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Case half sealing

BlackRV7

BlackRV7

Well Known Member
OK gang, while running yesterday at lunch, one of the guys in the group, who is an avid classic motorcycle builder, chimed in when I ask if anyone knew of a place in town where I could get silk thread. He ask why I was not using something a little more sophistacated than thread with all the new sealing agents. His father was a pilot who rebuilt several lycs. so he familiar with our applications and recommended I check out a Yamaha product, Yamabond 5B.

Any thoughts.

Dana Overall
Richmond, KY i39
RV-7, "Black Magic"
 
Case Sealers

Silk thread along with a Hylomar or an equivalant sealant is a proven method of sealing crankcases. What usually gets folks into trouble is the old story if a little is good --- alot is better.. Use a light coating. If too much sealant is used then the torque values maybe jeopardized,. which allows for leakage and crankcase freeting on the mating surfaces.

JT
 
I think one of the reasons for using thread is that it has effectively zero thickness when the case is torqued together. Any other sealant could add some thickness which would throw off some of the tolerances.
 
Bond Line control

Actually, the thread provides bond line control; that is, being relatively non-compressible, it assures that a very thin line of sealant will remain between the mating halves when the bolts are torqued. Otherwise, the sealant squeezes out, and sealing is (obviously) compromised. The thickness of the sealant has no significant effect on assembly tolerances. As JT pointed out, it only takes a little sealant.
 
I'll echo Joe T's suggestion. Silk thread and Hylomar work very well. The problem with RTV or other sealants which "set up" is that if you use to much, or apply it in the wrong location, it may plug up a critical oil or fuel passageway. In a former life, I owned a motorcycle repair business. I'm familiar with YamaBond. It's great stuff, but not the right thing for Lycoming crankcase halves. It's basically an RTV varient.
When you use a sealant like RTV, you have a limited amount of time to assemble the parts, or the sealant will "skin" and not adhere properly to the metal. Hylomar never "sets". This gives you unlimited time to work. It also ensures that the sealant won't fail in the future due to movement of the parts assembled.
Charlie Kuss
 
Old Thread but....

.....I'm researching this subject right now and find Hylomar makes a lot of products. Not sure which one is for this application.

I understand some engine shops use two different products, one with the thread and a Locktite product on the other half?

What is the product and technique giving leak-free results for those with over 1000 hours on their engine builds?

Thanks!
 
I am rebuilding my O-320 and plan to use an anaerobic sealant on the case halves. I have researched this and others have had success with it. I restored an old porsche (Alluminun, split-case, horizontally opposed engine with an overall case structure similar to the Lyc). Porsche rebuilders routinely use this with great success over the original method involving silk thread. Anaeorbics weren't developed when Lyc and others developed their engines.

I am with the others that this is bad application for RTV. Anaerobics, on the other hand were developed for pipe flanges (usually close tolerance, machined parts) and they are a perfect fit for crankcases. The sealant doesn't set up where it squeezes out, unlike RTV, and will mix with the oil and wash out. You should still keep the amount used to a minimum in tight fitting flanges.

Larry
 
I rebuilt a couple of hundred VW air-cooled and always used Aviation Permetex #3 sealant with no string. None ever leaked, but that does not make it right for a Lycoming.

There is a good thread on here by the late Bob Axsom on Lycoming school and what they recommend. Unless a very experienced engine builder like Barrett recommended something else, why experiment with that? Granted you may, but why should one deviate from a proven solution?
 
This defines what Lycoming recommends -

http://www.lycoming.com/Portals/0/t...rnator Crankcase Parting Surface Sealants.pdf

The use of POB No. 4 Perfect Seal sealant (POB) and silk thread has been used generally for sealing finished parting surfaces that do not employ gaskets. This practice has always been satisfactory when correctly applied. However, we have tested and approved General Electric Company’s RTV-102 and LOCTITE-515 as alternate sealants which may be used at field service overhaul facilities where trouble may have been experienced in applying POB and silk thread.

Spruce has the sealant -

http://www.aircraftspruce.com/catalog/cspages/perfectseal4oz.php
 
If you want to seal your case halves, send them to LyCon. They built two engines I own (one still for sale!!!).

What they do is split the case, machine out a grove and install a formed gasket. Never heard of a single one leaking.
 
Sig600 said:
If you want to seal your case halves, send them to LyCon. They built two engines I own (one still for sale!!!).

What they do is split the case, machine out a grove and install a formed gasket. Never heard of a single one leaking.
Click to expand...

I'm afraid I've spent too much money with them already!
 
Or you can use a very thin smear of Proseal on the parting surfaces like I do. Never have had one leak.
 
If you look at the datasheet, you'll see that 515 is not recommended for aluminum. What IS recommended is Loctite 518, which is what I used on my IO-360 about 6 years ago with great success.

Clean very thoroughly the flanges with acetone or brake cleaner and apply a small bead inboard of the flange holes on one side of the case. Don't touch the bead after that. Don't smooth it out, level it, or anything else. Don't touch it. If you do, you might trap an air bubble which will eventually create a leak path.

The good thing about an anaerobic sealant is that it will only harden in the absence of air (only within the flanges) which means that any that squeezes out inside the engine will remain liquid and not clog oil passages.

Heinrich
 
rocketbob said:
Or you can use a very thin smear of Proseal on the parting surfaces like I do. Never have had one leak.
Click to expand...

I saw you were looking for POB #4 a few years back. Have you switched over to Proseal now?
My problem is I have a buddy A&P helping and eventually signing the logs. He's by the book. I am not excited about using POB to hold the thread and that's it. Would much prefer some sealant properties in the product but will have to convince him. Everyone seems to have their favorite that has "never leaked" but I'm kinda stuck with approved materials.... Thanks all.
 
I have personally used Aviation Permatex and silk thread in hundreds of Aircraft engine builds, it has always preformed well when applied properly. Aviation Permatex is what Lycoming recommend prior to POB. The silk thread is what provides the seal not the Permatex, POB or Hylomar they simply hold the thread in place until final assembly. About ten years ago I became aware that Lycoming also recommended the General Electric RTV 102 with no silk thread and from that point forward to today that what we use to build all Titan engines. With consistent: excellent results.
POB, silk thread and RTV-102 are proven products used on thousands of engines with hundreds of thousands of operational hours. Do you really want to try something that is unproven in your very expensive engine that would require a total teardown and reassembly to fix
 
I've proven Proseal to work just fine on both Lycomings and Continentals. About a half dozen to be exact. Zero leaks, zero problems. The last engine I did with POB #4 and silk string leaked within 200 hours.

I started using Proseal after helping a friend install new heads and banks on a Merlin. It was recommended by Roush as I recall.

I can't name anything manufactured in the last 50 years that uses a silk string for a sealant on a parting surface, other than a Lycoming.

Really just about anything will work.
 
In Googling around RTV-102 it appears to be pretty basic stuff also used for most anything around the house. I guess that's OK per Lycoming.....:eek:

I sure like the technical description of the Loctite 515 better:
LOCTITE®
515™ cures when confined in the absence of air
between close fitting metal surfaces. It seals close fitting joints
between rigid metal faces and flanges and will flex with minor
flange movements. Provides resistance to low pressures
immediately after assembly of flanges. Typically used as a
form-in-place gasket for pumps, thermostats, compressors,
transmission housings and axle covers.

Now to figure out how thick 'wet' is.....
 
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Titan-Xpert said:
I have personally used Aviation Permatex and silk thread in hundreds of Aircraft engine builds, it has always preformed well when applied properly. Aviation Permatex is what Lycoming recommend prior to POB. The silk thread is what provides the seal not the Permatex, POB or Hylomar they simply hold the thread in place until final assembly. ....
Click to expand...

Does the silk thread really do the sealing. or does it just provide a fixed "gap" that keeps the Permatex (or POB) a nice constant thickness?

A while back a neighbor rebuilt a Lycoming with some non-silk thread. It leaked almost instantly.

Does a silk thread have different compression characteristics from a cotton thread? The requirement for silk seems quite definite.
 
About twenty years ago I was experimenting with different sealing materials and techniques while building some engines that were to be installed on the test cell, run for 100 hours then dissembled for inspection. I built one with no sealant of any kind only silk thread, it was very difficult to get the thread to stay in place so I used bearing grease. We ran this engine for 100 hours from 75% to full power at red line cylinder and oil temperatures. We had no crank case oil leaks. I believe this proves the double OO silk thread when used is the source of the seal. Not the POB or Permatex etc.
 
Titan-Xpert said:
About twenty years ago I was experimenting with different sealing materials and techniques while building some engines that were to be installed on the test cell, run for 100 hours then dissembled for inspection. I built one with no sealant of any kind only silk thread, it was very difficult to get the thread to stay in place so I used bearing grease. We ran this engine for 100 hours from 75% to full power at red line cylinder and oil temperatures. We had no crank case oil leaks. I believe this proves the double OO silk thread when used is the source of the seal. Not the POB or Permatex etc.
Click to expand...

Thanks, interesting data.

I still wonder what the specific property of silk is that enables it to work so well. :)
 
I wonder if Permatex Ultra Black, or their High Torque Ultra Grey is a step up from GE (now Motive Chemical) RTV-102.
Time passes, and better products come around. This stuff is used with great success in auto & motorcycle cases & covers.
I use it on my Non-Lycoming RV-8 with complete satisfaction.
I have not used it on my Lycoming. However, being a Non-certified Lycoming, I suppose it would be OK to try.
When the gear case leaked on the O-300, at the oil pan overlap, Locktite 515 had been used. It couldn't fill the gap. It was on Continental's approved sealant list but no mention was made about an activator, we learned about that from Loctite's site. That site offers Loctite 518 as (i think) a better choice, and Heinrich confirms with good results.
More than one way to 'skin a cat'...
Titan's comment about using only silk thread to seal a case reminds me that carvel planked boats are Calked with tow (greasy rope fibers) which is pounded in between the planks to keep (most of) the water on the outside of the boat.
 
SHIPCHIEF said:
I wonder if Permatex Ultra Black, or their High Torque Ultra Grey is a step up from GE (now Motive Chemical) RTV-102.
Time passes, and better products come around. This stuff is used with great success in auto & motorcycle cases & covers.
I use it on my Non-Lycoming RV-8 with complete satisfaction.
I have not used it on my Lycoming. However, being a Non-certified Lycoming, I suppose it would be OK to try.
When the gear case leaked on the O-300, at the oil pan overlap, Locktite 515 had been used. It couldn't fill the gap. It was on Continental's approved sealant list but no mention was made about an activator, we learned about that from Loctite's site. That site offers Loctite 518 as (i think) a better choice, and Heinrich confirms with good results.
More than one way to 'skin a cat'...
Titan's comment about using only silk thread to seal a case reminds me that carvel planked boats are Calked with tow (greasy rope fibers) which is pounded in between the planks to keep (most of) the water on the outside of the boat.
Click to expand...

Anaerobics have a limited gap filling ability and caution should be used with gaps over .01" You can find the spec's online and a kicker or curing agent will allow for greater gaps. I use anearobics for relatively tight flange surfaces such as case halves. When applying a cover that crosses that flange halves, most recommend a dab of RTV in that area for it's gap filling properties.

Anearobics are great, but like most things they have their limitations that most be observed.

Larry
 
flyingriki said:
Now to figure out how thick 'wet' is.....
Click to expand...

Not very much! A very light smear is all it takes as most of it will squeeze out. The nice thing about using Proseal is you can smear the bead off after a few hours, and look around inside the case with the cylinders off to see if any excess is inside the case.
 
Lycoming Service Instruction No. 1125D

"ONLY LYCOMING APPROVED SEALANTS ARE TO BE USED IN THIS APPLICATION. USE OF ANY OTHER NON-APPROVED SEALANT COULD RESULT IN A LOSS OF CLAMPING FORCE AND/OR TORQUE, WHICH WILL RENDER THE ENGINE UNAIRWORTHY"

The ONLY approved sealants for Lycombing engines is POB 4 and silk thread, RTV-102 or LOCTITE-515-- ONLY implies No exceptions. If you don't follow the rules or don't know the rules it might be a good idea not to admit it publically.

Call me overcautious.
 
Yamabond

I agree, only use the approved stuff. A short story. My friend had a well known engine rebuilder do his TSIO 520 in his 210. When the airplane came back the engine looked beautiful, including a small bead of grey material on the case halves. As I was about to rebuild my engine, I asked what he used and he said Yamabond. I thought it looked great, but elected to do the 'approved' method, not Yamabond on my engine. About a year later my friend's wife said his engine 'sounded funny'. He had his mechanic check it out - metal in the screen, pulled a cylinder and found a spun main bearing. The rebuilder blamed it on bad bearings. But I suspect this was due to Yamabond being too thick and not crushing the bearings. The rebuilder wouldn't offer any compensation, even though the engine only had a couple of hundred hours on it.

Tom
 
I just put my O-320 together today with Permatex aviation and a double line of silk thread. The IA I am working with has done 30+ engines this way in the past couple years. Before that he was rebuilding engines for an airline in Alaska. He does Lycoming and Continental's this way.

He told me a very light coat is all that's needed and all it does is hold the thread in place. Too much or using thicker sealants will cause a gap clearance issue which could cause incorrect torque values or in severe cases things like spun bearings.

2015-12-24-10.11.29.jpg


2015-12-24-10.37.59.jpg
 
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Silk thread

Silk thread is definitely different than cotton thread, and dacron and polyester and nylon, etc.
Pure silk thread has unique characteristics in handling, tensile strength, decomposition, etc.
Why Lycoming settled on specifically "00" as the size (diam) to use and why it is necessary to use two strands, is beyond me, but that's what they recommend.
I suspect that when they stumbled on to a method that worked exceptionally well, they stopped looking.

Dave A.
 
hgerhardt said:
If you look at the datasheet, you'll see that 515 is not recommended for aluminum. What IS recommended is Loctite 518, which is what I used on my IO-360 about 6 years ago with great success.

Heinrich
Click to expand...


Hope to resurrect this thread.

For those of you that used the Loctite products, did you use the silk thread as well?


Thanks, Terry
 
Nope, I used 518 without thread as I mentioned above in 2008 when I overhauled the engine and it's still dry. Granted, it only has 12.5 yrs and 760 hrs since OH, but still that's a reasonable amount of time to see that 518 works.
 
terry.mortimore said:
Hope to resurrect this thread.

For those of you that used the Loctite products, did you use the silk thread as well?


Thanks, Terry
Click to expand...

I used the loctite anaerobic without thread on two different engines (700 hrs & 130 hours). Neither have any case seam leaks. Anaerobics prefer small clearances, so no need for thread to add clearance, unlike many other sealants that need a certain amount of clearance in order to work effectively.

Larry
 
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We use Loctite 515 with silk thread. Rock solid results. We also use the same Loctite 515 on most accessory gaskets except for magneto gaskets. It works a treat.
 
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