engine conversion

[Wrongway105]

the boat i recently purchased a 81 19' Renken inboard 2.5ltr. come to find out that the engine got extremely hot with the previous owner and blew the head gasket, blown rear freeze plug, and cracked the rear piston. nice huh. Im looking to replace this engine with a much larger one. a 350 chevy since the previous engine was also chevy the motor mounts line up perfectly. My main concern is the engine supports that the motor mounts bolt to. This 350 is 100lbs heavier than the old iron head 4cyl. Will there be any torque issues I should consider? should i beef up the engine support beams? everything looks like it should bolt right up just fine to the stern drive its a omc. <br />and one more question. should there be any resistance in the stern drive when in neutral should i be able to turn shaft by hand? mine feels a lil stiff worried about possible bearing failure. thanks

 

[SS MAYFLOAT]

Re: engine conversion

WW, what outdrive do you have? Just because the bigger engine will bolt up does not mean that it is geared to handle the extra power. I do know for a fact that if it is a Mercrusier outdrive, you will need to change the gears. If they are not changed to the right ratio, you will be stripping them out with the larger engine.<br /><br />If the engine that you have is siezed up, you will not be able to turn the prop shaft if it is in gear. In neutral, the prop shaft should turn. If not, then there is problems in the lower unit.

 

[Bob_VT]

Re: engine conversion

I don't know if I would take that much of a jump in power. The 4.3 V-6 might be easier. I would absolutely strengthen the mounts and the hull considering it's an 81.<br /><br />Maybe you should look for an engine and a outdrive.... how much do you love this 81? Is it worth replacing the motor and maybe selling it?

 

[ondarvr]

Re: engine conversion

If you need to change everything, it's normally less costly to get another boat and be on the water tomorrow, sorry.

 

[Bondo]

Re: engine conversion

81 19' Renken inboard 2.5ltr. the stern drive its a omc.

I don't do OMCs,... But,.. If this 81 is a Stringer Drive,.......<br />You'll have to Junk Out your Whole Complete Driveline,........<br />None of it it Reuseable with a 350cid motor.......<br /><br />If it's the newer Cobra drive,....... It'll need to be Rebuilt with Taller Gears...........At the Very Least..........

 

[Wrongway105]

Re: engine conversion

the stern drive is a omc 800 series, finding another 2.5 is virtually impossible. and although i would like to truely believe i can run out and spend a few grand buying another boat would be far fetched for me at the moment.<br />I dont want to pour money into this boat if it wont work either though. why would i have to go to a taller gear? the 4 cyl was 120 hp and the small block is only gonna jump me about 60 hp is this truely a big deal? I really have no clue on what to expect.

 

[ondarvr]

Re: engine conversion

If you need a complete marine V8 or V6 it will cost a bunch, even used. An outdrive, even if all you need to do is rebuild yours with the correct parts will cost $$$. Then you will probably find some rot when you start digging into it and many things on an 1981 boat will need to be replaced just from age. After you spend all of that time and money on it, it still won't be worth half of what you've put into it, it may then be a good boat though. If you love the boat and want to restore it, then it may be worth it, but if you want to go boating soon for less money, you can buy a boat like it that has already had the work and money put into it for far less than what it cost the person selling it to fix it up.

 

[Mark42]

Re: engine conversion

There are also weight issues, exhaust routing issues, and fuel capacity for the larger motor. <br /><br />My suggestion is to pull the short block and swap it for a rebuilt or make the repairs and stay with that setup. Search the web for marine engine rebuilders and you will find that motor is still available (I did this earlier this year when looking at a boat that had a blown 153 cid)<br /><br />Here is one, 1700 for a long block, less for the short block. http://remanufactured.com/Chevrolet_4_Cylinder_Engines.htm <br /><br />Then spend the money you save on fine tuning the boats overall performance so that you maxamize the hp on hand. Make sure the prop is the right size, add trim tabs if needed, a few gauges if they are missing (temp and water pressure come to mind).