Older 305 to Newer 350 Swap Mercruiser Alpha gen 1

[dukeofwsu]

I've got a merc 898 (305 Chev, 1978) with a newer reman'd leg (Alpha gen-1 style, new in '07, running 1.47:1). I'm swapping the old engine with a brand new, zero hour, 350 TBI from Kodiak Marine. The new engine comes with a 14" flywheel, and I've ordered a conversion 12.75" flywheel from the engine manufacturer. The bolt pattern is different, of course, so my drive coupler will need to be replaced also.

I've been told in a round-about way on another forum that I should be keeping the 14" flywheel and matching starter, and get myself a new bell-housing. I'll post the conversation as follows below, and maybe someone can put their two cents in on what they think I should do--within the parameters of; I have this new engine, and I have this old boat, and I want to put the two together and go fishing--and I'll actually learn something and get the project done. See below and thanks in advance.

 

[dukeofwsu]

Re: Older 305 to Newer 350 Swap Mercruiser Alpha gen 1

've got a merc 898 (305 Chev, 1978) with a newer reman'd leg (Alpha gen-1 style, new in '07, running 1.47:1). I'm swapping the old engine with a brand new, zero hour, 350 TBI from Kodiak Marine. The new engine comes with a 14" flywheel, and I've ordered a conversion 12.75" flywheel. The bolt pattern is different, of course, so my drive coupler will need to be replaced also. Does anyone know the part number or description I'll be looking for?

Thanks,

-duke

#2
Yesterday, 07:43 AM

gonzo
Senior Member

Join Date: Aug 2002
Rep: 1046 Posts: 5,451
Location: Totnes, UK
Why are you changing the flywheel? If you do, the starter won't work. You will run into balancing problems with an old style flywheel too.
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Gonzo

#3
Yesterday, 08:44 PM
duke
Junior Member

Join Date: Jun 2009
Rep: 10 Posts: 8
Location: Seattle
I have to couple the new engine to the old bell housing, so I was planning using my old starter (from the 305 with the 12.75 ring gear). my old bell-housing is my only option, (as my motor mounts won't change and the shift linkage will bolt back on). I was under the impression I needed to drop down the flywheel size to keep my old bell-housing. Either way I need a coupler that works on the new crank/flywheel bolt pattern.

Am I missing something else? You seem to be one of the more knowledgeable people on this forum, so let me know what you're thinking.

-duke

#4
Today, 09:16 AM

gonzo
Senior Member

Join Date: Aug 2002
Rep: 1046 Posts: 5,451
Location: Totnes, UK
The starter is bolted to the block. Bellhousings are really cheap compared to the cost of a custom conversion like you are talking about. Also, custom balancing an engine to fit a different flywheel is quite hard.
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Gonzo

#5
Today, 03:39 PM
duke
Junior Member

Join Date: Jun 2009
Rep: 10 Posts: 8
Location: Seattle
Well, the flywheel is a custom job from the engine manufacturer. And, I know where a starter bolts on. But let's follow your path for a moment--Ok, what bellhousing would I need to keep my old gimbal and leg while using the new flywheel, and starter? And, once again, what engine coupler?

I'm really looking for some solid application of part numbers, descriptions, etc. I have a brand new engine, it cannot couple to my old gimbal and leg without some additional parts. Can someone spell out what parts they think those are, rather than just tell me what I don't have or can't do? That's all I'm looking for here.

 

[Bondo]

Re: Older 305 to Newer 350 Swap Mercruiser Alpha gen 1

Ayuh,... Does the new block have the bolt holes to mount the starter for the smaller flywheel,..??

Sierra sells a coupler to mount a New motor to an older drive,...
Part # 18-2172...
They should have it right here at iboats megamall...


Btw,... Don't listen to Gonzo....

 

[dan t.]

Re: Older 305 to Newer 350 Swap Mercruiser Alpha gen 1

The 1 piece rear main seal new style engines have the proper flywheel available in both diameters,nothing custom about it. the three point mount coupler should fit or can be redrilled to fit the smaller flywheel

 

[Bondo]

Re: Older 305 to Newer 350 Swap Mercruiser Alpha gen 1

the three point mount coupler should fit or can be redrilled to fit the smaller flywheel

Ayuh,.... Many of the old flywheel covers don't have the clearances for the 3 legged couplers, 'n swapping to a later flywheel cover don't work, because the rear motor mount spacing changed...

 

[dukeofwsu]

Re: Older 305 to Newer 350 Swap Mercruiser Alpha gen 1

Yeah, I checked the old bellhousing vs. the direct drive bell housing that came with the new motor, the difference in clearance is 3/16". I fit the 14" flywheel and the old merc bellhousing, and it clears fine, so I'll likely run the stock 14" with the new starter after all.

The coupler part I found at eBasicpower is a GLM11520, but I haven't been able to confirm that that is in fact the 3" bolt pattern (vs. the older 3.5") I'll check out the Sierra at the iboats store. Thanks for answering my question directly and to the point. It's always appreciated when people make an effort to show how smart they are--rather than how dumb other people are--when they respond in these forums.