Rocker arm issues.

So, as part of my refresh, I decided to replace my ancient Crane Golds. After some consideration, including the premise that they're made in the USA, I purchased a set of PRW rockers. In the end, this also necessitated a switch to new beehive springs. Now the engines all assembled and ready to bolt up to the trans and drop in. Just for the heck of it I put the dial indicator on the head tonight and measured up my actual valve lift. I'm at .513" net valve lift on a .575" roller, at .020" lash. With 1.6 rockers.
Wonderful.

That doesn't surprise me. I also wouldn't recommend PRW rockers with a solid roller cam. Unfortunately, high quality rocker arms are now super expensive. Even the middle of the road stuff has become really expensive.

Something is definitely not right. Your .575" roller is a .383" lobe lift (.575 / 1.5). If you take your measured lift of .513" and add .020" lash this gives you .533" gross lift. Divide that by the lobe lift (.383") and you get your actual rocker arm ratio - which is only 1.39 instead of 1.6

How's your geometry?

Just a thought ... with the 1.6 rockers your total lift should be around .608. This is "roughly" .100 more than the .513 you claim. Could you have read the dial indicator wrong ... .513 instead of .613 ???

measuring lift at the valve requires the dial indicator set-up/readings to be different than measuring a cam lobe. i think with that kind of difference there probably is a set-up/reading error. go back and re-think what you're doing. i think with that kind of lift you need a 1" indicator zeroed at .700" depressed.

I just recently had a builder verify the net lift at the valve was going to be under .700” for this particular build.
He checked two rockers, the theoretical lift would have been .690.
One was like .650, the other .665. The lobe lifts were .460” for both.
PRW steel 1.5 rockers.
This was on a BB. If you’re working with a SB and the stock 59* lifter bank angle, that alone will cost you about .05 worth of effective ratio.

I did double check my measurement. I measured the valve travel in both directions, by zeroing the indicator at both fully open and fully closed. Then I took my dial calipers and measured installed height and fully open height. Same thing. With my old Cranes, my actual net valve lift was better than .580", with the same lash.

The Cranes I have checked were always higher than the advertised ratio.

Also, if you’re using a shaft relocation kit for geometry improvement, I’ve seen instances where they have resulted in a lower effective rocker ratio.

And any deflection.

I’m saying that when the lift was checked with and without the relocation kit, there have been instances where the addition of the kit lowered the effective ratio.

So, if the OP has one of those kits installed, he could remove it and see if, in his particular situation, it has any impact on the ratio.

The highest departure from the “advertised” ratio I recall seeing was 1.67 from a set of HS 1.6’s on some Indy SR’s using checking springs.
With the full spring force(700lbs) at .700” lift, the effective ratio was still 1.63.

Edit- re-read the OP.
I didn’t see where it said if the lifters were solid or hyd.
You can’t get a good read on the true running lift using a hyd lifter for mock ups(it compresses)......... if that’s what you’re doing.

Solid roller, and no shaft relocation.

Did you measure lift at the cam lobe? I bought a Lunati roller that was supposed to be .600 lift but was actually a smaller cam - despite all the correct numbers stamped on the cam. Being in Canada, I had a hell of a time getting it replaced by Lunati and it was all at my expense !!

Can you post a photo of one of the rockers? Top and side view if possible.

Here's the thing with Mopar rockers, the length from the fulcrum to the contact point on the valve should be fairly close on any rocker - that length is fixed by the head design so its not something a manufacturer can vary by much.

So to vary the ratio the manufacturers move the pushrod location. To increase the ratio the pushrod is moved closer to the shaft. This is easily visible from 1.5 to 1.6.

Let's have a look !!

It should be....... but in reality, there are definitely length differences on the valve side between the different brands.
Stealing a pic from Andy’s book:

And:

Sounds like you just have to decide how badly you want that ratio to be closer to “correct”.

Yeah there were all these arguments on the forums years ago so I went and bought one rocker from each mfg and put them all on a shaft. Once I did that I said "okay, now I get it"!

The Mopar rocker arms are all over the map. You don't know what works until you try it. Eventually I created a little cheat sheet that told me which rocker arms worked with which cylinder heads. If a person just randomly selects a rocker arm package then good luck and may the force be with you. Not everything works on everything.

Well the Cranes definitely look like they'd have issues. Everything else being equal, they would have less lift at the valve than any of the others.

I have Harland Sharps on a set of Indy EZ's. The lift at the valve is pretty damn close to where it should be for a 1.5 rocker.

Have you shared this cheatsheet ?

I’ve used the Crane golds on stock heads, stage 6’s, Indy SR’s, Indy EZ’s, B1/BS, and RPM’s........no problems with the fit that were serious enough for them not to be used.

Plus...... they were pretty affordable too.

My go to replacement for them are the Mancini rockers, but I haven’t had the opportunity to test fit them on all of those applications.

The solid spacers between the rockers that the Mancini rockers use aren’t as universally install friendly as the springs that came with the Cranes.

I really hate to sound obtuse but I fail to see how a 'geometry correcction kit' can have a ratio effect (change) on a set of rockerarms. Regardless of the rocker ratio itself, all a 'correction kit' does is move the position of the rocker arm contact to achieve proper scrub angle...does it not? So, how then does THIS change the actual ratio or effective valve lift/ratio?

because the tip of the rocker arm moves on an arc.

Brad Haak had some really good examples, actual measurements, and CAD drawings in a detailed post about that very thing.

If you search through his posts you should be able to find it.

I wrote a couple of books

Years ago Racer Brown recommended going through a set of stock rockers and selecting those that had equivalent lifts. I have done this multiple times and yes, the ratio of a stock Mopar rocker is all over the map.

not to hijack here, but i've got a set of crane golds on my go to driver and was thinking about changing them out; over 20,000 miles on them. i thought i might have a geometry issue with new stuff seeing how i can't buy old stuff but that pic dwayne put up,.... . i thought things might be goofy but that's beyond goofy for me. i don't use a fast rate cam or big pressures but it looks like it's all head specific. i would have thought there might be some overlap as far as usage goes but maybe not. the deal with those prw rockers seems outrageous. were they the comp cams clones or the alum?

I checked the actual lobe back when I got the cam. I also have, in the past, checked the actual valve lift at zero lash. The Crane's were giving me pretty much the real deal. I think it was out by .005" from the theoretical .613", which can be attributed to arc and some deflection. I had killer valve springs.

Thanks Dwayne, I'll look into it...wb

The rockers aren’t marked for ratio, correct?

My guess is....... they’re 1.5’s in a 1.6 box.

.575 lift with a 1.5 is .383 lobe lift.
You getting .513 with .020 lash, which would put the number at .533 gross lift.
533/383 = 1.39.

I find it hard to believe they’d be that far off(1.6 > 1.39).

1.5 > 1.39 would be bad enough.

The rockers themselves are marked 1.6..

Pictures !!! Top and side.

Interesting. The ones that were on a motor that was just on the dyno here had no markings.
The two that were checked measured in the 1.45 range.

This isn’t doing much to make me change my mind about not using Chinese rockers.

I've measure a bunch of different brand BB Mopar adjustable rocker arms, stock Ductile iron Max Wedges, stock Street Hemi ductile iron rockers from many different motors, Isky, Cranes and Erson brand ductile iron rocker arms as well as several different brands of aluminum rocker arms like Harland sharp, both early and later made, and several sets of T&D single shaft sets, none of them were dead nuts on the ratio on the complete sets sent to me from the factories
I use to send the ductile iron sets to a company in northern, CA for blue printing and making them accurate, after checking several different sets I had done by them I stopped doing that
i have not yet check a complete set of Jesel paired shaft aluminum or steel rocker arms, that is next

Fair point. I'll probably find out on Monday what the manufacturer has to say.

How many of the eight common dialects spoken in China do you know?

I think one thing many take for granted is that the rocker ratio will yield the equivalent ratio of valve lift with every cam. However, the rocker ratio is exactly that - its the ratio of the distance from the center of the shaft to the center of the pushrod versus the distance from the shaft to the center of the valve contact point. Given the stock geometry of the shaft position, valve height and rocker design, a stockish .300 cam will yield .40 valve lift because its all designed to. But if you throw in a .400 lift cam with no changes to the shaft or valve length, you should not expect .600 lift. There are a few other factors that will affect the valve lift when you slap in a cam with double the stock lift. Without changing the shaft height or valve length, the rocker will be at a much great angle half way though the lift with the bigger cam. This results in a much lower lift ratio in the second half of the valve lift. It works similar to a piston - the fastest travel is is halfway in the bore but at the top or bottom its moving slower because of the crank angle.

That’s all fine and dandy, but it sounds like the Crane 1.6’s yielded .080” more valve lift than the PRW’s with the same cam(lobe lift).

I know which scenario I’d rather have in my engine.

My guess is that someone at the PRW factory stamped a set of 1.50 rockers with the 1.60 ID and then they got boxed and sold as 1.60 rockers. PRW gave me a set of their steel rocker arms when they first came out for a magazine article, but the rockers were a timebomb so I never used them. The rockers had ribs around the roller tip that were too big. The ribs hit the valve lock before the roller hit the valve stem so the load was all being carried by the valve lock. I never even started the engine when I saw that. Just boxed up the rocker arms and sent them back and never included them in the article. I assume they fixed this design flaw but I haven't looked at a set since.

The old unbushed will-seize-on-the-shaft CAT stainless rockers were also like that.

There is obviously no testing done on that stuff, or input from builders familiar with the platform for that matter.

I didn’t see where the OP mentioned if this is a BB or SB.

On the SB, there is a definite loss of effective ratio(as measured at the valve) from the 59* lifter bank angle and the pushrod angle.

I had the same issue with the ones that 440Source marketed briefly. Put them in the mill and fixed them.

Rocker body wasn't spot faced for the jam nut and when you tightened it down, it broke the adjuster. Source replaced them with new and improved but still had to trim the roller end.

Then discovered the adjusters were made of glass. Replaced them with Comp adjusters and thought we had beat them into submission...

Some time later, I had a valve cover gasket leak that was a big blessing in disguise. Pulled the cover and found one side of the roller end was broken on one rocker and when I took them off the engine discovered the rollers were loose enough on their axles that you could hear them rattle from across the shop when you shook them...

Shoulda just bought the Comp Magnums...

Kevin

small block PRW rocker i recently bought.
no lock interference on this setup.

Seen two vids on the new mopar small block trick flo heads, the rockers beating the tops of the retainers and one broke valve.

Wonder what the mis match in parts was here?

Hey pretty nifty, a built in valve spring compressor.

The only rockers I would have any real “expectation” about fitting those heads, without needing modifications to something, are the HS part numbers recommended by TF.

Anything else should get extra scrutiny(although they should all be checked).

If there is evidence of contact between the rocker and the retainer.......IMO, that’s on the one doing the final assembly.

I agree. In my opinion there are only a few rocker arms that work with each popular Mopar head. Many people assume that you can buy anything and bolt it to anything and have it work since the parts are advertised for a Mopar BB or SB. But I've seen enough data over the last 30 years to convince me otherwise. Everything doesn't fit on everything.

That's an interesting observation. I've just got a set of worked over J-heads. I have a hunch I will be able to do a real world comparison where I find out exactly what the power difference is between 513 lift and 585-590 lift, with no other changes.

If the engine combo is slightly “under-cammed”, then the added ratio(area under the curve) should pay off.
Adding ratio is no guarantee of added power.
I’ve swapped rockers from 1.5 to 1.6 several times where the result was a reduction of power across the board.

We have 1.2 break in rockers for SBC.
Sometimes even when swapping from those to the normal 1.5’s or 1.6’s doesn’t result in huge gains.

Are you sure that the cam with more lift doesn't have more duration at .020, .050, .100 and at .200 lift on the lifters?
All the BB Mopar V8 I've dealt with at the track and on a engine dyno like more air with more fuel Your on the right path