STUPID INJ. PUMP QUESTION
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=57485
Printed Date: 06 Sep 2025 at 11:42am
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Topic: STUPID INJ. PUMP QUESTION
Posted By: Mrgoodwrench
Subject: STUPID INJ. PUMP QUESTION
Date Posted: 26 Sep 2012 at 5:27pm
This may be a dumb question but i've asked several people i thought would konw without any luck. Why do the injector feed lines on diesel engines all have to be the same length? I was told that it was so the fuel traveled the same distance to each cyl. so the timing was right, but basic physics says that once the line is full the fuel can't be compressed so whatever amount of fuel the pump puts into the line will come out the other end reguardless of length. Iwouldn't think that it would be a pressure thing given the relatively high pressure and shortness of the lines. I'm deffinatly no expert especially when it comes to diesels, this is just something i've always wondered and most give me the answer "I don't know thats just the way they all are" Some of the site members have shown great experience on diesels i believe some having inj. shops. The answer may make me look dumb but i just want to know. thanks
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There are 3 ways to do job GOOD, FAST, CHEAP. YOU MAY CHOOSE 2. If its FAST & CHEAP it won't be GOOD, if it's GOOD & CHEAP it won't be FAST, and if its GOOD & FAST it won't be CHEAP!!!!
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Replies:
Posted By: Stan R
Date Posted: 26 Sep 2012 at 5:42pm
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My hunch as an engineer and not a diesel mechanic: though liquids are theoretically incompressible, in reality, they have a very minor amount of compressibility at the high pressures and with a minor bit of entrained air (which is compressible, equal lengths allows the timing to be optimal for all cylinders, i.e. time of fluid into each cylinder is equal for all cylinders with these two factors with equal lenght.
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Posted By: DrAllis
Date Posted: 26 Sep 2012 at 6:12pm
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Believe it or not, there is line expansion at each firing causing timing differences if they weren't the same length.
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Posted By: Mrgoodwrench
Date Posted: 26 Sep 2012 at 8:30pm
well you are the first guys to give me any answer and it makes sence. just seems like it would be easier to over engineer the tubes to fight expansion and route them conveniently insteasd of running little tubes everywhere! thanks guys
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There are 3 ways to do job GOOD, FAST, CHEAP. YOU MAY CHOOSE 2. If its FAST & CHEAP it won't be GOOD, if it's GOOD & CHEAP it won't be FAST, and if its GOOD & FAST it won't be CHEAP!!!!
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Posted By: injpumpEd
Date Posted: 26 Sep 2012 at 9:00pm
It is indeed to ensure as close as possible to exact timing from cylinder to cylinder, but it also ensures more exact fuel quantity being injected to each cylinder. I do believe some old diesels did have different length lines, 4010/early 4020 I have heard that. Not a dumb question at all.
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210 "too hot to farm" puller, part of the "insane pumpkin posse". Owner of Guenther Heritage Diesel, specializing in fuel injection systems on heritage era tractors. stock rebuilds to all out pullers!
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Posted By: MACK
Date Posted: 26 Sep 2012 at 9:27pm
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I beleve some of the MF diesels used different ID lines and same length to do the same thing. MACK
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