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Going to Take a Chance

Dibbons

Well-Known Member
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Nov 29, 2014
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Location
La Paz, B.C.S., Mexico
The "complete" core 340 I purchased had a forged crank installed without the drilled 1/2 and 7/8 rod journals. Don't know if it was from a 273 or 318 or what. I have been hesitant to put it back together with new rings and bearings because I don't know the history of the rotating assembly balance. It also had a hodgepodge of parts: front sump oil pan, two passenger side exhaust manifolds casting #3418623, .509 camshaft, Carter AVS from a non high-performance big block, etc. The installed bearings were dated 1982.

I previously decided to rebalance the rotating assembly, but I don't know of anyone in the area that is qualified for such an endeavor, and San Diego is 1000 miles away. So yesterday while I was doing some yard work, I decided to just put the motor back together anyway (hone the .040 over cylinders, new rings, bearings, valve job, new camshaft, gaskets) and hope for the best. I hope it doesn't shake itself to death. Best scenario is the previous owner had sense enough to re-balance it in the first place.

Foto is not mine, but I found it on FABO to demonstrate difference in crankshafts I am talking about.

crank balance.JPG
 
your a brave man I hope it works out for you.
 
The big question- how did parts look when you dissembled the motor? Did it look like the motor was running in that configuration for a while or did someone just slap some parts together and sell it? You are really rolling the dice though... You will hate how bad it vibrates if its not balanced and you will end up pulling the motor and doing all the balancing again anyway. When we did my dad's 360, we went from stock pistons to KB hypereutectic pistons without balancing and it was awful. I was scared to rev to motor over 4000 RPM. In the end we ended up pulling the engine with less than 10K miles on it to balance, along with new rings and rod bearings.
 
Have you checked with these guys?
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I know nothing about them but among the online photos was this....
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Which seems to indicate they have some engine machining capabilities & they are close to La Paz...... You may well know something negative, their 3.9 rating on Google might be a bad sign but honestly I don't put much faith in Google reviews...
 
That is one of the local machine shops (Kuhisa). I should go by to see if they know anyone that balances motors.

Being the fact that La Paz is the finish line of the Baja Mil/Baja 1000, I have spoken in the past with off-road racers here who have told me there is no local shop capable of engine balancing.
 
Balance needs to be close, not perfect... Guys get hung up on some shop claiming they balance within a half gram.... Get the crankshaft spinning 5000 rpms with a quart of oil caught up in the action & show me how a gram or even an ounce (28 grams) matters with that two pounds of oil effecting the balance....

If they can get it close it's probably good enough... Hell if it all you have available I'd drill the journals myself to the known dimensions before putting it together knowing the throws are to heavy...
 
the solid cranks were from the trucks 318 were better and stronger than the stock cranks that came in the 340 we ran one back in the day in a 70 dart never had a problem car went low 11s superstock I
 
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