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bought an xj650 desperately need help getting her going

Discussion in 'XJ Technical Chat' started by John Hopkins, Apr 3, 2015.

  1. John Hopkins

    John Hopkins Member

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    Hello everyone! I recently took a chance on a 1981 seca 650 that "needed the carb rebuilt" I tore them down, cleaned them up and bought the rebuild kit. Got them apart and back together just fine. However it still wont start. It'll start on starter fluid but die quickly after. I ran a compression test with terrible results..... its showing max 60psi and not holding pressure at all throughout all 4 cylinders. Im fairly new to motorcycles I was hoping some one could point me in the right direction here. Any help would be appreciated.
    Other details:
    11K miles
    Carbs don't seem to be sucking up gas
    Was filled with at least 5qts of oil when I got it. (didn't start it with all that oil in it)
     
  2. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Sounds like an engine teardown may be in order.......60psi is way too low for that engine (should be 145+ psi). You either have:

    a) a defective compression gauge
    b) bent valves/holes in the pistons
    c) a majorly blown head gasket (doubtful)

    BTW, the XJ650RJ Seca model was only made in 1982. If you post the first 6 characters of the VIN we can determine for sure what model it is, or you can look here:

    http://www.xjbikes.com/forums/index.php?threads/tech-topic-model-id-and-vins.14577/
     
  3. John Hopkins

    John Hopkins Member

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    Thanks for the reply! Im 99% sure the compression gauge is good because ive used it successfully on other engines before. It seems I will have to at least pull the head off. which is fine but I cant for the life of me figure out how to get the camshaft chain off. From what I see online ill have to snap the chain?! it just seems crazy to me. Any advice at all id really appreciate.
     
  4. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    There are four bolts on each of the cam gears. Remove those and the cam caps in order to remove the cams, then the cam gears, then you can pull the head without breaking the chain. Otherwise you will need a chain breaking/riveting tool (and a new chain and master link) as the cam chains are endless.
     
  5. John Hopkins

    John Hopkins Member

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    also, im assuming its not holes in pistons because the compression is consistently terrible across all 4 cylinders. (unless they all have equally sized holes in them) and when it say 60psi it peaks at 60 and instantly falls to 0 in about 1.5 - 2 seconds. and that's the same for all 4 cylinders.
     
  6. John Hopkins

    John Hopkins Member

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    Genius!! I know the bolts you're talking about, I'll try it out when I get off work this weekend. I definitely want to keep the chain intact if at all possible.
     
  7. trander

    trander New Member

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    You didn't mention checking the valve clearances, which you should do before pulling the head.
     
  8. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Ya. Make a chart to write down the clearances. Checking what shims are in there will be really easy once the cams are out. Tighten the bolts 1/4 turn at a time, working crossways on each bearing cap, and from the middle cap toward the outer caps. Bring them down slow and even.
     
    Last edited: Apr 3, 2015
  9. John Hopkins

    John Hopkins Member

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    ok Ill check the clearances before going any further. I did take the camshaft bearings off (cam covers? im not sure what they're called) and the camshafts moved up a little and now the chain is really tight and it they don't exactly wanna pop back into their seated positions. In other words im gunna have to use the caps/bearings to push them back down into place. does that sound normal? I already loosened up the cam chain tensioner. Also, would bad vales cause loss of compression like this? I really appreciate the responses. Im quickly finding out that Info on these bikes are hard to come by, your advice is invaluable!!
     
  10. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Yes, you will use the cam bearing caps to slowly and evenly set the cams back into place.
     
  11. John Hopkins

    John Hopkins Member

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    update: so the cam chain is super loose sometimes, to the point where I can almost just pull it off, and then tightens as I turn the motor over. Im assuming that's not normal. Im gunna post some pics momentarily to show you guys what im up against. Also, I haven't done the official rundown yet but just a quick test seems to show even the smallest feeler gauge cannot fit between the valve and the cam lope. ill post my results shortly.
     
  12. FtUp

    FtUp Well-Known Member

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    look up cam chain tensioner adjustment.

    FU
     
  13. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    You will need to get a very thin shim to swap in for clearance measurements. It sounds like your valves have never been adusted.

    I think you would do well to take a break and get yourself a service manual before doing any more work. I had assumed that you already took the cam chain tensioner off since that is typicaly one of the early steps to removing the head from a motorcycle. You can get all of the information you need here, but it's really nice to have that book by your side as you are working.

    Also: Really tight valves will not open enough for much air to be drawn in (and compression readings will be lower as a result), but your compression numbers still point to something else being wrong since they are so low.
     
  14. MiCarl

    MiCarl Active Member

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    Something is wrong with your compression gauge, it should hold the pressure until you press the release valve. It's bleeding off somewhere.
     
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  15. Rooster53

    Rooster53 Well-Known Member Premium Member

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    Totally agree. This seems like a bit of rush to tear the motor down. Only 11K and it needs rebuilt, that would have to be some serious abuse. I just did a compression check the other day out of curiosity, and 60 is the number on the first hit, taking about 7 hits on the compression stroke to peak at 150. If the gauge Schrader valve is missing or malfunctioning, you would never get a good result.

    Easy to forget also, make sure the throttle is held wide open for the test.
     
  16. MiCarl

    MiCarl Active Member

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    The longer the hose on the gauge the more hit's it'll take to pump it up too.

    Also, plenty of battery juice to spin it well. Even with a good battery you won't crank an XJ long without discharging to where it affects your numbers. Put on a boost box or jumper cables to a big battery.
     
  17. MiCarl

    MiCarl Active Member

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    ...AND all the plugs removed so you're not fighting four cylinders. You should also disconnect the TCI or coils so you don't risk damaging a coil.
     
  18. John Hopkins

    John Hopkins Member

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    Update: so I'm having doubts about my compression tester. I hooked it up to my jeep and it would bump up to 150 and then fall fairly quickly. So I'm getting a new one for sure. Also the valves read as such
    Cyl. 1 int. >.10mm exh. .18mm
    Cyl. 2 int. >.10mm exh. .20mm
    Cyl. 3 int. >.10mm exh. .20mm
    Cyl. 4 int. >.10mm exh. .18mm

    These are some pics just to show you what I'm working with
     

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  19. John Hopkins

    John Hopkins Member

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    Update: so my compression tester was busted. Now I'm getting accurate readings off a brand new one showing 90 - 88 - 91 - 90 across the cylinders. What would cause them to be 40-50 pounds off you think? I think my intake vales need to be adjusted because they're obviously tight.
     
  20. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Adjust the valves then recheck. Put a teaspoon of oil in each cylinder and check again. Could be valves not sealing. Could be worn rings or worn bores. Could be a head gasket leak. Could be lucky and it's just a combination of out of spec valve adjustment and stuck rings.
     

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