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  1. #1
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    Default Shovelhead Oil on Spark Plug

    1984 FXSB Shovelhead. Owned the bike for 6 years. A previous owner had engine work done (dual plugged OEM heads, S&S 80" jugs, Crane cam...) I honestly don't know the full extent of all the work done internally but it has been a rock solid engine for 6 years. Never had to open it up for anything..... but....

    The rear plug gets oil fouled after a bit. Has done it the entire time I have owned it. I'd finally like to at least pinpoint where it's comin from and resolve.

    I just put these NGKs in a few hundred miles ago. The rear plug as you can see is gettin oil fouled already. Notice only half the plug is getting fouled it appears. I wonder if this is where it faces the valve guide?







    Here's the front plug. Looks like my jetting is pretty clean according to the front plug....maybe a tad rich:





    Before I take a wrench to this I wanna do a compression test and leak down test to rule out any major issues.

    It seems with shovels this type of problem is *usually* due to either a bad guide, bad valve seal or a compromised head gasket at the oil return.

    Am I on the right track here?

  2. #2

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    pull the rear exhaust pipe , if there is oil in the port its getting bad and it dont matter where its coming from!

  3. #3

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    Rings, valve or guide: Thats pretty much it You say it's been doing it since you had it, so you inherited the problem, have had it for 6 years, and who knows how long the prob had been there before you got it

    Frankly, even if you narrow the prob down to either rings, valve or guide, I would not just fix the one prob (if thats the case) ,I would fix them all. The amount of labor is about the same whether you only do the rings or valve area.

    And you might consider doing or at least checking BOTH cylinders/heads: Once your remove the pipes, carb, manifold, and get that one head and cylinder off, its pretty quick to remove the other for inspection/rebuild

    You never said the mileage, but Ill bet its time for an upper end rebuild, and the other cylinder will need one as well, sooner, rather than later

    The good news you can do almost all the work yourself, saving bucks on labor costs And Ill bet $$ your bottom end is rock solid, but check for play while you are there anyways

    Don't half ass the solution: Thats how older bikes eventually turn to shit over the years Sloppy and band air "rebuilds" and poor maintenance

    Good luck, keep us in the know

    The heavy oil on the plug tells the story: Its time for a fix

  4. #4

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    Forgot: Scored cylinder can certainly cause it as well I had pan/shovel that I did a "complete" upper end on (had the heads completely rebuilt, I did new rings, and a quick hone: But when the motor would get warm, Id get smoke out of one cylinder Tore it down again, and there was a very tiny score that I didnt catch in the bore: Took the cylinders to a machine shop, matched rings/pistons, no more smoke

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    "Rings, valve, or guide: That's pretty much it."

    Nope, on a shovelhead, #1 on the list is a head gasket blown to the oil return passage. That is SO common on shovelheads but is often overlooked by people who don't work on shovelheads often.

    That would be my guess in this particular instance. A new set of > good < head gaskets (yes, you should do both head gaskets if you are going to do it at all) may well be all that is needed.

    Jim

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    Pulled the rear pipe to have a look at the exhaust port. Not wet but sooty. But..... I notice the rear portion of the head gasket is wet as shown. Rear exhaust pipe is also pretty sooty but not wet.










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    I hear people mention the head gasket/oil return quite often as a cause for sudden onset smoking. (Edited to add: -> As JB posted while I was typing this.) If it has to come apart anyway, it would be worth looking at.

    I know the blue "felpro" "fire ring" looking gaskets that came on mine were failing, and obviously so. The color makes it easy to see the progression of the failure.

    The new heads from S&S came with a fairly thick set of copper gaskets and after making sure everything was flat by touching it with a fine file and hitting them with a thin coat of copper sealer spray.. I am at a loss to see how a properly torqued and re-torqued gasket of that kind CAN leak?

    Assuming everything is flat and tight, and given copper's high tolerance for heat.. I'd think it would be about the perfect solution. I don't see how it could EVER fail?
    Last edited by confab; 03-13-2022 at 9:47 AM.

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    Shovelhead head gaskets fail because the aluminum head is constantly moving on the cast iron cylinder (different expansion rates). Some gaskets available now, most notably the blue ones, are just junk. The copper head gaskets work well on S&S cylinders because those cylinders have a raised ring just outboard of the fire ring that pinches the gasket an extra three thou or so. H-D cylinders do not have that raised ring and so the copper gaskets are not quite as effective on stock cylinders. Most fire ring gaskets work. I currently have fire ring gaskets made for my shop by Cometic and they are very reliable. I'm beginning to come around to the MLS head gaskets from Cometic (and others), but the heads need to be perfectly flat for those, as well as for the copper gaskets.

    Jim

  9. #9

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    Quote Originally Posted by JBinNC View Post
    Shovelhead head gaskets fail because the aluminum head is constantly moving on the cast iron cylinder (different expansion rates). Some gaskets available now, most notably the blue ones, are just junk. The copper head gaskets work well on S&S cylinders because those cylinders have a raised ring just outboard of the fire ring that pinches the gasket an extra three thou or so. H-D cylinders do not have that raised ring and so the copper gaskets are not quite as effective on stock cylinders. Most fire ring gaskets work. I currently have fire ring gaskets made for my shop by Cometic and they are very reliable. I'm beginning to come around to the MLS head gaskets from Cometic (and others), but the heads need to be perfectly flat for those, as well as for the copper gaskets.

    Jim
    Not sure if these are the same Cometic MLS you mention Jim , but i have some cometic gaskets for the heads and cylinder bases on my 63 pan built as close to stock specs as possible.so far they are working great. One added benefit of these particular gaskets is they really don't need to be re torqued after the motor has been run, because the gaskets are made of metal coated with a rubber like substance that is not thick. They are black. For the valve covers i use the cometic 1/8Ē thick fiber gaskets. So far no leaks after about 5k miles. I think these gaskets have worked well also because of the fact that they donít compress. Unfortunately cometic is not making them any more

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    James fire-ring gaskets works super well too ..

    Click image for larger version. 

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    That jug ^^ is Oem first year 80" Shovel that got the casting deburred and powder coated ..
    Also a spin in the lathe for the .003" crush lip ...


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    Waiting on the compression tester kit to come in this week to perform a solid test. Then, I will do a leak down test. I also ordered a dog bone wrench to get to those head bolts.

    Did yall catch that seepage I posted in post #6 at the rear of the head gasket? That's a separate issue in itself that I happened to catch today when I pulled the rear pipe for inspection. I'm thinking there it is either a bad gasket, surface imperfection or the head bolts need to be re-torqued. Regardless... none of that is gonna fix my oily plug.... well a new head gasket might if that is what I find to be the source of the fouled plug.

    Also, that is a shit ton of carbon buildup in the exhaust pipe and exhaust port. Is that due to the oily combustion issue I have? The front exhaust pipe is just as sooted.

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    Went for a ride today bike ran great. I purchased a new Bike Master compression test kit that I wanted to try. I got 150 PSI on the front cylinder and 135 psi on the rear....however. I'm not 100% confident the rear reading got high enough because the battery drained down on me. I can't get a good reading via the kicker.

    I am running a 2 year old Duracell AGM. Works fine for me since the bike fires off quickly but I guess it isn't enough power for the longer cranks for the test.

    I will try again after the next ride.

    If I continue to get 135 on the rear cylinder I'd like to add some oil to pinpoint if it's worn rings.

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    To revisit... I finally got a chance to go on a nice ride today and do a compression check. 150 PSI exact on both cylinders. I guess it's safe to say the rings are OK. Narrowing down to either a bad guide, valve seal or exhaust gasket. Leak down test coming up.

  14. #14
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    Some pretty smart fellas told you what the issue was 3 weeks ago...

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