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Thread: 136.5mm valves to be replaced with 130mm valves

  1. #1

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    136.5mm valves to be replaced with 130mm valves

    is it possible to change a cylinder head equipped with 136mm long valves with shorter valves (130mm)? if ever, what hardware needs to be done also? valve springs, camshaft, etc? in short, i'll be using the same head. only the valves needs to be done if ever. whats the effect on compression ratio, hp & torque band, starting (hot & cold), etc? btw, it's a mitsy 4d56 turbodiesel. i know you guys can shed light on this. thanks

  2. #2



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    I don't see why you couldn't do it. It's only 0.0065" shorter. You might need to cut the head for the springs just slightly to keep the same rate. And shorten the valve guide. Other then that they should open the same amount once adjusted. Does it have hydraulic adjusters or mechanical? Call a machine shop and ask what there thought is. I'm unsure on the diesels. But it can't be much different then any other engine. Why are you looking to go with a shorter valve?
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  3. #3

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    Quote Originally Posted by camoit View Post
    I don't see why you couldn't do it. It's only 0.0065" shorter. You might need to cut the head for the springs just slightly to keep the same rate. And shorten the valve guide. Other then that they should open the same amount once adjusted. Does it have hydraulic adjusters or mechanical? Call a machine shop and ask what there thought is. I'm unsure on the diesels. But it can't be much different then any other engine. Why are you looking to go with a shorter valve?
    mechanical valve adjuster .....how about changing the valvesprings designed for 130mm valves? the primary reason i'm thinking of going to a shorter one is to lower the compression ratio. but still debating myself on this one. don't know yet what will happen with the power band? how would the hp and torque behave with a lower cr?

  4. #4



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    A shorter valve won't change the compression ratio. You are not physically changing the amount of air that is compressed in the combustion chamber. To lower the compression ratio you would need to change the pistons to a dished piston. The HP and torque will go down a little if you lower the compression ratio. But it will run a tad cooler. From what I here the best thing is oil squirter's for the diesel engines. Thats the trick set up.
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  5. #5

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    Quote Originally Posted by camoit View Post
    A shorter valve won't change the compression ratio. You are not physically changing the amount of air that is compressed in the combustion chamber. To lower the compression ratio you would need to change the pistons to a dished piston. The HP and torque will go down a little if you lower the compression ratio. But it will run a tad cooler. From what I here the best thing is oil squirter's for the diesel engines. Thats the trick set up.
    i'll cancel my plan then.....but do you mind explaining that oil squirter thing for me. i'm curious. thanks again camoit

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    If you look through some of the other posts they talk about adding in the oil squirter's. It sprays oil up at the pistons. It helps to cool the engine and adds lots of lube in the cylinders. I know some of the engines had them stock but IDK just what ones. I would guess the later blocks have them. They just thread in to the oil galley. But I did here there are kits out there. Ask 4d55preformance. Thats his area of expertise.
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    The oil squirters were in the 2.6 conquest turbo motors - to add them you have to drill and tap the runner in the block where they are installed on the turbo block. Not sure if the 4d55 ever had them though.
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    Oil squirters are also found in the turbo 4g63's from Eclipses/Talons/Lasers.
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  9. #9



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    yep the oil squirters are stock on the 4d55......and the 4d56. if you shorten the valves that will bump your seat pressure up. which is a good thing. just make sure you get turbo valves....... there is a difference!
    Real Trucks dont need spark plugs,,,,,,black smoke dont mean it broke.....
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