It’s that time of year when the en­gine needs a bit of at­ten­tion for, hope­fully, trou­ble-free cruis­ing – ob­vi­ously you can get your boat­yard or mo­bile tech to do it or you can save money and do it your­self

Canal Boat - - Back Cabin -

If you want trou­ble-free cruis­ing this spring and sum­mer, give your en­gine some love

If you are go­ing to go down the DIY route on en­gine ser­vic­ing for the first time, get hold of the en­gine man­ual be­cause most en­gines have their own par­tic­u­lar lit­tle quirks. Have a hunt on­line, there are plenty out there for most en­gines.

Not only will you know what the en­gine com­pany thinks should be done and at what time in­ter­val, you’ll also get the tech­ni­cal in­for­ma­tion and set­tings you need. You will also nor­mally find that ‘ex­tra’ items are listed for longer ser­vice in­ter­vals and some things that good prac­tice dic­tates are rarely listed.

Per­haps the most im­por­tant task is the oil sys­tem, although with the risk of diesel bug some would say that the fuel sys­tem should come first – but we’ll stick with the oily bits this is­sue and deal with the fuel side next month.

Look in the man­ual to find the vis­cos­ity of the en­gine oil re­quired; on mod­ern en­gines it’s likely to be some­thing like SAE 15W40 or 10W40. Older en­gines may use 20W50 or even SAE 30.

Also check the qual­ity of the oil re­quired. This is crit­i­cal for in­land boats be­cause apart from how hard you use the en­gine, get­ting the qual­ity right is about all an owner can do to avoid cylin­der bore glaz­ing. Typ­i­cally you will find a range given, for ex­am­ple CC to CE. This means API spec­i­fi­ca­tion C (for com­pres­sion ig­ni­tion en­gines – diesels), per­for­mance C to per­for­mance E.

For in­land use with much light and no-load run­ning use, that’s the letter clos­est to A (in this case CC), for es­tu­ary and off­shore use choose the higher letter for better lu­bri­cat­ing per­for­mance (CE). The cor­rect oil may take a bit of

search­ing for but it’s well worth it. Some en­gine man­u­fac­tur­ers mar­ket suit­able oil un­der their own name, while smaller pro­duc­ers such as Mor­ris Oils also pro­duce it, es­pe­cially for older en­gines.

Petrol en­gines fol­low the same scheme but the pre­fix letter is S (spark ig­ni­tion).

If you have a sep­a­rate gear­box and re­duc­tion box, check the vis­cos­ity and/or type of oil re­quired. Mod­ern boxes use en­gine oil and have a built in re­duc­tion, but older ones could use any­thing from en­gine oil or au­to­matic trans­mis­sion fluid to EP80 gear oil.

Be­fore start­ing, place old rags or an oil ab­sorbent bilge blan­ket in the en­gine tray to catch drips and spills. If any en­gine mounts are po­si­tioned where oil can be spilled onto them, cover them in rag or some­thing like plas­tic wrap.

Run the en­gine to raise the oil tem­per­a­ture. Feel the sump and when it starts to feel hot, stop the en­gine and pump out the oil us­ing what­ever method is eas­i­est. A well marinised en­gine will have a drain pump fit­ted, oth­er­wise use a vac­uum oil ex­trac­tor or man­ual pump with a tube down the dip­stick hole.

A pump fit­ted onto the en­gine should ei­ther have a ‘bung’ fit­ted into its out­let and/or a tap. This pump might also drain the gear­box, in which case the tap should be switch­able be­tween EN­GINE, OFF and GEAR­BOX. If the tap is not turned off or the bung re­fit­ted after use oil might drip from the out­let when­ever the en­gine is run­ning.

Mod­ern en­gines use a ‘spin-on’ fil­ter that’s a throw­away unit, while older en­gines tend to use a throw­away el­e­ment in­side a metal hous­ing. In the case of the lat­ter look to see if it there is easy ac­cess to the bolt head that holds the bowl onto the fil­ter head. If not it might be eas­ier to take the whole as­sem­bly off the en­gine. If this is the case you will need a gas­ket for the fil­ter to en­gine joint.

Re­move and re­place the oil fil­ter and clean all the old oil away from the fil­ter etc. Then have an­other go at the drain­ing

to re­move any oil that has dripped down in­side the en­gine.

Fill the en­gine with fresh oil to a point any­where be­tween the max­i­mum and min­i­mum level on the dip­stick, then start the en­gine on idle and let it tick­over un­til the oil light goes out, check­ing around the fil­ter for leaks.

Stop the en­gine, leave it for a short while and top the oil up to a frac­tion be­low the max­i­mum, then run the en­gine at a higher speed and recheck for leaks.

Chang­ing the oil in the gear­box and re­duc­tion box oil is very sim­i­lar. If you have a PRM box it might be better to drain it via the drain plug be­cause us­ing an ex­trac­tor via the dip­stick hole on some of th­ese boxes will not ex­tract all the oil.

If there is any sign of a whitish tinge to the oil, the colour in­di­cates the pres­ence of wa­ter and re­quires fur­ther in­ves­ti­ga­tion; en­gine oil tends to look grey­ish and gear­box oil goes to a cloudy, creamy colour.


Check in the man­ual to find out whether the valve clear­ances are ad­justable (most are, but a few are not or use oil pres­sure to do it au­to­mat­i­cally), whether the en­gine has to be hot or cold; if both valves (in­let and ex­haust) are set the same or to dif­fer­ent gaps.

On most mod­ern en­gines the tappets are ad­justed cold and both valves are set to the same gap – but do dou­ble check. Some older Lis­ters, for ex­am­ple, used rad­i­cally dif­fer­ent gaps on the in­let and ex­haust valves.


You can in­spect them for wear and crack­ing, but in some re­spects it’s eas­ier sim­ply to re­place them ev­ery two or three years and keep the old ones as spares.

The cor­rect ten­sion for a ‘nor­mal’ V belt is about 1cm de­flec­tion in the cen­tre of the long­est run be­tween the pul­leys un­der mod­er­ate fin­ger pres­sure. While over tight­en­ing is likely to strain the wa­ter pump bearings, the fash­ion for retro-fit­ting high out­put al­ter­na­tors might de­mand a tighter belt.

If your en­gine has wide poly-V belts with lots of small Vs run­ning around the in­side face of the belt it needs to be ad­justed more tightly. Un­less you have a belt ten­sion gauge tighten the belt un­til you can twist it through just 90 de­grees in the cen­tre of its long­est run.

Older fil­ters usu­ally have a metal hous­ing

A well marinised en­gine will have an oil drain pump fit­ted

The dip­stick and filler hole on a gear­box

Us­ing ring span­ner, screw­driver and feeler gauge to ad­just the valve clear­ances

Check­ing the drive belt ten­sion

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