Practical Boat Owner – September 2019

Finding top dead centre

Q

I have an LM27 with a

Bukh DV20 engine and

need to adjust the valve

clearances, but in order to

do so I must find ‘top dead

centre’ (TDC). My flywheel

doesn’t have any markings

to guide me – is there an

easy way to find this? I do

the annual service and have

enjoyed getting to know this

engine, so am keen to do

this as well, especially as

the manual recommends

adjustment is

carried out

regularly. I could

get a professional

to do it for me but

that way I wouldn’t

learn anything and

couldn’t call

myself a practical

boat owner! Your

advice would be

gratefully received.

Richard Carvell

STU DAVIES RESPONDS

The Bukh DV20 doesn’t seem

to have any timing marks: the

workshop manual found online

http://tinyurl.com/y2jdkxde

refers to timing in quite a quaint

way. It says to release a valve

from the spring, let it rest on

the piston and use a dial test

indicator to find TDC.

Fortunately there is an easier

way. The two pistons rise up

and down together, one is on

the firing stroke whilst the other

is on the beginning

of the induction

stroke. Before you

start tie the stop

control in the stop

position. With rocker

cover removed turn

the engine in the

normal rotation

direction (clockwise

looking at it from the

front) with a big

spanner or socket.

Colvic Watson 24 and the

surveyor commented that

there was a bit of play on the

steering. The Morse helm

was installed in 2010

complete with new cable, and

the boat has only done 1,000

hours since then. I have

checked the rudder end and

examined all fastenings.

Could you tell me if this is a

characteristic of Morse

steering or should they be

precise? The steering wheel

is 18in diameter so does this

exacerbate the problem?

Edward Atkins

TONY DAVIES RESPONDS

I suppose the most important

thing to consider is whether you

noticed anything wrong before

or whether this ‘problem’ has

only arisen due to the comment

in the surveyor’s report. If you’ve

not previously thought the

steering was particularly slack

then there is nothing to worry

about. Surveyors will include

even minor faults in their reports

to cover themselves and to give

value for money. If there are no

recommendations for repair or

replacement just consider this

as something to keep an eye

on in future.

As far as I recall there are no

adjustments for removing

slack, apart from ensuring

there is no movement

anywhere else (which you have

already done). If you’ve always

been happy with your steering

then my advice would be to file

the information away until the

slack becomes a real problem

and at that point install a new

steering head and cable. The

size of the wheel will make no

difference, by the way.

Mixed up

by Morse

Q

I have recently had a

survey done on my

As you come up against the

compression, which you’ll

most definitely feel, ease it

towards TDC (which is where

the compression is the most

on one cylinder) and look at

the valves. One set will be

completely shut, the other set

will be going ‘on the rock’ ie

one valve will be closing and

the other just starting to open

(being pushed down). Use the

spanner to rock the engine

back and forwards a touch and

you’ll see the valves which are

‘on the rock’ move. You can

gently rock it until the valves on

the one cylinder are in the

middle of their transition

movement. It is at this point

that the engine is at TDC and

you should mark the flywheel

against a datum point – maybe

a piece of wire with a loop in it

attached to a nearby bolt. You

can then adjust the valves on

the set which isn’t moving.

Then turn the engine through

360° to your mark and you can

adjust the other cylinder.

Edward Atkins has a Colvic

Watson 24

Bukh’s online

workshop manual

shows how to adjust valve

clearances – but first you have

to find top dead centre (TDC)

Bukh DV10/20

workshop manual

ENGINES

PAINT AND

ANTIFOULING

Richard Jerram is

former UK technical

manager of

International Paint

50 of the most frequently asked boating questions are answered by our experts on the PBO website. Visit http://www.pbo.co.uk

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