1. Hello Guest. You have limited privileges and you can't "SEARCH" the forums. Please "Log In" or "Sign Up" for additional functionality. Click HERE to proceed.

'82 Seca 750 Refresh Project: Now Scooby's Bike

Discussion in 'XJ Technical Chat' started by Nuch, Aug 24, 2019.

  1. Franz

    Franz Well-Known Member

    Messages:
    3,646
    Likes Received:
    1,037
    Trophy Points:
    113
    Location:
    Scotland UK.
    No I don't think so. I thought the chain could have been caught between the crankcase and the crank sprocket but the chain could only do that if it was off the camshaft sprockets.
     
  2. k-moe

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

    Messages:
    19,613
    Likes Received:
    6,703
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    The chain could be off of he crank sprocket. I've done that myself.
     
  3. scoobydew

    scoobydew Member

    Messages:
    145
    Likes Received:
    16
    Trophy Points:
    18
    Location:
    new york
    I've posted a short video of what's happening. It might be popping off the crank due to one of the chain guides, I'm guessing it might be the back side , tensioner chain guide. Can't really know for sure.

     
  4. Franz

    Franz Well-Known Member

    Messages:
    3,646
    Likes Received:
    1,037
    Trophy Points:
    113
    Location:
    Scotland UK.
    If you can get the guide out between the camshafts you might be able to shine a torch down the cam tunnel to see if the chain is on it's sprocket. Have you got your timing plate bolt tightened to the specified torque? How did you set the tensioner blade in the crankcase? The bolt should be tightened until it stops on it's seat on the tensioner blade, then it is backed off a quarter turn and the locknut is tightened.

    Is the transmission in neutral while you are trying to turn the engine?
     
  5. scoobydew

    scoobydew Member

    Messages:
    145
    Likes Received:
    16
    Trophy Points:
    18
    Location:
    new york
    I think I found the issue. Its the intake cam. I've rotated the exhaust cam freely. it can hit 90 degrees no problem. Which is 180 for the crank right? The intake rotates only about 45 which is halfway to BDC which is where I'm experiencing resistance. The intake cam might be warped or the caps might have something wrong with them. Is it possible to switch intake with exhaust ONLY to test if they rotate? Obviously I dont want to run the engine with the wrong cams but I want to see if the intake cam or caps are truly warped or not. It could also be a warped head but I think it's more likely a warped intake cam. I might just buy a pair off ebay to see what happens. Will '82 Maxim 750 cams fit a '82 XJ750? Seems like Ebay mostly has Maxims
     
    Last edited: Mar 25, 2021
  6. Franz

    Franz Well-Known Member

    Messages:
    3,646
    Likes Received:
    1,037
    Trophy Points:
    113
    Location:
    Scotland UK.
    Yes for every 180 degrees of crank rotation cams move 90 degrees.

    Are you sure the intake cam timing is correct? When the engine stops where you said it does shine a torch or put a dowel into the spark plug holes to make sure the piston is not near the head. Look at the cams on the shims on the inlet side to see if any valves are open. If you put the pistons mid way down the bores with the cam sprockets off and timing chain off and held taught turn the inlet camshaft through a few rotations you don't need to exchange the cams.
     
  7. Franz

    Franz Well-Known Member

    Messages:
    3,646
    Likes Received:
    1,037
    Trophy Points:
    113
    Location:
    Scotland UK.
    I am not an engineer but l think you would need V blocks and a dial gauge setup to check camshaft for runout. And of course a manual for the specifications.
     
    k-moe likes this.
  8. scoobydew

    scoobydew Member

    Messages:
    145
    Likes Received:
    16
    Trophy Points:
    18
    Location:
    new york
    Right, yea I made sure the pistons weren't clashing with any valves. Put a straw down the spark plug holes to measure how close they were to the valves. I took the chain off the sprockets and just installed one cam. I used intake cam on exhaust side with intake caps, keeping the chain off the sprockets. Still had an issue turning the intake cam, triple checked they didn't clash with any pistons. Then I pulled it off and installed the exhaust cam on intake side with intake caps. also keeping the chain off the sprockets. Rotated fine. Probably not the best idea for obvious reasons...and I hope it wasn't a huge mistake but nothing seemed to go wrong. I'm also not an engineer not have the tools to measure the camshafts but by that little experiment I'm gonna assume the intake cam is warped. Though I don't know how that happened.
     
  9. k-moe

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

    Messages:
    19,613
    Likes Received:
    6,703
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    Assume nothing.
    Unless you beat on the camshaft, or dropped it several times, it's not going to bend.

    If it was bent you'd notice as soon as you set it into the bearings.

    Did you use oil or assembly lube on the camshaft bearings when you reinstalled the camshafts?

    I'd like to see a video of what's going on with the cams and cam chain when you turn the crankshaft.

    Also, the very last step in the whole process is to reinstall the camshaft chain tensioner. By installing it before everything else is in place it is possible for the chain to bind without you realizing, which is what I think is going on.
     
    Last edited: Mar 25, 2021
    Franz likes this.
  10. scoobydew

    scoobydew Member

    Messages:
    145
    Likes Received:
    16
    Trophy Points:
    18
    Location:
    new york
    Hey guys,

    I've done as you instructed, refit everything, Double, Triple checked. Intake cam still wouldn't turn. Unfortunately I didn't record a video as I just decided to order some cheap cams off ebay and check their specs matched my old cams, just to see if it was the cams or something else. They work great so I don't know what happened to the intake cam for it to bind like that. Got everything together and am checking valve clearances.

    I'm not quite sure why the clearances I took mostly differ from the old clearances the previous owner took. I'm not sure when he took them or if he changed shims. Perhaps reinstalling new cams, new chain has something to do with it? Here are the clearances. Top was previous owner, bottom is mine. I'm not sure why they are sideways when I upload them here. I messaged hogfiddles about shim pool. Gonna pull these, swap some around and see what I need. Looks like I just swap the Intake shims with the Exhaust shims and it should be good
     

    Attached Files:

    Last edited: Mar 30, 2021
  11. Polock

    Polock Well-Known Member

    Messages:
    9,751
    Likes Received:
    2,093
    Trophy Points:
    113
    Location:
    Beaver Falls, PA
    now would be a good time to measure the bearings
     
    Franz likes this.
  12. scoobydew

    scoobydew Member

    Messages:
    145
    Likes Received:
    16
    Trophy Points:
    18
    Location:
    new york
    Hey guys,

    Does anyone know the name of this little boot below the master cylinder? Looking to buy a new one as this one seems to be disintegrated. How do I replace it? Does it require a full disassembly of the master cylinder?
     

    Attached Files:

  13. k-moe

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

    Messages:
    19,613
    Likes Received:
    6,703
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    @scoobydew

    this is a seriously important bit of advice. Get some plastiguage and make sure the replacement cams will work in the existing bearings. Usually they will, but if they don’t you will have a junk top end very soon. And you absolutely do need to recheck valve clearances with different cams and adjust as necessary.
     
    Last edited: Apr 4, 2021
    Franz likes this.
  14. scoobydew

    scoobydew Member

    Messages:
    145
    Likes Received:
    16
    Trophy Points:
    18
    Location:
    new york
    The specs in the book for bearings would be "Camshaft to Cap clearance" right? I just measured it with some green plastigage. Intake, Exhaust right side had around a 0.020mm. Can't be for certain since the closest measurement they have on plastigage is 0.025mm and the mark was a tad larger. Intake, Exhaust on left side measured about 0.038mm. These are new cam measurements. Ran out of plastigage for old cams and no autozone sells plastigage green by me so gotta wait until Sunday.

    What do ya'll think of those measurements?
     
    Last edited: Apr 8, 2021
  15. Franz

    Franz Well-Known Member

    Messages:
    3,646
    Likes Received:
    1,037
    Trophy Points:
    113
    Location:
    Scotland UK.
    If the specs are the same as the 900f engine then the book states

    Camshaft journal to oil cap clearance
    Standard 0.020 to 0.054mm

    Service limit 0.160mm

    k-moe will know if they are the same.
     
    scoobydew likes this.
  16. scoobydew

    scoobydew Member

    Messages:
    145
    Likes Received:
    16
    Trophy Points:
    18
    Location:
    new york
    Yep, the specs in the XJ750 book look to be the same what you posted. I'll check the other cam on Sunday.

    I have a question about valve clearances. Are there any feeler gauges that step up by .10, .11, .12... .20, .21, .22? My feeler gauge at the moment is .10, .13, .15 etc. So when taking clearances, the valve might have drag at .15 but too tight at .18. There's no way to measure if .16 is too tight or not.

    Some shims I didn't swap out as they were .18 270mm. So I left them in but when reinstalling it seems to be .18 to .20 now but .23 is too tight. How can I know it sits at .20 and not .21 since I have no feeler gauge for that?

    I attached a pic of the new specs which are circled. Replaced shims, swapped some and left some in place. Specs changed a bit :\

    (I've just found some feeler gauges with .01 increments on partzilla, for some reason the Autozones by me don't sell .01 increments)
     

    Attached Files:

    Last edited: Apr 8, 2021
  17. Franz

    Franz Well-Known Member

    Messages:
    3,646
    Likes Received:
    1,037
    Trophy Points:
    113
    Location:
    Scotland UK.
    You are correct you are better with the proper feeler gauges. I had to buy a set too to make sure I was setting them correctly. When doing the clearances I aim for 0.15mm for the inlets and 0.20mm for the exhaust. The reason is the valves on our bikes pocket in that they get closer to the seats and the clearances therefore reduce from when the engine is new.
     
  18. k-moe

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

    Messages:
    19,613
    Likes Received:
    6,703
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    That is correct for all of the shafties.
     
    Franz likes this.
  19. k-moe

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

    Messages:
    19,613
    Likes Received:
    6,703
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    KD Tools 2274

    You stack the feelers to get the inbetween measurements.
    Use the 0.11 and the 0.10 in order to measure for 0.21.

    What really matters is that the measurement falls within the specified range. In-spec is in-spec, even if it's 0.01 mm in-spec. If necessary err on the loose side.
     
    scoobydew and Timbox like this.
  20. scoobydew

    scoobydew Member

    Messages:
    145
    Likes Received:
    16
    Trophy Points:
    18
    Location:
    new york
    These valve clearances have been driving me crazy. Whenever I swap one shim that was out of spec, another one seems to go out of spec. I must've swapped shims three times now. I've had all my exhaust valves within spec:

    Exhaust: .16 .17 .18 .20
    Intake: .14 .13 .15 .09

    So I swapped the 280 at .09 for a 275. Now the Intake valve is good at .13 but it seems like Exhaust .18 and .20 are both suddenly .21. I've double checked those valves and they were for certain .18 and .20 before the Intake shim swap and now they are both .21. Am I missing something here or is it normal to swap shims multiple times until finally they all line up correctly?
     

Share This Page