I began hearing a metal knocking sound from the engine of my 78 bronco 351M yesterday. Took it to my mechanic, and he agreed: 2 rods have broken. Problem is, I have had the truck for all of 2 months! I can't afford to get the engine rebuilt, and don't know what to do. Any suggestions?

Thanks!

David

 

how about a junk yard motor?

 

park it and mooch off your friends. nah, i'd buy a beater til i had the dough to fix the truck. my 2 cents. -wb

 

You might want to try to find a 351/400 from a wrecked 78 LTD. Should be cheap and should bolt right in. Bummer on the Engine. Good luck.

 

Check northern auto parts on the web they have rebuild kits cheaper than anywhere i've ever found.Yours should cost around 275.00 and you can get some rods from where ever.

 

That's a shame about your motor. If you get another motor by all means before you put it back in, put in new rod and main bearings!!!! Oh and also put in a new oil pump,believe me do it while it is out trust me!! Good luck!!

 

Yep green is right new rod bearings and oil pummp NEED to bone while you have it out.The kits from northern come with everything except rods crank and of course the block.they have good parts too like melling pumps and fel-pro gaskets not cheap crap.

 

I have checked the junkyard, and they have a 78 351M from a Torino. The mechanic said that it sould cost about $400-$500 to do the swap, taking lots of parts from the old and putting on the new engine. I am not sure if that includes all the other stuff, like oil and water pumps, etc or not. I will look into the northern company and see what they have to offer. The other major issue here is that we are moving 300 miles from where we are at now, so time is an issue. (We are moving next month!!) So thanks to everyone so far; I will keep looking and keep updating!

David

 

Well with the northern kit and machine work it should cost you about the same and I would rather have a rubuilt engine than a junk yard donor.but its up to you.

 

Could be just the rod bearings. If so, and you have run it for any length of time, your crank will need turning and your cylinders will be eggshaped. If you haven`t run it but very minimally since you heard the knocking, you may be able to clean the crank up a little bit, install new rod bearings, main bearings, oil pump and water pump just to get by until you can afford to do it right. This would by no means be a permanent fix! Be sure and check your clearances. If two of your rods have actually broken, your block is more than likely scrap iron. If you go with a junkyard engine, ask them if they have an engine run/test stand. Have them run the engine for you before you buy it. Verify oil pressure, temperature and have them do a compression check. Hate to see you put one in just to find out it was junk too. By all means, install a new oil pump and water pump on it. Once a used water pump sits around dry, the seal gets hard and will usually leak shortly after reusing it. Best bet, if you can afford it and with your time constraint, is a rebuilt long block with a warranty as your heads may be damaged too if the rods actually broke. Even if the heads look good, you may have a couple of bent valves. Good luck with whatever you decide.

 

I think that horton-racing may be right. Is it true that if the rods themselves have broken, then the engine wouldn't run? I have only put about 30 miles on the truck since the knocking started. I will have to ask the junkyard about what you suggested. I know that the engine man there is generally very reliable, but obviously, stuff happens! To do all the work above (main and rod bearings, crank, etc, wouldn't the engine need to be pulled? The oil pressure on the engine is very low anyway, so I would want to replace the pumps at that time. The oil pressure at it's height is about 20, and at the lowest almost 0 (warm engine, in gear, at idle). Now if I could only get my wife to understand!

Thanks!

David

 

I find it difficult to believe that you broke two rods in a 351. Thats pretty hard to do in a stock motor. If you have two broken rods (any for that matter) that engine is gonna shake when its running. An engine will run with at least one broken rod, but it sure is gonna let you know it. More than likely you have at least one bad bearing. The important info is, exactly when is it making noise?
Run the engine at 1500 rpm in neutral (or park), if it hammers at that time, but does not make noise when the engine is speeding up or slowing down, then you have bad rod bearings.

Best thing to do, is get a second opinion from a local qualified mechanic. I have found that at least 90% of so called mechanics are just parts changers, and have no idea how to diagnose a problem.

Steve

 

dwwebste

I had almost the exact same thing happen to me EXCEPT I had almost no knocking and I had decided to replace the rear main seal which was leaking like mad. When I dropped the pan I found I had spun a rod bearing. My Oil pressure was about the same as yours too. I'll bet you've "spun" a bearing. I'd only had my rig a month! Luck of the draw I guess. I'm waiting for warm weather and more money to fix mine...plus I'm going to put in a 460. I like the 400M but as far as parts goes you can find 460 parts a lot eaiser...at least I think so and I LOVE the power of the big block. There's my pennies worth.

 

The noise occurs at all speeds, though it is quieter at idle. When you speed the engine up, it gets louder. I haven't noticed any leaking oil, and I check it on a regular basis. I feel that I can trust the mechanic, but a second opinion is certainly a good idea.