Change font size


Post a new topicPost a reply Page 1 of 1   [ 3 posts ]
Author Message
 Post subject: Refinishing B18/B20 Rockers
PostPosted: Tue Jan 26, 2016 10:08 am 
Haha, I just built a W24 Octo-Turbo, now what?!
User avatar

Joined: Wed Dec 21, 2005 8:40 pm
Posts: 3383
Location: Calgary, Ab
B18/B20 engines are pretty hard on their valvetrain, and one of the components to wear are the rockers. Additionally, the rockers seem to be machined without as much accuracy as one would hope, but they were hammered out in the millions and are something that never seems to fail catastrophically, so I guess you take the bad with the good.

This weekend I tore apart three of my rocker shafts to see what's what, and here's what I found.

Image

Top left are the rockers from the B18B in my 123GT. Top right are the rockers from a '69 B20. At the bottom are the rockers that came with the B18 I got with the 122. All three sets are different.

The ones from the '67 were exceptionally clean and were in the best shape overall. The bushings were smallest and roundest, and the shaft was in the best shape of the three. They all had a manufacturer's name and a part number forged into them.

Image

The ones from the '69 were completely without marking, and though they were the same shape overall they also had more meat in some places.

Image

The ones from the older B18 (from a 544, apparently) had the manufacturer name but no part number, and overall looked the same as the ones from the '67 otherwise.

Image

Side-by-each, from the left we have the GT, the earlier B18, and the B20. You can see a wider, flatter forging parting line on the B20 rocker, a wider tip, and a little more beef at the adjuster boss. I'm not saying that ALL B20 rockers are different from B18s, or that they are better or worse, just that there are different styles.

Image

Image

Image


Image

You can also see the typical wear patterns of the rockers at each end. The one in the middle is the one I polished smooth, but didn't reshape. Even after one summer of driving, the wear is evident.

Image

The worn spot on the pad creates troubles in a few ways: The valve can be harder to set properly, the feeler gauge is wider than the worn spot and it doesn't get an accurate measurement of the gap. The worn spot is also not rounded properly to open the valve smoothly, and it's possible that the valve tip and the rocker tip don't meet in exactly the same spot each time, so the rocker may first contact the valve tip on a previously unworn part and then snap into the worn spot, causing noise. Finally, the worn pad contributes to the inaccuracy of the rocker ratio.

To properly refinish this pad, it should be ground with the proper radius, with the axis of that radius parallel to the axis of the rocker shaft, and at the right distance from the rocker shaft. This is quite tricky to do by hand, but without a fixture this is all we can do. In future posts I will show what I have done, and I invite others to show what they've done. I may even attempt to make a fixture to put the right curve in the right place so that they can be done the same way each time. We'll see how that one goes...


Top
 Profile  
 
 Post subject: Re: Refinishing B18/B20 Rockers
PostPosted: Thu Jan 28, 2016 8:03 pm 
Haha, I just built a W24 Octo-Turbo, now what?!
User avatar

Joined: Wed Jun 14, 2006 4:19 pm
Posts: 3007
Location: Lethbridge, AB
I've used a variety of techniques over the years, mostly relying on my belt sander to profile the pad. The last couple of sets I've done on my 12" disk sander as it puts a very fine finish on the pad. Nothing new in this picture. These are the best set that Ian had for his B20 (no PN or other markings on these ones).

Image

This is after the refinish - I've ground until the valve stem mark is gone (no further), very light pressure. Then I use a diamond hone to finish them off by hand. I really would like a fixture to do this job.

Image

Image

_________________
Coburn Performance - OCD comes naturally.


Top
 Profile  
 
 Post subject: Re: Refinishing B18/B20 Rockers
PostPosted: Sun Feb 14, 2016 8:52 pm 
Somehow completely sideways in 4th

Joined: Mon Aug 06, 2007 10:27 am
Posts: 207
Location: edm
544 (& I assume early spec 122/1800s) b18 rockers are quite different. They do not have the machined "Mohawk" rib on top, just a smooth forged rib.

One thing I didn't mention in the emails, but was alluded to in the one pic- at one point I had a harebrained idea for performance modifying the rockers- remove the adjusters, file the threads away to the inside for better ratio, and rethread for 3/8 (by luck 5/16 and 3/8 UNF is the same pitch) adjusters. You can also angle the adjuster to get the contact closer into the fulcrum. Never did a whole set or ran them. I think I have spare 3/8 adjusters in both cup and ball styles if you want me to look. I might have bought 16 of each.

Another thing- If you find rockers from another make that are a hair too long or you are fighting geometry, or pushrod hole clearance, the rocker shaft itself can be bored off center and a shoulder bolt used (or a bolt with a sleeve) to relocate it to the pushrod side.

The reason I thought of mentioning this, is back in the day I was thinking of making a jig to move the arc of the pad out to the tip and sell a bolt on kit on an exchange basis, of: a rocker shaft offset bored, rocker bolt sleeves, and rockers redone to 3/8 adjuster, high ratio, all moved toward the pushrods. Parker was having pushrod clearance issues with his Buick rocker based set ups and people didn't want to take the head off to enlarge the pushrod hole, so this was all an end run around that supposed issue.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post a new topicPost a reply Page 1 of 1   [ 3 posts ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
cron


Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
610nm Style by Daniel St. Jules of Gamexe.net