late model v-8 motor change

squirtis · #1 02-05-2009, 07:54 PM

Hey guys, new here, looking to change out the motor in the v20.

We are looking at putting an 89 chevy 350 motor in where used to be a 79 model chevy 350.

Here's my immediate question, the crank to outdrive bolt pattern is different. Is there a conversion kit, or adapter for going to late model motors from the old ones? It's got a mercury outdrive on it.

Thanks for the help if ya can..

Curtis

macojoe · #2 02-05-2009, 08:14 PM

Welcome to the site!!

Therm or Spare will be by soon and thy can answer them questions for you I am sure!!

spareparts · #3 02-05-2009, 08:36 PM

you will need to change the drive coupling to make it work, you need the triangular shaped coupler, it should bolt to the flywheel using the bolt holes that a pressure plate would bolt up to if you had it in a car. BTW, you will need to have a flywheel(manual transmission), not a flexplate(automatic transmission type) for the 89 motor for it to work in a Merc set up. Theer may be some interfearance between the coupler and teh bell ohusing once you get it bolted up, if I remeber correctly, therer are two square indentions on the bell housing right under the motor mount ears that teh coupler will hit, it will takes some grinding.

THEFERMANATOR · #4 02-05-2009, 10:42 PM

Sounds like your trying to use the flywheel from the 79 on the 89. If that is what your trying to do it won't work. In 86 they changed to the one piece rear main seal and the bolt pattern changed. Like SPARE said, you need a manual flywheel from an 86+. The bellhousing bolt pattern is the same though, so your only real obstacle is the flywheel.

squirtis · #5 02-06-2009, 12:15 AM

excellent and thanks very much guys!

Will let ya know how it works out

Curtis

spareparts · #6 02-06-2009, 06:58 AM

Couple of other things for you to know about if you haven't allready figured it out. If that new motor was a fuel injected engine, it may not have a mechanical fuel pump boss, some did, some didn't, some had the boss, but didn't have the holes drilled for mounting and for the push rod to go thru. If you new motor doesn't have provosions for a mechanical pump, you can use a Marine Rated low pressure electric pump. Second, if you didn't allready know, the intake manifold bolt pattern is different, the center bolts come in at a different angle, you can open up the holes in your existing manifold and make some angled spacers out of 3/8 id pipe, its doable without a whole lot of work, but just be for warned. Also, while you have the new motor hanging on an engine stand, replace all the freeze plugs with brass ones, if you don't you will be replacing them before long after you put the engine in, the steel ones just don't last in a boat. If it were me, I'd pull the timing cover and replace the timing chain with a good high quality chain, the factory GM chain that comes in boat motors is excellent for the money, a Cloyes is a good aftermarket chain. Your motor may have coem with the factroy plastic gear set up, it will not last in a boat.

squirtis · #7 02-06-2009, 12:56 PM

Thanks again guys,

It's a buddies boat and I was helping him pull the motor etc. He already saw this morning the replies and is on it as we speak..LOL

I will post up how it goes and try and take some pics, and thanks again for all the really damn helpful input.

You guys rule

Curtis

squirtis · #8 02-07-2009, 11:21 PM

A special thanks to therm and spare!!!

You guys were exact on the money and it was really appreciated, we decided to put some spacers in to prevent the triangle converter bolts from catching on the bell housing.

She started up this evening...lots of work to do still, but she's running

Thanks again for all the help!

Curtis

squirtis · #9 02-08-2009, 10:41 PM

Well we took her out on the inland waterways around baytown today and into the bay a bit...pretty funny looking running with no engine cover so we could make adjustments as needed. She backfired a couple of times (pop) but nothing serious and think we got it figured out. The only real issue is that the linkage for going in and out of gear needs some tlc. Other than that she ran (according to the speedo) about 35 top end! Ran her for about an hour and a half with no problems other than the linkage issue. Thanks again for all the help guys.

Also ran into (pun LOL) chum stain on his 20V...sweet ride Rob!

Curtis

garagenc · #10 02-09-2009, 12:45 PM

Welcome to the site;

I have a 91 V-20 cuddy and I replaced my 5.7 (cracked block) I bought mine from rapido marine and I'm pleased with the motor. With the old motor and the new one they both would push mine 41-42mph (by gps).

Good luck