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Compression levers


Roxylass
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Don't remember so long ago for sure but this may help. Many moons ago I only used levers if hand starting or battery was low. Now I have a vintage Perkins P3.144. This always uses the levers but that is connected to a foot pedal that operates the levers which makes it easy when turning the key. The pedal is on the floor in a small cupboard.

In your case I'd suggest that not using the levers is fine if your batteries are good and it's awkward to use them. Using the levers does help your batteries, your choice.

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If you use decompression levers you will increase the running hours of the starter motor. It will still have the shock loading of the inertia due to the flywheel. If engine starts quickly, I would say leave them alone. It might be interesting to test with and without, using a clamp meter to see how much difference it makes to the current. Remember, also, that starting an engine takes remarkably little in terms of Amp-hours. (200 amps for 5 seconds is 0.28Ah)

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It's not just about how easily it starts, or indeed wear and tear on the starter.

 

There is also the issue of lubrication of the engine, and the advantages of getting some oil flowing before you actually have the thing taking off at good revs.

 

We have just had an HA2 fully rebuilt, and it will start in a jiffy on compression if that's what you choose to do. However the engineer is adamant that life of the rebuilt engine can be greatly improved by always having it spun over without compression, before firing it up.

 

The one that we have just had rebuilt has a raised hand start, and his advice is to crank it over on that, before using the starter.

The HA just about to go into the other boat no longer has a raised hand start, but it can still be spun first on the starter, with no compression.

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It's not just about how easily it starts, or indeed wear and tear on the starter.

 

There is also the issue of lubrication of the engine, and the advantages of getting some oil flowing before you actually have the thing taking off at good revs.

 

We have just had an HA2 fully rebuilt, and it will start in a jiffy on compression if that's what you choose to do. However the engineer is adamant that life of the rebuilt engine can be greatly improved by always having it spun over without compression, before firing it up.

 

The one that we have just had rebuilt has a raised hand start, and his advice is to crank it over on that, before using the starter.

 

The HA just about to go into the other boat no longer has a raised hand start, but it can still be spun first on the starter, with no compression.

All good points, but perhaps this is necessary only when an engine has been standing for a long time? The bearings generate oil pressure internally if there is enough oil left in them after the engine stops. No one uses decompressors on vehicle diesels, marine propulsion engines, tractors and the like. Or are vintage engines more vulnerable to bearing wear?

 

Can anyone quote from an engine manual that recommends this practice?

Edited by mross
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No one uses decompressors on vehicle diesels, marine propulsion engines, tractors and the like.

 

Surely decompressors were only fitted to engines to enable them to be hand started. As soon as electric start became common, manufacturers no longer fitted decompressors, albeit that some older engine designs continued to have them fitted on electric-start as well as hand-start versions.

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Surely decompressors were only fitted to engines to enable them to be hand started. As soon as electric start became common, manufacturers no longer fitted decompressors, albeit that some older engine designs continued to have them fitted on electric-start as well as hand-start versions.

I'm sure electric start has a lot to do with it but a modern diesel engine is smaller, lighter and easier to turn over than my lister ST2!

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These engines have a submerged piston type oil pump which pumps pressure virtually immediately the engine starts to turn, unlike most other engines which have gear or centrifugal pumps which delay a little building up pressure.

LR SR, ST, HA and whatnot engines, among others often had no electrics at all in some work boats and in industrial use, like pumps, on site only dumper trucks, pile drivers ect ect, but were hand started by handle on the camshaft stub, ''The Listers''. It was more economical and much simpler and more reliable to hand start them rather than messing with electrics and having the batteries stolen, hence the real original use of de-compressors. Marine versions usually had the overhead hand start arrangement.

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Im referanceing the HA series manual, but should be the same for variants where there is both hand and electric start options e.g. SL/SR/ST/Hx

 

Hand start - decompressors ON Turn the engine 3-10 turns, according to temperature, to prime combustion chamber(s) and lubricating oil system, then turn smartly moving the decompression levers to start

 

Electric Start - Decompressor levers 'must' be left in the off position so the engine is on full compression.

 

HA Instruction book, 582/163, page 22

 

Hope this is of help cheers.gif

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Glow plugs might have something to do with it as well?

 

Indeed - although I'd forgotten about them. Yes, they would also make a modern engine easier to start. I do recall how grumpy my Rover 218TDi was when the glo-plugs wouldn't work if I didn't allow enough time for them to do their stuff.

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Until very recent times glow plugs are used used on indirect injected engines because they are inherently more difficult to cold starts than direct injected engines although some indirect units were said to start easily without glow plugs. Modern direct injected automotive units use glow plugs to reduce pollution and noise during the warm up period.

 

For my own information - never too old to learn, especially from someone with experience - Biz, what engines use a centrifugal oil pulp?

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Until very recent times glow plugs are used used on indirect injected engines because they are inherently more difficult to cold starts than direct injected engines although some indirect units were said to start easily without glow plugs. Modern direct injected automotive units use glow plugs to reduce pollution and noise during the warm up period.

 

For my own information - never too old to learn, especially from someone with experience - Biz, what engines use a centrifugal oil pulp?

 

The little Listers use the piston pump. The H series use a gear pump.

 

Richard

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Interesting thread.

 

Halsall has a HA2 fitted, with hand start,electric start & decompression levers.

 

My starting routine is flick the decompression levers over, give the hand start about 10 turns slowly. Flick decompression levers back and then press the big red 'start' button. It kicks into life instantly in all weathers.

 

Engine runs for 12hrs a day every day.

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Until very recent times glow plugs are used used on indirect injected engines because they are inherently more difficult to cold starts than direct injected engines although some indirect units were said to start easily without glow plugs. Modern direct injected automotive units use glow plugs to reduce pollution and noise during the warm up period.

 

For my own information - never too old to learn, especially from someone with experience - Biz, what engines use a centrifugal oil pulp?

My mistake Tony, not actually centrifugal of course. I meant the concentric rotor and annulus pumps as fitted to certain f/w/d car engines, like the end of camshaft driven pumps on early mini's and suchlike, and certain Lotus V8 engines where there was no room in the sump for a gear pump. Not unlike the rotary Wankel engine principal.

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My mistake Tony, not actually centrifugal of course. I meant the concentric rotor and annulus pumps as fitted to certain f/w/d car engines, like the end of camshaft driven pumps on early mini's and suchlike, and certain Lotus V8 engines where there was no room in the sump for a gear pump. Not unlike the rotary Wankel engine principal.

 

Thanks Mr B, I suspected that might be the case but not having much (any!) practical experience on proper traditional engines I could not be sure.

 

Actually loads of BMC engines used those pumps, I think the 1.5 did at some time but I would not be surprised if they changed to suit what they could buy for the best price.

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Thanks Mr B, I suspected that might be the case but not having much (any!) practical experience on proper traditional engines I could not be sure.

 

Actually loads of BMC engines used those pumps, I think the 1.5 did at some time but I would not be surprised if they changed to suit what they could buy for the best price.

Yes, mainly A series as far as I can remember. They were not particularly that efficient compared with gear pumps. They're pumping efficiency tended to drop at high revs, ok at low revs and relied on more regular oil changes, and like the mini usually used a magnetic drain plug to trap swarf.

Edited by bizzard
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