Need help Today PLEASE! Differences between Chevy 2.5 and 3.0

TwoBallScrewBall

Lieutenant Commander
Joined
Sep 14, 2003
Messages
1,695
Hi all,<br /><br />I blew up my 3.0L OMC as you may have read about. There is a swap meet (auto) in my area this weekend and I was considering picking up a Chevy 2.5L iron duke block, preferrably that I can see runs, and rebuilding it to 3.0 specs. I am not at all familiar with this engine. I have done a few small block rebuilds and am comfortable with my ability as far as engine assembly and blueprinting, but don't know the peculiars of this engine. <br /><br />Is the 3.0 just an overbored 2.5? Or is there a different crank in the 3.0 (stroked?)? Or both? I have all the marine accessories from my 3.0, there is just a hole in the block and a shattered connecting rod. If I pick up a 2.5L block for dirt cheap, and have it cleaned, magnafluxed and bored to 3.0L specs (if that is the difference), can I just build up the internals using a 3.0L rebuild kit and then replace the auto dist, water pump, etc, with my OMC parts? I am mechanically inclined to a point and would like to save some bucks on this project by doing it myself. Need a reply as soon as possible, I'm attending the swap meet tomorrow AM and this whold idea just popped into my head last night. <br /><br />Another question, does the 2.5 and 3.0 use the same conencting rods? Most rebuild kits do not include these and it would make it easier i I could use the 2.5 rods when rebuilding to 3.0 spec. <br /><br />Thanks!
 

CCrew

Chief Petty Officer
Joined
Sep 10, 2003
Messages
416
Re: Need help Today PLEASE! Differences between Chevy 2.5 and 3.0

2.5 and 3.0 have different stroke and crankshaft diameter. Subsequently, you're not going to make a 2.5 into a 3.0 without additional work and parts. <br /><br />As to whether they're the same block casting I'll let someone else answer, but with different bearing diameters the bearing saddles in the block at the minimum are different.
 

TwoBallScrewBall

Lieutenant Commander
Joined
Sep 14, 2003
Messages
1,695
Re: Need help Today PLEASE! Differences between Chevy 2.5 and 3.0

Well there goes that idea.
 

TwoBallScrewBall

Lieutenant Commander
Joined
Sep 14, 2003
Messages
1,695
Re: Need help Today PLEASE! Differences between Chevy 2.5 and 3.0

OK, I've confirmed that the 3.0 is a stroked 2.5, not on overbore like I had hoped. I have my 3.0 crank, I'll just need to see if it can be ground since it lost a rod under power. If so, I am going to pursue the 2.5 to 3.0 job since it will be my cheapest option. <br /><br />Anyone done this?
 

CCrew

Chief Petty Officer
Joined
Sep 10, 2003
Messages
416
Re: Need help Today PLEASE! Differences between Chevy 2.5 and 3.0

2.5 has a smaller crank rod journal, so you'll need 3.0 rods, and the 3.0 crank. Main journals are the same. Pistons are different, as the tops are different. Rings are different. <br /><br />So, the 60 million dollar question is whether the block casting is the same. With the difference in stroke, it may not be. I don't know that..
 

MrBill

Senior Chief Petty Officer
Joined
Aug 4, 2002
Messages
710
Re: Need help Today PLEASE! Differences between Chevy 2.5 and 3.0

huminski:<br /><br />There is usually an abundance of 3.0 L mercruiser engines available for sale, used and rebuilt. Check locally and eBay...how much are you willing to invest?
 

TwoBallScrewBall

Lieutenant Commander
Joined
Sep 14, 2003
Messages
1,695
Re: Need help Today PLEASE! Differences between Chevy 2.5 and 3.0

I was hoping to get back in the water (reliably) for under $1000. Know anyone??? :)
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: Need help Today PLEASE! Differences between Chevy 2.5 and 3.0

Hello<br /> the "Iron Duke" was actually a pontiac (GM) design 151 cid that was used in automobiles of the late 70's and 80's. the only thing that will interchange between the 2.5153 cid marine engine and the 151CID iron duke is the paint color. the heads on some 120 140 2.5 marine engines had differnt intake exhaust ports. the 153 cid and 181 cid marine engines shared a lot but there is no total way to interchange all the parts. best you can do is find an engine that has the same intake/exhaust ports on the heads as your old one. we have enough trouble with carb problems without so much mix and match on the 3.0 engine. good luck and keep us posted. in my area you can usually find complete running 3.0 for about 1500.
 
Top