Loctite, aluminum & bronze

Discussion in 'General Engine Discussion' started by petertha, Dec 5, 2019.

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  1. Dec 5, 2019 #1

    petertha

    petertha

    petertha

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    I was perusing one of my favorite sites, Ken-ichi Tsuzuki, where his current project is a Harley.
    http://modelicengine.la.coocan.jp/harley191102.html

    What caught my eye (near the bottom of his connecting rod build) is where he is mentions 'fast reaction between aluminum & copper alloy'.

    I noticed the same thing installing bronze valve cages into my 6061 head. On one of my testers I was twirling the cage slightly to get a nice annular coating & then, surprise, it started bonding & I barely had time to push it down bottomed in the recess hole. Caught me off guard. Usually one can play with it for a while. It was 648 & the specs say 3 minute fixture time.

    Anyone else had this experience or know of information that pertains to certain alloy combinations kicking the set up time like this?
     

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  2. Dec 5, 2019 #2

    Peter Twissell

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    It is my understanding that oxides on the surface of the materials catalyze the polymerisation of the Loctite. Both aluminium and bronze quickly develop a thin oxide layer on exposure to air.
    Also, rotating the assembled parts is likely to generate a certain amount of local heating within the Loctite layer. My preference is to apply an excess of Loctite at the entry to the bore, so that the inserted part becomes coated as it is assembled. It's much easier to wipe away the excess than to add some more in later,or indeed to dismantle partly assembled and bonded parts.
     
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  3. Dec 5, 2019 #3

    WOB

    WOB

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    Copper is most effective in polymerizing Loctite. Some aluminum alloys( 6061 for example) contain enough copper to initiate the reaction as well. Bronze and brass react rapidly as many have noticed.

    WOB
     
  4. Dec 5, 2019 #4

    petertha

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    Good to know. I was on the low side of annular gap specs for this particular Loctite number, but kind of reluctant to open it up to the looser end because the head will see heat and i'm already kind of crossing my fingers the cages stay put at operating conditions. Do you think if I warmed the aluminum head a bit prior to assembly it would promote faster cure & aggravate the situation? I don't mean crazy heat, maybe 50C or something, warm enough to give me a bit of extra working time. everything i know about composites, glues, epoxy, cyano... heat speeds things up = a bad thing.

    Somewhat related, at this stage of assembly the ~ 0.010" valve cage seat will have been carefully cut & pre-tested with vacuum. The cage is not getting pressed into the head in order to mitigate chance of distortion. Its slipping in, counting on the annular adhesive to keep it put once cured. If excess Loctite does happen to overflow a bit onto the seat itself, will I be able to wipe any residue off with a Q-tip so it doesn't affect seal? I always understood it was the gap (or lack of air) that promotes cure & open Loctite will remain liquid longer than the joint. But this accelerated cure based on alloy might be a new wrinkle. Maybe just a small amount of alcohol or something might be ok, as long as it doesn't get into the gap itself. I was trying to think of a way to mask it, maybe like a wax crayon?
     
  5. Dec 5, 2019 #5

    WOB

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    You are other thinking it. Just make the cage a snug slip fit ( finger pressure to seat). or even a little looser. Coat it with Loctite and push it in. There will be no problem wiping off the excess liquid. You will have time to insure correct alignment before the cure begins on bronze. Do it at room temp. Heat is bad because it shortens the cure time to a few seconds if hot enough. Once cured, it will withstand 350-400 deg.F without problems. I seriously doubt your cage will ever run that hot. I used this method for my 9 cylinder Hodgson and never had a problem.

    WOB
     
  6. Dec 6, 2019 #6

    Cogsy

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    Where do you buy annular loctite? All mine comes as a liquid in a bottle...:p
     
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  7. Dec 6, 2019 #7

    Brian Rupnow

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    I use #638 Loctite on brass valve cages going into aluminum cylinder heads, and I have never had it react super quickly nor have I had any problems with it "letting loose" under engine operating conditions. You can't put much pressure on a valve cage to force it into an undersize hole in the cylinder head or it will collapse or deform.
    Best fit is a "thumb push fit", not something mechanical.
     
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  8. Dec 6, 2019 #8

    minh-thanh

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    Brian Rupnow !!

    Thanks for the information!
     
  9. Dec 6, 2019 #9

    petertha

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    I'm using 544 Bronze which has different ingredients than brass. Now which ingredients are acceleration contributors or inhibitors I cant say. Some typical compositions I found:
    Brass (free machining): 62% Copper, 35% Zinc, 0% Tin, 3% Lead
    Bronze (544 alloy): 85-90% Copper, 1-3% Zinc, 3-4% Tin, 3-4% Lead​

    As mentioned the cages are easy slip fit into the head, nothing mechanical.
     
  10. Dec 6, 2019 #10

    chrsbrbnk

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    a loctite rep. gave a bunch of us a "class " on different loctite and its uses he's statement was most grades of loctite need iron or steel to harden the accelerant was supposed to have iron particles in it.
    we used a heat resistant gap filling loctite # 620 for all permanent assembles and various others for more temporary stuff . the 620 could set pretty fast if used in cast iron with a bronze bearing there is a primer that is supposed to be used on any non ferrous parts but we had pretty poor luck with it. bonding problems in general seemed to mostly because of dirty surfaces, stuff needs to be completely degreased like acetone like finger prints or hand oil could screw it up , sandblasting helps or roughing up with say like sand paper or scotch brite
     
  11. Dec 6, 2019 #11

    WOB

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    Iron will certainly cause hardening as will copper. Copper works faster. Clean surfaces are essential for max performance. A rough surface is always better as with any adhesive.

    WOB
     
  12. Dec 6, 2019 #12

    mayhugh1

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  13. Dec 7, 2019 #13

    petertha

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    The attachment Terry included is consistent with what I've seen, excerpts attached.
    - if you have 2 active alloys (for example aluminum & bronze are considered active), primer not required
    - when 1 surface active, the other inactive, primer not required
    - when both surfaces are inactive, use a primer
    *primer is intended to speed up reaction & assist bond

    But I've never picked up on any verbiage that says certain combinations of active alloys may trigger faster cure reaction than normal open set time. Having said that, I really haven't played around with this particular retaining glue much, so maybe I should try steel on steel or steel on aluminum. What I'm more concerned with is some of my old Loktite might be getting way past best before date, slowing down & that has been my mental reference. I've gotten in the habit of dating the bottles now.

    Just to clarify, I don't think I have a critical problem here. It was more of an observation I thought was in my head until I read it on Ken's website.
    Yes WOB, I am guilty of venturing down rabbit holes LOL.
     

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  14. Dec 7, 2019 #14

    Cogsy

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    A very long time ago I worked for a bearing company that sold loctite products and I was involved in shutting down one of the retail outlets. When we came to pack up the loctite stand we found the sun had faded the labels of the front bottles on the display (obviously the customers had been drawing stock from the back) and so we wrote off the damaged stock and the employees took what they wanted with the rest getting chucked in the bin. Now I don't know how long those bottles sat there to have their labels fade so much, but I do know that I still have some of those faded bottles (they were the large, expensive size) and am still successfully using the loctite nearly 20 years after I got it. I can't say if its performance has degraded after all this time but it still sets up in a 'normal' time frame and I haven't had a failure of an adhesive yet. I think the colour of the fluid may have slightly darkened over time but I could even be mistaken about that. Also, all my loctite lives on a shelf in my shed, which routinely hits 50 degrees C in the height of summer (like it did yesterday). It's surprisingly robust stuff, no wonder it costs a small fortune.
     
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  15. Dec 16, 2019 #15

    madmike

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    one that we use in our machine shop - FLUID WELD-sold by silver seal
     
  16. Dec 17, 2019 #16

    petertha

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    Interesting, thanks. Crazy high temperature specs. I'm trying t find the manufacturers site for more technical specs but not having much luck.
    Do you happen to know, is the viscosity of Fluid Weld & part to part gap width about the same as Loctite?
    https://www.cylinderheadsupply.com/kl1378.html
     
  17. Dec 18, 2019 #17

    BobsModels

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    Hi
    Just to add to the thread. I was building a 1/8 scale Galloway and needed to push the head into the base. the ignitor face needed to be perpendicular to the base. Loctite tech recommended 640 retaining. It was designed for fixture alignment. It has a 30 min working time. here is sheet https://www.henkel-adhesives.com/us/en/product/retaining-compounds/loctite_640.html

    I use it now for most any part I am doing, unless really need fast set up.

    Bob
     

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