273 rocker losing adjustment

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Uncle Bob

Uncle Bob

Shiny paint causes stress.
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See below, the #7 exhaust rocker has backed off while I was driving. This happened once before but that time I blamed it on old age mind fog while doing the initial adjustment. Same rocker.

It was fine for about 3 miles or so then it started pecking so I turned it around and back home. It was obnoxiously loud by the time I got it back home. It wasn't missing so I'm trying to be confident that the cam/lifter isn't damaged.

I took the adjuster out with my fingers. The threads look A-OK. I think the way to fix this is to stake the rocker body so the hole is ovaled to lock the adjuster in. Maybe?

1750436427463.png
 
Cuda416 said:
Are you opposed to machining them to be able to use jam nuts?
Click to expand...

Seems like that would lead to different length pushrods and I don't want to go through that.

I was unsuccessful trying to stake the rocker and to crush it a little with the vise with no joy, but both times I tried it with the adjuster screwed in. That's probably sub-optimal.
 
Uncle Bob said:
Seems like that would lead to different length pushrods and I don't want to go through that.

I was unsuccessful trying to stake the rocker and to crush it a little with the vise with no joy, but both times I tried it with the adjuster screwed in. That's probably sub-optimal.
Click to expand...
Machining the tops for a jam nut doesn't change the length of the pushrod. Just makes a flat landing pad for the nut to tighten against.
 
Uncle Bob said:
Where do you get them? I keep seeing "Mancini" in google searches, followed up by "out of stock for years"
Click to expand...

Off the top of my head i don't know but I see them around here once in a while for sale.

I could be wrong so I'm sure someone will correct me, the threads should be 3/8-24? Could probably get something suitable from Grainger in a hardened jam nut with the right threads. Comp cams also has some options that might work.

This has been done before and I've seen some really clever solutions but can't seem to find them now.
 

Cuda416 said:
I could be wrong so I'm sure someone will correct me, the threads should be 3/8-24? Could probably get something suitable from Grainger in a hardened jam nut with the right threads. Comp cams also has some options that might work.
Click to expand...
I'm almost sure there's not enough thread above the rocker for a jam nut. Seems like I'd have to grind a lot off in the spot facing to get it to work. Look at #7 intake in the photo - it's adjusted correctly and looks like there might be 1-1/2 threads above the rocker. Maybe even less. I don't think a jam nut is going to work for me, at least not right now.

I just want to fix this one rocker and get back on the road.
 
Remove that rocker. Remove the adjuster. Place the rocker on the anvil portion of your vise and smack the bottom portion of the adjuster with a large hammer. Don't smack it like the strongest caveman in the world. Just one or two firm smacks. Try the adjuster and see if it has interference. If not, rinse and repeat until it does.
 
Uncle Bob said:
I'm almost sure there's not enough thread above the rocker for a jam nut. Seems like I'd have to grind a lot off in the spot facing to get it to work. Look at #7 intake in the photo - it's adjusted correctly and looks like there might be 1-1/2 threads above the rocker. Maybe even less. I don't think a jam nut is going to work for me, at least not right now.

I just want to fix this one rocker and get back on the road.
Click to expand...
No there's not. Not with those adjusters. If you want to do that mod, it requires new adjusters with lock nuts. I think Mancini has them. But, that REQUIRES spot facing the top of the adjuster holes in the rockers to assure a flat surface for the nuts to torque down against.
 
Uncle Bob said:
I'm almost sure there's not enough thread above the rocker for a jam nut. Seems like I'd have to grind a lot off in the spot facing to get it to work. Look at #7 intake in the photo - it's adjusted correctly and looks like there might be 1-1/2 threads above the rocker. Maybe even less. I don't think a jam nut is going to work for me, at least not right now.

I just want to fix this one rocker and get back on the road.
Click to expand...

Ah yeah sorry, hence the need for longer pushrods. Got it.
 
Have you tried staking around the perimeter of the hole with the adjuster out? You use a center punch or an awl with a hammer. That is done in aviation, normally on bearings or bushings in certain circumstances
 
RustyRatRod said:
Remove that rocker. Remove the adjuster. Place the rocker on the anvil portion of your vise and smack the bottom portion of the adjuster with a large hammer. Don't smack it like the strongest caveman in the world. Just one or two firm smacks. Try the adjuster and see if it has interference. If not, rinse and repeat until it does.
Click to expand...
OK I think I finally found a way to hold it so I can smash it. I smacked the top half of the adjuster, since the threads are all above the oiling hole. It got a little tighter, but looking at it again I'm not sure I'm smacking it the way you describe. I am pounding on it with adjuster part of the rocker laying flat on the anvil so it crushes the hole into an oval. Did you mean for me to stand it up and smack it like I'm trying to crush it so it's shorter?

I guess a smart man would go ahead and smack all of them a few times just to be sure, after I've got this figured out. Would loc-tite help?
 
racerdan80 said:
Have you tried staking around the perimeter of the hole with the adjuster out? You use a center punch or an awl with a hammer. That is done in aviation, normally on bearings or bushings in certain circumstances
Click to expand...
I haven't tried that yet, but I haven't put the engine back toghether yet either.
 
Uncle Bob said:
OK I think I finally found a way to hold it so I can smash it. I smacked the top half of the adjuster, since the threads are all above the oiling hole. It got a little tighter, but looking at it again I'm not sure I'm smacking it the way you describe. I am pounding on it with adjuster part of the rocker laying flat on the anvil so it crushes the hole into an oval. Did you mean for me to stand it up and smack it like I'm trying to crush it so it's shorter?

I guess a smart man would go ahead and smack all of them a few times just to be sure, after I've got this figured out. Would loc-tite help?
Click to expand...
Lay the rocker on the anvil so the adjuster hole is horizontal on the anvil, not vertical. You want to smack the BOTTOM of the adjuster hole. This way, you will still be able to start the adjuster. If you smack the top of the hole and compress the hole too much, you won't be able to start the adjuster.
 
Uncle Bob said:
OK I think I finally found a way to hold it so I can smash it. I smacked the top half of the adjuster, since the threads are all above the oiling hole. It got a little tighter, but looking at it again I'm not sure I'm smacking it the way you describe. I am pounding on it with adjuster part of the rocker laying flat on the anvil so it crushes the hole into an oval. Did you mean for me to stand it up and smack it like I'm trying to crush it so it's shorter?

I guess a smart man would go ahead and smack all of them a few times just to be sure, after I've got this figured out. Would loc-tite help?
Click to expand...
I wouldn't use locktite. You want to be able to adjust them in the future. If you use locktite, you'll have to remove the adjuster every time you adjust the valves, reapply locktite and reinstall the adjuster and adjust the valves.
 
What post #15 said. Easiest & safest way. Trying to change the shape of something by using impact could start a crack.
 
The top end is back together - once I got started I just kept going. If I got that right with no noise after starting I will run a test back and forth on a local highway that keeps me closer to home in case it backs out and starts making a racket again.

If it backs out again I'm going to red loctite it in place and send it. It's either that or BOAT (Break Out Another Thousand) for rockers and pushrods and I just spent a wad on getting it to not overheat.
 
RustyRatRod said:
Remove that rocker. Remove the adjuster. Place the rocker on the anvil portion of your vise and smack the bottom portion of the adjuster with a large hammer. Don't smack it like the strongest caveman in the world. Just one or two firm smacks. Try the adjuster and see if it has interference. If not, rinse and repeat until it does.
Click to expand...
Exactly. That procedure has been used for decades. The interference is in the threaded end of the rockers and not the adjuster. You know that, I know that but it seems many here don't. . Sometimes you can replace the adjuster and fix the issue and if that doesn't take care of it, the hammer trick works. You could always replace the rocker with a known good one. Not rocket science here. Gluing the adjuster in place isn't a smart idea. They are made adjustable for a reason.
 
Rockers probably worn out get another rocker or get it rethreaded.thread pitch too loose
 
Mtrhead said:
Rockers probably worn out get another rocker or get it rethreaded.thread pitch too loose
Click to expand...
Where's my red X . The interference that holds the adjuster tight is in the threads of the rocker. If you run a tap through the threads, it will take the interference away and it will be just like a nut and a bolt. Geez!
 
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