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Cam Question

Discussion in 'XJ Technical Chat' started by todd, Jul 14, 2010.

  1. todd

    todd Member

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    I just got done rebuilding my 1980 xj650. I set the motor top dead center and lined up the cam marks with arrows. I checked the commpression and only have 85psi in each cylinder.I used seating compound on all the valves and checked each one with water and none of them leaked. I honed the jugs and checked the ring gap and was well within operating standards. The bike used to belong to a mechanic who had passed away and it was running 15 years ago when it was parked. The question I had was there was a mark on the rotor that was not top dead center that someone had put and wanted to know how to tell that someone put a different performance cam vs stock. I am weary to set that as TDC because I do not want to bend my valves. Any ideas?
     
  2. c21aakevin

    c21aakevin Member

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    I have the same problem. Checked the cam several times and rolled it over by hand to be sure that the valves aren't hitting. I checked the mark and did the screwdriver in the plug hole trick - both showed TDC, and cams were correct.

    My compression is about 90 on all cylinders - with new rings. I am going to put a couple hundred miles on it, change the oil and recheck the compression to see if it comes up.

    It runs fine. The more I ride it, the more power it seems to have. It may be that the rings need to seat.

    It had more compression before the build. - I was thinking it was my gauge, now I am thinking it is normal
     
  3. tibor

    tibor Member

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    sounds like you are doing everything right. as kevin mentioned, likely the rings just need to seat. they say not to use synthetic oil for the break-in period because it lubricates too well, you actually want the rings to wear into place for a better seal. after the break-in period, synthetic is often preferred to protect your investment.

    cheers,

    Trev
     
  4. wizard

    wizard Active Member

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    check the compression wet, it will tell you if the problem is valves or rings.
     
  5. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    You did fit new rings, right? If you honed the cylinders, it should have been in preparation for new rings.

    Just checking...
     
  6. RickCoMatic

    RickCoMatic Well-Known Member

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    You did have the Throttles Wide-Open during the Compression Test, ... right?

    (( I have seen "Other" Marks in the the Crank Rotor. I think the PO marked the Rotor to compensate for the FLIMSY Pointer getting bent or bumped out-of-place. And, rather than move the Pointer, ... scratched a new Visual on the Rotor. ))

    Check to see that your TDC Marks all line-up.

    Let's hope your situation is that your are dealing with an Engine that needs to be Bedded-in.

    Run "Break-in Oil" for 500 Miles.
    Don't exceed rpm's -- 50% of the Limit for 500 Miles.
    Change to Operating Oil.
     

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