Lifter preload tolerance..

[zep058]

Lots of learning on my first top end refresh..

Car is 66 300, 383. Very much a street cruiser.

Stretched timing chain kickstarted said top end refresh.

Lunati 10230702 cam, matched lifters and springs.

Stock stamped rockers, currently no budget for adjustable rockers…but may have to.

8.575 pushrods.

This question is about lifter pre-load. Lunati spec between 0.20-0.60” tolerance. Using a dial indicator I have measured varying preloads from .38 to .65” on intakes (40,40,40,65,42,44,43,45) and some big swings like .23-.48” on exhausts (41,44,28,44,45,23,29,43) I intend to swap out a .20 longer or shorter pushrod to get some of those numbers closer to the others.

Does the preload need to be identical on all valves or just within the spec’s 0.20-0.60”?

I understand for efficiency they should and that I should be running adjustable rockers.

But worst case, can I change pushrods and get them between 40-50 at least. TIA

 

[Lefty71]

Subscribed..... i'd bet you are a-ok to just run them. I would be curious if this situation in mentioned in the factory service manuals tho??

 

[mr gtx]

i would at least get the 23, 28,29 up .020 more. I would like them all at least to .065.

 

[CBODY67]

Subscribed..... i'd bet you are a-ok to just run them. I would be curious if this situation in mentioned in the factory service manuals tho??

Never seen ANY mention of lifter pre-load on Chrysler B/RB lifters from the factory, in the FSM. As the rockers are not adjustable, just install them. Lunati knows the factory set-up, so you should be fine.

When and IF you do get the adjustable rocker arms, THEN pre-load them like a SBC.

Personally, I'd be more worried about getting the cam broken-in correctly than valve lifter pre-load. I DO understand your concerns, though.

As to the SBC lifter pre-loads, FWIW, the factory-spec pre-load was 1.5 turns, although many people only use .25 turns pre-load, so less is better. Keeps the plunger more "toward the top" than "in the middle".

The whole pre-load issue is about having enough pre-load to prevent valve train sounds upon cold start-up and as the engine warms up. Some run their SBC engiens at .25-.50 turns pre-load, with no issues. It all relates to how much oil is in the lifter plunger bore to extend it.

In prior times, some Olds guys would use brass shims to shim the valve holders to get more rpm out of their motors. Same might be possible with a Chrysler V-8, too. This can take time to orchestrate and install, though. To not go too thick.

Enjoy!
CBODY67

 

[Trace 300 Hurst]

Does the preload need to be identical on all valves or just within the spec’s 0.20-0.60”?

First, I think those Lunati specs are 0.020-to-0.060, meaning 20 to 60 thousandths. Not 0.2 to 0.6, meaning 2-to-6 tenths which is over one-half inch.


Anyway, you just want to be somewhat close to those specs. There's plenty of tolerance on hydraulic lifter systems, which is why they're used in the first place with no adjustment provisions with the stamped steel rockers. This makes for easy mass production and assembly of engines with no need to ever worry about valve lash/clearance. For the past 70+ years random hydraulic lifters have simply been dropped in, followed by random pushrods and random rockers are slid onto the shafts and it's all bolted into place. Done! Lots of tolerance in these systems.

You'd prefer to not have less than .020 (by swapping pushrods) but a little over .60 isn't a problem because of all the available travel of the lifter plunger. No need to fret about all this. Just get close.

Finally, in regard to those Lunati specs: Those are prefered numbers so that if a high-revving engine experiences valve float, the lifter plunger won't "pump up" to the point where it 1) holds the valve off the seat for more than an instant, and worse, 2) the valve is extended so far that it hits the piston. This is not something you have to worry about with a cruiser, and you absolutely do not need adjustable rockers.

 

[Trace 300 Hurst]

Subscribed..... i'd bet you are a-ok to just run them. I would be curious if this situation in mentioned in the factory service manuals tho??

The FSM does not address preload because there is no provision to adjust it, and no need to be concerned about it because of the amount of plunger travel and valvetrain component tolerances.

It does talk about lifter noise. Typically, a bit of trash gets in the lifter and affects the hydraulic action:

 

[Trace 300 Hurst]

i would at least get the 23, 28,29 up .020 more. I would like them all at least to .065.

.065 is a good number in general, but when I was building VERY high-revving 340s (including T/As) I was setting preload (w/ adjustable rockers) at .040 because I was concerned about float/pump-up. Cold start noise was not an issue, of course.

 

[mr gtx]

the factory lifter has 200 thousand travel. the factory preloads I have seen were over 100 thousand. i had the stock retainer clips pop out because of too little preload. not enough valve spring pressure will cause lifters to pump up a lot more than 100 thousand preload. 5500 rpms was red line stock for a lot of factory lifters if you are going to go over 5800 rpms run the high rev lifters or a solid lifter cam.

 

[mr gtx]

getting all the preloads the same will not give you any performance gains. but having too little or too much will cause problems

 

[Trace 300 Hurst]

the factory lifter has 200 thousand travel. the factory preloads I have seen were over 100 thousand. i had the stock retainer clips pop out because of too little preload. not enough valve spring pressure will cause lifters to pump up a lot more than 100 thousand preload. 5500 rpms was red line stock for a lot of factory lifters if you are going to go over 5800 rpms run the high rev lifters or a solid lifter cam.

Agree with your statement about revs, etc.

In my advice to the OP I was going to mention that the lifters have "nearly a quarter-inch of travel so don't worry", but decided not to confuse things beyond his original question.

Bottom line: Bolt it all together.

 

[zep058]

First, I think those Lunati specs are 0.020-to-0.060, meaning 20 to 60 thousandths. Not 0.2 to 0.6, meaning 2-to-6 tenths which is over one-half inch.


Anyway, you just want to be somewhat close to those specs. There's plenty of tolerance on hydraulic lifter systems, which is why they're used in the first place with no adjustment provisions with the stamped steel rockers. This makes for easy mass production and assembly of engines with no need to ever worry about valve lash/clearance. For the past 70+ years random hydraulic lifters have simply been dropped in, followed by random pushrods and random rockers are slid onto the shafts and it's all bolted into place. Done! Lots of tolerance in these systems.

You'd prefer to not have less than .020 (by swapping pushrods) but a little over .60 isn't a problem because of all the available travel of the lifter plunger. No need to fret about all this. Just get close.

Finally, in regard to those Lunati specs: Those are prefered numbers so that if a high-revving engine experiences valve float, the lifter plunger won't "pump up" to the point where it 1) holds the valve off the seat for more than an instant, and worse, 2) the valve is extended so far that it hits the piston. This is not something you have to worry about with a cruiser, and you absolutely do not need adjustable rockers.


View attachment 706693

Thanks for all your detailed responses!
This is the exact reassurance I needed and relieved to know it should be fine.
I will get those lower numbers lifters closer to the others for peace of mind.
Thank you, thank you!