January 29th, 2017, 12:06 PM | #1 |
ninjette.org member
Name: Kyle
Location: Raleigh, NC
Join Date: Jan 2017 Motorcycle(s): 2008 Triumph Speed Triple (Blazing Orange); 2010 Nina 250r (Race Project) Posts: 97
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Cheating with Tight Valve Clearances
Attached is a picture of what I found to be my valve clearances. The top row is exhaust, while the bottom row is the inlet (attachment may be rotated, but the "IN" and "EX" give proper orientation). The inlet are within spec, but I may adjust them wider while I'm working on my exhaust shims. In the past, I read (and may have taken ) a shortcut too tight clearances. More specifically, with an older ducati, I simply wet sanded the tops of the shims to increase the gap clearance. I did this with the finest of sand paper, and on a piece of glass (for an even surface).
Has anybody heard or utilized this shortcut? Tempted to do this again, as my valves are all tight, rather that loose and in need of tighter shims! |
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January 29th, 2017, 12:11 PM | #2 |
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Name: Bill
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From the hip without a lot of thought: anything you sand will tighten the valves, not loosen them!
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January 29th, 2017, 12:14 PM | #3 |
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I've heard of this being done, but you need to be careful about sanding away the surface treatment of the shim. Valve shims are typically case hardened steel and you ought to make your next clearance check earlier, should you go forward with this.
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January 29th, 2017, 12:23 PM | #4 |
n00bie to wannabie
Name: Bill
Location: St Ives, BC (Shuswap Lake)
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Sorry! Brain fart! You specified tight clearance, not tight valves
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January 29th, 2017, 12:53 PM | #5 |
ninjette.org member
Name: Kyle
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You worried me there! I thought my logic was on point!
If you don't mind extrapolating, what would cause me to want to check clearances sooner? I'm trying to better understand the inner workings of my bike. Would compromising the finish simply lead to a rusty/broken valve? |
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January 29th, 2017, 01:31 PM | #6 |
ninjette.org sage
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A shim is just a round steel disc. Case hardening dissolves carbon into the outside of the shim to harden it. If you grind away too much of the case hardening, you expose the shim's softer insides to the forces of engine operation and it might split.
I haven't seen any real world data on this happening to people, nor do I know to what degree the shims are hardened, but its still something to watch out for. Make sure to keep the surface you have sanded against the bucket. At the end of the day, the Ninja 250 uses a souped up lawnmower engine, and you'll probably end up fine. Just don't be racing or anything. |
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January 29th, 2017, 02:45 PM | #7 |
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Can you obtain a surface that is perfectly flat and parallel to the other surface of the disc?
If not, you will create points of excessive presure and subsequent wear between shim and disc bucket and between bucket and valve's stem. Please, see this: https://en.m.wikipedia.org/wiki/Surface_grinding
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January 30th, 2017, 08:24 PM | #8 |
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just buy a 7.48 shim kit. cheap insurance.
or buy 10 shims each that are 1-4 sizes smaller than what you have currently. |
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January 31st, 2017, 05:23 PM | #9 |
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Name: bruce
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I've done it on a belt sander, no ill affects.
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January 31st, 2017, 07:09 PM | #10 |
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^ that had to hurt! Bu da bum.
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