BMC 1.5 only starts if pump bleed screw open

[beanpole]

My BMC 1.5 will only start if I first loosen the upper injector pump bleed screw, the one above the idling damper adjusting screw. I have to loosen it enough to let a little fountain of fuel come out while cranking, and then it will start immediately, even with no glow plug preheat.

 

It started doing this after cleaning the injector pump filter gauze and replacing the fuel line. At first I could not start it, no matter how much fuel I bled from the system. If anything, it seemed like not enough fuel was coming out of the injector pipes when cranking the engine. Out of frustration, I thought that maybe there was air trapped in the injection pump that required cranking to get out. So I slackened the upper bleed screw and started to crank the cold (no preheat) engine. It started immediately! I tightened the bleed screw, broke the head of the screw off, observed a pretty little fountain of diesel (not unlike that from a male infant letting it go while getting his diaper changed), stopped the engine, and cleaned up some of the fuel mess.

 

I removed the idling damper locknut and screw, extracted the broken bleed screw, and replaced it with one I made (I'm in Canada, none to be found anywhere here, and Calcutt doesn't ship across the big pond). Cleaned everything thoroughly, reassembled, and am able to repeat the odd starting procedure every time. After the engine starts and I (gently) close the bleed screw, the engine keeps running for at least a minute or two. I stopped it intentionally a few times, and other times it reduced rpm and stopped on its own. But it would always restart right away with my newly patented crank-bleed-start procedure. When the engine is running, the idle rpm is too high, maybe 1500 to 2000, and it varies each time I start the engine. The throttle response is also really slow, so I believe the idling damper is out of adjustment. But what could require bleeding in order to start?

[Tony Brooks]

The revs issue is most likely a lack of fuel so pressure inside the pump is unstable. When you cleaned the strainer in the injector pump did you also make sure the regulating valve was free to move and did it and the associated springs go back in the correct order?

 

The bleed screw thing suggests an air leak so did you ensure the seal around the big hexagon nut you remove to get at the strainer was in good order and if copper did you renew it? The transfer pump could suck air at that point.

 

If that is not the cause then start looking back along the fuel feed lines. maybe the cap seal on the lift pump. Double check all joints in the fuel feed. make sure you have plenty of fuel in the tank. Did you reset the idle damper as per the manual? If not that could explain the unstable idle speeds.

[RLWP]

As you have replaced the fuel line, I would be checking that for air leaks

 

Richard

[beanpole]

Fixed! No leaks anywhere, but I completely cleaned and carefully reassembled the front plate of the injection pump and after bleeding it started no problem. Then after adjusting the idling damper the rpms behaved as well, better than before in fact. My home-made vent screw above the idling damper also works fine.

 

Now, regarding the front plate of the injection pump. The problem was either from me improperly putting everything back in after the first time I checked the gauze, as it appears that the little regulating piston was sitting sideways down at the bottom, or it was because I had disturbed the disintegrating "washer" at the bottom of the regulating sleeve. I think the latter, because the piston probably fell out of the sleeve when I I lifted it out of the front plate, and because I don't think it's possible to assemble the front with the piston under the sleeve. The sleeve washer looked like a piece of swollen paper, and was coming apart in pieces and fibres. When I removed the front plate and gave it a good cleaning, I found bits and strands of this washer at the bottom of the front plate. So I cleaned off all remnants of this former washer and replaced it with a thin Viton o-ring I happened to have, exactly the right diameter (nice and snug). So far so good. It started beautifully 5 or so times and has run a total of 30 minutes or so.

 

I followed the brief idling damper adjustment procedure from the shop manual, and the rpm response is also very good. This was all late at night, so tomorrow I hope to take her out on a test run.

[Captn Black]

Hi guys, I think I have a related issue, but probably caused by diesel bug. Any tips on removing end plate and cleaning the gause? It may be possible to do so in-situ, if that would create less problems in the long run.

[Tony Brooks]

Please do not ask almost the same question in two threads, it confuses. Answered in the other thread.