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Valve clearances - Determine Top Dead Centre?

Discussion in 'Bling and Appearance' started by klau, Oct 20, 2008.

  1. Adjusted the valve clearances on the 4 stroke v-twin today. Followed the workshop manual regarding cold engine, TDC marker alignment, etc. The valve clearances were all extremely tight to begin with, and I had to loosen the adjuster screws a few millimetres to get the feeler gauge to even fit.

    Question - Is it enough to follow the TDC markings, or do I need to check that I'm actually on the compression stroke (discovered afterwards; google, youtube, that this is important)?


  2. At TDC the cam lobes will be on the opposite side to the valves, if you were on the wrong TDC, both valves would be partially compressed, probably a few millimetres as you suggest..

    For setting valve clearances, close enough is good enough. For timing cam shafts, one degree of crank movement is critical.
  3. was the bike hard to start or seem to lack power?

    if the valves were really that tight you may want to to think about checking the valve seats if you want to keep the bike a while longer.
  4. Johnny O - That makes sense regarding the tight valves. Will do the valves again with the correct TDC.

    bonox - The bike starts easy when cold, and with a bit of throttle when hot (running rich). Not sure about lack of power as I've only ridden the bike an hour at most and don't have a benchmark to go on. I think Johhn O hit the nail with the wrong TDC so will go with that first.

    Thanks guys,
  5. a few mm's of screw out.. woh baby... thats massive.. surprised they even shut.
  6. they wouldn't. Given the bike starts fine I think we've confirmed that he didn't have the cam in the right position for the valve he was adjusting.

    A valve adjustment to those specs should now be very loose and the lift will become a problem - you can loose power both ways (always open valves or very low lift on the valve) but you can only get hard starting with valves that are always open.
  7. true.. a touch loose for longer engine life im down with but thats one area you dont want to stuff up. all good now i hope.
  8. a simple way to verify TDC for any cylinder is to put a small stick through the spark plug hole and when it stops coming out, then you are at TDC with enough accuracy for a valve adjustment. If you can't get the feelers under any valve on that cylinder, try another rotation.

    edit: klau - the reason the compression TDC is specified is that is the point at which inlet and exhaust valves are closed (ie valve clearance at its widest). Just means you can check both at the same time.
  9. i never thought of that.. nice one.. have always lined marks up and got the sh!ts and gone by lobe position..my car never needs the valves adjusted so its nice to have to do them on the bike.
  10. Thanks bonox. One more question for the dummies (me). I set the TDC alignment marks again. The clearance were as per I left them. Rotated the rear wheel (bike in highest gear) until the markings aligned again. Now the valves are extremely wide (millimetres off). Is this the true TDC where I was/am suppose to adjust the valves? Don't fancy putting a stick in the plug hole in case I break the stick in there...

  11. probably, given what you told us initially.
  12. use a length of welding rod or screwdriver.
  13. Yeah, sounds like you've adjusted them on the wrong TDC, did the same thing on my CX. Thought the valves were way out, turns out they were pretty much fine to begin with. You live, you learn.

    Good luck!
  14. I think that what everyone here has missed is that he is working on a V TWIN. It will have 2 TDC's. One for each cylinder. Marked T1 & T2 on the flywheel. If it's a Honda then T1 will be the rear cyclinder.

    PS Use a drinking straw to feel for TDC if you must use anything. No damage can be done that way

    PPS Yes, Visa will be accepted. Scotch Whiskey will also be viewed favourably :LOL: :LOL: :LOL: :LOL:
  15. Thanks for all the replies.

    I ended up using the 'thumb over plug hole, and check for pushing pressure' trick to ensure I was on the compression stroke. As soon as I felt pressure, I rotated the wheel slowly until the relevant cyclinder marker appeared (the correct TDC).

  16. umm, you do realise that any multicylinder engine will have more than one TDC aren't you? Timing marks are usually used to get you to TDC on a particular cylinder and then you follow the check in order as detailed in the manual. That's why they write manuals - so you can follow them and do the job right.
  17. anyone selling an NSR250.. stick ya valves up ya bum
  18. Too true. I'd rather replace a set of smoker rings than adjust the valves on my VFR 400 any day of the week thank you very much :grin: :grin: .