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Just bought it, drove it for a hour ran great. Then started with a rattle an loss of power, found and oil leak sprayed all over the prop. Distributer cap cover and probably clogged up some, decided to cut to to chase and do a compression check, all cylinders are 150, except #2 is 100. What causes this? Did I buy a motor with a blown cylinder or did it happen with in the first hour?? :(Seller suggest dropping a new motor in.
 

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Just bought it, drove it for a hour ran great. Then started with a rattle an loss of power, found and oil leak sprayed all over the prop. Distributer cap cover and probably clogged up some, decided to cut to to chase and do a compression check, all cylinders are 150, except #2 is 100. What causes this? Did I buy a motor with a blown cylinder or did it happen with in the first hour?? :(Seller suggest dropping a new motor in.
So was it a brand new engine? There is a break in procedure. Sounds like it ran good for a hour did you get any burnouts in at least.
 

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Could be a multitude of things. Bad or bent intake or exhaust valve, Worn piston rings, or you broke something else. You mention a rattle that sounds like it could be a big problem if it is from the bottom end or if it is from the top of the engine it could be a valve issue. Don't know until you take apart and investigate. No reason to replace an engine until you diagnose the problem. Maybe the previous owner knows something and was hiding a problem.
 

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Pull the valve cover. Sounds like #2 bought the farm. Might be a bent push rod, bent or hung valve, broken spring, or cam lobe going bad. Compare the movement of the rockers to other like rockers.
Well 150 is not a ton of compression sounds like a mild 383 small cam and a low compression motor my guess is if the seller told you to get a motor he knew there was a problem and doctored it up. if your sharp and know your stuff you can fix patch or doctor up something just to sell or get rid of a problem . my guesstimate is he had his fun was tired of the car and said lets unload it .the logic here is if he liked and still wanted the car he would fix it. many years ago I bought a 55 150 post coupe that had a 370 Pontiac engine in it. after many beatings it let go I liked it so much I put 5 engines in that car all Flynn,s auto salvage good used motors that I put cams in and some other goodies. I finally sold it with a truck 409 engine in it . the kid that bought it had it three years at least. I would go back to the seller tell him keep his car and you want your money back. you must have some kind of protection laws for the customer. up my way we have too many of them and sometimes they are a double sided sword that works in favor of the wrong party. give it a try you have nothing to loose you already lost. as far as your engine goes you have to take it apart to see the damage but don't expect to luck out because you will be disappointed. on the other hand you could be lucky. Remember this "since man to man is so unjust the world alone knows whom to trust I,ve trusted many to my sorrow. good luck Al
 

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1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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Getting any back firing? what's the spark plugs look like and I agree with the others that the seller knew the engine had problems, do you want to try to repair it? or get your $ back? and did the seller mention he'd give you your $ back, used cars sold around here usually have a "Sold As Is" deal unless you get a written warranty
 

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I built a 389 (which is a .060 over 383) several years ago for my 51 Chevy. In less that a year, it had almost the exzct same symptoms as yours. Ran a compression check and no.1 cyl was down. Pulled the heads and pan and removed no.1 rod/piston. This is what I found..
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I took the damaged piston to my machinist, and instantly he and another machinist said it was from detonation.
Rather than replace just one piston and risk that other pistons were also damaged, I replaced all 8 pistons and rings.
Backed off the timing, changed from a Q-jet/early Z28 intake to a VERY EARLY Chevy 2x4 setup and ZERO problems for the past 3yrs.

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