Email Password
  1. #1

    Default Shovelhead straight pipes or mufflers?

    Good day guys.
    Here are the facts. Got a 96 sidewinder kit .590 S&S heads, .560 cam. Was running a 2 into one straight long pipe exhaust system. After 300 miles my front exhaust valve seal got toasted. Im on 3500 feet the bike was running rich. Called S&S, the first guy was telling me that the straight long pipe set up is causing the issue, the second guy I spoke to told me that I should run straight pipes cause bufflers would not allow enough heat to leaf the pipes and would cause to much back pressure and the valve seals would burn through. After they run the product number of my heads, they found out that my particular set of heads was siting for over two years on a shelve and the valve seals just got to hard, so they couldn't handle the heat anymore. They send me
    A new set of seals.
    No I have three theories why the seals got toasted but no clear answer. What are u guys thinking about it? Any thoughts, experience? Thx

  2. #2
    Senior Member

    Content on this page requires a newer version of Adobe Flash Player.

    Get Adobe Flash player

    Join Date
    Apr 2013


    Exhaust seals lead much hotter lives on hundreds of millions of emission-controlled engines with catalytic converters so I question their hypothesis.

    Failure in 300 miles suggests an apprentice forgot the assembly lube, may have damaged them during installation, or they bought a bad batch of seals. Pics of the failed seal surfaces would be useful along with the valve stems and guide bores which should be inspected under bright light. Shelf time should not affect quality valve seals and an engineering explanation with citations is in order (every mechanical assertion is testable and seals are well researched and not some exotic part) or someone is probably making shit up.

    Does your exhaust have a make and model? If it's custom a pic would help since the verbiage other than it being a 2-into-1 is not useful.

    It's hard to read minds over the internet.

    Rich mixtures run cooler, not hotter.

    You can find out what the old seals were made of:
    Nitrile will burn easily and produce thick black smoke that
    smells like burning rubber.
    Polyacrylate will also burn easily producing a less dense
    black smoke that smells like burning plastic.
    Silicone will turn white when burned, regardless of the original
    color of the seal, producing smoke that has little color and no
    Viton/fluoroelastomer seals will be difficult to burn and
    produce white smoke with no odor. The seal color will either remain
    the same or turn black.
    I would ask on Harley Tech Talk and post a very detailed description of your setup and link to clear, well lit pics of your spark plugs. Also post your engine serial number and any cylinder head batch info. is interesting and though it covers TC engines relevant seal info could help diagnosis. I don't know what stem seal S&S specifies for their shovel-style heads/
    Last edited by farmall; 09-12-2020 at 10:46 AM.

  3. #3
    Senior Member

    Content on this page requires a newer version of Adobe Flash Player.

    Get Adobe Flash player

    Join Date
    Dec 2018


    1) None of the explanations offered by S&S make any sense.

    2) What was the symptom that pointed you toward a bad valve stem seal? If it was that the motor was smoking, how did you determine that the oil was going past the valve stem seal, and not coming from somewhere else? It ends up in the exhaust whatever the case.

    3) As far as I know, S&S uses K-line valve stem seals on their shovel heads. These are a steel bodied seal with a Teflon wiper. Same as H-D used in the last shovels. They have a service life of about 20k miles. They will not seal if the guide to stem clearance is loose. There is also the possibility that the seal could have sustained physical damage from the upper spring collar if the head was not set up properly. Their shelf life is indefinite.

    4) I think you can run pretty much any pipes you want as long as you can tune the motor.

    More information on this issue is needed.


Share This

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts

Log in

Log in