Sun Dec 28, 2008 3:10 pm
This is top thread, more please. Nuts and bolts, dismantled engines and airframes, parts being made, things coming together, broken bits. More please!
This is what makes WIX GrrrrrrRRRRRREAT!!
Thanks Scott and all your contributors.
This is what makes WIX GrrrrrrRRRRRREAT!!
Thanks Scott and all your contributors.
Sun Dec 28, 2008 5:46 pm
Before guessing the problem, lets wait till that affected cylinder is removed, and valve train is checked out. That one could have been overloaded, stuck valve?? Previous metal fatique ??? I agree keep the pictures coming. So are these the guys doing the overhaul or just the tear down?
Sun Dec 28, 2008 9:47 pm
Come on, you are the engguy!! Tell me what you think happened. It will be easy to figure out when the cylinder is pulled but that will probably not happen. This engine was overhauled about 5 times already so it will probably stay a mockup for the time being.
Dave
Dave
Sun Dec 28, 2008 9:49 pm
Tell you what you give me a theory and I'll pull the cylinder and see if your right.
Dave
Dave
Sun Dec 28, 2008 11:30 pm
Well if it was a bent or stuck valve, that would cause extra loading. Though I think it was a fatique failure and the one roller was the lucky one there when it happened. Those cam tracks are pretty hard material it looks like some spalling or pits on the tracks that means stress risers. With high loading and beliving all followers rolled okay if there was something that stopped at the other end of the push rod, the push rod would most likely bend before causing that cam track damage.
Other cause would be FOD of some sort. Did something happen around there that you haven't taken a picture of yet?
Other cause would be FOD of some sort. Did something happen around there that you haven't taken a picture of yet?
Mon Dec 29, 2008 8:00 am
No other damage that I saw. Your theory sounds reasonable. I'll let you know what I find when I pull the cylinder.
Dave
Dave
Mon Dec 29, 2008 8:02 am
Hey Dave, the panel looks good. I thought I'd given enough room for the switch casings, but got concerned after looking at the switches on the B-24. I'm glad the machine operator was able to solve the problem. It's what I would've done in that case.
Can't wait to see it fully complete and painted!
Can't wait to see it fully complete and painted!
Mon Dec 29, 2008 3:27 pm
Dave please keep the photos comming, this is a nice thread.
Something else, the damaged follower roller looks like it picked up some of the debris and it caught between the roller wheel and the lifter guide or lifter clevis and that is what caused the rough looking area on the roller, so like I said earlier either it was lucky first or even down the line for the broke off material. They will want to check out that case that holds the lifters real well for cracking etc. I wonder how long they ran it with the damaged cam? That is sure better than having a main or rod bearing, or master rod flange failure, and a dynamic disassembly in flight. Any idea of time on that engine at time of failure? It would be nice to know time on that cam, how many grinds etc.
Something else, the damaged follower roller looks like it picked up some of the debris and it caught between the roller wheel and the lifter guide or lifter clevis and that is what caused the rough looking area on the roller, so like I said earlier either it was lucky first or even down the line for the broke off material. They will want to check out that case that holds the lifters real well for cracking etc. I wonder how long they ran it with the damaged cam? That is sure better than having a main or rod bearing, or master rod flange failure, and a dynamic disassembly in flight. Any idea of time on that engine at time of failure? It would be nice to know time on that cam, how many grinds etc.
Wed Dec 31, 2008 12:08 pm
Ok, here's what I found! The cylinder with the damaged lifter roller had a broken lifter housing.
It broke right at the base. As you can see it had a fairly good size piece brake away and did probably cause the damage we saw on the cam.
This allowed the lifter roller to hammer at the base of the slot on the lifter housing, which caused the damage to it. It also explained why just one was damaged.
This picture doesn't show real well but there's an area about 3/4's of the way around this lifter housing base that the metal is dark and some what worn. This is where it likely cracked due to fatigue. The other 1/4 area is very shiny, which is the place where it finally broke away.
Good call engguy!
I did find one other lifter housing broken but there was no damage to the roller on that one.
Dave
It broke right at the base. As you can see it had a fairly good size piece brake away and did probably cause the damage we saw on the cam.
This allowed the lifter roller to hammer at the base of the slot on the lifter housing, which caused the damage to it. It also explained why just one was damaged.
This picture doesn't show real well but there's an area about 3/4's of the way around this lifter housing base that the metal is dark and some what worn. This is where it likely cracked due to fatigue. The other 1/4 area is very shiny, which is the place where it finally broke away.
Good call engguy!
I did find one other lifter housing broken but there was no damage to the roller on that one.
Dave
Wed Dec 31, 2008 3:31 pm
I guess it looks like that guide may have done it. Had to restudy the pictures.
Do the corners of the slot look like they were digging into that cam? And why only one lobe?
Do the corners of the slot look like they were digging into that cam? And why only one lobe?
Wed Dec 31, 2008 3:48 pm
The only thing I know for sure, the engine was removed for metal in the oil screen. Other than that, It's fun to speculate.
Dave
Dave
Wed Dec 31, 2008 4:04 pm
I had noticed first off that the bad guide slot was farther away from the casting than the other one, but just wasn't sure on that since I couldn't see all the rest. Its funny since it was a lower cylinder too. At first I thought the damaged guide was caused by the side load from the bad cam.
It is a real strange deal. Was the lifter and guide galling before or was it all the debris? Why did it break? Fit in case? That is a low stress item.
And why just move up and crap out one lobe? That is why I always suspected the cam itself.
It is a real strange deal. Was the lifter and guide galling before or was it all the debris? Why did it break? Fit in case? That is a low stress item.
And why just move up and crap out one lobe? That is why I always suspected the cam itself.
Wed Dec 31, 2008 6:55 pm
Dave, whats the blue stuff in the hole of the tappet guide flange?
Fri Jan 02, 2009 10:43 am
engguy wrote:Dave, whats the blue stuff in the hole of the tappet guide flange?
Not sure what that was. Just a color on the fabric I suspect.
Fri Jan 02, 2009 12:36 pm
For those who haven't torn into one of these, I thought I'd show you what we had to do to get ready to separate this adapter case. Remember what this looked like from an earlier shot. To remove this, you need to take all those bolts out that are safety wired and pull/lift the case off. Before you do that, you have to get all those lifter rollers backed away from the cam and out of the way, so they will clear the gears when you lift it off.
So here is how that is done. First, take all the rocker box covers off all 9 of the rear cylinders. That's 18 if you're counting!
Then loosen the lock screw that holds the valve adjustment screw. Once loose, you back off the valve adustment screw all the way. 18 of those too!
Now you loosen the nuts on both ends of the push rod tubes. Yep, 18!!
Now take all 4 of these nuts off the pushrod tube flange. 72 nuts in all!
Once you have those off, you can slide the flange back enough to clear the studs. In order to do that, you take one hand and put it under the rocker arm and pull. This will depress the spring in the lifter. Then with your other hand, use a small screw driver to hold the depressed lifter thats right in there behind the flange. If you did this right, you can now let go of the rocker arm and work the pushrod tube away from its mounting studs.
When you get it cleared of the studs, you can grab the lifter and spring and pull it right out of the lifter housing.
Then you get to wrestle with the push rod tube and the push rod. You see, you can't get the tube off/out from the other end until you get the pushrod pulled out far enough to clear the rocker box.
This is when you have to just move it around and hold your mouth just right, then it will come out. Ahh, got it! only 17 more to go.
Now you can get the lifter housing loose and pulled away from the case so the lifter roller will be able to clear the gears which is why you had to go to all this trouble in the first place!!
This was another one we found broken.
After all that, the only thing left was the oil tube, which I removed while Nolan, my help for today, took all the bolts out that hold it on. Then we popped the case off and prepared the new adapter case for assembly.
Old case.
New case.
Finally, My trusty volunteer, Nolan putting the rocker box covers back on. He is a student at the A&P school here. He was a great help with this and I think he didn't mind getting dirty!
Thanks Nolan
So here is how that is done. First, take all the rocker box covers off all 9 of the rear cylinders. That's 18 if you're counting!
Then loosen the lock screw that holds the valve adjustment screw. Once loose, you back off the valve adustment screw all the way. 18 of those too!
Now you loosen the nuts on both ends of the push rod tubes. Yep, 18!!
Now take all 4 of these nuts off the pushrod tube flange. 72 nuts in all!
Once you have those off, you can slide the flange back enough to clear the studs. In order to do that, you take one hand and put it under the rocker arm and pull. This will depress the spring in the lifter. Then with your other hand, use a small screw driver to hold the depressed lifter thats right in there behind the flange. If you did this right, you can now let go of the rocker arm and work the pushrod tube away from its mounting studs.
When you get it cleared of the studs, you can grab the lifter and spring and pull it right out of the lifter housing.
Then you get to wrestle with the push rod tube and the push rod. You see, you can't get the tube off/out from the other end until you get the pushrod pulled out far enough to clear the rocker box.
This is when you have to just move it around and hold your mouth just right, then it will come out. Ahh, got it! only 17 more to go.
Now you can get the lifter housing loose and pulled away from the case so the lifter roller will be able to clear the gears which is why you had to go to all this trouble in the first place!!
This was another one we found broken.
After all that, the only thing left was the oil tube, which I removed while Nolan, my help for today, took all the bolts out that hold it on. Then we popped the case off and prepared the new adapter case for assembly.
Old case.
New case.
Finally, My trusty volunteer, Nolan putting the rocker box covers back on. He is a student at the A&P school here. He was a great help with this and I think he didn't mind getting dirty!
Thanks Nolan