Ok Friends, Got My 71' 307 5.0 Up to Par, Excluding the Gas Tank, in my 40' Chevy, and Turned it over. There was a Knocking noise coming from what sounded to be the pan underneath. This Car I Bought on Ebay and It was supposed to have a Rebuilt Engine and Trans. I Did a Diagnostic and found out that Cylinder No. 8 had a PSI of about 60. All others 120-130 PSI. Could This Be the Connecting Rod? The Oil Pump? It Has Brand New Oil.Help I Hope I don't Have to pull the block out. Please Help Friends.
It could be a few things, but the low compression in #8 tells you something is not well, plus any kind of knocking noise is not good. First, pop the valve cover and make sure your rockers are adjusted properly. (turn the engine to TDC for that cyl, adjust rocker nuts untill the pushrod just barely starts to drag, then go another 1/2- 3/4 turn) If you have some broken parts, or a rocker too tight or loose, it can affect the cranking compression reading. If your rocker arms/valves look OK, you need to pull the head and have a look at your piston tops and valves/seats. Your compression reading is a function of the piston ring and valve seal. You might see a hole in a piston or little chunks of piston ring on top of the piston, or you might see something in the cyl head. Bad things here will affect your cranking compression, but may or may not cause a knock....if all still looks OK, then pull the pan and remove #8 rod and piston assy. Usually a knock is too much clearance somewhere...usually a rod bearing..but the only way to know for sure is take it apart and have a look. Good luck and let us know.. -Abone.
Thanks Flamed.. The Noise Is Coming from the Bottom Pan Area. Not The Top. Thought it was the oil pump, but that wouldn't cause compression loss. Did a Dry Compression Test. Could it be the Connecting Rod or The Ring?
Found This Advice. Is This Correct? You can rule out that possibility by doing a wet compression test. It's the exact same test, but you squirt some oil in the cylinder through the spark plug hole. If the compression goes up dramatically, then there's a problem with the rings. If there's little to no change in compression, then the head/valves are suspect.
If you put can fit an adaptor on a airhose and the sparkplug hole on cyl. 8. Then you listen for air comming out. If it leaks thru the exhaust or intake you know its a Valve, if it leaks In to the pan, it's piston, ring or bore. If it goes to both intake and exhaust or the water, the head is cracked. Simpel and cheap, and it tells alot more. Regarting the knocking sound, only manual tear down, tells you whai it is. Try talking to the seller, there might be another way then a law suit. It might be a shop involved, whoem is willing to redo there fault.
Both sound serious and all good advice above. You can also remove plug leads one at a time and see if the knocking sound changes, that will tell you what cylinder to look at. Good luck. JW
you cant sue. its a used car. all used car sales are AS IS. he didn't sell you a rebuilt engine, he sold you a used car with a purportedly rebuilt engine. rebuilt WHEN? how many miles on it? who did the rebuild? used car purchases are Caveat Emptor (Buyer Beware!) if the seller won't do anything about it, you can TRY to dispute the sale thru ebay, but thats about it. good luck.
All good advice on the motor-checks. Wet compression test and leak down tests like stated before. If the noise doesn't go away after a Very short run time; don't run it any longer than you must. Sounds like you'll have to pull it out and apart for a rebuild. Really sorry about whatever it ends up being if it's serious. Ps. I'm assuming the new oil in the motor is full on the dipstick?
Pulling Pan Tomorrow. Very Curious what the Hell Is Banging.(Guessing Rod). Anyways Seller is Willing to Donate a 350 and Pay for The Master Rebuild Kit. Will All The Components from The 307 fit on the 350?
curious. is the seller willing to pay for the master rebuild kit AFTER the machine shop determines how much work your 'new to you' 350 needs? in other words, he cant supply you with a correct kit until you know what the cylinders look like or what the crank main and rod journals look like. might need a new set of pistons for all you know. the 350 he's supplying you might be a whole other piece of junk. determine the cause of anguish with your 307. you already got hosed once. it might be just as easy to simply rebuild the 307 you have.
Actually Bro, He Listed the Car for a Friends Family. His Friend Dies of Cancer, so He Offered to sell his Car for them on Ebay. I Felt Bad Because It wasn't Even his car, he was doing the family a Favor. But Still, He did list it as rebuilt and that's why I Bought It. He owns a Rod Shop and He Offered me 350 someone left there cause they went to fuel Injection. He said it was a runner, but he said he'll check it out before saying anything, not to put his foot in his mouth again.
If he gives you a 350,put the 307 crank in the 350 block and get a set of 327 pistons, build it as a 327 !! all the other bits interchange. Sell off the parts you dont need on keep for something else. JW
I suddenly stopped caring about your problem as soon as you mentioned the word lawsuit. Buyer beware is a general rule of life.
Interesting ??? Are you sure you didn't dent the pan on installing it so crank is hitting????. If it sat for a long time a valve could just be hanging up from sitting for a long time. Definitely will affect compression. Because you didn't check it out is your fault even if it is junk. Judgement for the defendant, Sounds like he's trying to make it right. He doesn't have to.
I'd do this first just 'because',and I'd also make sure to completley back off the adjuster nuts first as well----------
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