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Valve Job on SV

Discussion in 'Tech' started by etemplet, Aug 28, 2013.

  1. etemplet

    etemplet Well-Known Member

    I was told, years ago "not" to machine or lap the valves on the SV ( I have a First Generation). I just did some checks and my valves are too tight on the rear cylinder. I don't do millimeters so I am getting .003" clearance on the rear cylinder valves.

    I have 25% leak down on the rear cylinder (intake side is leaking) and less than 10% on the front.

    If you don't lap the valves, what do you do ?
     
  2. benprobst

    benprobst Well-Known Member

    It is suggested that you do not lap new valves upon installation.


    That has nothing to do with machining or lapping the valve seat.
     
  3. RM Racing

    RM Racing Tool user

    You can lap the seat with an old valve, or use a diamond hone on the seat.

    It would be best to have a complete valve job done, both heads. Valves can be inspected and replaced if needed. Those valves are not expensive.
     
  4. benprobst

    benprobst Well-Known Member

    Yes, I know. Thats why I said what I said.
     
  5. benprobst

    benprobst Well-Known Member

    22-25 bucks a valve. Replace them et.
     
  6. RM Racing

    RM Racing Tool user

    I didn't mean to quote you, I meant to quote the OP. Sorry.
     
  7. benprobst

    benprobst Well-Known Member

    Dont let it happne again, bucko!!! Or ill stop emailing you with my questions when my limited knowledge is depleted. :D
     
    track wagon likes this.
  8. etemplet

    etemplet Well-Known Member

    Just some questions. Why replace the valves ? And what is the reasoning NOT to lap the valve and the set together. I was told that by one mechanic that the valve surface is coated and if you remove that surface that valve will wear more quickly.

    Question. Are these valves prone to stretching and failure ? I was told by an old friend and very good mechanic that the leakage was acceptable but to check the valve clearance on the rear and RIDE IT !!

    Ben, I also have a SV intake cam to install on the exhaust (you may remember there are Yosh cams in there now.) I am debating whether I should deck the cylinder.
     
  9. benprobst

    benprobst Well-Known Member

    25% leak down is not acceptable, hell, 10% isnt.

    Yes, you do not want to wear through the finish on the valve. lap the seat with a properly shaped old valve, and intall the new one.

    You should replace the valves because your investing 15 hours or 800 dollars in rebuilding the thing, why not spend 100 dollars to replace parts that you know are worn out.

    Decking the cylinder is an option of course, but if youre open on rules more power and reliability can be gained with better pistons to make up compression, and the cost probably isnt radically different than a deck and a set of new rings.
     
  10. Mr Sunshine

    Mr Sunshine Banned

    I've been told that SV valves do not have a history of failure without something like a piston hitting them first. This is after I had a valve fail on a newly built motor. But in this case we think the cam chain adjuster lost tension for a moment and with the build that wasn't acceptable.

    Which generation intake cam? And yes if you want more power...increase the compression. :)
     
  11. Mr Sunshine

    Mr Sunshine Banned

    If you can change the piston then you do both, piston and decking.
     
  12. benprobst

    benprobst Well-Known Member

    No, you dont. You can, but you dont have to. And why in the world are you telling anyone how to put together a motor?
     
  13. RM Racing

    RM Racing Tool user

    Okay. Your motor did how many laps?

    There is a very solid limit on how much compression the SV650 can tolerate with stock rods. Stop giving poor advice.
     
  14. benprobst

    benprobst Well-Known Member

    SV valves also do have a history of failure, in a few different ways. Though they are often a part of a chain of events. :D
     
  15. etemplet

    etemplet Well-Known Member

    Oh you guys are frisky today for sure !!

    I deck my own cylinders (lathe at home) - currently there is a thinner head gasket in there. It isn't a big deal for me to machine the surface.

    I can also machine the head surface at home, cuz I made a contraption to do it. LOL On my OLD SV, the guy cut the surface of my head with a tool and messed up the gasket surface. Otherwise, I wouldn't have messed with it.

    What valve clearance settings do want if I am not installing Adjustable cam gears ?

    This is just my FUN bike but it should be pretty quick. I want reliability and don't want to take it apart for a long while.
     
  16. benprobst

    benprobst Well-Known Member

    Set your quench band at 45thou and forget about it, this should be attainable without machining surfaces.

    Valve clearances or PTV clearance? Lash - Stock cams, valves and pistons I go full tight on intake - .004 and mid range on exhaust at .010. PTV numbers for superbike motors are bit harder to come by Between 40 thou and 80 thou :D

    Keeping compression and cam profiles reasonable and safe is crucial to making the bikes worry free. Just small steps in compression will cross the barrier of stock rods in short order, and you start running into all sorts of valve spring issues when the cams get aggressive. From very short life but no seat pressure issues, to long life, but big seat pressure issues and everything in between.

    Zman sells a nice outer spring that works well and lasts a long time with cam swap motors.
     
  17. Mr Sunshine

    Mr Sunshine Banned

    On that build it was 17laps. It failed right at redline just as I released the throttle going into the horseshoe at Auto Club.

    As to the compression limit...I know this.

    As to poor advice...how so? I said if you want more power you increase the compression. Do I need to give all of the various gotcha's you need to watch for when you replace your pistons, shave your head, increase the compression, change the cams, etc from that single statement?
     
  18. etemplet

    etemplet Well-Known Member

    On my first SV, I installed Yosh Cams, decked the cylinder and took .010" off the head because the surface was damaged. My drag bike building buddy told me to make the piston flush with the top of the cylinder. I didn't, I left .005" on there just because. LOL Stock head gasket, Spiers head bolts and that was it. It was up about 9-10 hp from the initial checks.

    He did some work on porting the head and told me he took a lot of metal out of there. I figured, "so much for any compression gains." I think I had about .090" PTV clearance but I am remembering from about 8 years ago.



    As
     
  19. RM Racing

    RM Racing Tool user

    No. Your reputation for posting dreck and trolling precedes you. I didn't make that happen, you did. You also post items as if you're a professional engine builder. You have a long way to go.

    You made a statement to the effect that more compression is better (until the pistons touch? When?) and that's not necessarily true, especially in that motor, so it was misleading and overly simplified. What part of that do you want to disagree with?
     
  20. benprobst

    benprobst Well-Known Member

    So many people forget this is a big slow revving sport touring bike and dump a ton of compression in them. The wonder why 80hp pump gas motors go flying by them at the end of the straight on their 90hp Dyno jet power sweep special
    Motor.
     

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