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355 Secondary air delete

Discussion in '348/355' started by spaghetti_jet, Feb 28, 2021.

  1. spaghetti_jet

    spaghetti_jet Formula Junior

    Jan 5, 2005
    598
    Europa
    Full Name:
    Bob
    Can anybody tell me the male thread size for the spigot on the secondary air pipe?

    Better still, does anybody know of a European source for cap nuts that would fit?

    And before I get the lecture about emissions compliance — my 355 is now formally in the “classic/historic vehicle” category for fiscal and inspection purposes.

    I’ve checked & double checked the rules with the government dept. of transportation and they have confirmed that the emission test for my car is only conducted with the oil temperature above 90C.

    They have also confirmed that there is no obligation for me to keep the secondary air system since it is not a testable item. So I’m taking off the secondary air system and mothballing it.

    Thanks in advance for any help.

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  3. 275GTB

    275GTB Formula 3

    Jan 12, 2010
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    I have some spare air systems in the garage, will try this week to get the thread/nut size.
    you can remove the rest of the secondary air system and just leave the above non return valve in place, as long as its not stuck open no exhaust gases can come out of it.
     
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  4. spaghetti_jet

    spaghetti_jet Formula Junior

    Jan 5, 2005
    598
    Europa
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    Bob
    Hi, thanks a lot for the offer of help, that's really good of you.

    I don't have the means/gauges to size it myself and because of Covid we're in semi-lockdown & all the "non-essential" (non-food) businesses are basically closed to the public, so I can't even go somewhere and get it sized -- need to order it in. Any help really gratefully received.

    I'd really prefer to remove the check-valve for a "tidier" look, if possible.

    Thanks again.

    Bob.
     
  5. 275GTB

    275GTB Formula 3

    Jan 12, 2010
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    totally understand, it will look a lot better with a capped nut.
     
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  6. Targatime

    Targatime Karting
    Silver Subscribed

    Feb 22, 2014
    196
    Los Angeles
    Good idea. I know on 993's that for the '95 OBD1 cars you can just scrap the SAI system, but on the '96+ OBD2 cars you get a CEL since the ECU is programmed to communicate with the SAI system. No idea if it's same on a 355 but I would assume w/ the 5.2 you will get a CEL.
     
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  8. spaghetti_jet

    spaghetti_jet Formula Junior

    Jan 5, 2005
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    I’ve got a 2.7 so no worries about a CEL:)
     
  9. 275GTB

    275GTB Formula 3

    Jan 12, 2010
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    I have a 5.2 motronic, and ran the car for over a year without an air pump, until i sourced a new one, no CEL in that time
     
  10. 275GTB

    275GTB Formula 3

    Jan 12, 2010
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  11. spaghetti_jet

    spaghetti_jet Formula Junior

    Jan 5, 2005
    598
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    thanks a lot for trying to help -- really, really appreciated.

    I'm going to try and figure it out myself, but if you happen to be going to the shop and remember to bring the parts to measure then I'd be obliged, but don't worry if not.

    If I figure it out before I'll come back here & post.

    Thanks again!
     
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  13. spaghetti_jet

    spaghetti_jet Formula Junior

    Jan 5, 2005
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    so I got out my strongest reading glasses, my digital caliper and some blu tak and I've measured the thread. I'm fairly sure its an M24x1.5 so I'm going to order some cap nuts and see if they fit. I'll report back...
     
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  14. emac

    emac Formula Junior
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    Sep 14, 2014
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    upstate SC
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    ernest
    If you knew you were never going to go back with the secondary air system, you could cut the pipe, weld up the nut and put it back in place. I have seen that done on other systems.
     
  15. spaghetti_jet

    spaghetti_jet Formula Junior

    Jan 5, 2005
    598
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    yes, good point & I did seriously consider that option, but since the system is currently fully functional I’ve decided to make the change reversible.

    Maybe one day if the car gets sold the new owner might want to put it back to stock for some reason, or if they change the regulations emission testing...
     
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  16. eulk328

    eulk328 F1 Rookie

    Feb 18, 2005
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    I did this years ago. Couldn't find nuts that size so I had them made. Was spendy but... attached are photos and my original, beautiful drawing I made with the measurements I took.



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  17. 275GTB

    275GTB Formula 3

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  18. eulk328

    eulk328 F1 Rookie

    Feb 18, 2005
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    Happy to provide the info. Might be a small market for these if someone with the means were to produce a batch of such sealing nuts.
     
  19. eulk328

    eulk328 F1 Rookie

    Feb 18, 2005
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    This was my photo with measurements I sent along to the machinist to assist with the tapered sealing plugs (in one of the photos) that go in the port before the nut is screwed down. Might be overkill but that's the route we went. Image Unavailable, Please Login
     
  20. spaghetti_jet

    spaghetti_jet Formula Junior

    Jan 5, 2005
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    Sweeeeet. Hats off to you - they look great.

    I’m happy that I sized the thread right!

    I ordered two cap nuts, €3,50 each, but I might reconsider that now that I’ve been inspired by what you did!!
     
  21. 275GTB

    275GTB Formula 3

    Jan 12, 2010
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    Bob, please post the nuts you ordered when they arrive and are fitted, may need this in the future.

    thanks
     
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  22. KevZep

    KevZep Formula Junior

    Feb 17, 2020
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    Kevin Bennett
    #19 KevZep, Mar 4, 2021
    Last edited: Mar 4, 2021
    You'll actually want to pull that rail off as well, that whole rail attaches to the head and it can be removed, you can buy anodized alloy blanking plugs with the washers. Easy. They screw straight into the head, job done.
    On the 348 head the thread size is 16mm X 1.5mm. I take a bet its the same on the 355 heads, its just a standard fitting that secondary air shenanigans.

    Here's some pics of how mine turned out.
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  23. spaghetti_jet

    spaghetti_jet Formula Junior

    Jan 5, 2005
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    That would be really cool, but the pipes are welded in, at least on my car (‘95 355).
     

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  24. KevZep

    KevZep Formula Junior

    Feb 17, 2020
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    Oh yes, I see that's completely different, looks like they made it part of the exhaust manifold.....Stink buzz!!
    I'll have to have a look at my friends 355 next time I see him and check out how the Euro spec ones are and if they are different too.
     
  25. 275GTB

    275GTB Formula 3

    Jan 12, 2010
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  26. KevZep

    KevZep Formula Junior

    Feb 17, 2020
    251
    New Zealand
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    Kevin Bennett
    I'd be cutting those off and blanking them off, which is fine in New Zealand with our emission laws and so forth.
     
  27. eulk328

    eulk328 F1 Rookie

    Feb 18, 2005
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    Same with my U.S. spec. '96 5.2

    Bob - sent you a P.M.


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  28. spaghetti_jet

    spaghetti_jet Formula Junior

    Jan 5, 2005
    598
    Europa
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    Bob
    The nuts arrived and there’s good news and bad news.

    The good news is that the thread on the air pipe is confirmed M24 x 1.5. The “bad” news is the nuts they sent are not the brass cap nuts I ordered but steel pipe nuts (with a big hole where the pipe would go)

    After an email exchange and a phone call it seems their website had the wrong description and they don’t carry exactly what I want.

    I am contemplating using the nuts they sent me in some way, but since they are zinc plated steel am concerned about them seizing to the spigot. I want to make the change reversible.

    So, the hunt is still on for brass cap nuts.
     

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