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Anyone ever done a compession test on J series?


Mike Adams

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I noticed the huge amount of smoke given out by the kelvin in a boat at Braunston. I have the same problem on start up but once warm after about 20 minutes the smoke reduces considerably. I cannot make it start without the diesel burner in the intake going even in this weather on the electric start so there must be another problem. The injectors seem to make an even creaking sound. I know this engine is indirect but it still seems to me to be incomplete combustion. Very white smoke so diesel rather than lubricating oil? I cannot find a figure for the compression pressure anywhere.

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The white smoke is most probably incomplete combustion as you suggest. Mi e smokes for a while when cold but clears as it warms up.  I try to moor up so there is a 10-15 minute clear run  before locks or moorings which clears the chimney nicely.

Sniff the smoke!  Part burned diesel has a smell of its own and is easilly recognised ( like napalm in the morning I guess).

I have never done a compression pressure test either but possible causes for your white smoke are (reverse order of seriousness):

Dirty injectors ( Carbon on the pintle can really spoil the spray pattern even though they creak nicely)

Mis-set injection pressures

Spill timing a little out

Leaking starting valve(s) -Open the priming cocks when running and see if smoke comes out. It should not.

Misaligned venturi (the diesel combustion chamber) 

Wear or damage to the throat of the venturi

General wear to the rings and/or bores.

 

I would never expect a J2 to cold start without extra heat,even in this weather.  There is just too much opportunity to cool the air because the bore is quite small and there is a lot of metal to take the heat of compression away. 

N

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if it gets better when warmed up and everything else seems ok I would try not to worry too much about worn rings and bores, a good many lorries used to smoke prodigiously on chilly mornings and last for many years more, old design I s'pose,

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Thanks

I will start with the spill timing and the injectors. I am not sure how easy it will be to get them overhauled. I can clean the pintles but resetting the pressures might be a little tricky.

I have checked the starting valves and they are OK and there doesn't seem to be much blow-by coming out out the crankcase. Interestingly I have just looked up the venturi in by spares book and someone has annotated it with dimensions -could they have made their own or something? looks like a cylinder 2 1/8 OD 1 1/2" long ?

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I have the works drawing on file. It is also on Mike Skyners site redrawn as a CAD file. I cannot recall the exact dimensions but the tolerance on the OD is a bit tight ( 5 tenths of a thou IIRC) unless you have a really good lathe or the kit to grind it to size or make it to fit a specific head.  The rest involves some tricky angle drilling and hollow turning/milling a hemisphere.

They can be a reet bugger to get out of the head too.

Any diesel injection shop that deals with heritage stuff can sort the injectors. Pattern nozzles are available (BDN40S2) and the dismantle clean and reset is basic stuff. Probably though a gentle stroke or two across the tip with a brass wire brush is all they will need. A suede shoe brush is good.  Keep well away from brass effect wire which is really coated steel and far too agressive.

N

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Ok so I have had the injectors out - no build up of carbon, checked spill timing. Changed engine oil. Still smoky on start up but noticed when it is in gear smoke is substantially reduced(on tickover) whereas the engine off load is producing a lot of smoke including smoke rings. So it seems to me that the governor is not working properly and over/under fuelling and is not in full control of the injection amount. In this case the engine appears to be running rough on no load. When I removed the injector pipes they were in poor condition and the seats and olives on the pipes marked. How easy is it to refurbish the seats on the ininjectors or get new pipes?

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Might be time to give the piston rings a good clean.  Not a difficult job once you have worked out how to manipulate the crankshaft to get the pistons and rods out  (no need to disturb anything other than the pump side crankcase doors and the big end bolts.)    Should take about 30 minutes to get the lot out.   My guess is that the oil control rings in particular are a bit gummed up and the holes behind and below the rings which drain the surplus oil  into the sump are mostly or entirely blocked, so you are burning a little oil.  The outward load on (and so the effectiveness at scraping oil off by)  the oil rings is lowest at tickover and rises as you put load on.  That is why (I think)  it is smoking less when in gear than when out of gear ticking over.

 

 Putting the pistons  in again is even easier than getting them out.    Get crank in the right position, manipulate piston below the liner, with the mouse bite towards you,  and get the piston vertical.  Push upward and it slides in, the taper on the base of the liner will take care of compressing the rings.  Manipulate rod and crank to get big end together and bolt up.  Repeat for the other one.

 

It is practically impossible for the governor to be working and  awry- it either will govern, or it won't.  I can think of  nothing in the governor action  that can cause the engine to smoke at idle or to run rough. The most common fault (horizontal piston type)  is diesel leaking from round the rack output at the top.  Insufficient or thin oil in the governor (or a hot governor) causes a high tickover speed.  A sticking governor piston or fuel  pump rack will cause the engine to hunt at  idle.     A good trick in hot weather or when running with a hot engine is to thicken the oil in the governor casing with half-a-dozen squirts of engine oil.

 

New injector pipes are fairly easy to get - but you need a diesel injector  heritage place.  Either be prepared to bend your own to shape or take a pattern for them to bend to.  The pipe is 2mm ID and ~6mm OD so not easy to bend without practice and heat.   The injector connector is NOT usually the standard metric thread to fit a 19mm  AF nut used on the pump end but (IIRC ) 7/16 BSF.  Check  first!!!!   The maker may need to salvage the injector nuts from the old pipes.  Refurbishing the injector and pump connections  is also something a heritage injection specialst can do. However, all is OK if there are no leaks from the pipes at either end.    FYI, there should be  no olives on the pipes- the flare on the end should be formed from the pipe with a special tool.   Very early injection pipes had a brazed on nipple at each end.  The nipples are now made of unobtainium and the pipe has to be cleaned very carefully internallly after the brazing so it is very rare to see new replacements.

 

N

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Thanks BEngo for such a comprehensive reply.

I ran it up to the pub (3miles) last night and by the time we got home it was running very wel and the exhaust was almost clear. I can only put this down to a change in oil. I had not changed it from buying the boat. I am wondering if it might be a good idea to run it on fully synthetic for a couple of hours as this tends to disolve everything and then clean it out.  I have the pipes with the brazed on ends so the pipe nuts would be made to fit those brazed on ends and may not fit formed ends. I wonder what steel the nipples are made of - perhaps I could run up some on the lathe. I have a pipe flare tool so maybe a bush inserted into the old nuts? Time for a bit of experimentation!

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We had a new fuel injection pipe made up for the National in Fulbourne by Diesel Fuel Injection Services of Watford https://www.yell.com/biz/diesel-fuel-injection-services-watford-487863/. The old pipe split when we were in Berkhamstead, and this was the nearest place we could find to fix it. I left the old pipe with them, took a walk from their place, along the disused railway to the canal, and then down to Batchworth Lock, had a bite of lunch and walked back by which time he had made up a compete new pipe, and cropped the broken end of the old pipe and formed a new end, so we have a (slightly shorter) pipe as a spare. Can't remember the cost now, but it wasn't that bad.

.

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