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Thread: GM 350 Motor question.

  1. #1
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    GM 350 Motor question.

    Ok, i have a k1500 blazer with 272,800 miles on it. She's gettin old, but still runnin. Now this is a current problem, but i deal with it. Lets say im at dunkin donuts, and its all zigzaggy and crap, so when i give it a little gas, and let off, it sounds like she's chokin, and the rpms drop to under 100. I think she's losing compression. What do you guys think, suggestions?


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    kcnewell is offline Cadillac Owners Connoisseur
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    Re: GM 350 Motor question.

    An engine doesn't just "lose compression". That's a wrong guess I would say. I would look at the idle speed control mechanism as it sounds like the idle speed control is not catching the throttle at a high enough throttle angle to keep the engine speed up. That or an injector is leaking and it's running rich and just almost stalls when the throttle is let off due to the rich condition. Or, it could be an EGR valve that is sticking open and not closing when the throttle is closed.

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    Re: GM 350 Motor question.

    everything was checked by certified mechanics, she's getting old. Loosing compresstion by either worn seals or rings, or worn sleeves.

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    Re: GM 350 Motor question.

    Quote Originally Posted by RBraczyk
    everything was checked by certified mechanics, she's getting old. Loosing compresstion by either worn seals or rings, or worn sleeves.
    In the first post, you said you think it's losing compression, and wondered if we had any thoughts. In your second post, you said it was checked by certified mechanics, and it's losing compression. Which tells me you have your answer.

    Your mechanics, since they are there, in front of the motor, can tell a lot more than we can from the Dunkin Donut behavior you described. I'd say it's time to move on. Right?

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    Re: GM 350 Motor question.

    Im going to overhaul the engine for my senior project. But i wanna up it from a 350 to a 383? how difficult is it to change the headers you think?

  7. #6
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    ljklaiber is offline Cadillac Owners Fanatic
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    Re: GM 350 Motor question.

    Your 383 requires a crankshaft from the 400 inch SB and rods from same . unless you are willing to check the 5.7 rods at each and every turn. Rods rom 400 SB are 5.56 and weaker than 350. My advice is to ovrbore ,030 and install better rod bolts and careflly assemble a potent 355 CI SB Chevy.

    Pay attention to the cylinder heads, and if possible , find a machine shop with a Serdi 100 Valve and seat machine and let them spec your heads.

    JMO

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    Re: GM 350 Motor question.

    Thank you for your wisdom. Keep in mind the engine is pushing 271,000k. How much is this gonna cost.

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    Re: GM 350 Motor question.

    wait 271K

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    ljklaiber is offline Cadillac Owners Fanatic
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    Re: GM 350 Motor question.

    IMO, unless you really want to get involved with engine building, The 'Crate motor program that GM has in place will actually cost less. With the mileage you have, all moving parts will need inspected ,and most replaced.

    I believe Chevy has a base 350 that goes for about 1400 exchange.

    Check out the cost of a replacement out right, and you may even want to keep your old engine, and work on it , in company with a local Machine shop.

    I am 64 and rebuilt my first engine at 16, as well. Outside of 4 years in the ARMY, I built engines until I sold my business and retired. I will pass on here what the old guy who hired me first, said..."The engine you are working on, is the engine called yourself."

    Good Luck and keep us posted. 271K is the sign of one hell of good old engine'

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    Re: GM 350 Motor question.

    Oh yea she's still running strong. The rebuild is for my senior project so, i don't know if fixing the caddy comes first or rebuilding the motor. Gotta check with my dad and see if I can get a grant.

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    Re: GM 350 Motor question.

    Whatever you decide, just do it. Don't count on grants..LOL I had that boot on my ass, many a time.

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    Re: GM 350 Motor question.

    Quote Originally Posted by ljklaiber
    IMO, unless you really want to get involved with engine building, The 'Crate motor program that GM has in place will actually cost less. With the mileage you have, all moving parts will need inspected ,and most replaced.

    I believe Chevy has a base 350 that goes for about 1400 exchange.

    Check out the cost of a replacement out right, and you may even want to keep your old engine, and work on it , in company with a local Machine shop.

    I am 64 and rebuilt my first engine at 16, as well. Outside of 4 years in the ARMY, I built engines until I sold my business and retired. I will pass on here what the old guy who hired me first, said..."The engine you are working on, is the engine called yourself."

    Good Luck and keep us posted. 271K is the sign of one hell of good old engine'
    If you are rebuilding as part of your senior project, and feel confident with the work you are going to do. I say "what the heck?" The parts won't be that much.

    But if you need a solid, no excuses motor (I'm not saying you can't build this) the crate program is great. Pick up a short block and go on your way.

    I had the stock motor in my Vette rebuilt by a pro, and I spent way more than a crate would have run. Granted, I picked my own parts, but the ZZ4 probably would have been a better option.

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    Re: GM 350 Motor question.

    The truck's short block is fine, i need the heads though. Thats gonna be the expensive part. The thing i wanted to do was to strip the front of the chassis down, remove wheel wells etc. and work on the motor while still in the truck to make it interesting.

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    Re: GM 350 Motor question.

    You are gonna need piston rings. Those kinda miles kinda say that. Take your time and do the entire rebuild. If we can help, we will, K?

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    Re: GM 350 Motor question.

    yea chevy performance has 300dollar rebuild kits that should be pretty useful. I just don't know how expensive new heads and new headgaskets are gonna be.

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