engine swap: 250 to 292?

[merc200]

Hi! First time poster, long time reader. I bought a 1977 18' Mark Twain last fall with a 165 mercruiser. This has the GM 250 inline six. The engine runs, but has major freeze damage to the block and to the manifold. I bought a new manifold and riser and WAS going to buy a reman long block 250, but I happened upon an old Gleaner F2 combine that has a GM 292 that runs like a top. Could I buy the 292 engine, install a marine cam, brass freeze plugs, swap distributors, and jet the 250 2 barrel carb up a little and be all right? It is my understanding after reading the forum at inliners.com that the only difference between the 250 and 292 is that the 292 is about 2 inches taller than the 250, but are the same length. Also, what about the crankshafts? Do the marine inlines have special balanced cranks, flywheels, and harmonic balancers? I've never run this boat on the water yet, so I don't know if I even need the extra 40 horsepower the 292 would produce. Please help! Boating season is approaching FAST!!!!

 

[Bondo]

Re: engine swap: 250 to 292?

Welcome merc200,<br />I'm not Sure about the differences in the Physical Dimensional aspect of the motors.....<br />But, I'm Sure you Don't need to Change the Cam, Crank, or balancer.....<br />The Flywheel will depend on the Year of the engines,+ Which Coupler you're trying to bolt on to it.....<br />I have No Idea what a Gleaner F2 is....<br /><br />BTW, I've Never seen a boat with Too Much HorsePower........

 

[merc200]

Re: engine swap: 250 to 292?

Sorry, a Gleaner F2 combine is used to harvest corn, soybeans, and other grains from the field. Also, I thought that you had to have a special cam for marine applications?<br />-Thanks for your replies.

 

[mercrewser]

Re: engine swap: 250 to 292?

Do it and keep us posted, sounds like an interesting project.

 

[Bondo]

Re: engine swap: 250 to 292?

The Different Cam thing is a Very OverBlown Short Answer, to a Very Long Winded Question.......<br /><br />For Your Purposes, The Industrial/ Tractor Cam is the Perfect Cam Grind.......<br /><br /> BASICLY ,<br />Cams found in Industrial, Marine, RVs, Trucks,+ Yes, Passenger Cars Are Close Enough to Interchange.....<br />What you Don't Want is, Generally known as High Performance Cams..... <br />There are Many dimentions that can be altered in a Cam Profile......<br />Without getting into Cam Design,+ the Physics of How engines make Power,<br /> It's a Loonnngggg Explanation that'll take me Days, typing with 1 finger..... <br />The Idea is to make Power at a Usable RPM.....

 

[Dhadley]

Re: engine swap: 250 to 292?

The 292 is slightly taller and longer than the 230 or the 250.<br /><br />Good luck!

 

[merc200]

Re: engine swap: 250 to 292?

Uh-Oh. If the 292 block is at all longer, I would have to majorly modify my boat because there wouldn't be a stringer to mount the engine to! Maybe I'll stick with the 250......

 

[seahorse5]

Re: engine swap: 250 to 292?

Check over any 6 cyl. block carefully, I understand that the automotive versions do not have the drilled and tapped bosses for the front mounting bracket, but the industrial versions do.<br /><br />Many folks came close to tears after converting and installing accessories to an auto block, then finding out they couldn't install in due to no front mount attaching points.

 

[rodbolt]

Re: engine swap: 250 to 292?

hello<br /> Oh man this brings back hot rodding days.<br /> we ran a stroked 250 using the 292 crank and v8 rods and it was pretty quick in a nova. something keeps bugging me that we had to rebalance the flywheel to mate with the 292 crank. seems the balancer and the flywheel were balanced differntly than the 230-250. ask about on some of the hot rod sites about the 292-250 crank swap.<br />its been close to 25 years since we raced that one. best I recall both were externally balanced engines.<br /> good luck and keep posting

 

[merc200]

Re: engine swap: 250 to 292?

Yeah, I'll have to go to the combine and see if the 292 has the front mounting holes. I'll also have to measure it to make sure it's not to long to bolt into the original stringer holes. Height isn't a problem. Someone commented at another website that the 250 will handle higher rpms than the 292. I don't know if that's true or not..... Does anyone know if the 250 flywheel housing/mount and outdrive coupler will bolt to the engine?

 

[merc200]

Re: engine swap: 250 to 292?

Spoke with a gentleman at O'Reillys today who, lucky for me, also tried to swap the 250 for the 292 about a year ago. He said that it was too long, flywheel housing wouldn't bolt up, and the intake/exhaust manifold wouldn't fit. So, without a lot of extra money and time, the engine swap idea is dead. If I was going to go to that much work, I'd drop in something a lot bigger than a 292 inline! I'll stick with a 250 reman. Thank's for everyone's help!

 

[Doug Durako]

Re: engine swap: 250 to 292?

Merc---I had a Cobalt---same year, same size, same motor. Those old boats are heavier than some newer 19 or 20 footers so don't expect a lot at the top end. That motor was great out of the hole and at the low to mid range.<br /><br />But, if you are going to the expense of a rebuild, you might want to look at sticking a 350 in there----you'll love the extra top end and all the new boats won't be roaring by your Mark Twain classic!<br /><br />If I would have stuck a v8 in my old Cobalt about five years ago, I would never have sold it!<br /><br />Good luck!