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need help

736 Views 8 Replies 6 Participants Last post by  jerrspud
i was coming home last nite from a show and over heated i have a 235 engine in my 56 and and when i am driving it feel like some thing is holding me back and i was wondering could it be my rear end . and today went to start it started rite up sound fine but when i give it gas i hear a knocking sound what can it be
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almost anything but sounds like spun brg.????
:hello: hi ruben and welcome. good to have you here. sorry your having a problem. did you forget to put the emergency brake off? :stupido2:
brake was off and it runs fine but when i give it more gas thats when it starts to knock it sounds like its coming from the bottom of motor
Sorry, but that sounds bad as it may be a rod bearing. One old mechanic's way to check this (yes I'm an old mechanic) is while it's running pull a plug wire off starting at plug one and see if the knocking seems to stop, if it don't put that plug wire back on and pull number two off and see if the knocking stops. Do this with the rest until the knocking seems to stop. The one that you pull and the knocking seems to stop or get much quieter on is the one with the bad bearing, if it's a rod bearing. When the bad cylinder fires it jams the piston and rod down on the crankshaft and makes a knocking sound due to the gap where the babbet is gone from the bearing, without the cylinder fireing, it don't get jammed down and won't make the knocking sound. Good luck and let us know if this works. I hope it's something simple and not a bearing, but it sure sounds like one to me.

P.S. one other thing it could be is when the starter bendix gets weak with age, sometimes the starter gear will bump on the flywheel when the engine is running and it will make a rapping noise also, but this is very rare.
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oil pressure..??

brake was off and it runs fine but when i give it more gas thats when it starts to knock it sounds like its coming from the bottom of motor
Ruben, are you sure you haven't lost oil pressure..? sounds like the bottom end is about to seize up to me. sorry, doesn't sound like it's going to be anything simple, good luck with it.
thanks for the info i was outside and did a comp test the 1 cyl is 130, 2-125, 3-120, 4-125, 5-125, 6-115 i was reading a book it tell me to put a liberal amount of oil on top of piston how much is a liberal amount
How much oil to use?

My "Motor's Manual" says you should have at least 130 psi at cranking speed, but I have seen them run fine with what you have. As far as how much oil to use, you need enough oil to cover the top piston ring to make a seal. I doubt a little extra oil wouldn't hurt, however, I don't think the knocking noise is due to the compression and you are most likely wasting your time by doing that. Try the running the plug wire pull test I talked about earler, and put a guage on the engine and check to see if you have oil pressure also. I think those would be your best bet to check for the knock, Good Luck
yeah, you could have perfect compression and still have a bad lower end. it won't show up in a compression test

a full rod bearing set is not too much. around $85
the individual rod bearings numbers are 1950CP (I'm in the middle of replacing mine.)

it's really easy to change the rod bearings. It's just a pain to get to them. you need to take off part of your idler arm and it helps to jack up the front of the motor to get the pan off. Take the radiator out, remove the nuts on your front motor mount, and jack up the front of the motor a bit.

you should check your main bearing clearance while your in there as well. Those are a little over $100.

so for around 200 bucks your lower end will be good as new (assuming your crank does not need to be turned)
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