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Thread: jet valves

  1. #1

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    jet valves

    i have an 87 d50 2.0 ive read that some ppl are doin jet valve eliminators on the 2.6 motors can i delete the jet valves on my 2.0 do they make a kit for this if so where can i buy this kit ? and are there any benifits to deleting it and what is the purpose of the jet valve is it just for emissions?
    thanks for the help

  2. #2



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    Jet valves were put in these heads to create a swirl condition for the intake charge for better power and lower emissions. The problem is that over time, the iron jet valve housings cause the aluminum heads to crack from the different expansion / contraction rates of the 2 metals. If the motor is running fine, leave it alone. If you need to pull the head, then I would look into putting in the eliminators. I am not sure if the ones for the 2.6 will fit a 2.0 head - check with DAD at engine machine services - he would know - he does a lot of work on starquest motors.
    Last edited by pennyman1; 02-22-2013 at 07:31 PM.
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  3. #3

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    Here's a bit of info on the MCA Jet Valves and Mitsubishi engines. http://en.wikipedia.org/wiki/Mitsubishi_Astron_engine. This site has The eliminator kit. http://www.silver-seal.com/category/...scengineparts/

  4. #4

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    Thanks guys also if I do the jet valve elimination does the head need to come off to do it or can i do this with the head still on the block

  5. #5



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    All you do is pull the rocker shafts and swap them out. I recommend replacing them. It was a bad idea then and a bad idea now.
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  6. #6

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    So its a bad idea to do the elimination kit ? Why is it a bad idea I want to make the best decision and not the wrong one

  7. #7



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    Its not a bad idea to pull the jet valves and put in the eliminators - I just don't like messing with something that is not giving problems. I have an 86 2.0 with the jet valves in and I am not going to touch them as the motor only has 75k miles on it. Its the "if its not broke don't break it" mentality, but its your truck, do what you feel is right.
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  8. #8

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    Do the jet valves still serve their purpose with a Weber carb or just the Mikuni?

  9. #9

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    The problem with the jets is the steel "cap" at the end that sits in the combustion chamber. It gets bloody hot and doesn't dissipate heat as well as the aluminum head. Both from the additional milling, and that extra heat you get cracked heads.

    I would have to disagree with Penny on this one, the whole design is broke, and if you can't replace the head with a non-jet, then mitigating the existing engineer-caused damage is the best bet.

    Will temper my response a bit, though. My head went over 150k miles without cracking, and some (by means of unknown miracle) never do.

    As far as them working? Yes, they are just an emissions trick for what it's worth.


    Edit: and I shoulda read the first response, Penny already pretty much said what the problem with them is.

  10. #10



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    Remove them... Or cut that end of the arm off the rocker arm. They are also knows as a lean burn valve.
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  11. #11



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    just remove the screw that contacts the jet valve instead of cutting the rocker arm - easier and no mess from cutting the tab off. Also, once you put the Weber on, the jet valves are useless, as the adaptor plate covers the air feed to the valves. I also agree that the best fix is a non jet valve head.
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  12. #12

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    Here's a bit of nostalgic info on the Jet valve http://books.google.ca/books?id=rwAA...0valve&f=false

  13. #13

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    I have a elimination kit ( haven't put in yet) that fits my 87, it's a 2.0.

  14. #14



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    Quote Originally Posted by Andy 2 View Post
    Here's a bit of nostalgic info on the Jet valve http://books.google.ca/books?id=rwAA...0valve&f=false

    YA I would say 1978 is nostaligic, that magazine was a time warp for sure. Advertising a Pinto Station Wagon, lol
    I used a kit on my old Mits head, best thing I did to that head was remove MCA jet valves and install a 20 dollar kit. They always seem to crack heads between them and whatever is closest to them. Great idea, but Mitsubishi just kept using inferior materials in their manufacturing. The normally known 8 valve head was strangely called the 12 valve head.

  15. #15

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    Quote Originally Posted by BradMph View Post
    YA I would say 1978 is nostaligic, that magazine was a time warp for sure. Advertising a Pinto Station Wagon, lol
    I used a kit on my old Mits head, best thing I did to that head was remove MCA jet valves and install a 20 dollar kit. They always seem to crack heads between them and whatever is closest to them. Great idea, but Mitsubishi just kept using inferior materials in their manufacturing. The normally known 8 valve head was strangely called the 12 valve head.
    I'm wondering if by 1988 they had revised those things whereas if you are proactive with maintenance they really don't have a head cracking problem.

    The reason I say that is I had a bad fan clutch and a leaking radiator at 150K or thereabouts that caused overheating and therefore a blown headgasket. I just replaced the gasket and kept on truckin'- there was no damage to the head even though it overheated into the red...that means it got HOT.

    Mine are still in there and I see no reason to remove them i.e. "if it ain't broke don't bother"...just an 70s era emissions 'gimmick'.

    The truck has spark knocked since day one with the factory carb and 2 different model Webers. (DCES and DGEV)...stock timing or retarded to 0' BTDC...which leads me to think it just needs 89-91 octane.

    In other words they don't help nor harm in my 350K miles of experience.

  16. #16



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    Well, I would not be surprised is you are correct, though there were recall on other items that ran on past that year. Exhaust manifold cracking was going on for a long time and then it was removed from the list for some reason. But, I think if you have not had any problems that you are one of the lucky ones. I'm not saying that each and every head will crack or does crack, they just do this much more then other vehicles. Mitsubishi had some management problems back in the days too that caused some bad manufacturing.
    I probably shouldn't condemn every truck, but I can say with experience that I hear more issues with overheating and head damage resulting in some form or another then any other major problem with them. My truck is on it's fourth head in a span of 275K miles and only the last one has held up longer then them all and doing well. Though it is one that was cracked and was repaired professionally. So, again, not every single one is bad, but many are and many are cracked and people don't even know it. The cracks don't always rear their heads up until a head is removed and inspected carefully.

  17. #17


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    jet valve uh oh!

    Gabe's been working on the white truck. Who ever, (a dickweed) worked on it last didn't match/timing chain plated links on either chain to the timing marks.
    Jet valves, #4 was stuck and broke off, #3 was making the motion but broke off.
    #2 was working, #1 jet valve was functional but the lever off the rocker was broke off.
    On the head you can see perfect indents from pieces of the valve rod. Found a jet valve keeper sitting in under the cam but none where missing...more info, wrong thread.
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