Ironhead Pushrods Won't Hold Adjustment

[Staffords]

Update:

Parts arrived.

I pulled the chromoly pushrods. They are still straight. No appreciable difference compared to the replacement aluminum pushrods other than the thinner diameter. I'm 99.99% sure they were not related to the problem. But for $50 I now have Colony USA aluminum pushrods and I'm not mad about it.

I pulled the lifter blocks and lifters. One thing I noticed when comparing the old lifters to the new Eastern units I installed is that the Eastern lifters have an oil drain hole at the top of the lifter. Not sure how important that is or if it's found on the OEM lifters but it seems like it will help aid oil return. More importantly, I noticed that the wear pattern between the tapered bottom of the lock nut on the adjuster and the female taper on the lifter showed a very small contact ring. Since I had already swapped the adjuster screws and lock nuts, I think it's safe to assume the problem was the lifters. There was no damage to the female taper at the tip on any of the lifters I removed, so they're likely just a crappy replacement part made slightly out of spec

I have taken the bike for 2 short rides since and so far the pushrods have not come loose again! Hopefully this means problem solved! Thank you to everyone that helped troubleshoot this!

[Magneto Sportster]

Good news!

[Chuckthebeatertruck]

Originally Posted by Staffords

More importantly, I noticed that the wear pattern between the tapered bottom of the lock nut on the adjuster and the female taper on the lifter showed a very small contact ring.

This is actually a VERY important observation.

First -- you will only see a small contact ring; not a whole taper to taper contact. If you dye the parts, you'll see a slightly different picture. The split in the lock nut together with the 32tpi also affect the contact pattern. It's smaller than most people think.

Second -- your description sounds like you adjust your p-rods by setting the play first and the lock nut second. This the most common way people do it -- but also the method which ensures any issue in the taper, lock nut, threading, or neck of the lifter results in the lock nut loosening. In essence, the nut is "tight" but it isn't actually "torqued." As the dynamics of the valve train get moving . . .it suddenly moves on you and once it starts moving it all moves very fast.


This doesn't mean you're doing it wrong. It means if the problem repeats even with the new parts; try flipping your thinking and taking a more "aggressive" approach to setting the lash on the offending tappet.


Here's what I mean: adjust the p-rod so there is no free play and barely any rotation. Hold the adjuster there with your 1/2" wrench and lock the nut HARD. Then set the final lash by screwing the 1/2" adjuster INTO the lock nut. You are now setting the final lash by tightening things - not trying to hold them still. It's not only faster in the end; but this method ensures the locking force is always pushing into the taper vs hoping you got the nut tight enough without causing issues while you hold something still. Dynamic vs. static to put it another way.


To further illustrate - study this diagram by Dr. Dick and think of what it means and how the small ring of contact you observed could be affected.