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found oil on the floor, grounded

Good info!

No pictures because I forgot my camera but yes, I had not one but two locations where pliobond was on the shaft under the seal. I'm convinced that was the cause of the seal wear. I don't know how to be more careful with that stuff so the next time around I will use DC 737.


Thanks, Steve!

I really appreciate your thorough, evidence-based study and unbiased reporting. In aviation, as in life, facts work better than opinoin. Thanks!

In mentally preparing for when it is my turn to do this operation, perhaps greasing the strike surface of the crankshaft before applying any sealant, and then applying sealant just to the exterior cylindrical surface of the seal proir pushing the seal into its bore will prevent this type of seal failure.

Tricky operation. Need clean surfaces to allow bonding. Need enough sealant/adhesive to seal/retain the elastomeric seal. Need lubricant between shaft and seal. Grease in wrong place prevents bonding. Excess sealant squeezes out intrnally and drips onto the crankshaft, bonding lip to crank.

Accept my apologies, if indeed that is exactly what you did. You obviously are a thoughtful guy.

Suspect that very fine crocus cloth "cleaning/polishing" of the crankshaft strike surface may enhance seal life. Seal experts tell us that a seal needs to leak a small amount to lubricate the lip/shaft sliding surface for long life. Too smooth a surface doesnt allow any oil to lubricate the seal lip. ... but I deferr to experts.

I still hold Pliobond in high regard for this particular application. No experience with DC-737. Probably should get a tube to see what it does on test coupons.

Please post detail pix when able. ... thousand words...

Thanks for the great post!
 
no, I didn't add lube to the crankshaft before or this time. it's a tight working space and I didn't trust myself to contaminate the bonding surfaces. it's a personal call.

some tools. stab the old seal and work it out. I also used a wooden trim piece to help push the edges. I heated the seal in boiling water to soften it before stretching. plastic bag to help it slide over the flange. I needed to use small hemostats to hold the spring in order to link it. the tweezers in the photo were not sufficient. applied a thin coat of dow corning 737 to the inside of the crankcase side and then the outside of the seal and put it in wet. if the RTV sets up before install it will not hold, as I was told. I had more control with the application of the RTV than the pliobond I had used on the previous repair.

note: the conduit is the seal stretcher. cut a groove to match the crank flange.

note: MEK used to remove the prior pilobond. my final clean of all surfaces was with brake cleaner

total cost for part, materials and shipping = $50

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Conduit?

I'm having a hard time visualizing how you use the conduit.

I've read the whole thread, but not some of the reference materials that might explain it, so sorry if it is already described somewhere.
 
Please check Crankcase pressure

I'm not sure if you did but please check your crankcase pressure (use an old oil cap with an AN fitting and an airspeed indicator to find out how much pressure is in the crank case I think max is 5" of water) try in climb decent and level flight
 
I'm having a hard time visualizing how you use the conduit.

I've read the whole thread, but not some of the reference materials that might explain it, so sorry if it is already described somewhere.

put conduit under the seal. put cut slot on the flange and pull.
 
I'm not sure if you did but please check your crankcase pressure (use an old oil cap with an AN fitting and an airspeed indicator to find out how much pressure is in the crank case I think max is 5" of water) try in climb decent and level flight

the vent is open. extra slot cut in the rubber breather tube. the first failure was caused by the white silicon adhesive used at the factory. they don't use that anymore. the second failure was my fault because I used pliobond and some of the pliobond adhered to shaft and wore the seal after 100 hrs. for the third seal I used Dow Corning 737 adhesive. I hope that solves the issue.

no leaks so far.

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The only leaks you may have is the tent later today, by the looks of the forecast. ;) Coming up tomorrow with the cousin. Enjoy.
 
Great Thread

Steve,

Thanks for the step by step on this - great job. I'll be coming back here when I need to do mine.

Enjoy the show!!
 
Steve,

Thanks for the step by step on this - great job. I'll be coming back here when I need to do mine.

Enjoy the show!!

Great Idea Pete - I pulled that post to a single, then went to print-save-as-pdf and saved it in my maintenance folder. Great How-To! Thanks Steve. I on the final push for the airport next week, See you guys next year!! Maybe SnF.
 
credit goes to Sam Marlow at HAO for teaching me how to do this repair. teaching a man how to fish is more important than giving him a fish. thanks Sam and get well soon.
 
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You don't nessesarily need to oil the crank seal surface if you're afraid of contaminating the seal to case bond, just wipe a thin coat of grease on the id of the seal or three or four very little dabs distributed will do. But you really need a little lube of some kind on the dry rubber or crank or it will burn before the oil can work its way in and do its thing. A completely dry seal surface is a recipe for failure here.
Tim Andres
 
You don't nessesarily need to oil the crank seal surface if you're afraid of contaminating the seal to case bond, just wipe a thin coat of grease on the id of the seal or three or four very little dabs distributed will do. But you really need a little lube of some kind on the dry rubber or crank or it will burn before the oil can work its way in and do its thing. A completely dry seal surface is a recipe for failure here.
Tim Andres

after adhesive cure I did oil the outside of the seal at the shaft with engine oil. I'm not sure how much good that will do since the airflow is in the opposite direction.
 
Question...

A very slight drift, but since it is mentioned in the SI, I thought that I would ask.
I noticed throughout the thread that no one has mentioned using the split seal. Any valid reasons for this? Over the years, I have replaced a few seals, and always used the split seal. Much simpler operation, and endorsed by Lycoming. What am I missing?
 
I use the split seal, and have never had any leaks. That's what came with my engine, and I have changed it once; It wasn't leaking, but I thought it was. I might consider using the continuous seal if I ever have to change it again but I have never found a cross-reference to the proper part number.
 
Thanks for the update Steve.
I posted my opinion in post #6 on this thread on how I had replaced my seal in year 2.
Now I will be replacing it again this weekend.
BTW, I used pliobond on my initial replacement and will be doing the same again.
I'll let you know how it goes this time.
Sorry I missed you at Oshkosh, but I did purchased a couple of your quick drain fairings. Very nice.
 
Thanks for the update Steve.
I posted my opinion in post #6 on this thread on how I had replaced my seal in year 2.
Now I will be replacing it again this weekend.
BTW, I used pliobond on my initial replacement and will be doing the same again.
I'll let you know how it goes this time.
Sorry I missed you at Oshkosh, but I did purchased a couple of your quick drain fairings. Very nice.

thx Dan, I'm glad you like the fairings. I sold a lot of those. clean up the mating surface with a file to get a good fit because I didn't have time for that.

upon my first repair seal removal I noted the pliobond made a strong bond. just don't get any on the shaft.
note: I used a 1/2 x 1 piece of wood trim molding to push on the sides of the seal to help break it free. I would never be concerned with pliobond failing if done correctly.
 
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I tested my crank seal replacement yesterday and found the new seal is leaking.
I used pliobond, but I suspect I didn't butter it up enough on the interior form.
I'll be pulling it apart again on Saturday to see if the seal is floating or detached.
Not fun having to remove everything once again. What I feel I should have done is the butter up of the interior prior, to allow me more real estate to do the application before having the new seal present.
 
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