Sharing this experience out of a deep sense of shame and embarrassment. Hopefully others don’t make this mistake.
About 4 years ago the ‘51 in my tagline was experiencing severe clutch chatter. Experience and forum advice all said leaking rear main and oil soaked clutch disk. That was exactly what was going on. So, a new rope seal kit from Best Gasket, a bit of work and all was good. For a while. The clutch chatter started again. Just a tad, then progressively got worse. Since I didn’t drive the truck daily or even weekly I just did the best I could until I couldn’t.
Fast forward to today, the truck has been in the shop for a couple weeks up on stands with the oil drained and drippage inside the block slowing.
I dropped the pan and when I pulled the rear main bearing cap, the upper half of the rope seal pulled out a couple inches. First thought was “dangit” the plan was to insert a section of stainless windshield wiper reinforcement strip above the upper seal to force it into the crank, stopping the leak. Only option now was to pull the seal out. It was easy. Too easy.
Now for the unexpected discovery, the upper seal is about 3/8” to short. Just out of curiosity I dropped it into the rear bearing cap and it fell into place and was much too short.
Well, at least I know why it was leaking.
Now for the new plan. I found a NOS asbestos seal that’s currently soaking in 0w16 Pennzoil. I’ll see just how easy or not, it is to install.
I don’t remember the details on installing the last seal, I’m sure though that I cut it off flush if not slightly proud. What I do remember is it was really hard to pull into place even after loosing all the main bolts and dropping the crank a bit.
My guess is that the seal was stretched and over time it contracted and leaked like a big boy.
Not having a brass drift the plan this time is to make a few wood drifts from some very old oak boards. Or perhaps something plastic and with a proper hammer pack and pack and pack. Pack both ends of the upper seal. Maybe let it set for a day or two first, or before trimming and with the crank bolts loose, then hold again one end while rotating the crank in the proper direction to tighten the seal up prior to cutting.
The good news is it really can't get any worse than what I found today.
Ron - Your picture has me wondering and scratching my head a bit. The two sections of the new rope seal on the left look to be completely different diameters. Is that an optical illusion I'm seeing?
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
I tried to copy a page out of a '64 Pontiac manual about packing rear seals, I couldn't get to work so here's what Pontiac did. This is with crank out of the block, the crank will need to be away from the block to install the seal with out stretching it, it needs to go in loose. Once you have it in the block, tighten the main caps to push the seal into place.
Pontiac used this method for all V8's from the start to the last one in 1979. 3" and 3.25" crank journals, seals were different size but installed the same way.
Make a tool out of 1/2" brass rod with the packing end matching the groove in the block. The packing portion should be 3/4" long. Install the seal without stretching it and trim even with block after pushing it into the groove with tool or crankshaft. With the crankshaft firmly in place, pack the seal down with the tool you made till it bottoms outs ( 3/4" ) per side. Carefully install the seal in the cap not stretching it and use a socket or round tool to compress it into the groove. A slight compression of the seal is recommended. Trim off excess leaving a small portion proud of the cap mounting surface. Form the ends to small mounds or pyramids. Cut the excess seal material into four 3/8" long pieces. Pack each side of the seal in the block with one 3/8" piece with the tool going half the distance as the first packing. Pack the second 3/8" piece on each side leaving a small portion proud of the block deck. Form the ends into mounds or pyramids so the seal stays off the mounting deck when assembled. Apply a small portion of sealer to the deck around the seal area but not on the seal. Assemble the rear cap and torque to spec's.
The ideal behind the packing is as the engine runs, the seal will start to unpack forcing its way around the cap compressing it to make a tighter seal. Only the old style seals will take to packing, the new stuff will just fall apart. Best gasket material does not take to packing, its not needed. I find if I compress the seal as I put it into the grooves, it works better than just laying it in.
They’re flat/oval shaped. One laying flat, the other is on edge. RonR
Thanks Ron.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
When I rebuilt the engine in my Pontiac Tempest, I didn't have to do the packing procedure with the brass rod. The manual just said to roll the seal into its slot and make sure there was plenty in there, then I left some sticking up, which mashed together when I put the cap on. Didn't leak a drop.
The absolutely foolproof way to deal with a rope seal is to cut a new seal into pieces no longer than 1/2", throw it into the nearest trash can, and machine the back of the block for a full circle lip seal. Yes, it's an expensive procedure, one that requires the block to be stripped down to bare bones. "Buy once- - - -cry once"! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Made a rope seal tamping tool today. Luckily, even though I like pretty, I’ll settle for functional. Hoping the few degrees of cant will help with the curvature of the seal groove. We’ll see tomorrow.
Jerry, I do agree that your solution is the best. If this effort doesn’t work out, I may have to retrieve the 1959 (?) 261 build from a 1954 mold out of it’s corner.
Tronman, sounds like you engine was out of the vehicle when you installed the seal. No doubt that’s best.
The seal groove and bearing holes must be concentric for a lip seal to work. The seal area was cut before the final bearing surfaces were honed, so they are not a perfect match. Pontiac did the same thing. You need to find center of the bearing surfaces, then cut the seal groove to that center. The few that use the lip seal and don't have leaks, get lucky that their blocks are closer to centered that others. Lips seals don't have a lot room to be off center. The older Cummin's 5.9 had terrible lip seals on the front, they used a plastic sleeve between the seal and crank to center the timing cover before you tightened down the bolts on the cover and they still leaked. We used to install two seal per engine just to slow down the leaking. The bearing clearance let the crank move around and the seal didn't have enough lip to compensate. For years guys in the Pontiac world tried lip seals, most all of them leaked. The trick now is to use a one piece rubber seal that you make a clean cut across, roll it on to the crank, then fill the seal groove with sealer. As you install the crank, the sealer fills the voids of the non concentric groove. Once it dries, the seal is held by the sealer, not the block.
Thats a good looking packing tool, the Pontiac one looks the same only they cut a radius on the crank side to compensate for the curvature. It should work good, just keep an eye on the seal as you whack it into place, you want it tight but not frayed out everywhere. The engine will be quite stiff to turn over for awhile once done.
Well, it’s a good luck bad luck story. The install went smoothly, almost too smooth. I loosened all main cap bolts a turn or a bit more, depressed the clutch pedal and scotched it with a convenient piece of 2x4, removed the asbestos rope seal from the 0w16 oil it’d been soaking in for 3 days, molded it into shape in the rear main bearing cap, used two big screw drivers one for each side of the flywheel to leverage it down, coated the seal with Vaseline, hooked up the Sneaky Pete, and then,,,,,,,,pulled the rope seal into place in about 20 seconds! What, What, I’ve spent all day trying to get one in place.
I used a 2” socket to to mold the seal into the main bearing cap. One unexpected thing was that a new single edge razor blade doesn’t like cutting asbestos. I finally resorted to a new sharp 8" set of dikes.
Almost done. But then Karma bit. It was while torquing the cap bolts (two were already at 105 lbs) when taking the 3rd from 80 to 105 ft lbs there was a moment when it didn’t feel right and then SNAP! Yep, broke bolt. Karma was back.
At that point I gave it a good quick look, slid out from under the truck and headed to the house. Later that evening we were getting ready to head to town for supper and I couldn’t stand it. With the wife still getting ready I went back to the shop, pulled the bearing cap and decided to give the broken piece a go. With a small diameter sharp punch and small brass hammer it took all of 5 minutes to back the stub out. Take That Karma !
A few years ago I took apart an older 235 in which somebody had drilled small holes and pressed little nails in tightly so that the rope seal would not be able to turn nor shift...top and bottom. The nails had been ground (like a knife edge) so they had little raised metal lines which stuck up about 1mm from the surface of the channel. I figured they thought that would be more effective than a single sharp point. I think I still have the image of it. I'll look for it sometime.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
Jon, I suspect one would have likely had a few choice observations about the nail anti-slip option if they'd tried to pull that top seal.
Again, learn from my mistakes. It's a pretty sure thing I'm going to pull the just installed top rope seal in a couple days and replace it with a new one.
While chasing the rear main cap bolt hole threads earlier today I noticed a bit of the rope seal I'd driven in on both sides had squeezed out of the seal channel and was between the crank flange and oil passageway. Reason is I didn't tighten the front 3 sets of crank cap bolts tight enough before packing additional asbestos into the channel. I tightened them with a ratchet till I thought, they were snug. I guess they were but not snug enough.
Lesson, go ahead and torque the front 6 bolts to at least 60 ft.lbs. before packing the rope gasket. From what's been said this only applies if you're using a nos asbestos rope gasket.
I ordered the hopefully, last rear rope gasket I'll ever need. Well for a 216 anyway. Not sure what the 1954/59 261 might need.
OK, after sleeping on this snafu I have a question for those who know. What would be the expected consequence of just putting everything back together and running the engine for a mile or two, and then changing oil to get rid of any asbestos fibers/strings that escape the stock bypass filter. I would expect that on startup the asbestos captured by the crankshaft pinch would turn into extremely fine asbestos particles and be washed by oil into the engine oil flow with any big strings or pieces being caught by the oil pickup screen, and or filter. In the history of installing these rope seals, I'm pretty sure I'm not the first to have made this misstep. I also can't see a lot of old time mechanics taking time to pull the rope and redo the job. Actually, I'm not sure I can pull the rope without pulling the crank. Maybe, and if that's what it takes????
Well, I've about beat this poor horse enough. I went out this afternoon and pulled the new asbestos rope seal back out. Wasn't nearly as bad a job as I'd expected. I'd forgot about the screw in Sneaky Pete extraction tool, that and a pair of forceps and vice grips and a little work and it was out. The packed in rope sections came out in fuzzy wads, about 3/4" worth on each side.
I'll finish this project with the new nos gasket when it gets here later this week, hopefully.
While I was under the truck pulling the just installed gasket, I did remember my thought process while installing it. My flawed logic was if I left the crank abit loose, causing max clearance for installing the gasket, I'd be able to pack in more asbestos rope so that when I did tighten the main cap bolts it'd never leak. If, I rotated the crank all through the torquing process so I didn't lock it up.
What I didn't anticipate was the packed in rope might squirt out the side.
Oh well, as my Dad used to say, "Live and learn, die and forget it all".
You will get some Squirt out, it's just what happens. Just watch as you pack it in and quit when it starts coming apart. The cranks does need to be tight to the bearing, if not, when you tighten it down it will be to tight to turn. Small pieces in the oil won't kill the motor, it will go in the filter or get crushed by the oil pump gears.
Joe, you are correct Sir (and thanks for all the help). I did pull the just installed upper asbestos rope seal. I molded the second nos asbestos seal to the #4 cap after soaking it overnight in 15w40 and let it drip for an hour and then pulled it in place above the crank.
Next I torqued the front 3 cap bolts to 105 ft.lbs. With the packing tool I packed in an additional 1/2” of rope on both sides of the upper seal. I had cut the seal in the cap 3/16” long on each side and hopefully the +1 1/2” of packed rope seal will tighten everything up, preventing the rope from getting loose and moving or leaking.
There was a bit of squeeze out but less than the previous effort.
Next step was to install the lower cap. After spraying (only) the 4 ends with brake cleaner and wiping it off I coated the ends with Great Stuff, twisted the cap rope ends into points and carefully put the cap in place with the pointed ends going into the divots left by the packing tool in the upper seal. Torqued the 1/2” cap bolts to 80 ft. lbs. and installed the pan.
24 hours later I added 5qts of Tech 15w40 diesel oil (has 1200 ppm of zinc) Cranked the rig, slid under and with the flywheel dust cover off it was easy to see, No Leaks! I did make a 10 mile drive next and when I checked again there was a little seepage but no dripage. I’m hoping that goes away soon.
I mentioned the other day having seen an engine where a person had drilled holes and set little machined nails or brads. Well, I finally found buried with the notes I made at the time. I had forgotten I was also comparing the machined areas in two situations to see if the neoprene seal could have been used in this case (the one with drilled holes was from a 235 from around 1952). In this case, yes...my notes show the machine work matched and was centered with the crankshaft. The seal fit fine.
But please take a look. In each image you'll see 3 drilled spots. There were 6 little pieces to restrict movement of the rope seal. That in itself would have naturally prevented use of the rubber/viton/neoprene (call it what you wish) seal but it would have fit in the earlier 235 in this case. Anyway here are the little no-shift doo-dads I mentioned.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
Jon, almost makes one want to try a two piece neoprene seal with appropriate amount of Great Stuff in a 216, but not quite. I’m betting the seal installed on the nail anchors stayed put.
