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Poorman's guide to Vacuum Testing

Discussion in 'Chainsaw' started by Four Paws, Jan 18, 2007.

  1. Four Paws

    Four Paws Addicted to ArboristSite

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    Well, I have learned a thing or two from this site, so I figured I would give something back. We all talk about vacuum testing crankcases to determine if a saw has an air leak. Seems as if the "how do I vacuum test my saw" question gets asked quite often here, so I put together a step-by-step pictorial guide.

    The first thing you need is a vacuum bleeder. Since we are doing this on the cheap, you probably don't want to fork out the money for a Mity-Vac, so this model from Harbor Freight works just fine, and is currently on sale for $17, normally $25.

    [​IMG]

    Now, you will need to determine how you are going to hook the vacuum bleeder up to your saw. I made this handy adapter to hook into my impulse hose on the saw I am working on. Cost me $2.50 - $1.25 for each nipple, and I had the connector laying around in my box of parts.

    [​IMG]

    Okay, now you need to block the intake and exhaust ports. This step requires some disassembly of the saw, but I am assuming that if you are vacuum testing your crankcase, you feel comfortable taking your saw apart. I used some rubber from a rim strip - covers the spoke nipples on the inside of a dirtbike wheel - you can also use an old bicycle inner-tube, gasket paper, etc. Cut the pieces to length, use your exhaust and intake gaskets as a template to transfer the bolt holes to the rubber, and use a punch or leather working tool (like I used) to punch holes in the rubber.

    [​IMG]

    Now, this piece of rubber will be insterted, as a gasket would, on your intake/exhaust ports. The only difference is the rubber covers the ports. Now, install your muffler and intake boot and sandwich the rubber gasket between the ports and the muffler/intake boot. You can see the rubber gaskets I made, installed as I described, in the pictures below. If you have a spigot mount carb, you can use a piece of innertube and a hose clamp to seal the intake.

    [​IMG]

    [​IMG]

    Now, make sure your spark plug is installed and hook up your vacuum bleeder to the impulse hose.

    [​IMG]

    Looks like you are ready to go to work. Pump the vacuum bleeder until you reach your desired vacuum.

    [​IMG]

    Go have a beer :cheers: then come back in 5 minutes or so, and check to see if your vacuum gauge is reading the same as when you left it...hopefully it is. Now, rotate the crank slowly by hand. Do this 5 times or so...is your vacuum still holding? If it is, GREAT! Now, port that big bore kit you bought, get it installed, file your chain and go make some chips!
     
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  2. KMB

    KMB Addicted to ArboristSite

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    Thank you and good job. Nice clear pics, easy instructions, and done on a poor man's budget :) . I've added the link to my favorites and will be referring back to it to do my 044 once I get all the parts and get it back together.

    Kevin
     
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  3. kd460

    kd460 ArboristSite Operative

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    Yes, very nice work and very nice pics.

    This one will be saved in my "chainsaw" files.

    Very timely as I am working on an 028 project saw, this will be a big help, thanks for taking the time to do this. KD
     
  4. Lakeside53

    Lakeside53 Stihl Wrenching

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    GREAT JOB!!!!! I'm rep'd out for the day, but I'll hit you tomorrow!
     
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  5. Urbicide

    Urbicide Addicted to ArboristSite

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    Nice job paws! Excellent pics! :cheers:
     
  6. Scooterbum

    Scooterbum Addicted to ArboristSite

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    Great step by step!!! Thanks :hmm3grin2orange: :hmm3grin2orange:
     
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  7. ASEMASTER

    ASEMASTER ArboristSite Operative

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    real nice job thanks for taking the time to do so.
     
  8. Justsaws

    Justsaws Addicted to ArboristSite

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    Very nice!:clap:
     
  9. 046

    046 Addicted to ArboristSite

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    good job!
     
  10. GASoline71

    GASoline71 Mr. Nice Guy (Moderator)

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    Thanks for that post FP!!! Nice clear pictures too!:clap: :clap: :clap:

    Gary
     
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  11. troutfisher

    troutfisher Addicted to ArboristSite

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    VERY Impressive!!! Posts like that are the reason I visit this site daily, THANK YOU!!!!
     
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  12. Lakeside53

    Lakeside53 Stihl Wrenching

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    I know some of you are thinking "why rotate the crank 5 times..."


    Many seals can be fine in one crank postion, but not another. I rotate them left and right a few times, and sometimes gently poke the seal when under vac. Don't exceed 0.4-0.6 bar though... you may get fake results.
     
  13. Four Paws

    Four Paws Addicted to ArboristSite

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    Thanks for the compliments guys! Just trying to help out.

    Andy, thanks for mentioning why I rotated the crank - I guess I took the reason for doing that for granted. For those that aren't good with conversions, .4 -.6 Bar = 11.8 -17.7 in-Hg.
     
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  14. Trigger-Time

    Trigger-Time Guest

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    Thank you! rep is on the way :rock:
     
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  15. par38lamp

    par38lamp ArboristSite Lurker

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    Rent a vacuum pump?

    Autozone rents vacuum pumps for free. That is a real poor man's way!
     
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  16. Sethro

    Sethro Heathen

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    [​IMG]
     
  17. Urbicide

    Urbicide Addicted to ArboristSite

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    :clap:
     
  18. RiverRat2

    RiverRat2 Addicted to ArboristSite

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    Fp!!!!!!

    Great post,,,, repped all good!!!!!!:rockn: :rockn: :rockn:
     
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  19. rahtreelimbs

    rahtreelimbs A.K.A Rotten Tree Limbs

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    Amoungst My Saws........Fool That Has Too Many!!!
    Hey Four Paws,

    Did you pressure check as well???
     
  20. Four Paws

    Four Paws Addicted to ArboristSite

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    Not this particular saw. It was just something I had apart on the bench and figured I would do a quick "how-to" write-up. The saw ran sweet, and there was no reason to suspect an air leak. Pressure testing is kind of like a security blanket, as 9 times out of 10, the saw will leak under vacuum before it leaks under pressure. "Poorman's guide to pressure testing" - Sounds like a good idea for a future write-up, LOL.
     
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