Nonadjustable Rocker Arms

[65 Mustang]

Hey Guys. I noticed today that my cylinder compression varied significantly depending on how tight I made the rocker arm shaft assembly screws. When I torqued them to specs I got no compression in the first two cylinders and 150 psi in the rest. When I loosened the first two rocker arm shaft bolts the compression on those cylinders jumped up. Even got them to 160. I am not sure what the cause of this is. I would like to be able to torque them to specs and get high compression. I do not want the bolts too loose. Could it be that the valve springs need to be replaced? Could it be a worn or warped rocker are shaft causing it not to seat correctly? Has anyone experienced this? Any ideas would be appreciated. Thanks.

 

[rickwrench]

Was the head or block recently machined/skimmed/decked?
Hydraulic lifters?
Head gasket thickness?

If the head or block was skimmed and you have valves not closing now, you have two options using the current rockers; shorter/adjustable pushrods, or shims under the rocker shaft posts.

Alternately, you could round up an adjustable rocker assy and pushrods.

Rick(wrench)

 

[65 Mustang]

Thanks. Would washers be alright to use for shims? Also, does the spacing need to be equal under all posts or should I place the shims in as needed to achieve the correct compression?

 

[CoupeBoy]

The spacers *should* be the same across all pedastals, but since the actual shaft that goes through the rocker arms does not move/rotate I suppose you could try it under just the problem pedastal.. I would prefer if you did it under all stands first, if it works good that way I'd probably leave it alone.

I wonder if somehow you got non-matching pedastals? Like if one or 2 are physically shorter then another, or if the pushrods somehow are not all the same length.

If you do go with spacers that are different under the pedastal stands you should consider that to be a bandaid and you really should determine if there is a real problem that should be taken care of..

One diagnostic step could be to rotate (change which piston/valve uses it) all the push rods and see if the problem follows the rods. (or measure them all)

Any chance the rockers themselves are different ratios?

-ron

 

[MustangSix]

It could also be that the lifters are either stuck or pumped up and are not collapsing under preload, acting like a solid lifter. It only takes one to lose compression on a cylinder.

With the rocker and pushrod in place, try to push down on the lifter. It should move about .100" before bottoming out. If not, you probably have a pumped up or stuck lifter that isn't bleeding off. If that's the case, shimming would be the wrong move since you don't have a clearance problem.

You would have to have a significant mismatch of decking, head milling, and too-long pushrods to go past the hydraulic preload limits in a stock lifter.

 

[turbo2256b]

I have ha rough running engines before as a quick fix on the cheep for someone I explaned it to. Its because of several causes. I adjust the valve lash by using a compression gage in the usally noisy cylinder and adjust the lash untill the best compression is achieved. Dosent mean the issue is resolved but sometimes a quick fix. Possibly just a lot of stuff out of speck.
Non adjustable rocker shaft set ups comon issue is valve installed heights are different. This can be because the machinest screwed up or didnt realize the importance of it with shaft mtd rockers or valve seat wear over time (some seats sinking). Lifters going weak or face wear. Cam wear.

 

[turbo2256b]

Remove the rocker shaft and lay a realy straight edge across the valve stems see if there all the same height. first place to start.

 

[65 Mustang]

Thanks for the info everyone. I'll look into everything that was mentioned.

 

[MustangSix]

Remove the rocker shaft and lay a realy straight edge across the valve stems see if there all the same height. first place to start.

Good suggestion. It could be that valve seat erosion has one or more of them sticking up too high. Again, shimming is the wrong move.

 

[65 Mustang]

Removed the rocker arm shaft assembly today. I placed a straight edge along the pedestals. It did not align evenly. Only pedestals 3,4 and 5 were even with the straight edge. The first, second, and sixth were high with the first being the most prominent. I am going to take the whole assembly to a machine shop tomorrow. I'm wondering if the shaft somehow got warped. The shop manual says to place all six screws in and then turn them two turns a piece until the pedestals all sit flat. At that point you can torque to specs. Perhaps some previous owner ignored that and as a result the shaft got warped.

 

[wsa111]

At this point rather than spend money on the non adjustable rocker arms this would be the time to purchase adjustable ones.
Will cost some more $$$. but your problem will be solved.
Yes you will also need different pushrods for the adjustable rocker arms.
You could get the 1.6 rockers from Mike at classic inlines as well as the pushrods.
Mike sells quality parts at a decent price. Bill

 

[170-3tree]

If you weren't into getting new rockers, and a lot of shops won't machine the, you should pull the head and have the valves reseated with hardened seats by a good shop. Or even get a new head, this would be the right time for a bigger log and valves.

 

[JackFish]

I see rocker shafts on ebay regularly.
http://www.ebay.com/itm/200-ford-6-cyli ... es&vxp=mtr

http://www.ebay.com/itm/Rocker-Arm-Shaf ... es&vxp=mtr

 

[turbo2256b]

Removed the rocker arm shaft assembly today. I placed a straight edge along the pedestals. It did not align evenly. Only pedestals 3,4 and 5 were even with the straight edge. The first, second, and sixth were high with the first being the most prominent. I am going to take the whole assembly to a machine shop tomorrow. I'm wondering if the shaft somehow got warped. The shop manual says to place all six screws in and then turn them two turns a piece until the pedestals all sit flat. At that point you can torque to specs. Perhaps some previous owner ignored that and as a result the shaft got warped.

It is important to tighten the shaft down rather evenly in icriments.

You must check with a strait edge across the top of the valve tips