Yamaha XS850G Specifications download pdf (Page 45)

d.

After installing thevalve guide, use

7mm

reamer

(special

tool)to

obtain

thepropervalve

clearance.

Afterfittingthevalveguideintothecylinder

head,besure

to

grindthevalveseat,andper

-

formvalvelapping.Thevalvemustbereplaced

withanewone.

5.Grindingthevalveseat

a.

Thevalveseat

is

subject

to

severewearsimilar

tovalve face. Wheneverthevalve face

is

re

-

surfaced,thevalveseatshouldalsobere-sur

facedat

a

45°angle.Inaddition,ifanewvalve

guide

has

beeninstalled(withoutanyvalvere

-

pair),thevalveseatshouldbe checked

to

guaranteecompletesealingbetweenthevalve

face

and

seat.

CAUTION:Ifthevalveseatisobviously

pittedorworn,itshouldbe cleaned witha

valve seat cutter. Usethe 45° cutter, and when

twistingthecutter,keep an evendownward

pressuretopreventchattermarks.

If

cuttingsection

"

A'

oftheintakevalveseat,

use

"

FLAT

"

cutter(radiuscutter).

If

cutting

section

"

A

"

oftheexhaustvalveseat,use

"

FLAT

"

cutter

(also:

radiused).

If

cuttingsec

-

tion

"

B

"

,

usethe45°cutter.

b.

Measurevalveseatwidth.Applymechanic's

bluingdye(suchasDykem)

to

thevalveface,

apply

a

verysmallamount

of

finegrinding

compoundaroundthesurfaceofthevalve

seat,insertthevalveintoposition,

and

spinthe

valvequicklyback and forth.

Lift

thevalve,

cleanoffall grinding compound,

and

check

valveseatwidth.Thevalveseatwillhavere

-

movedthebluingwherever

it

contactedthe

valveface.Measuretheseatwidthwithvernier

calipers.

It

shouldmeasureapproximately

1.3mm (.05").

Also,the seat

should

beuniform

in

contactarea.

If

valveseatwidthvaries,

or

if

pits

still

exist,thencontinue

to

cut with the

45°cutter.Removejustenoughmaterialto

achieveasatisfactoryseat.

Seatwidth

StandardWidthWear

Limit

1.3mm 2.0mm

(.050") (.080)

c.

If the valve seat is uniform around the perim-

eter

of

thevalveface,but

is

toowide

or not

centeredonthevalveface,

it must be

altered.

Use either the

"

FLAT

"

,45°

or

30°

cutters

tocorrecttheimproperseatlocation

in

the

mannerdescribedbelow:

1)

If

thevalve face shows

that

thevalveseat

is

centeredonthevalveface,

but

toowide,

then lightly use

both

the

"

FLAT

"

andthe

30° cutters toreducetheseatwidth

to

1.3mm (.05").

2)

If

theseatshows

to

be

in

themiddle

of the

valveface,

but

too

narrow,usethe45°

cutteruntilthewidthequals

1.3mm (.05").

3)

If

theseat

is

toonarrowandrightupnear

thevalvemargin,thenfirstuse

the"FLAT"

cutter and then the 45° cutter

to

get the

correctseatwidth.

4)

If

theseat

is

too

narrowanddownnearthe

bottom edge ofthevalveface, then firstuse

the30°cutter and then the 45° cutter.

I

6.

Lappingthevalve/valveseatassembly

a.

Thevalve/valveseatassemblyshouldbelapped

if (1)

neithertheseatnorthevalvefaceare

severelyworn,

or

(2)

if

thevalve face andvalve

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