Reference Modification no.
- 0 -
Page
108
Date
1997 02 01
Main
914 F
01477
12.3.20)Check of compression
See Pic. 55.
Ignition switch for both ignition circuit in "OFF" position.
Two methods to check compression are feasible:
1. Compression test
It needs a compression tracer to check compression. The compression
should be between 9 and 12 bar (130 and 174 psi).
PROCEDURE:
Bring engine to operation temperature (engine oil temperature between 30 to
70° C (90 - 160° F). Remove top spark plug and press compression tracer
against plug tap hole and set engine with open throttle into rotation by
activating starter until maximum pressure is reached.
Successively take readings on all four cylinders and compare results. Indi-
vidual readings of the cylinders must not differ by more than 2 bar (29 psi).
If readings are below 9 bar (130 psi), check compression by the more exact
pressure difference method.
If readings are below 6 bar (90 psi) inspect pistons, cylinders, valves and
cylinder heads (consult Repair Manual)
- or with
2. Pressure difference method
For this method you need the following: Compressed air supply of 5 to 7 bar
(70 ÷ 100 psi), two pressure gauges, an orifice of 1 mm (.04 in) ∠and 3 mm
(.12 in) length and an adaptor to connect line to plug tap as well as connection
hoses.
PROCEDURE:
Bring engine to operating temperature. Lock crankshaft in ignition T.D.C.
Remove respective spark plug and fit adaptor Q instead, and connect line
with the two pressure gauges and intermediate orifice W. Now put constant
pressure on the line E and take readings on pressure gauges R and T.
The maximum allowable pressure drop is 25 %, e.g. from 6 to 4,5 bar (87 psi
to 65 psi).
Successively take readings on all four
cylinders and compare results. Indi-
vidual readings of the cylinders must
not differ by more than 1 bar (15 psi).
â—† NOTE:
Standard pressure readings on a new
engine - 5,8 ÷ 6,0 bar (84 psi ÷ 87 psi);
on an engine after 600 hrs of operation
- approx. 5,2 ÷ 5,8 bar (75 ÷ 84 psi).
If the pressure drop is not within the allowance, check pistons, cylinders,
valves and cyl. heads.
Pic. 55
2
6 bar / 87 psi
bar
0
5
6
7
4
3
1
2
bar
0
5
6
4
3
2
1
7
Ø 1mm (0,039 in.)
L = 3 mm (0,12 in.)
4
5
2
1
3
Zyl. Kopf /
cyl. head
00156
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