Swap 1990's GM 3.0 for my 1970's 3.0?

[jeffconnell12]

Hi all - i have a bad motor in my 74 starcraft - it is the GM 140hp with a cracked block.

Prices are crazy for short blocks - but I just found a local 1998 3.0l complete/running motor. I've read about different flywheels and the couplers but I am confused - is there any reason I cannot just swap in this entire new setup without swapping components?

Will the original outdrive fit into the new coupler?

thanks for any help!!

 

[Bondo]

Hi all - i have a bad motor in my 74 starcraft - it is the GM 140hp with a cracked block.

Prices are crazy for short blocks - but I just found a local 1998 3.0l complete/running motor. I've read about different flywheels and the couplers but I am confused - is there any reason I cannot just swap in this entire new setup without swapping components?

Will the original outdrive fit into the new coupler?

thanks for any help!!

Ayuh,...... Sorta,..... Yer gonna find the rear motor mount spacing is different,......

'n I don't know whether a '84 or newer inner transom plate swap will fix it,.....

Also, the drive input shaft on yer drive is 'bout an inch shorter,....

 

[jeffconnell12]

Thanks Bondo - so how would I pair my 74 flywheel, coupler and housing to the new motor.. I have access to a good machine shop.. wondering what the most economical way to do this..

 

[Rick Stephens]

I believe you will need to swap the inner transom plate and purchase the longer drive shaft.

 

[Bondo]

Thanks Bondo - so how would I pair my 74 flywheel, coupler and housing to the new motor.. I have access to a good machine shop.. wondering what the most economical way to do this..

Ayuh,.... I Think, you'll need to use the old flywheel cover, 'n get the sierra conversion coupler, that looks like yer old coupler, but bolts onto the new crankshaft bolt pattern,.....

 

[Scott Danforth]

1991 was the first year for new stuff - new block, new crank, new flywheel housing, and the A1G2

are you getting a new bob tail or new long tail?

 

[jeffconnell12]

Hi Scott - the new "used" engine (from 1998) is a complete running engine from front mounting plate to the coupler and housing.

I guess my options are:

1. find a replacement shortblock for my existing (cracked motor) and rebuild everything. Short block is approx $1000 canadian plus hone and machine then all other misc parts (aprox another $800).. if it matters i already have the entire motor disassembled.

2. purchase a newer 3.0L and attempt to do the conversion to make it work with my existing outdrive.. or purchase a gen 2 outdrive to match it. If i know its as simple as buying a newer motor then putting on the matching transom plate and driveshaft i'd go for it.. but it looks like the exhaust is different and who knows about fitment issues?

 

[fishrdan]

Option #3 - Find a rotter hull with good engine and drive, then swap everthing over, crank pulley to prop.

 

[Scott06]

Option #3 - Find a rotter hull with good engine and drive, then swap everthing over, crank pulley to prop.

This is probably best route then you get newer drive and trim

https://www.michiganmotorz.com/base-marine-engine-1967-current-replacement-p-8871.html

on the bottom of this listing it outlines using a 12&3/4” flywheel and different coupler to swap for a pre 1990 3.0 likely this would allow u to swap using the old flywheel cover etc

 

[Scott Danforth]

you can use the 1998 motor with your old drive, you just need to use a different flywheel (purchased from GM industrial motors) and all your old flywheel housing, etc.