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Of Hei Question

Discussion in 'Early CJ5 and CJ6 Tech' started by wheelie, Apr 23, 2022.

  1. Apr 23, 2022
    wheelie

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    I'm putting an HEI distributor in a 225 odd fire. I've read something about a "heat sink compound" that people put under their ignition module. Some kind of paste. I've never heard of this step in the HEI set up and wondering if it's helpful or just a high performance engine type thing.

    And the rubber isolator between the coil and cap.....that gets totally coated in dielectric grease? Just one side of it? Or don't worry about it? I've used before on the 231 but don't recall how much I used or which side of the isolator.

    Thanks gents.
     
  2. Apr 23, 2022
    47v6

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    The IM should have any paper or other material removed and thermal paste applied to help the IM dissipate heat and prevent failure. Thermal paste can be found easily on amazon or another online provider.. Radio shack would have been a source, but they are outta buisiness.
     
  3. Apr 23, 2022
    wheelie

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    The module is already installed in the remanned distributor. Not sure if it came that way or if the guy I bought it from installed the module in the housing. The whole set up is brand new and never run.

    So, I should probably yank the module out and smear that stuff on the bottom of it????
     
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  4. Apr 23, 2022
    47v6

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    Yes, I had a brand new one that failed and it had no thermal paste. I installed a new one WITH thermal paste and it didn't fail. Maybe its anecdotal, but they say to use it.
     
  5. Apr 23, 2022
    Walt Couch

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    Depends on how long it has been stored. That paste does tend to dry out and harden over time. Heat kills electronic parts so the heat transferring paste is very helpful to the life of the module.
     
  6. Apr 23, 2022
    timgr

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    NB - dielectric grease is not thermal paste. These modules sometimes come with a little tube of translucent stuff that is probably just silicone grease. Maybe better than air, but the actual goo is even better.

    Bought this tube at the hamfest maybe two decades ago. I've been using it for mounting transistors and ICs since then. This tube will last the rest of my life, if it's not lost or squashed in transit or something. This or something similar is what you want.

    heatsinkcompound.jpg

    The compound is basically dielectric grease (silicon grease?) and zinc oxide. The grease does nothing but carry the zinc oxide. It's the metal oxide that makes the thermal coupling between the two surfaces. I don't think drying out is a worry with this stuff.

    Radio Shack used to sell a tiny tube of this in their stores - maybe someone else does now. The most commonly available heat sink compound is for computer CPUs, and you'll find that everywhere. It's fine for this, but you'll pay extra for the exotic materials used (silver oxide?) since it's marketed to the CPU overclockers as some kind of super-duper tweak that will let them run that much faster (fast equals more heat).

    Example: https://www.amazon.com/Arctic-Silver-AS5-3-5G-Thermal-Paste/dp/B0087X728K/ref=asc_df_B0087X728K

    https://www.digikey.com/en/products/detail/nte-electronics-inc/NTE303/11646856 - minimum quantity 10, but this looks like a good option.
     
    Last edited: Apr 23, 2022
  7. Apr 23, 2022
    wheelie

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    Thanks guys. I understand the dielectric grease is not for module but for the rubber isolator….to prevent spark jumping inside the cap supposedly.

    Should I coat the entire ignition module or just the bottom where it contacts the distributor body?
     
  8. Apr 23, 2022
    SFaulken

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    Just the metal, where it contacts the distributor body.
     
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  9. Apr 23, 2022
    timgr

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    I don't know what the rubber isolator looks like, but usually you use dielectric grease for waterproofing. Keeps moisture out from under the isolator? Seals the isolator to the body?
     
  10. Apr 23, 2022
    wheelie

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  11. Apr 23, 2022
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    Looks ok. It's a huge quantity for what you need.

    Why not buy the product I linked above from Digikey? Ten 1 gram vials at 65c each. You'd have some to give away, and plenty for your needs. One of those tubes would be plenty for your module, probably with some left over.
     
    Last edited: Apr 23, 2022
  12. Apr 24, 2022
    wheelie

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    I'll look into it, Tim. I was just looking for local sourcing. I'll see what McMaster-Carr has to offer. They have really fast shipping and I'm told they have the paste. Maybe the brand you linked.
     
  13. Apr 24, 2022
    timgr

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  14. Apr 24, 2022
    wheelie

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    McMaster Carr has the Dow product you have, Tim. That little tube is like 60 bucks ( I think that’s what I saw).

    I’ll be checking into the the options you posted unless my friend has some he can share with me. He said he thinks he has some but has to find it. :shrug: I guess he suffers from the same thing I do. I’m always trying to remember where I put this or that.
     
  15. Apr 24, 2022
    SFaulken

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    BestBuy carries the stuff, Walmart *might* back in the Computer section of electronics, I don't know about that one, they did at one point, but I haven't set foot inside a walmart in about a decade. I don't know about Target or other stores like that. Pretty much any local computer vendor is going to have the stuff in small tubes.
     
  16. Apr 24, 2022
    47v6

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