On Liquid Gaskets And Their Application

Discussion in 'Workshop Forum' started by Paul Valente, Jun 21, 2017.

  1. Paul Valente

    Paul Valente Automotive Engineer

    Motor City USA
    In my observations, liquid gaskets take a fairly regular beating by xweb members which fuels misconceptions that liquid gaskets are somehow improper or a lesser gasket than a hard (paper/rubber) gasket. That's unfortunate as liquid gaskets can be perfectly valid solutions and are in some ways superior to hard gaskets. For one thing, they allow metal to metal contact which ensures correct bolt tension throughout the life of the assembly and eliminates the need for re-torquing as paper and rubber gaskets can creep over time. It will also fill-in imperfections in the mating surface to a much greater extent than hard gaskets, will tolerate more joint movement and will seal difficult areas like T-joints. Perhaps a little information will make people not so mistrusting of it.

    OEMs have widely embraced liquid gaskets in many engine and drive train applications with great success. If you ever watch the “How It’s Made” TV show when they show the car factories, you’ll see liquid gaskets being applied robotically to all sorts of flanges.

    The problems seem to stem from either improper application or inappropriate applications. By that I mean people either do not adequately prep or apply the product wrong or they are applying it to a joint that was not designed to be sealed with a liquid gasket.

    I didn’t invent any of this. The chemical companies figured all this out long ago. As I am suggesting you take some of the other forum members posts with a grain of salt, I would suggest you do the same for mine as well. You probably don’t know my background or mental state so by all means, check it out yourself. Here is a very good summary on liquid gaskets from Henkel (they make Loctite products)


    For the sake of this post, I’ll focus on RTV as that seems to be the “goo” that people have the most negativity towards….

    Really, for an RTV joint to work well it has to be designed to be an RTV joint. I’m currently rebuilding a spare transmission for my Lancia Beta that has a joint that was designed for RTV so I’ll use that as an example. The Beta transmission is similar to an X1/9 unit in some ways but the Lancia has a joint that runs right down the center of the differential bearing bores. There are two seal carriers that bolt on from either side that seal via an o-ring in a triangular gland. This joint presents some challenges.

    1. In order to maintain roundness and concentricity, the cover and case were machined when they were bolted and doweled together. Putting a paper gasket in between them after that fact would make the bores into ovals.

    2. Where the seal carriers meet the case/cover there is a T-joint.

    You need metal-to-metal contact and you need to seal a T-joint. The Lancia guys figured this out, of course, and designed the joint to be sealed with RTV. How exactly can you spot a joint designed for RTV? Well, you first have to understand a little bit about RTV and I won’t bother regurgitating what you can read on Henkel’s website but basically, RTV that is zero inches thick does not seal very well. Any movement will shear the molecules. So you want some thickness of RTV. What manufactures do is put in features that allow metal-to-metal contact but allow for a continuous bead of RTV. You’ll see steps or grooves sometimes, but the issue with those is that they have a fixed thickness and as it turns out, if the RTV is too thick, it can blow out. So what you need is a chamfer on one half and an overhang on the other.

    Here is the Lancia transmission case.


    Do you see the 30° chamfer all around the inside of the flange? That is not there by accident! It is so that when the RTV squeezes out from between the flanges, it fills up that triangular space creating a continuous, triangular bead of RTV all around the inside of the joint. If some movement occurs (thermal, stress due to load, whatever) it may locally tear the RTV where it is really thin but the thicker section will maintain the seal.


    As (bad) luck would have it, after I sealed this up I realized that I forgot to put the debris magnet in so I had to pull it apart. The good news is, it makes for some nice pictures.

    You can see how the flat part of the diff cover flange overhung the chamfer on the carrier.


    You can also see that in-between the flanges there is essentially no RTV. It almost all gets squeezed out. I think that is probably the thing that throws most people off is that they see the bead and think that it is just messy and start picking at it. Just leave it!


    I went a little heavy on the application. Being it is a transmission, if a piece did break off, and start floating around; it isn’t going to hurt anything.

    Here is magnet back in its happy home. You can see there is no chamfer on this side of the joint. There is a bit of a corner round but you can see the ghosted image of where the edge of the chamfer is on the mating part.


    So that is what a proper joint that is designed for RTV looks like. There are other factors of course, mainly to do with surface finish and making sure the bolt tension is distributed over your sealing surface, but we can’t influence those at this point so refer to the Henkel document referenced above for more of an explanation if you are curious. Most joints that people struggle applying RTV to on the X1/9 are not designed for RTV in the first place. Also, Fiat seems to have missed it on the bolt spacing and placement in some cases like the infamous cambox. Again, refer to the Henkel document if you want to see where the bolts should ideally be and compare that to actual cambox. It is a lot to ask of any gasket to seal that joint let alone one that it isn’t designed for it.

    X1/9 cambox (picture from JJay’s eBay auction). Note there are no features on either part to allow any thickness of RTV to build. No chamfer, groove or step.

    s-l1600 (2).jpg

    Cylinder head is the same thing. Just a sharp corner. This is NOT a good application for a liquid gasket.

    s-l1600 (1).jpg

    The other part of getting a good seal is the application of the product itself. Cleanliness is key! Any oil of dirt will be detrimental to the integrity of the seal. In a production environment you’d check the surface tension of the parts with a special pen (Dyne pen) or you would do a plasma treatment before applying the liquid if you really wanted a strong bond. I've seen Honda air-cooled engines where the valve cover is just glued on (with Hondabond..which is an RTV). No screws or clips. You basically have to destroy the valve cover to get it apart. Since we aren’t going to do either of those, just clean the flanges really well. There are specialty products for this, but brake cleaner ought to do it. Don’t use anything mineral oil based. Make sure you clean the chamfer area too now that you know how important it is. Once it is clean, apply about a 2.5mm continuous bead along the inside about 1mm from the edge and bolt it together. That’s all there is to it.

    In conclusion, liquid gaskets are a perfectly acceptable and in some way superior sealing solutions when applied correctly. Don't be afraid of using them in appropriately designed joints on properly prepped surfaces.

    Last edited: Apr 30, 2018
    Yves, Stoney#1, myronx19 and 6 others like this.
  2. aarpcard

    aarpcard True Classic

    After having way too many brand new conventional gaskets leak on me after a short period of time, I've resorted to using RTV as a replacement gasket on everything that I can (with obvious exceptions of course).

    Longevity of repairs has increased monumentally in my experience.

    The key, like you said is to have the surfaces really clean and dry. I'll scrub all surfaces with a brass brush and use an ample amount of break clean.

    If there are any scratches or imperfections in your mating surfaces, it's almost garuanteed a traditional gasket will leak in short order. RTV fixes that.
  3. FamilyMan

    FamilyMan Daily Driver

    NW Arkansas
    Great write-up! I learned something! Thanks.
  4. kmead

    kmead Over half way.

    Are there any joints in particular on an X that you would use a RTV or similar material on?

    The cambox to head joint doesn't seem to be a candidate or are you suggesting the technique you delineated to deal with that joint would make it work out?

    Not meaning to being obtuse or confrontational, just would like to clarify. Personally I would prefer to use liquid sealants assuming they can be successfully done. I know there have been diatribes about masses of rtv in bad places (the screen of the oil pump for example)

  5. Paul Valente

    Paul Valente Automotive Engineer

    Motor City USA
    Hi Karl. I'm saying that the cambox would not be a good candidate for RTV alone. I've been using the paper gaskets that it was designed to use but have been dressing the gasket with Hylomar blue. I think Bernice suggested that years back and I have been using it fairly religiously ever since. What I like about that is that it is neither an RTV or an anaerobic. It stays flexible.
    I really haven't had my x1/9 apart in years so I'm not recalling any particular joint that would be a good candidate. Like I say, I tried to use the factory designed sealing method when possible. If you want to use it on a joint that was designed for paper, just make sure you have it really clean and degreased like aarpcard says .....but you are going away from best practices if there is no relief feature to allow a bead to form.
    Last edited: Jun 21, 2017
    Ulix and kmead like this.
  6. kmead

    kmead Over half way.

    Thanks for clarifying. That's what I thought you meant.
  7. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    This is a good topic of discussion, glad you brought it up. I think a lot of the beliefs surrounding 'liquid gaskets' seem to fall into two (or three) camps. Over the years I've noticed a trend of sorts; guys that specialize in Euro vehicles have tended to resist the use of liquid gaskets, while guys that specialize in US domestic vehicles seem to really like it. And I'll throw another (3rd) camp of opinion into the mix. The motorcycle crowd tends to have their own belief; liquid gaskets are great, but only if the really thin variety is used and it is used very sparingly. These are just generalized observations but my point is the difference in opinions may result more from 'tradition' than fact. I'm not taking any sides here, I think there is a right and wrong application for these products (as Paul points out) and they should be used accordingly (as he states).

    A couple years ago while attending a major trade show I had a great discussion with one of Loctite's engineers about this. He pointed out (to my surprise) that they offer a vast line of liquid gasket products, each with different formulations intended for different applications. Somewhere I have a product catalog he gave me that outlines them. But some of the variables affecting product choice include things like exposure to various temperatures, chemicals, pressures, vibrations, as well as gap thickness, mating material types, assembly techniques, etc. A real science indeed. Following my discussion with him (and observations I've made over the years) I am of the opinion that 'misuse' is very common; poor choice of product type, over-application (too much) of it, improper prep, and use in places where it was not intended. This 'misuse' has likely led to a lot of the negative views found.

    To me there is a bit of an art to using them. Not only realizing when to use them and which one to use, but it also took me a little practice to achieve a consistent coating of the correct thickness. I hate to say it but us Americans often tend to follow a "more is better" way of doing things. Thanks to Paul for the excellent material...keep it coming.
  8. beezee

    beezee True Classic

    Thanks for the post Paul. I didn't realize that surfaces were machined/designed differently for RTV.

    For gasket-less applications I typically use Permatex Moto-Seal. It's a non-hardening gasket maker and is used extensively on motorcycles, hence the Moto-Seal name. Its always worked well for me and it is removed easily with acetone.

    I think one of the problems with RTV is "the bigger the blob the better the job" philosophy that some people live by. Excess RTV gets squeezed out in the engine, breaks free, and then plugs up an oil way or oil pump screen. I've seen this happen on motorcycles. Obviously not the fault of the RTV, but rather the fault of the user.
  9. Paul Valente

    Paul Valente Automotive Engineer

    Motor City USA
    That's that's a excellent point, Dr. Jeff. Whenever we have a seal guy in to talk about an application whether it's a radial lip seal or liquid gasket or whatever the first thing they ask is, "what fluid are you sealing?" Some of the additives we put in oil especially, EP additives, are very surface active. That is they afix themselves to the surface of whatever the oil touches which may or may not be detrimental to them.

    As to using RTV on a joint that wasn't intended for it... Again, you can see in the photo above that there is hardly any RTV left in the flange area after it is squeezed out. In some spots there is none (metal-to-metal). This is fine if nothing moves but if the joint isn't adequately clamped (the right number of screws in the right locations with the load distributed correctly.....blah blah blah) and the flanges gap at all (due to thermal or physical loads) it won't seal. The very thin areas may tear (one wouldn't expect a .010mm thick layer to stretch 100% to span a .020mm gap) and the parts where it is metal to metal has no ability to cope at all. So, RTV seal on flange that was not designed for if it is going to be risky.

    Really, there may not be a good X1/9-specific application for RTV. I looked back through some old pictures and found this one from when I took my X1/9 4-speed apart. Looks like (from this picture anyhow) that this joint may have been designed with RTV in mind. I certainly see a chamfer. Fiat used a paper gasket from the factory* but maybe they wanted to put the RTV features in in anticipation of someone using RTV in service. Again, I don't have the parts taken apart sitting in front of me. I'm just going off of this one picture. This was my failed input shaft ball beaing cage. Looks like whoever was in here previously used RTV as a gasket dressing rather than as a stand alone seal.

    *Sometimes a component like a transmission will fail some quality check and need to be reworked before it leaves the factory. It is a lot easier to rework an assembly put together with paper gaskets than it is to pry apart and clean a joints sealed with RTV. So, Fiat's requierments for how to seal this transmission joint would have included "ease of rework". In fact, it could have been a very big concideration to them so don't assume that they chose a paper gasket over a liquid gasket because they thought it made a better seal. They also probably liked that paper is cheaper ;-)
  10. rocco79/138

    rocco79/138 True Classic

    Fairview nc
    Very good information... A couple things jumped out as I read. The word "robotic" grabbed me and I fully expected to see it in any discussion on liquid gaskets. How the RTV is applied is just as important as where I would think. And as previously stated more is better seems to be the common school of thought. But replication of a robot applied liquid gasket by a person, once, is not very likely.
    Our cars even new did not have mechanics clamoring to work on them. Things are in tight/hot spaces and although I enjoy working on them and having successful repairs I have not met many mechanics that share my like for these cars. I have seen really bad repairs and although I can't say for certain it looks like "whatever gets this out of my shop" was the prevailing motive.
    I place some blame for the many bad results on marketing as well. To sell a product called "Form-a-gasket" is rather misleading. But "Form- a-2mil gasket on a properly machined/preped mating surface designed for RTV sealing" won't fit on the packaging. The rest of the blame lies with the father of invention, lazy. It is always going to be easier to squirt some goo on a joint and button 'er up than get the proper die-cut gasket for a shop that never sees our cars.
    I am totally behind enhanced sealing with the addition of Hylomar blue. But after reading your post again I am further convinced that the use of RTV as a "gasket" is false economy. Especially on our cars since virtually none of the mating surfaces were designed for sealing with just a liquid sealant. This makes perfect sense when you consider manufacturering tech and practices when these cars were designed and built. You could meter the amount by telling Bep just one squeeze of the trigger but if he doesn't get all way around then what? Squeeze number two. Having the tech available to utilize better sealing options is ok but doesn't warrant mass retrofitting... IMO
    Thanks and regards...
  11. lookforjoe

    lookforjoe True Classic

    Cool read. The RTV seal was an issue for Volvo with their early AWD Bevel gears. The fix was to disassemble, and file a specific angle & depth chamfer around the entire inner lip so that the RTV could do it's job.

    Since we are talking X1/9 here, I wouldn't use RTV on anything. There are no parts of the engine that used RTV from the factory, so why would you? Unless you modify the casings (front & rear main seal carriers for example) there is zero point applying any RTV. I've yet to dismantle my transaxle, so I don't know from personal experience if there is an application of RTV there. At a glance, it looks like paper gasket to me.

    I've used anaerobic sealant for years on Volvos, but those castings are much tighter tolerances, and as you pointed out, are machined specifically for that sealant. It would be folly to use those on a X1/9 also.

    I've also never found the need to coat paper gaskets with any additional sealant (some used to require a light oil or other lubricant, but not a sealant), so I'm still unclear on the logic behind that. I've certainly had to fix many a car where RTV was spooged all over gaskets & created subsequent failures & leakages...
    Paul Valente likes this.
  12. Paul Valente

    Paul Valente Automotive Engineer

    Motor City USA
    I suppose my larger point was, don't expect RTV to work if you are using it where it was not designed to be used or are not applying it to clean surfaces. On the other hand, don't let data from poorly applied or misapplied RTV be a condemnation of liquid gaskets as a whole. In the right situation, it is a great seal.
    To Hussein's point, this Lancia 'box is the first time I have done an RTV-only application with either of my Italian cars because it is the only time I have run across a joint where it was the proper seal for the joint.
    lookforjoe likes this.
  13. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    Also, depending on what year the parts were originally designed, the use of liquid gaskets may not have been very common yet. I don't recall seeing much of it in automobile applications back in the seventies...it was more of a 'aerospace' thing in those days. And it was rather expensive (relatively) back then, so cost issues would have been a real concern as Paul said. It seems it wasn't until the eighties that its use (OEM) began on newly designed components, long after the X's were designed.

    Typically I tend to stick with whatever the factory did at the time of manufacture, although that may not necessarily be 'ideal' by today's standards. So I guess the question then becomes deciding where it would be appropriate to utilize liquid gaskets now, particularly in places where it was not originally used ("retrofit" applications), as well as which one to use. I'll be honest, back when I reviewed the documents I received from the Loctite guy it was a bit confusing. These are not the same documents I received but they will give you an idea.
    Product choice (see pages 18-23):

    Product application (Henkel is Loctite's parent company):

    The second one includes some of the things Paul discussed. As you can see there are a lot of choices and a lot of criteria to fulfill (and this is only one company's selection). Naturally they would like you to use their products EVERYWHERE so they can sell more. But it would be nice if some basic guidelines could be listed that summarize best practices for 'retrofit' situations. Kind of a "Liquid gaskets for dummies" guide. :)

    I think this was Permatex's attempt to do that (sorry but it is a 'fail' in my opinion):

    On a related topic, here is a little article that outlines the popular "sealers" from Permatex (note sealers are not necessarily gaskets, rather they are often used with gaskets):
  14. Paul Valente

    Paul Valente Automotive Engineer

    Motor City USA
    Thanks for the data point, Hussein. I couldn't find an official TSB like I was looking for but I did find a blog entry on this: https://www.fcpeuro.com/blog/posts/how-to-fix-amp-reseal-your-volvo-5-cylinder-angle-gear . Pretty amazing that a Lancia transmission designed c.1970 had the chamfer and a Volvo gear box designed in the 2000's didn't. I mean, the chamfer is free if you put it in the pattern (for the casting) so it couldn't have been an economic issue. Surely whatever chemical supplier they were working with knew about it. That's a real head scratcher.
  15. myronx19

    myronx19 True Classic

    Toronto, ON Canada
    Although anecdotal, I used Permatex Ultra-Black on my X1/9 race transmission. That thing came apart quite often, and I never had a leak (it possibly didn't have enough time to form a leak).

    My factory gearbox isn't leaking either, but my cam box does have a small leak - in the areas that Paul pointed out in the other thread. I don't think I've seen Hylomar for sale here in Canada, but I have used Permatex Aviation "Form a Gasket" which you typically use on gaskets.

    On my race car, I'd grease one side of the gasket of my cam box cover - so that it was easier to remove the next time. That's a trick that was described in a Grassroots Motorsports article. It works!

    And as pointed out - more isn't better... my friend bought a Testarossa with a seized cam. Turns out some RTV plugged a gallery that feeds the cams (RTV was put on at some point), and boom.. he repaired it :)

    If you look at the How It's Made video of the Alfa Romeo 4C engine going together, you'll see that they use RTV of some sort on the bottom end (main bearing cap girdle to block & oil pan).
  16. Paul Valente

    Paul Valente Automotive Engineer

    Motor City USA
    Just more data....
    I was looking at a bunch of parts from a specific drivetrain company that are a split-bore/RTV designs this morning and they don't seem to do the chamfer or a groove. It looks like they have a particular surface roughness (not too rough and not to smooth) and are relying on that to control the film thickness. It does apear that they overlap one flange to the other in some cases making in effect a 90°chamfer.
    myronx19 likes this.
  17. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    For some 'split case' applications with cast aluminum housings on motorcycles and air-cooled engines, they use a very thin product that is something between a liquid gasket and a sealer, and no gasket is used. VW/Porsche recommends "Curil K-2" and most of the bike companies recommend "ThreeBond 1211"...back in the 70's it was often just referred to as 'snot'. It is a bit tacky and does not feel like RTV. The instructions say to spread a very light skim coat evenly on one of the mating surfaces and let it sit a minute before mating the halves. It fills any texture irregularities on the surfaces and sort of glues the case halves together. That makes it a little harder to separate them after it has fully cured (however it is not permanent, they will come apart), but it works very well to prevent leaks. One of its properties is the lack of material thickness to prevent changes in the case's internal dimensions. I wonder if something like this can be used for things like the X gearbox?
  18. Paul Valente

    Paul Valente Automotive Engineer

    Motor City USA
    This is an old thread now but I thought I would add this picture from one of Steve H's posts just for completeness. Even though this had a paper gasket from the factory, it is an X1/9 joint that is a good a candidate for RTV. Note the chamfer. They either thought it was going to be a liquid gasket at some point or wanted to provide for a liquid option in service. As mentioned, liquids can be a PITA in a production environment (imagine if you had a day's production worth of transmissions that you needed to re-work for some reason).

    AKimball92 likes this.
  19. Yves

    Yves True Classic

    Great post
    Paul Valente likes this.
  20. Paul, great posts on this topic, and quite timely.

    Great information here. Over the years I have seen lots of cam boxes with orange RTV on them, obviously there to try and fix cam box leaks. The results are worse than the leak in most cases. Cheap gasket sets often use the same thickness material for the cam box as the rest of the gaskets. This is even worse than the Orange RTV mess. Fiat used a very thin paper gasket to seal the box and maintain valve clearances. The thick gasket won't do that. Cam box leaks typically result from the thin paper gasket cracking from age and heat cycling. Or a replacement gasket poorly installed.

    I learned to use the old spray Hi-Tac gasket adhesive on these with good results. It also helps to let the gasket soak in hot water to let it swell as a NOS Fiat gasket can shrink or get mangled in the packaging and won't hold their shape.

    As with so many "tools" RTV can be misused more easily than properly. I often find transmissions that have big globs of RTV that were expelled from the mating surface everywhere. While it shouldn't hurt anything, if these globs drop away from the bead they often get circulated up into the oiling trough and block the flow of oil to the gearset. I have even found hunks blocking the oil path to the case extension. Not good.

    I use Permatex Ultra Black on X1/9 cases. It works very well if applied properly. And as Paul noted the sealing surface needs proper cleaning. I never apply from the tube but instead wipe it on with my finger. If it doesn't stick the case wasn't cleaned adequately. I use a clean blue paper towel and brake clean. If I use a gasket it gets a light coating on the main case seal. The extension housing typically don't need it.

    In a previous post on the subject I noted the improved stability of the diff preload when using RTV instead of gaskets. Thus I only use RTV on racing builds.
    Paul Valente likes this.

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