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mcjweller
Samba Member
Joined: October 05, 2022
Posts: 57
Location: Kitchener Ontario Canada
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 Posted: Fri Jul 04, 2025 4:24 pm Post subject: Re: Cam end play after assembly |
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| Yes - and similar to txoval's comment, it is an activator itself. Loctite's 7649 is almost totally acetone in composition. I think (but not sure) that the other ingredients are just propellant and a carrier to keep it from evaporating too quickly. The loctite (Henkel) support guy mentioned acetone could be used in place of the activator if it wasn't available (this was for another application) but not needed on the 518 with magnesium. I used acetone to prep because it plays nicely with the 518 and while not needed, is an activator. |
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txoval
Samba Member
Joined: January 23, 2004
Posts: 3839
Location: The Woodlands, TX
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| Posted: Fri Jul 04, 2025 4:39 pm Post subject: Re: Cam end play after assembly |
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The fact that the 518 just peeled up tells me there’s a difference. Again, used it on my 36hp build and had to take the case back apart. It took me hours with a razor blade to remove it.
Ive used old school gaska-cinch since |
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Brian_e 
Samba Member
Joined: July 28, 2009
Posts: 3960
Location: Rapid City, South Dakota
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| Posted: Fri Jul 04, 2025 4:43 pm Post subject: Re: Cam end play after assembly |
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I scotchbrite mag cases on both sides, then acetone, then spray the primer on the stud side, and apply the 518 to the non-stud side.
Magnesium starts to corrode immediately. I think the scotchbrite removes the corrosion and makes a better fresh surface.
Brian
_________________
So more or less the lazier and stupider you want to be, the nicer quality parts you need to buy.
-Modok
www.type-emotorsports.com
Type E Engine Parts and Supplies
https://type-emotorsports.com/collections/engine-parts |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 23095
Location: Oklahoma City
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| Posted: Fri Jul 04, 2025 5:24 pm Post subject: Re: Cam end play after assembly |
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| Brian_e wrote: |
I scotchbrite mag cases on both sides, then acetone, then spray the primer on the stud side, and apply the 518 to the non-stud side.
Magnesium starts to corrode immediately. I think the scotchbrite removes the corrosion and makes a better fresh surface.
Brian |
This is the correct point here.
Bare, stripped, magnesium begins to oxidize literally the second it comes in contact with oxygen. That patina (also known as white rust) is Magnesium oxide and whatever you put on that oxide.....may stick to the oxide but that oxide is now a poorly attached powder.
Yes, a scotch Brite or razor blade can strip to bare metal and if you have so.e sort of primer or want to apply a primer layer of adhesive or sealant, it should go on within about the same minute or so that you finish stripping the surface while there is unoxidized metal available.
Or, if we want to get spendy like the aircraft boys....you can have you case Alodine coated and the sealants will stick right to it. Ray |
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mcjweller
Samba Member
Joined: October 05, 2022
Posts: 57
Location: Kitchener Ontario Canada
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| Posted: Sat Jul 05, 2025 4:10 am Post subject: Re: Cam end play after assembly |
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I like the idea of scotchbrite on both sides. If it were just one side, then you are bonding the sealer to just one side only, given the comment about oxidation...which makes sense. I know with aluminum, once you expose it you have seconds really, before a new oxide layer is formed.
The warnings I have had about it though are that magnesium is so soft, that using a scotchbrite pad will leave high and low spots (potential leaks) due you the uneven pressure of your fingers on the otherwise "true" machined surface, and you are now relying 100% on the sealer to fill, instead of the tolerance between the machined surfaces being what actually closes the gap. I've seen that be the case in other applications! Which is why I stayed away...but I really do think it needs some sort of "tooth" in the surface. |
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74 Thing
Samba Member
Joined: September 02, 2004
Posts: 7630
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| Posted: Sat Jul 05, 2025 4:30 am Post subject: Re: Cam end play after assembly |
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| And be careful cleaning since scotchbrite is an abrasive and will leave debris. |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 23095
Location: Oklahoma City
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| Posted: Sat Jul 05, 2025 6:06 pm Post subject: Re: Cam end play after assembly |
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| mcjweller wrote: |
I like the idea of scotchbrite on both sides. If it were just one side, then you are bonding the sealer to just one side only, given the comment about oxidation...which makes sense. I know with aluminum, once you expose it you have seconds really, before a new oxide layer is formed.
The warnings I have had about it though are that magnesium is so soft, that using a scotchbrite pad will leave high and low spots (potential leaks) due you the uneven pressure of your fingers on the otherwise "true" machined surface, and you are now relying 100% on the sealer to fill, instead of the tolerance between the machined surfaces being what actually closes the gap. I've seen that be the case in other applications! Which is why I stayed away...but I really do think it needs some sort of "tooth" in the surface. |
Yes, kind of....on the magnesium softness issue. But, if one is doing this right.....and the surface really is pristine as original and it just has the dark magnesium oxide, you really only need to "buff" the surface lightly to get through the micron or so of oxide.
If there is more than just a couple microns or you have white powder....then yes, getting through that with a scotch Brite can make an uneven surface. Scotch Brite green with the yellow sponge and or scotch Brite green pads with no sponge are ~600 grit. The light gray are 800. The white ones are 1200-1500.
Putting a tooth on a surface with a file or sandpaper is only one method of adhesion. It does not work with every adhesive or coating on every surface.
Some believe scratching the surface creates greater surface to adhere to. That is true but only works on specific coatings/adhesives. In some cases it actually prevents adhesion.
Some believe scratching the surface creates valleys/ledges that shrinking coatings or adhesive use like traction pads to adhere better. That is also true but again, only works with certain coatings and surfaces.
Other adhesion methods are dyne level specific, electrochemical attraction specific (and therefore PH specific) or extreme tack level specific. Many coatings use a range of several of all of the methods mentioned, each contributes a different percentage of the total.
The only way to know is to test. Do the very bare minimum to the surface to start with. With magnesium, I would polish a test spot without scratching it. Degrease it with something that does not entrain moisture unless moisture is required for curing like with RTV. Put it on super thin in one spot and 2-3 times thicker in another spot (some sealers/adhesives pass or fail based on thickness). Adhere a test plate or piece of metal and let it cure completely and see what it does.
Next, do the same thing but make the final cleaning wipe with a mild caustic (original windex with ammonia is perfect). Then if that fails try something mildly acidic (wipe with vinegar and water). Repeat.
If all else fails, then move on to gesturing the surface.
Yes, I work with adhesion of coatings, inks, paints and sealants as part of what I do for a living. Ray |
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