Rope Trick Woes

Bill Rusk · Post by **Bill Rusk** » Fri Aug 29, 2003 1:11 am

All

I had a stuck exhaust valve and did the old rope trick. All went well until I tried to put the rocker arms back on. I could not get the intake valve push rod to go all the way in. The little cup that the end of the push rod goes into was cocked off center down in the hole. Tried everything to get it straight. No go. Took the push rod tube cover off the crankcase to see if I could get to the cup. As I did so chunks off metal fell out. NOT GOOD!! These chunks of metal turned out to be pieces of my lifter. Now we are looking at splitting the case and basically doing a total overhaul. Big Bucks!!
I don't know for sure but I suspect that the cup cocked off in the hole and as I rotated the enging to do the rope trick I pressed the lifter into the cup and broke the lifter. I never felt any resistance but a prop is a big lever.

Recommendation... If you do the rope trick, leave the other valve assembly on that rocker installed and under tension so this can't happen to you.

Bill

N1478D · Post by **N1478D** » Fri Aug 29, 2003 2:29 am

Don't take the arms off to do the rope trick! You are just trying to use the soft rope laying on top of the piston to unstick the valve and have it pop back into place. All you have to take off is the rocker cover and the spark plug. And you want to gently use the prop to unstick the valve.

kloz · Post by **kloz** » Fri Aug 29, 2003 3:00 am

If you are going to clean the valve guide you have to remove the rockers and the valve spring for the valve you are working with. the push rods don't have to come out but if you take them out turn them and pull slowly.
If the hyd unit and the push rod cup are the only damage I would pull the cylinder and check things out first before I began an engine overhaul unless it's that time anyway.

Post by **GAHorn** » Sat Aug 30, 2003 6:56 pm

Don't rush to split that case and do an overhaul. You might succeed at pulling the cylinder and the lifter covers off the crankcase, and re-installing the lifter correctly, and only needing a cylinder base o-ring and a few gaskets. In fact, if the cylinder isn't completely removed from the piston you might not even have to consider rings, etc.

lcranton · Post by **lcranton** » Tue Sep 02, 2003 4:27 am

Bill, Sorry to hear about the lifter episode. Unfortunately I know of at least three cases of this happening. Two of the instances were a surprise to the people involved but the third one happened to someone that knew of the problem. This shows how easy it is for this to happen. If the lifters are of the type that do not have circular clips installed to keep the cup from coming out of the lifter then the cup may be withdrawn when the push rods are remove. When the push rod is removed, the cup sticks to the pushrod due to oil film and hits the little guide tabs inside the push rod housing cover at the base of the cylinder. If the cam lobe for the affected cylinder is at its inward throw there is enough room between the little guide tabs and the lifter for the cup to be fully withdrawn from the lifter and turn sideway. Then when the crank is moved and the cam lobe starts back up the cup is caught between the lifter and the guide tabs thus resulting in a broken lifter. There is so much mechanical advantage when turning the prop you will never feel the lifter break. It is possible that the cup may have broke but if the pieces are from the lifter the only fix I know of for a broken lifter is to split the case and install a new lifter. Have a local mechanic look at it a see what he thinks. Again, sorry to hear of your problem but I thought others may wish to know that this is a very real problem with the non circliped lifters installed in the C145/0300.

Larry

david harvey · Post by **david harvey** » Wed Sep 03, 2003 3:34 am

Yea, you can add one more to that list Larry. Several years ago my mechanic had a cyl. off of my c-145. As nearly as we were able to determine either someone came through the shop and moved the prop; or my mechanic said it was possible he did it, although he was very aware that it could happen, and I doubt he did. Anyway, I got a somewhat reduced priced bottom overhaul. Still very expensive, because even theough the engine was below "mid-time", you just can't open up the case without doing things right. As far as a fix without splitting the case, we looked and checked very carefully and determined that at least on this engine, it couldn't be done.

Good luck

Bill Rusk · Post by **Bill Rusk** » Wed Sep 03, 2003 6:54 pm

Larry

Thanks for the info. I read all the rope trick threads and stuck valve threads I could find, looking for the "gotchas". Nowhere is this mentioned. Hopefully, others will read this thread and avoid turning a simple job into a very expensive one.

Bill

N3243A · Post by **N3243A** » Wed Sep 03, 2003 10:48 pm

gahorn wrote: In fact, if the cylinder isn't completely removed from the piston you might not even have to consider rings, etc.

This may be a little off topic but what difference does it make if the rings leave the bore? If I understand the premise correctly, if the piston rings do not leave the bore so as to required a ring compressor for re-installation, you can avoid having to buy new rings and do a cylinder hone and subsequent break-in for that cylinder? My question is: as long as the original rings go back into the original cylinder bore why should it matter whether the rings remain inside or got removed completely requiring a ring compressor to re-install? I have heard this before from others but I don't understand the logic. Do the rings "lose something" if they get freed from the bore?? Since the rings (should) rotate freely at will inside the piston grooves there should be no special orientation of each ring that must be preserved by leaving it in the bore. Any answers?

Bruce

n3833v · Post by **n3833v** » Thu Sep 04, 2003 9:24 pm

Rings don't rotate in the cylinder. Once seated in the wall, they stay at the position to seal on the piston and the cylinder. If removed, the seat has changed on the piston groove wear pattern and on the wall.

Tom Downey · Post by **Tom Downey** » Fri Sep 05, 2003 3:17 am

I simply don't buy that, I have removed and replaced the same rings to many times sucsussfully to believe it.

If I removed a cylinder and did NOT check the ring wear I would feel like I cheated the customer.

Post by **GAHorn** » Fri Sep 05, 2003 7:37 pm

Rings do indeed move around on a piston, unless their lands are full of carbon and the rings stick. (Next time you intall a piston and rings, take notes as to the ring alignment vs the piston marks. You'll notice how that relationship is very different more than a few hundred hours later.) IF the rings are stuck, you get low compression. IF you check for low compression and the rings are turned around until their gaps align, then a few hours later they'll be moved back out of alignment again.
In any case, it's considered good practice to replace rings whenever you remove the piston from the cylinder for several reasons. Rings can wear eccentrically, the piston lands can become filled with carbon and should be cleaned, and new rings will have greater chance of remaining in good condition on thru to TBO.
Confession to Father GAR: Having said that, I have personally removed a cylinder completely off the piston on a C-90 engine, un-stuck the rings from the lands by soaking them in penetrating oil and gentle working, media-blasted the piston to clean it up, and re-installed the same rings and the owner flew away. It was several years ago and he's still happy with the situation. (We did it in a field with no spare parts and he was in a hurry.)
I'd prefer to install new rings, hone the cylinder for cross-hatch if necessary, and run it on mineral oil for 5-10 hours.

Bill Rusk · Post by **Bill Rusk** » Fri Sep 05, 2003 10:45 pm

All

The engine has been torn down at an Engine shop (Poplar Grove Airmotive) and all looks good except for the lifter. All will be cleaned, checked, and reassembled with new bearings,rings, lifters etc. The pistons only had about 200 hrs on them and looked good except for one ring that was tight. The crank and cam appear to be excellent as does the oil sump (often pitted/corroded). At least when done I will have had a good look inside the engine.

Bill

funseventy · Post by **funseventy** » Mon Sep 08, 2003 3:42 pm

This forum saved me a tear down for sure! I replaced 3 cylinders this weekend and if I wouldn't have know to look I would've damaged the engine with out a doubt. The first cylinder I pulled was trying to do it but I set it straight.

Thank you 170ers.

Thanks to George as well for the advise on Knisely stacks, they were reasonable on price and fit great!

Kelly

Psmith · Post by **Psmith** » Thu Sep 11, 2003 6:45 pm

I have run into the cups coming out with the pushrods and and have delt with them in this manor. First I stick a welding rod down beside the pushrod to try to keep the cup from following. If I am not successful (I always verify with a good light) I use a 1/4 in dowel rod with a headless brad in the end to reinstall the cup. This has never failed me.

Pete N1320D 170A

Bill Rusk · Post by **Bill Rusk** » Fri Sep 26, 2003 1:46 am

All

Well, here is an update on the engine. Although the engine was low time, about 450 hrs SMOH, as ya'll know you can't tear one down without finding all sorts of stuff thats less than perfect. We now have new main bearings, rod bearings, oil pump, lifters, and case inspected, cleaned etc, new valves, rings, guides serviced, a new cyl, all cyls honed, and a new cam, and I can't remember what else. Basically a complete overhaul although the engine shop calls it a "repair" and about 7600 bucks. Probably not a bad price for all thats been done. It should go to the test cell next week then hopefully back on the plane.

Should I invest the extra money for the Lord mounts or are the regular ones OK? Do they really make a difference?

Bill

The International Cessna 170 Association

Rope Trick Woes

Rope Trick Woes

Rope Trick Woes

add one

Lifter cups