L79 rebuild in Dallas

[Gary H.]

[David H.]

Re: L79 rebuild in Dallas

.... Now blowing smoke out of the left exhaust, clunky idle, dead miss, no power. ...

Gary

Color of smoke?

Flat tappet or roller cam?

Coolant in oil / oil in coolant?

Appearance of spark plugs?

Dave

[Gary H.]

Re: L79 rebuild in Dallas

Should have pulled the valve covers first. OOPS! Suggestion on method to pull the stud.

IMG_6487.jpg

[Leif A.]

Re: L79 rebuild in Dallas

Gary,
That's better news. Let's see a picture of the broken stud in the head. There may be enough to grab. If not, this is still going to be easier and WAY cheaper than the alternative.

[Bill M.]

[Tim G.]

Re: L79 rebuild in Dallas

Gary, it looks like the push rod is still in place, that's also very good.

[Gary H.]

Re: L79 rebuild in Dallas

Gary,
That's better news. Let's see a picture of the broken stud in the head. There may be enough to grab. If not, this is still going to be easier and WAY cheaper than the alternative.

I'm going with using a die to thread the remaining stud. Then using a nut to pull it. Then tapping in a new stud.

[Mark E.]

Re: L79 rebuild in Dallas

What's the cause of this? It looks like the rocker stud AND the rocker arm broke.

Did the rocker stud fail, which somehow broke the rocker arm? Or the other way around? Did the valve hit the piston? Over revving?

It's curious the pushrod remained in place. It seems more likely the lifter would push out of its bore. The pushrod must have made a LOT of noise bouncing against the valve cover.

[Tom D.]

Re: L79 rebuild in Dallas

It looks as if the push-rod is no longer on the lifter. Looks angled on the top end.

[Gary H.]

Re: L79 rebuild in Dallas

What's the cause of this? It looks like the rocker stud AND the rocker arm broke.

Did the rocker stud fail, which somehow broke the rocker arm? Or the other way around? Did the valve hit the piston? Over revving?

It's curious the pushrod remained in place. It seems more likely the lifter would push out of its bore. The pushrod must have made a LOT of noise bouncing against the valve cover.

It looks like the stud just snapped. No clue why. Rocker is fine. The spring was in place so the valve never dropped. Yea. It was making a hell of a noise by time I got home. I'll post the final result after I replace the stud and adjust the rocker.

[Gary H.]

Re: L79 rebuild in Dallas

Gary,
That's better news. Let's see a picture of the broken stud in the head. There may be enough to grab. If not, this is still going to be easier and WAY cheaper than the alternative.

Absolutely enough stud to try my rethread with die and pull idea.
IMG_6488.jpg

[Mark E.]

Re: L79 rebuild in Dallas

So the rocker arm is ok but the rocker stud broke. Maybe a bent pushrod, or the stud suffered metal fatigue or was defective? If the pushrod is bent, consider checking, maybe replacing all the pushrods (if not done during the recent head work). If the rocker stud just mysteriously broke, consider checking, maybe replacing all the studs.

Is the lifter still in its bore?

[Duke W.]

Re: L79 rebuild in Dallas

A close up photo of both sides of the break might reveal a cause.

The stud is subject to cyclic loading so fatigue can be an issue. Fatigue failures usually start with a small surface flaw. Then the cyclic loading causes the flaw to propagate as a crack. Once the crack has weakened the part sufficiently, it will suddenly fail. Most connecting rod failures are due to fatigue, but bearing seizure can also break rods due to the huge bending load placed on the rod as the bearing seizes up, and the failure is often about one third the way up from the big end.

A fatigue failure will usually show a relatively smooth area, which is the progress of the crack. Then the rest of the section where the final sudden break occurs will have a comparatively rougher finish.

The above is a classic fatigue failure script for a cyclically loaded part.

Duke

[Gary H.]

Re: L79 rebuild in Dallas

A close up photo of both sides of the break might reveal a cause.

The stud is subject to cyclic loading so fatigue can be an issue. Fatigue failures usually start with a small surface flaw. Then the cyclic loading causes the flaw to propagate as a crack. Once the crack has weakened the part sufficiently, it will suddenly fail. Most connecting rod failures are due to fatigue, but bearing seizure can also break rods due to the huge bending load placed on the rod as the bearing seizes up, and the failure is often about one third the way up from the big end.

A fatigue failure will usually show a relatively smooth area, which is the progress of the crack. Then the rest of the section where the final sudden break occurs will have a comparatively rougher finish.

The above is a classic fatigue failure script for a cyclically loaded part.

Duke

I think it's that simple.

[Gary H.]

Re: L79 rebuild in Dallas

Well... it wasn't that simple. I went the rebuild route. I found Engine Rebuilders in Dallas. Check them out; the shop, builds at various stages, some of the guys, online reviews. They seemed okay. Before I dropped it off (and when I dropped it off) I told them, please do not touch the block stamp in any way. It was clearly communicated to the owner and the manager. You see where I'm going. They didn't communicate it to the shop. So! They didn't completely grind off the stamp, but, it's pretty bad now. Here are the pics (original and now). How bad is this?

original.jpgnow.jpg