommendations ar all over the map.Others will chime in . I need to recind my half turn and say at least a full turn. :lol:
 
You have to know the threads per inch on your adjusters to use “turns”.
 
45 years ago, if you were running performance hydraulic cams, including MP cams, and your goal was maximum performance, you ran zero to 0.010” preload. Maybe that is impossible with today’s junk lifters.

One thing is for sure, if your pushrods are falling out, you need new lifters. It is not a preload problem. If you “fix” the pushrod falling out problem by tightening the preload, you are treating the symptom, not the problem.
 
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If you want to address the problem of the pushrod falling out, without sourcing a myriad of different lifters to find a set that won’t bleed down excessively after shutdown, then I’d suggest going with Lew’s suggestion and running the preload to something close to “half way down”.

The pushrods falling out isn’t that uncommon with adjustable rockers that utilize cup style adjuster screws.
The typical cup style adjuster has a cup depth that is far shallower than a factory stamped rocker.

It’s a specific set of things that have to occur for the pushrods to fall out…….but with todays lifters, it’s not that uncommon.

But what it boils down to is this……..
To make it so the pushrods can’t fall out, you need the remaining plunger travel(after preload) to be absolutely less than the depth of the cup in the rocker/pushrod(depending on which has the cup).
You need to create a situation where if the plunger is bottomed in the lifter, the pushrod still can’t fall out.
 
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The pushrods falling out isn’t that uncommon with adjustable rockers that utilize cup style adjuster screws.

….with todays lifters.
 
You have a Mopar cam in a Mopar engine. I've got a crazy idea. Why not pull out your Mopar Performance Parts, Big Block "B-RB Engines book and look it up. I know that sounds far out, but I'm a weirdo. It happens everyday. People work on a Mopar engine without reading the appropriate engine book. I've never understood that. I even have friends that do it. Anyway, turn to page 151...and if you're wondering the sequence to adjust the valves...the Mopar way is the easiest. All that crap I hear on the internet about bumping the starter 500 times...when this valve moves adjust this one, blah, blah, blah.

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You have to know the threads per inch on your adjusters to use “turns”.
They are 3/8", 24 tpi, ie 1 full turn = 0.0417", so our 3/4 turn is only 0.03125", so well short of being mid-way thru the lifter plunger's travel :rolleyes:
 
Run .090" preload. Mopar tappets have about .210" of plunger travel which seems to be very generous. I prefer the plunger to be somewhere close to mid travel. Pretty sure Hugh's says .090". Factory with stock rockers is about .110". I never was satisfied with the .060" or less but you can always experiment if you have adjustable rockers.

That is a lot of plunger travel, I was told it was more like 0.140" !
The Hughes info I have says for cast iron heads and block, use .120" -.140" pre-load, which is waaaay more than any other recommendations I've seen.
 
I just poked around and read 1 turn to 2 1/2 turns. Not a clue. Recommendations ar all over the map.Others will chime in . I need to recind my half turn and say at least a full turn. :lol:

Best reply so far, thanks :lol:
 
If you want to address the problem of the pushrod falling out, without sourcing a myriad of different lifters to find a set that won’t bleed down excessively after shutdown, then I’d suggest going with Lew’s suggestion and running the preload to something close to “half way down”.

The pushrods falling out isn’t that uncommon with adjustable rockers that utilize cup style adjuster screws.
The typical cup style adjuster has a cup depth that is far shallower than a factory stamped rocker.

It’s a specific set of things that have to occur for the pushrods to fall out…….but with todays lifters, it’s not that uncommon.

But what it boils down to is this……..
To make it so the pushrods can’t fall out, you need the remaining plunger travel(after preload) to be absolutely less than the depth of the cup in the rocker/pushrod(depending on which has the cup).
You need to create a situation where if the plunger is bottomed in the lifter, the pushrod still can’t fall out.
Good answer, thanks :thumbsup:
The build sheet we got says the cup depth is 0.320 but that's under the heading of 'tappets'. Would that be the depth in the top of the lifter or under the rocker where the pushrod (hopefully) locates?
 
You have a Mopar cam in a Mopar engine. I've got a crazy idea. Why not pull out your Mopar Performance Parts, Big Block "B-RB Engines book and look it up. I know that sounds far out, but I'm a weirdo. It happens everyday. People work on a Mopar engine without reading the appropriate engine book. I've never understood that. I even have friends that do it. Anyway, turn to page 151...and if you're wondering the sequence to adjust the valves...the Mopar way is the easiest. All that crap I hear on the internet about bumping the starter 500 times...when this valve moves adjust this one, blah, blah, blah.

View attachment 1656095

View attachment 1656096

View attachment 1656097
^^THIS^^
 
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