273 Rocker and Shaft rebuild

-
midnight340

midnight340

Well-Known Member
Joined
Mar 19, 2014
Messages
469
Reaction score
286
Location
Lawrence, KS
Hi Guys,
I need to rebuild my old 273 rockers and shafts that I run on my 340. I believe when I first thought about it, I got a recommendation (probably from someone here) for a place called Rocker Arms Unlimited. Has anyone used them recently? Is this the go-to place? Thanks.
 
I'd appreciate hearing from anyone who has dealt with Rocker Arms Unlimited recently or has any experience with getting the stock adjustable rockers and shafts rebuilt.

I just didn't want to ship mine off without knowing more about these guys. Thanks. ��
 
I think I used Rocker Arm Specialists. Could be the name you are using. they are out of California.

Ok I just did the google thing and you have the name correct. I have used them. their work is awesome.

I had some rockers on W-2 stuff and was using 320 om the seat. RAS (or as they are now call RAU) machined them down and added thrust washers.

I trust them.
 
Thanks a lot!! Appreciate the response. Yeah, looks like the same guys but a business name change.0
 
Hughes says the ratio on oem mechanical rockers can very greatly. Any truth to that? and how would a feller check that? Hope this aint too big of a hijack.
 
On each rocker arm tip at the valve you would put a dial indicator to measure the amount the rocker arm would move downward from zero to full lift, cam base circle to top of the lobe.
Now try on each rocker arm.

It would help if you had a known cam, new if possible, with a known lift with a quality rocker arm.
 
Bodyperson said:
Hughes says the ratio on oem mechanical rockers can very greatly. Any truth to that? and how would a feller check that? Hope this aint too big of a hijack.
Click to expand...


Dave say a lot of things. If you are using 273 rockers...they had SOME issues, but not as bad as reported by folks looking to sell you rocker arms. The Isky and Crane rockers were very good.

FWIW RAU can take any of those ductile rockers and make them 1.6 ratio, and correct them at the time, if they are off. I'd use the ductile iron rockers long before I used aluminum and I never, ever, NOT EVER use a rocker with a needle bearing on the shaft if it uses a Chrysler diameter shaft.
 
Yes, I'll swear by these iron rockers after all they've been through... Countless 7K shifts. And they were fairly worn when installed them on my fresh 340 about 70K miles back. But the last time I checked them I had to use locktite on a couple of the adjusters ...there was no "interference fit" left. Time for some work.

Is there a downside to going to 1.6 ratio? I'm running an old Lunati Bracket Master 284 with 218 @ .050 and a .458" lift. By no means a modern grind but it's been a great street cam in this motor. I hope to get a Voodoo cam in it at some point. Not sure about a 1.6 ratio.
 
midnight340 said:
Yes, I'll swear by these iron rockers after all they've been through... Countless 7K shifts. And they were fairly worn when installed them on my fresh 340 about 70K miles back. But the last time I checked them I had to use locktite on a couple of the adjusters ...there was no "interference fit" left. Time for some work.

Is there a downside to going to 1.6 ratio? I'm running an old Lunati Bracket Master 284 with 218 @ .050 and a .458" lift. By no means a modern grind but it's been a great street cam in this motor. I hope to get a Voodoo cam in it at some point. Not sure about a 1.6 ratio.
Click to expand...


There really isn't a down side to 1.6 except cost. RAU can take your rockers and make them 1.6 and change them to adjusters with lock nuts. then they will go forever.
 
midnight340 said:
Yes, I'll swear by these iron rockers after all they've been through... Countless 7K shifts. And they were fairly worn when installed them on my fresh 340 about 70K miles back. But the last time I checked them I had to use locktite on a couple of the adjusters ...there was no "interference fit" left. Time for some work.

Is there a downside to going to 1.6 ratio? I'm running an old Lunati Bracket Master 284 with 218 @ .050 and a .458" lift. By no means a modern grind but it's been a great street cam in this motor. I hope to get a Voodoo cam in it at some point. Not sure about a 1.6 ratio.
Click to expand...

I ended up putting new adjusters with nuts on my 273 rockers after having a couple loosen up on me, MP used to sell them, not sure if they are still available from them.
 
I think Crane has the adjusters with lock nuts available.

I know my shafts were not great when I assembled the motor… some galling, that I polished out with emery strips thinking it was temporary. As I said, 70K miles of "spirited" driving later, I'll feel better getting them done right.

As I research more I see that the only time the extra lift from the 1.6 rockers is a problem is if your heads are already flowing at maximum. (or on bigger cams getting into coil bind or not enough clearance for the pushrods) I am running little more than a stock cam so that shouldn't be a problem. And my heads (being ex-race prepped X heads, ported, and polished out) are certainly not anywhere near their flow limit.
 
Triple R gave me some great advice about filing down the cast surface where the jam nut goes when using the crane ajustables. I used a flat/fine file and just knocked down the high spots in the casting so the jam nut would have a flat surface. And almost needless to say - clean them up real well and re oil.
View attachment 20150227_210007.jpg
 
How does RAU change the ratio? Only way they could do it would be to move the shaft ( yeah with no rocker arm mod.., right) or move the adjuster closer to the shaft,, fill and redrill?
 
pishta said:
How does RAU change the ratio? Only way they could do it would be to move the shaft ( yeah with no rocker arm mod.., right) or move the adjuster closer to the shaft,, fill and redrill?
Click to expand...


They use an oversize adjuster. It's simple math after that. To go from 1.5 to 1.6 ratio requires a RELATIVELY small move of the adjuster.

BTW, you almost always move the adjuster to change the ratio. It's a PITA to change the length of the rocker.
 
I am pretty sure my engine builder used Rocker Arms Unlimited to rebuild my 318 Poly rocker arms and shafts. Also had them all machined to be a true 5:1. They look and work great, the adjusters are a 12 pt locking nut (not sure if the builder added them or they came with the rebuild).
 
midnight340 said:
Is there a downside to going to 1.6 ratio? I'm running an old Lunati Bracket Master 284 with 218 @ .050 and a .458" lift. By no means a modern grind but it's been a great street cam in this motor. I hope to get a Voodoo cam in it at some point. Not sure about a 1.6 ratio.
Click to expand...
Just one added factor is that the pushrod side of the system sees increased stresses and force. It amounts to about 7% at low RPM's but can peak as high as a 10-20% increase at the highest RPM's. This all increases pressures on the lifters and cam lobes so makes good break-in procedures and oil selection more important.
 
Appreciate the info. I've started running ZDDP every oil change. With my Lunati I'm using good springs and pushrods from Comp Cams but, like I said, I've got some miles on this motor. (If the cam started to go I'd just move to a VooDoo ...)
 

You must log in or register to reply here.
-
Back
Top Bottom