Banjo Bolts AHHHHhhhhh

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pandos

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I lost last years sailing because of issues with air in my fuel system. I am in the process renewing the system from the tank up.

I had considered some exotic backup system and additional filters etc but for ease of doing things given the lockdown I am refitting inline with the original layout.

I have only some of the parts from the boat at home and some new parts have not arrived in the post yet, but I am trying to pre-empt problems which might be easily solved with some knowledge (rather than trial and error).

I have a new lift pump and two new filter heads with spin on filters.

One of my previous problems seems to have flowed from mixing up banjo bolts which seem to have several different threads.

The replacement pump takes the same banjo bolts/thread as the original Guiot /Volvo pump. these look like a metric fine thread (pump for 88 euros incl delivery from German tractor parts)

The filter heads are said to replace CAV filter holders, but it seem that my original CAV filter holders may use two different threads,,,, or they have been rethreaded by the incorrect thread being forced in. I think the banjo bolt onto the top of the high pressure pump and the majority of the original CAV connections are identical.

So. 1. What thread is used into the top of the injection pump on a volvo md21b?

2. Are an M14 banjo and a 1/2 UNF visually similar? and if so are they compatible/interchangeable....?

3 Should I use thread sealant or ptfe tape or someting similar assembling the system.

Thanks in advance..
 
M14 is similar to 1/2 UNF but the two are not interchangeable. You should not need PTFE tape or sealant on banjo bolts as I would not expect them to be tapered. Banjo bolts usually use copper, fibre or Dowty washers and, providing the metal surfaces are not damaged, should seal fine.

Richard
 
Not an answer to your problem, but a gotcha I came across a couple of years ago. I've got an older Volvo, a 2003, and in order to tighten the cylinder head I had to remove the pipes to the injectors, all fastened with nice green painted banjo bolts On putting it back together, I tightened up said banjo bolts quite carefully, and one sheared at the narrow neck where the hole to supply fuel is drilled. Went to French Marine to get a replacement and was told it was a known problem, and they supplied a much stronger and better engineered replacement.

Moral is that banjo bolts can be unexpectedly weak!
 
My view is that you should definitely NOT use any ptfe or sealant anywhere near a banjo bolt. The seal in a banjo connection is not in the thread anyway, its between the copper (for example) washers, the bolt and the engine part it runs from (most likely the filter). If you were to get bits of ptfe or sealant in the fuel post-filter they may end up in your lift pump, injection pump or injector itself, not a good thing, obviously.
 
Thanks for the replies,

No sealer makes sense, when explained.

I found yet another different sized banjo bolt on the tank connection and that is 14mm looks like a metric thread so I am guessing that is an M14 and that it is an M12 which resembles the 1/2 Unf.

In someways the system was more robust than it ought to have been given the selection of disparate parts and fittings...

I did not find any bolts which looked weak or any parts which seemed weak other than the thread in the aluminium pump/and the filter housing but I think I ruined these threads with the incorrect bolts...

I have new copper washers and hose tails in the post and will be sanding and painting the metal lines in the coming days... If I see water before June I'll be delighted...
 
pandos said:
Thanks for the replies,

No sealer makes sense, when explained.

I found yet another different sized banjo bolt on the tank connection and that is 14mm looks like a metric thread so I am guessing that is an M14 and that it is an M12 which resembles the 1/2 Unf.

In someways the system was more robust than it ought to have been given the selection of disparate parts and fittings...

I did not find any bolts which looked weak or any parts which seemed weak other than the thread in the aluminium pump/and the filter housing but I think I ruined these threads with the incorrect bolts...

I have new copper washers and hose tails in the post and will be sanding and painting the metal lines in the coming days... If I see water before June I'll be delighted...
Click to expand...
I always had more success with dowty washers rather than copper.
 
AntarcticPilot said:
Not an answer to your problem, but a gotcha I came across a couple of years ago. I've got an older Volvo, a 2003, and in order to tighten the cylinder head I had to remove the pipes to the injectors, all fastened with nice green painted banjo bolts On putting it back together, I tightened up said banjo bolts quite carefully, and one sheared at the narrow neck where the hole to supply fuel is drilled. Went to French Marine to get a replacement and was told it was a known problem, and they supplied a much stronger and better engineered replacement.

Moral is that banjo bolts can be unexpectedly weak!
Click to expand...

Similar thing happened to me on my old 2003T. I'd spent weeks trying to trace an air leak into the fuel system. On about the fifth time of dismantling and refitting all the joints, as I tightened the banjo bolt of the fuel pick-up pipe, the head snapped off. It had obviously been failing for some time, allowing the joint to relax and let air in.

banjo.jpg
 
pvb said:
Similar thing happened to me on my old 2003T. I'd spent weeks trying to trace an air leak into the fuel system. On about the fifth time of dismantling and refitting all the joints, as I tightened the banjo bolt of the fuel pick-up pipe, the head snapped off. It had obviously been failing for some time, allowing the joint to relax and let air in.

View attachment 89387
Click to expand...
Yes, mine went in much the same way, but with no sign of pre-existing weakness. However, on mine, the bolts connecting the fuel pipe to the injector, or maybe it was the fuel return line from the injectors - the bolts are all the same - had a "neck" just below the head of the bolt, where the holes to pass the fuel are. The amount of metal left at that point was remarkably small, and after the fact I wasn't at all surprised that it had snapped at that point after what I regarded as the use of reasonable force to tighten the bolt.
 
I have also seen that Banjo bolts can catch diesel bug and become blocked before the first fuel filter. Many people recommend binning Banjo bolts if favour of a full flow joint.
See Distant Shores on YouTube to show the issue.
 
Live and learn, I had a look at some sites detailing the process of annealing copper washers and I now understand why it took me excessive pressure to get a good seal after the original washers had been work-hardened..

Annealing Copper Washers

My banjo bolts look ok and less weakened by holes than those in the pictures. (two holes in stead of three)

I will wait till the rest of the supplies land (suppossedly posted in the UK over a week ago, probably only half of my address used even though postage cost me more than a courier cost to bring me an anchor and mounting frame a few weeks ago)

If I can reduce the number of different size connections then it will be easier to be careful with annealed washers or perhaps i'll obtain some Dowty washers.
 
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