350 swap help

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corley.david

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David
Truck Year
1985
Truck Model
K10 Silverado
Engine Size
305
I have a 1985 K10 Silverado that had a 305 in it. I am assuming it was the stock motor as it had very low compression. I purchased a used 350 that came out of a old Chevrolet Winnebago. Ended up being a good low mileage 4 bolt. So got it all cleaned up and put into the truck. The transmission I assume is a 700r4 as it has 16 bolts and MD8 on the side of it. The problem I have is now that it is in the truck and the transmission is mated with the engine, my torque converter/flex plate bolts do not line up. I am assuming that the Winnebago it came out of had a much larger transmission. THe bolts are off by 1/8th of an inch or maybe a little more. I have spun the flywheel all the way around to check each hole. I still have the old stock 305 that I pulled out. Can I use the flex plate/flywheel off the 305? I am confused on the entire internally/externally balanced or how to know if this is something that is going to cause problems. I did notice that on the 305 (old motor) the flex plate has holds partially drilled into it in a straight line. Not sure if this means it is balanced to the engine of just a balanced flexplate. I may be overthinking this but I appreciate any help. Thanks.
 
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gpmorgan

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If both engines have the 2 piece rear main seals, the flex plates should interchange. Lay one on top of the other to double check. I think they both should have 153 teeth. They need to be the same for starter to work. New flexplates aren't very expensive and would be another option.
 

Honky Kong jr

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Unless the camper had a th400 and the 168 tooth and the 6 bolt converter.
 

74 Shortbed

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Gonna have to change the flex plate, one on the 305 should have both bolt patterns so it should work..
 

corley.david

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K10 Silverado
Engine Size
305
What about the balancing issue? If I use the plate off the 305 on the 350 is this gonna cause a balance issue?
 

corley.david

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Thanks for all the help. I will swap them out and see how it goes.
 

74 Shortbed

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Anytime, let us know how it turns out..
 

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