Tick Over Speed Issue

[GRLMK38]

I would appreciate your view on the following tick over characteristics for a recently acquired 3LW.

 

Engine starts (from cold) and tick over is approx. 400 rpm.  I haven't measured it, but that is the indication on the tacho.  I can measure prop rotation speeds if necessary taking in to account the PRM gearbox ratio of 1.5:1.

 

Every few minutes (random rather than consistently) the revs climb to approx 600 rpm and then the returns back down to tick over (it takes about 10 seconds to complete an "up and down" cycle).  I think you call it "hunting".

 

Half an hour later it has settled down and happens less frequently.

 

The engine has been recently serviced (not by me) but has done very few hours over the last 18 months.

 

We will be increasing the hours over the next few weeks.

 

Any ideas?

Edited June 7, 2020 by GRLMK38

[Split Pin]

Probably caused by a slightly dry rack and quadrents, the amount of rack movent required to maintain a steady tickover is miniscule so any stickyness causes overshoot.

Manualy oil the rack where it exits the pump body at both ends, and work the rack backwards and forwards, you may have to remove a plate at the front end of the pump, If you have the slotted screw in the front cover pump some oil in as well, if not I find it better to remove the cover and cold start assembly and oil everything directly,

 

Steve

Edited June 7, 2020 by Split Pin

[GRLMK38]

Hi Steve,

 

Ah, the mystery BA screw.  It's running at the moment so I will do the external oiling and then remove the screw etc. once stopped.

 

I hope that is the solution, I don't want to go down the governor dismantling route.

 

Thanks

 

 

[Split Pin]

It may clear itself after a period of running as the oil mist works it way up and everwhwere gets a coating.

Edited June 7, 2020 by Split Pin

[GRLMK38]

13 minutes ago, Split Pin said:

It may clear itself after a period of running as the oil mist works it way up and everwhwere gets a coating.

Thanks, that seems to be the case.  I have oiled the rack externally anyway.

 

It's not until you study it that you realise how small the movement is.  I reckon it's about 1-2mm of travel to replicate the the "hunting range". 

 

Updates to follow over the next couple of days.

 

 

 

[PeterG]

You also might find that this is being prompted by the alternator kicking in varying the load on the engine starting that off.  Not unusual if you have just taken over the boat and hence it has been little used but see you are going to squirt some oil in via the BA screw as well so think you have it all covered.

[GRLMK38]

So I have added oil via the BA screw hole and the issue has been resolved.  In 7 hours cruising today there was no hunting (lots round the prop, but no hunting).    The "Captain" is now telling me that she has a variable throttle now, rather than something close to binary.

 

Now we just need to fix the temperamental starter motor i.e. half hearted engagement.  With 59 ohms in circuit between the battery and starter, the wiring and switching is the first place to start.

 

Thanks to @Split Pin and @PeterG for your input.

 

Steve, for your info the serial number is 96006 and we will be in touch shortly about GEF membership.

[Split Pin]

(Now we just need to fix the temperamental starter motor i.e. half hearted engagement.  With 59 ohms in circuit between the battery and starter, the wiring and switching is the first place to start.)

 

Also make sure that the starter hasen't moved back a little in its mounting, to large a gap also causes mis engagement problems, 59 ohms resistance in the circuit certainly won't help especially if you are on 12 volt. Does your starter have an oil plug in the nose end? depending on the original application of the starter it may be on the bottom. Toping up the oil will also help as the bendix also dries out over a period of time.

 

Have noted the engine number, there was already one in the list so have you changed your engine?

Hope the cruising goes well, at least as a full time ocupant you can move whilst the rest of us await a change of rules.

[GRLMK38]

9 hours ago, Split Pin said:

(Now we just need to fix the temperamental starter motor i.e. half hearted engagement.  With 59 ohms in circuit between the battery and starter, the wiring and switching is the first place to start.)

 

Also make sure that the starter hasen't moved back a little in its mounting, to large a gap also causes mis engagement problems, 59 ohms resistance in the circuit certainly won't help especially if you are on 12 volt. Does your starter have an oil plug in the nose end? depending on the original application of the starter it may be on the bottom. Toping up the oil will also help as the bendix also dries out over a period of time.

 

Have noted the engine number, there was already one in the list so have you changed your engine?

Hope the cruising goes well, at least as a full time ocupant you can move whilst the rest of us await a change of rules.

I will investigate the oiling points and alignment on the starter - thanks.

 

This engine is an "add" (in a "his and hers" kind of way) - V will be sending you the Membership Form as soon as we can get to a printer.

 

I understand your pain about lockdown.  We sold our house on 16th March to move onboard temporarily while we look for another.  Good timing for us but not good for people who don't live aboard. Instead of looking for a house we have bought another boat instead, hence the additional 3LW.  

 

[GRLMK38]

So that's another screw positively identified.  I verified it using the CAV manual downloaded from the Internal Fire Museum.