YZ450F valve shim precision

[72degrees]

Sorry if this is a stupid question, but the manual talks about rounding off the installed shim figure before looking up the measured clearance in the table but says shims are only available in .05 mm increments.

 

So having found  179, 182 and 198 shims in mine (also 200 and 205) does that mean three are 'special' or the OEM from the first build?

 

A good job I have the jeweller's loupe my old mum used to use for fly-tying or I would never have been able to read them. My digital vernier gauge isn't super accurate but it confirms what they are within the rounding off limits at least.

 

I'm pretty sure I only need to change one inlet that was significantly on the wide side but was confused by finding shimming more precise than now seemingly available.

 

The good news is that there is still enough adjustment left on the manual tensioner to get the timing chain tension back to spec.

 

This is my first ever shimming job on any engine, so could someone double  check my work?:

 

Inlet 1 : 0.23mm 198 shim - so needs a 210

Inlet 2:  0.15 so OK (205 shim in place)

Inlet 3: 0.15 so OK (200 shim in place

 

Exhaust 1: 0.20 so OK (179 shim in place)

Exhaust 2: 0.20 so OK (182 shim in place)

 

[Geoffit]

All of those in between sizes do exist at the "factory level" and unless you have a vast collection of shims there hard to come by.

A 210 shim on the 1 intake would put you to the tight side .13 and a 205 might put you at .18 ish when possible you would want to end up on the loose side if you have to choose. It's not common for valves to get looser, sometimes a bit of carbon can hold it open and give a unexpected reading.

[SAthump]

A honda dealer we'll sell you the half sizes ?

[72degrees]

All of those in between sizes do exist at the "factory level" and unless you have a vast collection of shims there hard to come by.

A 210 shim on the 1 intake would put you to the tight side .13 and a 205 might put you at .18 ish when possible you would want to end up on the loose side if you have to choose. It's not common for valves to get looser, sometimes a bit of carbon can hold it open and give a unexpected reading.

 

Hmm, good point, I'd much rather run a bit on the loose side than tight. I did wonder why just the one was loose. No sign of any wear on the cam base circle. I'll  order a 205 and 210 then triple check the clearances once reassembled with a 205 and turned over a few times.

[grayracer513]

The factory builds all of the heads as close to the tight limit of clearance as possible by using shims in increments of .01 mm.  Tighter is better for several reasons. 

 

Bear in mind, however, that the difference between the tight limit and the loose limit is all of .002".  Where you are within that range doesn't seem worth worrying about to me.  As long as the valves are with tolerances, they are within tolerances. 

 

Check the condition of the top of the valve stem on the loose one.   It may be mushroomed.

[72degrees]

Thanks, I didn't think of checking the valve. As far as I know it has trick Willpower cams and possibly valves. On my Morini with L5 'race' cam I was recommended  to run a  tad wider than standard (.10  - 4 thou) clearance (so 6 thou). Now I no longer race it I run a 'loose' 4 thou . That's a (high) pushrod motor not OHC though

[72degrees]

In the end I decided to go for the 210. I couldn't see anything obviously wrong with that inlet valve. Once installed it measured at 0.13 mm so I'm happy with that. Nearly made a  boo-boo by not double checking the timing *after* refitting the manual tensioner and adjusting it. The mark on the exhaust cam wheel seems a bit 'lightly popped' compared with the inlet - perhaps because of the Willpower cams? Plus there are extra timing marks at 90 degrees so they are at the top of the wheels when the proper ones are in correct alignment. So I had to have the cams off again and redo it. I didn't drop the special cover to view the mark on the crank but used a probe through the plug hole to confirm TDC.

 

Anyway, it started second kick. Noticeably mechanically quieter with a correctly tensioned cam chain. A bit more popping and banging on snapping the throttle shut  once off 'choke' than I remember. It was pretty cold in the garage to be fair. Perhaps some goo built up in the idle jet. Also the hot start plunger cap isn't absolutely fully screwed as tight  as it should  be yet so perhaps being held open a tad or bleeding in a little air. I'll sort that and if necessary tweak the idle mixture screw a gnat's richer before I start fiddling seriously with the carb.

 

Good to hear it barking again though after my first ever shimming job.