Cheating with Tight Valve Clearances

Speedy3 · January 29th, 2017, 12:06 PM

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!

SLOWn60 · January 29th, 2017, 12:11 PM

From the hip without a lot of thought: anything you sand will tighten the valves, not loosen them!

Flying · January 29th, 2017, 12:14 PM

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.

SLOWn60 · January 29th, 2017, 12:23 PM

Sorry! Brain fart! You specified tight clearance, not tight valves

Speedy3 · January 29th, 2017, 12:53 PM

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?

Flying · January 29th, 2017, 01:31 PM

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.

Motofool · January 29th, 2017, 02:45 PM

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

mgentz · January 30th, 2017, 08:24 PM

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.

bruce71198 · January 31st, 2017, 05:23 PM

I've done it on a belt sander, no ill affects.

mgentz · January 31st, 2017, 07:09 PM

^ that had to hurt! Bu da bum.

January 29th, 2017, 12:11 PM	#2
SLOWn60 n00bie to wannabie Name: Bill Location: St Ives, BC (Shuswap Lake) Join Date: Sep 2015 Motorcycle(s): 2012 250R (Red), 2005 VFR800A (Red), CRF450X (Red), 2012 F800GS (Wants to be Red!) Posts: A lot. MOTM - Nov '15	From the hip without a lot of thought: anything you sand will tighten the valves, not loosen them! __________________________________________________ The Smart Money: #1 - ATGATT, #2 - Training (machine skills and survival skills), #3 - The bike; whatever floats yer boat with the money you have left over

January 29th, 2017, 12:14 PM	#3
Flying ninjette.org sage Name: - Location: somewhere cold Join Date: Jun 2013 Motorcycle(s): 2010 Ninja 250 Posts: 596 Blog Entries: 1	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.
	1 out of 1 members found this post helpful.

January 29th, 2017, 12:23 PM	#4
SLOWn60 n00bie to wannabie Name: Bill Location: St Ives, BC (Shuswap Lake) Join Date: Sep 2015 Motorcycle(s): 2012 250R (Red), 2005 VFR800A (Red), CRF450X (Red), 2012 F800GS (Wants to be Red!) Posts: A lot. MOTM - Nov '15	Sorry! Brain fart! You specified tight clearance, not tight valves __________________________________________________ The Smart Money: #1 - ATGATT, #2 - Training (machine skills and survival skills), #3 - The bike; whatever floats yer boat with the money you have left over

January 29th, 2017, 01:31 PM	#6
Flying ninjette.org sage Name: - Location: somewhere cold Join Date: Jun 2013 Motorcycle(s): 2010 Ninja 250 Posts: 596 Blog Entries: 1	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.
	1 out of 1 members found this post helpful.

January 29th, 2017, 02:45 PM	#7
Motofool Daily Ninjette rider Name: Hernan Location: Florida Join Date: Mar 2011 Motorcycle(s): 2007 Ninja 250 Posts: A lot. MOTY - 2016, MOTM - Dec '12, Jan '14, Jan '15, May '16	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 __________________________________________________ *Motofool* *.................................Never ride faster than your guardian angel can fly* "Mankind is composed of two sorts of men — those who love and create, and those who hate and destroy. Love is the bond between men, the way to teach and the center of the world." - José Martí

January 29th, 2017, 12:53 PM	#5
Speedy3 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	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?

January 30th, 2017, 08:24 PM	#8
mgentz Board Member Name: ... Location: WI Join Date: Dec 2011 Motorcycle(s): 250R (street), 250R (dirt) Posts: A lot.	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.

January 31st, 2017, 05:23 PM	#9
bruce71198 ninjette.org sage Name: bruce Location: northern illinois Join Date: Jan 2012 Motorcycle(s): Race bikes:08 Ninja 250,11 R6,16 ZX6,SV650.3 HD-1947,2-2003,2010. 1946 Indian and a lot of dirt bikes.2 Posts: 999	I've done it on a belt sander, no ill affects.

January 31st, 2017, 07:09 PM	#10
mgentz Board Member Name: ... Location: WI Join Date: Dec 2011 Motorcycle(s): 250R (street), 250R (dirt) Posts: A lot.	^ that had to hurt! Bu da bum.

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