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Old 01-02-2014, 17:01   #1
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fuel return banjo bolt question, Yanmar

I'm slowly working my way through systems on old boat we bought. One of the 3HM35F's has started running rough since the delivery trip. I had the three injectors tested yesterday, all okay, and reinstalled today. Examined all the hardware as I put it back on the engine, and one of the three banjo bolts holding the return fuel harness to the top of the injectors was really bad. Half way cracked through, with the other half just about to let go.

I can see that fuel would be going down the crack in the bolt, and getting around the lower copper washer. I can't see that this would hurt anything, other than being a small fuel leak onto the top of the injector. However, I thought I better ask some of you more knowledgeable diesel mechanics.

Would a slight leak in the fuel return line cause any issues on one of these engines? I can imagine that this is low pressure fuel, so I'm thinking it wouldn't affect anything going on in the engine.
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Old 01-02-2014, 19:33   #2
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Re: fuel return banjo bolt question, Yanmar

I think, your going to want to replace that bolt. Plus verify that the return piping is not obstructed at all..
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Old 01-02-2014, 21:20   #3
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Re: fuel return banjo bolt question, Yanmar

Replace the banjo bolt and both copper washers. Diesel engines are very sensitive to air leaks in the both the supply and return fuel lines. Learned the heard way on a BMW turbo diesel in my RV.
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Old 02-02-2014, 20:17   #4
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Re: fuel return banjo bolt question, Yanmar

Why would a bubble in the return line affect engine running????______Grant.
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Old 02-02-2014, 20:31   #5
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Re: fuel return banjo bolt question, Yanmar

That banjo bolt is the victim of overtightening.
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Old 03-02-2014, 05:35   #6
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Re: fuel return banjo bolt question, Yanmar

Yeah yeah, I KNOW the banjo bolt is damaged. Duh. That's kinda why I went to the trouble of taking the photo and posting it. Question is if this could possibly have any effect on engine performance. Of course I am hoping that it would, because this would be a very easy fix. I'm still new to working on diesels. I'm thinking that a leak in the fuel return line isn't going to do anything other than dribble fuel.

By the way, you don't have to replace those expensive copper washers. Just heat them cherry red and let them cool. That anneals the copper. Presto change, all soft again. Good as new.
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Old 03-02-2014, 07:44   #7
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Re: fuel return banjo bolt question, Yanmar

1Stink of diesel fuel. 2 already weakened bolt if you break it retightening WOW you will never forgive yourself. Probably a hard place to get parts. If you can't find them e me we have a local Yanmar dealer. Perhaps I can help.
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Old 03-02-2014, 11:34   #8
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Re: fuel return banjo bolt question, Yanmar

Bet you could go to the local auto parts store and match it up with a bolt used on automotive brake systems if needed.
Fuel return shouldn't matter running wise
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Old 03-02-2014, 11:57   #9
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Re: fuel return banjo bolt question, Yanmar

If the return line is plumbed back into the supply side. It would introduce air into the system and cause problems. If it returns to the tank by separate piping, no on most diesels. But could be a fire hazard.

Lloyd

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Originally Posted by Canibul View Post
Yeah yeah, I KNOW the banjo bolt is damaged. Duh. That's kinda why I went to the trouble of taking the photo and posting it. Question is if this could possibly have any effect on engine performance. Of course I am hoping that it would, because this would be a very easy fix. I'm still new to working on diesels. I'm thinking that a leak in the fuel return line isn't going to do anything other than dribble fuel.

By the way, you don't have to replace those expensive copper washers. Just heat them cherry red and let them cool. That anneals the copper. Presto change, all soft again. Good as new.
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