Rocker arms on Rocker Shaft: how tight

edhapApril 27, 2014

Vanguard V Twin 303777001702

I am re-assemblying my head and valves and have found the rocker arms take a decent amount of force to rotate on the rocker shaft. I took them apart, soaked a few minutes in acetone, then oiled, still feel pretty tight.

Is this normal?

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Well, Briggs does not give any specs or tolerances regarding the fit of the rockers to the shaft.
If it is just so "close" that you can barely detect the slight grip between the two parts, I would not worry about it, expansion of the rocker arm when heated up may cause a much lighter contact between the two parts.
If these parts are being re-used, I would feel comfortable in knowing that they had already been in service prior with no issues. If you still feel like they are way too tight, try buffing the shaft surfaces with some 1" wide strips of 600 grit "wet or dry" auto body sand paper cut lengthwise from an 8-1/2" X 11" standard sheet of the stuff from automotive parts stores.
I would not use anything coarser than 600 grit, and be certain you thoroughly wash away any residue from your efforts before final assembly.
It may also be possible that you have inverted the shaft from its original orientation, and thus encountered a "wear pattern" that has been established already.
Rocker arms, by the nature of how they are loaded in service, only wear on 1/2 of the diameter of the rocker and of the shaft. The rocker arms wear on their lower surface (bottom half of circle) and the rocker arm shaft wears on its lower surface (also bottom half) because the upthrust of the valve springs and the camshaft/push rods causes the respective portions of each component to bear the load only on the areas I described.
If you somehow flipped the rocker arm shaft upside down, you may now be feeling some interference caused by "cold flow" of material on the rocker arms and the shaft.
Try the rocker arm shaft in various orientations to see if there is a position where the fit is a bit looser. If you find this sweet spot, assemble it this way.

This post was edited by mownie on Sun, Apr 27, 14 at 21:29

    Bookmark   April 27, 2014 at 6:43PM
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Thanks mownie, that info helps. They were stiff before i took them apart, i will try different orientations. Etc. Thanks!

    Bookmark   April 27, 2014 at 6:56PM
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Well, I worked on the shaft and rocker arms with 600 wet/dry and I got one rocker arm to move well.

the other arm got tight whenever I put both shaft openings on the shaft. either side by itself would move smoothly. I tried different orientations as suggested by Mownie, but no improvement

when I put both ends on, all oiled up, it would go back and forth a bit then get tighter as I rocked back and forth.

I started to suspect the alignment of the two rocker arm holes and found the opening between the sides of the problem rocker a few thousands narrow, compared to the opposite side. I spread the openings 2-3 thousanths and it went on smoothly.

    Bookmark   April 28, 2014 at 3:33PM
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Check this photo of my rocker pivot. It is bent with a break at the corner. Thats why the alignment was off. No doubt a victim of the exhaust valve guide that raised up hitting rocker.

    Bookmark   April 28, 2014 at 9:27PM
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Ooooh, that's nasty. Good save. Yeah, that whole stamping is probably skewed from the forces imposed on it.

    Bookmark   April 29, 2014 at 12:34AM
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I have been having the hardest time trying to get a rocker arm replacement. The briggs parts diagram only show the newest style rocker.

Anyone know why I cant find a rocker for this engine? my briggs manual shows 3 styles, mine is the stamped steel with the holes for the horizontal shaft?

    Bookmark   May 3, 2014 at 3:37PM
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You might make a phone call to Briggs & Stratton to see if they can still furnish the old style.
There may not be any of that "New, Old Stock" part left.
I would guess that design had some weaknesses, so Briggs moved on from that style.
Looking in the service manual, I see the text you referred to, but I have to wonder why Briggs does not show the cast aluminum style of rocker arm in the IPL, because the IPL DOES show the old style rocker arm shaft (item 1031, B&S # 690693). Which, by the way, also fits the larger 350700 Vanguards.
Give Briggs a call and see if they can give you some relief.

    Bookmark   May 3, 2014 at 4:09PM
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yes, I will call them Monday. I did read on another thread where someone said that the solution is just to get the newer style rocker, a new stud, and a new rocker support piece and just convert to the new style. They said it would fit and and work fine on the old heads. I will ask Briggs about that also.

I saw a couple of used parts on ebay that look like my rocker arm too. I will report back what I find out.

Have a good evening!

    Bookmark   May 3, 2014 at 8:11PM
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Another route that I personally would not have a problem with would be to have the broken rocker arm straightened and welded by a competent TIG weldor (Heliarc). I'm not talking about some guy down the street with an old buzz box welder and a can of old musty welding rods. I'm talking about a sure 'nuff GTAW professional who knows how.
Tomplum, raise your hand please.
Seriously, a good TIG weldor could put that back in shape and add a bit of reinforcement by deposition of filler material and it may never give a bit of trouble.

    Bookmark   May 3, 2014 at 10:03PM
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