Engine swap, 305 to 350

[Skutt]

I picked up a 88' Bayliner cuddy cabin 19' with trailer and extras for $1000. It was cheap because the engine has a bad knock in the bottom end. It is a Chevy 305, I put water to it and it starts right up, sounds good, smooth, shifts easy but the engine isn't getting oiled even though the oil pressure gauge reads 50lb at an idle. Bad knock in the bottom end as the seller said. I even pulled both valve covers and started the engine expecting oil to fly and make a mess but there is hardly any oil getting up to the rocker arms. Even above 1000RPM's there is little oil in the top end and that bad knock in the lower end. Ok I am not going to fix the 305 but replace it with the 350 using all the marine accessories from the 305 plus marine head gaskets and soft plugs in the 350. I am an engine guy so I have already picked up a rebuilt 350 long block from a trusted family friend. Only had to give $550 for the 350. So far I am only into it $1550.oo and I can do the work myself, I have the skills and tools but no real boat experience so here is my question. I have been told that all I have to do to pull the engine from the out drive is to unbolt the bell housing from the engine and the drive shaft will simply slip from the crankshaft. Is that correct? If so is it that easy to reinstall the new engine? Since it isn't a large cruiser the engine sits at deck height, I mean the engine mounts are at deck height rather than in a lower engine bay. Looks like it should be an easy swap but I am taking my time so I don't run into unexpected surprises.

 

[Howard Sterndrive]

I have been told that all I have to do to pull the engine from the out drive is to unbolt the bell housing from the engine and the drive shaft will simply slip from the crankshaft. Is that correct?

no, you want to remove the drive from the back of the boat first. Then remove the engine. Drive goes back on last after new engine in and aligned. (get an alignment bar)
What year is the 350?

 

[Skutt]

The 350 is a 79' 4 bolt main, bored .030 over, supposed to make it a 355 , crank is ground .010 with over sized bearings and an RV cam. I think it should make a good boat engine as long as I install the right head gaskets and soft plugs.

 

[jerryjerry05]

The drive is different from the 305 to the 350.
Different gearing.It will still work just not perform as well.
I believe???.The cam in a marine engine is different than a car.
Get a manual and learn about the oil in the drive and proper filling.VERY IMPORTANT!!

 

[Bondo]

The 350 is a 79' 4 bolt main, bored .030 over, supposed to make it a 355 , crank is ground .010 with over sized bearings and an RV cam. I think it should make a good boat engine as long as I install the right head gaskets and soft plugs.

Ayuh,... Welcome Aboard,..... The Problem yer gonna have is the change from the one pc rear main seal on the '88, to the 2 pc. seal real main on the '79,....

The crankshaft bolt pattern is different, the flywheel, 'n coupler won't fit,.....

If ya use a '87 'n up motor, it'll be a plug, 'n play swap,.....

 

[Skutt]

Thanks for the input guys. After reading the posts about OMC out drives and watching some youtube videos along with what you guys add I think I have a much better idea about what I am doing. I will get this job done now. Perhaps I should consider selling the 350 and just rebuild the 305. I will get the 305 out, pull the oil pan off and check it further.

 

[Skutt]

I have been checking on EBay for couplers and alignment tools. There are a lot of them for sale so should be easy to get what I need to make this engine work fine.

 

[Skutt]

After checking more on these two engines I come to realize that the heads on the 350 really are not the best. They are 76cc smog heads with 1.94 valves. The heads on the 305 are 58cc heads but have smaller valves, at this point I don't know if they are the 1.72 or 1.84. Everything I read makes me think the 305 heads would be the better choice. More torque at lower RPM's. I will keep doing more research.

 

[Bondo]

Everything I read makes me think the 305 heads would be the better choice.

Ayuh,.... Too much compression, 'n not enough flow,.....

It's the coupler/ flywheel ya gotta deal with to use the older motor,...

 

[Skutt]

I am reading and watching a lot of peoples videos regarding using the 601 heads on a 350. I am still not convinced of anything but I'll get it. I just don't want to put the engine in the boat and as some have said, they have trouble getting the boat to get up and plane like it should. It is just a 19' boat so I would think the 350 would be able to move it along nicely. I have pulled the outdrive this morning. Came off easy as it should. The engine should lift out easily now. I see there are couplers on EBay and flywheels should be easy to find too. I appreciate any advice though. Just kinda new to working on boats.

 

[legend 550]

Drive coupler for a 2 pc rear main is 0983902. Flywheel is just a standard stick shift flywheel. The problem with the newer 350 one pc main is very few came down the line with the fuel pump boss machined,almost all were fuel injected so there out there but rare. Also give the Vortec heads a good look

 

[Scott Danforth]

save you some time. get a 86 and up motor with a 1 piece rear seal. or build one with vortec heads.

plenty of post 86 motors with fuel pump boss. or just switch over to an electric pump.

heck, if you wanted, I would sell you my '88 motor complete and I could then get a supercharged 383 stroker....

 

[Skutt]

For now I will buy the coupler and flywheel I need to install the 350 I have. I'll just use the 487 heads, will run on regular pump gas and should have adequate power. I'm not looking to build a hot rod boat. It's only a 19' so even a low hp 350 should be more than enough. It's a 4 bolt main truck engine with RV cam so it should work well. I am just about ready to pull the engine now. Removed the trailer wheels and it's sitting down nice and low on small wood blocks so I should be able to lift the engine over the transom with my cherry picker shop crane. Lower drive is removed so it's just about ready. My question now is do I have to remove the intermediate drive unit or will the engine simply pull away from it when I lift the engine?

 

[Bondo]

Ayuh,..... Pull the drive Off, so ya don't bend it's input shaft,......

Ya gotta have it off to align the motor when ya put it back in anyways,.....

 

[Skutt]

I have the lower drive removed already so the shaft is out. I am going to leave the bell housing in place just so I don't screw anything up. I just checked the engine block casting number. It's 14010201, that is 80 to 85. Not sure why the engine is of a prior year than the boat, 88' but I think it should be a two piece rear main seal as is my 350 so I bet I find that the flywheel and coupler bolts on the 350. I can always hope just to make it easier. I will have the engine out today or tomorrow and know for sure then.

 

[Skutt]

Another addition to my ongoing engine saga. Excuse me a minute............................................ .....................a bit out of breath. The engine is out. Curious thing I find. The flywheel has the unmistakable rust marks of a clutch pressure plate on the surface. That means either that its not the original engine or............ They bought used parts such as the flywheel when it was first put in the boat. I am thinking it's not the original engine. Either way it is what it is. The good news is that it is the same vintage as my 350 and the flywheel and coupler will bolt right on. Luck trumps skill and knowledge every time.

Lowering the boat by removing the wheels and jacking the front of the trailer high in the air to lower the transom worked. I had a good six inches of clearance over the transom but I well get help putting it back in. That took too much muscle because my driveway has a slant to it and of course the entire crane and engine wanted to roll down the hill. I didn't let it but it was a little bit of a work out. I think it's time for a couple fingers of medicinal whiskey.

 

[Skutt]

Well, another strange thing about this engine. I went back out to the garage to do a little more work on the engines. I removed the coupler and flywheel from the 305. I found that the coupler has been drilled with new bold holes. It has two sets of bolt holes and one set of holes shows fresh looking shiny metal. I am not sure I want to put that one back in the boat. I will check it further, perhaps install it and see if I can rotate the engine and get a reading on the coupler to make sure it is running true. It might not be a problem at all but I find it very curious. It looks like a machine shop probably did the work. Could it be that some couplers come that way for more than one engine application?

 

[Scott Danforth]

Another addition to my ongoing engine saga. Excuse me a minute............................................ .....................a bit out of breath. The engine is out. Curious thing I find. The flywheel has the unmistakable rust marks of a clutch pressure plate on the surface. That means either that its not the original engine or............ They bought used parts such as the flywheel when it was first put in the boat. I am thinking it's not the original engine. Either way it is what it is. The good news is that it is the same vintage as my 350 and the flywheel and coupler will bolt right on. Luck trumps skill and knowledge every time.

Lowering the boat by removing the wheels and jacking the front of the trailer high in the air to lower the transom worked. I had a good six inches of clearance over the transom but I well get help putting it back in. That took too much muscle because my driveway has a slant to it and of course the entire crane and engine wanted to roll down the hill. I didn't let it but it was a little bit of a work out. I think it's time for a couple fingers of medicinal whiskey.

the motor could be a simple salvage yard replacement. there is not much different between the same vintage truck motor and the marine motor. in fact they come out of the same assembly plant and most of the same parts bins.

I have the lower drive removed already so the shaft is out. I am going to leave the bell housing in place just so I don't screw anything up. I just checked the engine block casting number. It's 14010201, that is 80 to 85. Not sure why the engine is of a prior year than the boat, 88' but I think it should be a two piece rear main seal as is my 350 so I bet I find that the flywheel and coupler bolts on the 350. I can always hope just to make it easier. I will have the engine out today or tomorrow and know for sure then.

this post stated that you didnt want to pull the upper portion of the drive because you didnt want to "screw things up" As bondo pointed out, you have to pull the drive anyway to align it anyway. its a 20 minute job to pull the drive on a mercruiser. then the motor and flywheel housing come out together leaving only the transom shield.

 

[Skutt]

This is a learning process for me so I left the bell housing and the upper portion of the drive in the boat. It worked well that way but I suppose you are right Scott. I need to buy myself an OMC manual so I have the answers to these questions at my fingertips. Having the upper drive out of the boat would make the reinstall easier I am sure. It will also allow me to inspect the entire drive unit and do any maintenance it needs to be in the best shape for a good summer season of boating.

 

[Scott Danforth]

by leaving it in the boat, you turned a 1/2 hour removal job to a 1-1/2 hour removal job. if you try to put it back in with the flywheel housing in the boat, it will take about 3 hours vs a 45 minute job. as stated, you have to have the complete drive out anyway to align it when you re-assemble.