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| | | | Joined: Jan 2010 Posts: 61 New Guy | | New Guy Joined: Jan 2010 Posts: 61 | My mechanic suggested i replace the rocker arm shafts in my 216 engine because there is some visible wear to the shafts. I got a set from Bowtie Bits. The issue is that my mechanic pointed out that the bottom of the shaft is slightly ground along the length of the shaft( please see photos ). Our old set of shafts does not have the underneath grinded. Does anyone happen to know why? My mechanic thought that perhaps this was an improvement... that GM or someone determined that the oil will flow better with that area grinded down a little. We're concerned that with the grinded area, the oil wont spread around as its intended to do. I appreciate your input as always. http://www.flickr.com/photos/union4487/sets/72157623358552886/
'51 Chevrolet 3100 216 5-Window
| | | | | Joined: Dec 2003 Posts: 2,733 Shop Shark | | Shop Shark Joined: Dec 2003 Posts: 2,733 | I can't tell you why it is that way but I don't think I would hesitate to use it either if it appears to be a new one and not remanufactured. | | | | | Joined: Mar 2002 Posts: 9,115 'Bolter | | 'Bolter Joined: Mar 2002 Posts: 9,115 | One of my GM manuals explains the origin of that grind. They started that when hydraulic lifters came in because the rocker was in constant contact and they want to oil the area better. I put one like that on my 216 and the oil still goes all over as required. I also thought that if I didn't like it I could drill the oil holes through and install it upside down. I don't think it would have any affect on the top. | | | | | Joined: Oct 2006 Posts: 9,671 'Bolter | | 'Bolter Joined: Oct 2006 Posts: 9,671 | Fred, if you happen to run across that explanation in you GM manual post it would you please. I wasn't aware of that and would like to ad it to my reference file.
Thanks
Denny Graham
Sandwich, IL
Never mind!! I got out the January, 1950 Chevrolet Sevice News and on page 5 it explaines it. As you said, the aditional pressure of the hydralic lifters called for additional oil flow to the bottom of the bearing surface. Thanks for remembering that.
Last edited by Denny Graham; 02/06/2010 3:46 PM.
Denny G
Sandwich, IL
| | | | | Joined: Jan 2010 Posts: 61 New Guy | | New Guy Joined: Jan 2010 Posts: 61 | Sorry, I can't make sense of this.
Given, that extra oil is desired to the rockers because of the continuous spring pressure (no "lash" interval), and that they wanted to distribute the oil to the bottom (load bearing area) of the rockers.
Both rocker shafts are continuously fed by the distributor block in the center, and they feed each adjacent pair of rockers through a single hole.
A flat or groove along the length connecting the hole to the inside of the 2 rockers will deliver more oil, but the groove should not extend beyond the edge of the rocker on either side. If the groove reaches this point, the pressure is lost, and the oil will always take the shortest path: out the sides, instead of into the rocker bushing. This means that the rockers closest to the distributor (#3 & 4 intake) gets more oil, the rocker next to it ($3 & 4 exhaust) gets some, and the other 8 rockers farther away (at cylinders 1, 2, 5, 6) get less than before.
The rockers I've examined all have a radial groove to distribute oil inside the shaft hole - but not to the edge. The "squirt" hole on top is not connected to the groove.
The RAS shafts have "banana" grooves that connect each pair of rockers to the original shaft hole - but not to the edge.
Possible explanations:
1. it's not an original shaft, and was made by someone who doesn't understand how it works ("I'll just save some time by making a single groove").
2. it's an original shaft, but a machining error (why it wasn't sold)
3. there are more parts needed to do this
4. ??? Well this was the exact concern of my mechanic. Youve brought up a great point that the shafts could be machining errors. Im hearing about 60% of the responses say Im ok to use these shafts with the grind, and 40% say they're not sure if they will be OK.
'51 Chevrolet 3100 216 5-Window
| | | | | Joined: Mar 2002 Posts: 9,115 'Bolter | | 'Bolter Joined: Mar 2002 Posts: 9,115 | The rocker tube is not under pressure, so to speak. It is fed by a pipe that has an opening or overflow below the top of the tube. The tube cannot completely fill up. So oil is pumped into the tube and it leaks out all over. The flat area on the outside bottom of the tube makes sure that the rocker bearing points get lots of oil. | | | | | Joined: Dec 2008 Posts: 1,922 'Bolter | | 'Bolter Joined: Dec 2008 Posts: 1,922 | | | | | | Joined: Jan 2010 Posts: 6 New Guy | | New Guy Joined: Jan 2010 Posts: 6 | Hey chevnky. My computer knowledge is sadly limited. Where are you at in Ky? Im in northeast Ky. Give me a call sometime. 606 757 3418 thanks noone | | |
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