Valves; Running-In - CITROËN Amicale 5 HP Manual

15 - ENGINE SEGMENTATION AND COMPRESSION
When you feel the compression of each cylinder by turning the crank, you can feel a lower compression than
the others.
A simple test will make it possible to determine the cause: if there is no device to measure the compression, it
suffices to inject a small quantity of thick oil into the offending cylinder and resume its compression.
If segmentation is the cause, the cylinder will regain its compression for a few turns of the crank, the oil
ensuring the seal for a time. On the other hand, if a valve is burned out, the oil will have no effect. The oil will
not have any more effect if the loss of compression is from a ruptured cylinder head gasket.
As an indication, a 5HP engine has a compression pressure of 3 to 5 Kg / cm2, but from the end of 1925
(chassis no 63000), the blocks are shorter by 2mm (140mm) which increases the compression (a little ...)
A 2mm brass plate was inserted under the block by those who wanted to return to low compression.

16 - VALVES

Running in and adjusting the valves is less complex than it seems.
16 a - Adjustment
The valves are accessed through the right side hatch closed by a rectangular cover,
The two valves of the same cylinder are adjusted when the piston is at top dead center, at the end of
compression, then we switch to next cylinder in the order of firing: 1-3-4-2
Recommendation: set of 20 hundredths for the intake and 25 hundredths for the exhaust.
16 b - Grinding
If the valves are dismantled, start by sliding a thin sheet underneath to avoid dropping a nut in the crankcase.
Insert the valve stems into the numbered holes in a cardboard box to avoid a mistake during reassembly.
Carefully check the clearance of each valve in its guide. If this clearance is greater than 2 / 10th, replace them
with "repair" valves with larger diameter tails.
Valve lapping is done with commercial lapping paste deposited around the valve seat. Put it back in its guide
and, with a suction cup, rotate it on its seat, in an alternating movement as regular as possible.
From time to time, lift the valve and turn it a 1/4 turn, then resume the back and forth movement.
The grinding is complete when the valve face and its seat have taken on a uniform gray tint. Finish by carefully
removing all traces of lapping paste.
For an even finer finish, put a drop of motor oil on the seat and valve. With a small drill equipped with a
screwdriver tip, and a finger under the valve stem to lift it, give it a shine, therefore a perfect seal.
- Recommendation: carefully avoid dropping lapping paste into the valve guides where they would cause
irreparable damage.
Tips and tricks...
- Before using the lapping paste on heavily carbonated seats, give a few turns of a not too large piece of
abrasive paper, pressing it on the seat by means of the corresponding valve. Without this precaution, the
lapping paste will spend a lot of time before attacking the metal.
-To get rid of a major annoyance when adjusting the valves which requires two 12 mm open-ended wrenches:
... in order to prevent the wrenches from wandering where they should not, it suffices to put a simple washer
between the nuts which will guide the tools. "Let us add that it is also very practical to use a grinding wheel to
thin one of the two 12 wrenches which will be used for the locknut, the other attacking the acorn nut which
serves as a pusher ".
- If the engine farts on the exhaust when going downhill, when you lift your foot, it may be that the carburetion
is too lean: supply or jet blocked, tank almost empty. It is not a real problem.
But if the carburetion is not weak, it can also be a valve that closes poorly. Either burnt or stuck in its guide. If
it was a sluggish return spring, we would have known it for a long time. So to check
- If an engine runs very well but when hot starts are difficult, it is quite simply because, because of the heat
accumulated after stopping (especially with our thermosiphons cooling), the expansion of the block reduces the
play of the valves (0.2 for the exhaust 1.5 at the intake). A valve remains poorly closed, you lose the
compression without which the engine no longer sucks in to breathe . So pay attention to the valve stem
clearance. Otherwise painful hot starts, and at worst burnout exhaust valves