I broke the rocker arm on #6 intake last week. I figured it was a fluke, so I replaced it with a new one. Took it for a drive this AM, ran great. Got back to the garage shut it off for 30 minutes. Started it up and drove away, and the clattering started again. Took the left valve cover off. The SAME rocker is broken. The rebuilt engine (LR from a '65 GS) is stock with the exception of a TA-25 cam. The only thing I can think of is insufficient valve to piston clearance. But why on just one? I will be pulling the intake and valley cover to check it out, but any suggestions are welcome.
David, it could also be insufficient retainer-to-guide clearance. Another would be coil bind. Best way to check would be to make up a solid lifter for testing, and slowly rotate the engine by hand and measure clearances.
Last fall I had a similar problem; -except that the whole rocker shaft broke into three pieces. What I was finally able to determine is that they sent me three different sized lifters in the rebuild kit. Once I replaced the Chinese made lifters with proper US made one, there hasn't been a problem. Make sure your lifters are the correct ones if you replaced them. Also check and see if they have a flat bottom, concave ones would be incorrect in a stock application, and could cause rocker or cam failure. I found my problem out when I ran the car with the covers off. Sometimes it helps just to see what is going on. Watch and see how oil flows. Nails aren't the best when it comes to upper cylinder oiling,and this could be the problem. Another thing to check is the pushrod, - is it bent? Is there oil starvation? Is the rocker shaft so full of crud that oil doesn't make it to the spurt hole? The rocker in your photo looks like it was running dry. Aluminum doesn't like running dry, and will break first if exposed to high heat caused by oil starvation. Piston to valve clearance; - you would have probably bent the valve if that was the case. A fast way to check is to put it on a vacuum gauge once you get it running again. If the needle swings rapidly between 18-14 chances are you have a valve that is no longer sealing, and could be bent. A steady needle would indicate good sealing, and probably straight valves. There is an outside possiblility that the cam is made wrong, and that particular lobe is somehow screwed up. I'd consider this remote though. Hope this helps,
The pushrods all look the same (and not bent) on the left bank (I haven't opened the right side up yet). There appears to be plenty of oil around, but I did not run it with the valve covers off. I will when I get it back together. Here is my plan : 1. Using the compressed air trick, pull and check the valve springs on that cylinder. 2. Check for valve binding in guide. 3. Pull the valley cover and check the lifters for failure and/or mismatch. 4. Check valve to piston clearance. As this is my first nailhead, I don't have any spare lifters (I should have taken all the old parts from the machine shop, but too late for that). Tom T. said he had a solid one made up that I could borrow if needed. I guess light weight springs are also needed? Do you check every cylinder? Thank you all for your help.
Coil bind as mentioned is a possibility, in my case caused by a machine shop installing generic shims under the outter valve springs that covered the recess for the inner valve springs. Willie
And the winner is......coil bind! Thank you all for playing! Along with the TA-25 cam, I got the recommended 'stage one' springs. The inner spring on #6 was NOT seated in the recess, but hung up on the edge. I will not know for sure until it's all together again, but I am confident at this point. The inner springs fit quite tightly in the recess. I suspect the person who assembled the valve train just plopped the springs in and got lucky 15 out of 16 times! I will follow up when I am back on the road. BTW, the folks at T/A Performance were GREAT! They answered the phone immediately (can you imagine?) and got the engine shop involved while I waited. They really know these engines and how their products fit and operate in "real world" situations.
Glad that the problem is solved! I bought a set of Chinese rockers - shafts and all when my 425 was rebuilt. The engine builder who is an old hand didn't like them. He did a lot of measuring and the rocker geometry was not correct. He found a supplier of American-made rockers and they were sweet! No problems. I got the import rockers from Kanter and they were great about it. They took them back and gave me a full refund even though I had them beyond the stated return period. I would buy from Kanter again in a heartbeat - just not rockers.
