Cold Start Compression Test - 103cc Screamin' Eagle

Discussion in 'Touring Models' started by Header14, Mar 10, 2019.

  1. Header14

    Header14 Member

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    Can't find any information on what compression test pressures are good for a 103cc Screamin' Eagle Twin Cam...these values seem low???

    Front head = 110psi
    Rear head = 118psi
    2001 Ultra Classic (FLHTCUI)
    Current mileage = 82,400

    Bike is new to me and has had two engine rebuilds and a lot of aftermarket components so troubleshooting is a PITA!!!
    Bike burns through maybe a 1/4 quart of oil for a 250 mile ride. The right side exhaust has a lot of visual "black" build up and the left pipe is relatively clean.
     
  2. joel

    joel Senior Member

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    Compression tests help understand the condition of the valves, seats and compression rings.
    Oil consumption is from valve stem seal, oil rings, and the drain slots in the piston for the oil rings not allowing oil to drain quickly.
    Compression rings allowing compression to pass and create high internal pressure aka blow by.
    Looking at the spark plugs and the way they become contaminated with the oil can help determine possible cause.
    If the negative electrode has build up from the threads around to the tip.
    Often the valve stem seals.
    Oil packed inside towards tip of the positive electrode can be oil rings.
     
  3. Header14

    Header14 Member

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    Plugs only have about 2k miles on them!
     

    Attached Files:

    Last edited by a moderator: Mar 10, 2019
  4. joel

    joel Senior Member

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    Looking at image 1774 you can see the positive electrode is being contaminated with oil deposit buildup, as well as the edges of the threads.
    This plug in that picture at that low mileage of use would lead me to a ring related issue.
    Do you have access to a bore scope to look at the top of the pistons?
    You may see 1 is cleaner like the spark plug in picture 1776.
     
  5. Jeff Klarich

    Jeff Klarich Experienced Member Contributor

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    I see a 3rd rebuild in your future. 82,400 miles and already 2 rebuilds seem excessive, these engines if taken care of can go over 100,000 without touching them other than general maintenance.
     
  6. Breeze3at

    Breeze3at Experienced Member

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    CCP on an engine with unknown cams are not very helpful. A lot of overlap will lower CCP. You are within 10% of each other which is considered ok. The comparison of the L & R mufflers is not helpful if you have the stock Harley head pipes, as most the exhaust comes out of the right pipe due to the extreme angle in the rear pipe to the left (feel the heat difference after a short ride). I agree, that something has been done wrong for that many rebuilds in 82k miles.
     
  7. dolt

    dolt Senior Member

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    There was no CVO FLHTCUI produced in 2001, so I am not sure how the OP came up with 103". The only CVO models in 2001 were a Dyna and a Roag Glide; the Dyna was 88" and the Road Glide was 95". We need to know the correct displacement of the OP's motor. Stock configuration would be 3.750" x 4.00" or 88 CI. On stock cases, the largest the motor could be would be 95"/98".A couple of thoughts going forward:
    1. Assuming that the latest intake close of say, 38*, CCP should be close to 160psi for the 88" motor or close to 170psi for the 95" motor; so if the compression test was run correctly, the top end definitely needs a rebuild. For a compression test to be accurate, the gauge must be known to be accurate, battery full charged, both plugs removed and throttle butterfly in the wide open position. If the compression test was not run this way, the results don't tell us anything.
    2. A compression test is too general to reveal the condition of the top end; next test should be a leak down test to find out where the compression is being lost.
    3. 1/4 of oil consumed in a 250 mile ride = 1 quart every 1000 miles. While the MoCo will tell you that level of oil consumption is "normal" and that "they all do that", burning a quart of oil every 1000 miles is a sure indicator of poor ring seal.
    4. 2001 was the last year for the Magneti Marelli (M/M) fuel injection system which was/is difficult to tune and had many problems. which is why the MoCo switched to Delphi in 2002. I suspect that previous rebuilds were never tuned properly which led to problems. The OP needs to find a tuner that can dial in a new rebuild with the M/M system. Any rebuild without a proper tune could turn out like the previous rebuilds.

    So, to summarize for the OP.
    1. Run another compression test as outlined above, run more than one with different gauges; post results.
    2. Run a leak down test, post results.
    3. Find a tuner that can dyno tune the M/M EFI system.
    4. Pull the top end, bore cylinders to 95" or 98" and fit new CP pistons, maybe with a dome for compression.
    5. Have heads cleaned, maybe basic street port but at least check guides and valves for wear, replace springs with beehives to accommodate higher lift cams and slightly mill surface to true up deck.
    6. Determine what cam has been installed and set up heads and compression for that cam, or replace.
     
  8. Header14

    Header14 Member

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    All great advise!
    I do have access to a bore scope and the attached photos don't look promising.
     

    Attached Files:

  9. Header14

    Header14 Member

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    If I put the VIN number in the H-D service site, it says its an 88 and does not list it as a Screamin Eagle but look at the engine photo. Also included engine serial number if that's helpful?
     

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  10. dolt

    dolt Senior Member

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    [QUOTE="Header14]If I put the VIN number in the H-D service site, it says its an 88 and does not list it as a Screamin Eagle but look at the engine photo. Also included engine serial number if that's helpful?[/QUOTE]

    The engine case number is a shortened version of the frame VIN. So, if you compare the frame VIN with the engine stamp you should see a sub set of the frame VIN numbers which will verify that the engine case is the same case that was installed in that frame at the factory which is what I expect you will find.

    The motor might very well be 103" which would have been the result of installing a Stage I 103" stroker kit, PN 29877-06 which would have been dealer installed. The kit included heads, pistons, SE 253 cams, 4.375" stroker crank and clutch spring. The motor was relatively low compression with published static compression of 9:1. With the late closing SE253 cams, CCP, at sea level, should be about 165psi. You should be able to go to any dealer and enter the VIN and any work done at any dealer on that VIN will show up. If the SE 103" Stoker kit was installed, the cams will be the SE253. If you pull the cam cover, you should be able to see the cam ID stamped on the face of the exposed cam journal.

    In any event, your compression numbers, if accurate, do indicate a compression loss which could be the result of many things. Your pictures are not really all that bad. The streaks you see on the cylinder walls are very common and usually occur on break in, particularly if the assembly wasn't as "clean" as it shoud be. There is always some machine grit on rings and if the cylinder walls, rings and pistons were not cleaned properly, the result will be some streaking on first start up which doesn't harm anything. The pictures of the piston tops don't show a lot of carbon accumulation which indicates to me that the motor doesn't have many miles on the last rebuild. The only picture I see that might be troubling is the picture of the valve.

    Bottom line? Go back to my previous post, #7 and do the work to narrow down the issue. IMHO, you need to rebuild the top end by boring the cylinder to 3.885", fit a set of .010" OS pistons, have heads cleaned up and maybe a street/Stage I port job done, replace the SE253 cams with an aftermarket cam set to set CCP about 190psi, find a tuner that tunes with the Power Vision, buy a license and have the motor properly tuned. There are some associated upgrades that should be done at the same time, mainly in the cam chest. Keep the cost down by retaining the OEM cam plate, replace the inner and outer cam bearings and replace the OEM chain tensioner pads with a set of CYCO chain tensioner pads. Replace the OEM head breathers with a set of the later stamped head breathers.