GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

Desyfering1

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Sep 20, 2006
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Okay so I bought a nice 84 Doral 15' boat for $500. It needed a motor.

Took the motor apart and found it had a broken piston (number 3) and a bent rod and scuffed up cylinder wall.

Took it a rebuilder, claims he only rebuilds MARINE blocks. He bored all 4 cylinders to 30,000 over and put new pistons, rods, lifters, machined the cam, new oil pump, all new bearings and seals etc. etc.. Supposed to be like new.

Put the motor in, went out for 10 minutes, water temp read 180 degrees, got some blow back, and then KNOCK KNOCK KNOCK.

Pulled the motor out, took it back to the guy. He said it had a bad piston. (number 4)

I put it back in. Took it out for a day, it ran at 180 again. Next day KNOCK KNOCK KNOCK.

This time I opened the motor, saw another piston seizing up (number 3). I changed the piston, honed the wall. This time I changed the water pump, the impeller, and thermostat (I know I should have done that the first time).

The exhuast manifold was all cleaned out, the carb rebuilt, I went over everything with a fine tooth comb.

I thought NOTHING could go wrong.

Sure enough the 3rd time, 30 minutes in, we got the knock, ran at 180 (which I don't know how).
Got into shore, took the thermostat housing off, steam was coming from the engine. We checked for lots of water flow from the impeller, no problem. The thermostat was opening up as it should at 160. The water pump is brand new.

I took the thermostat right now and it was running at 110 or 120 if that helps.

So here we are again. I will be pulling the motor again today. I cannot afford to continue to put new pistons in.

Is this a sign of overhearing? or another problem altogether? I didn't think 180 would be enough to cook a piston, I thought it would blow a head gasket before this.

Was there a mistake when the engine was rebuilt the first time?

Any help would be appreciated.

Thanks in advance
 

Desyfering1

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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

I should add some more detail.

Each time the engine had problems, what actually was seizing up was the WRIST PIN on the piston, First number 4, then 3 and now it sounds like 2 (haven't opened the motor yet) which leads to me believe this was an oil flow problem or something along those lines?

Hope this helps.
 
D

DJ

Guest
Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

You checked the thermostat, with housing off-fine. Just because you have water coming in doesn't mean it can get out-meaning FLOW.

I would never put old manifolds/elbows on a new rebuild.
 

xtraham

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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

never seen a chevy seize a wrist pin, they are oiled from oil slung from the crank, make sure the pistons are on the rods right and that the rods are on the crank right if not it will put the pin in a bind
 

Desyfering1

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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

xtraham said:
never seen a chevy seize a wrist pin, they are oiled from oil slung from the crank, make sure the pistons are on the rods right and that the rods are on the crank right if not it will put the pin in a bind

Yeah my thoughts are that when they did the rebuild, the tolerenances were not calculated right. The wrist pin is pushed in the rod and floats. I think it's not getting enough oil once they get warm and it's binding up and then the piston starts to cuff the wall.
 

xtraham

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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

if the pins have been floated were the rods drilled so the pins could get oil? and did you change to pistons with snap rings to keep the pin centered?
 

Desyfering1

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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

xtraham said:
if the pins have been floated were the rods drilled so the pins could get oil? and did you change to pistons with snap rings to keep the pin centered?

The pin only floats on the piston. It's fixed on the rod. There's no snap ring.
 
D

DJ

Guest
Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

If you want to blame DEEP engine problems-go ahead. Knock yourself out, over and over and over.

Your solution is allot simpler than you are thinking. See above.
 

Desyfering1

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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

DWJ said:
If you want to blame DEEP engine problems-go ahead. Knock yourself out, over and over and over.

Your solution is allot simpler than you are thinking. See above.

The manafold has been disassembled and cleaned thoroughly. Lots of water coming out and moving through, in and out. I don't see how that's what it could be. Please explain.
 

fendersfender

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Mar 23, 2005
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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

take it back to the rebuilder and make him fix it...thats what you paid him for, is'nt it?
 

Buttanic

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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

The bent rod and broken piston sounds like a case of water ingestion. I would bet you have a hole rusted through in the manifold allowing water to enter either the exhaust or intake side of the manifold and into the cylinders. If it is the original manifold I would replace it. I would pressure test the manifold and riser for a water leak into the intake or exhaust. Any water is going to go to the back cylinders because of the angle of the engine.
Also because marine engines run at higher loads and generate more heat in the piston and rings, ring end gaps and pistion to cylinder wall clearences neeed to be greater than used in automotive engines
 

Bt Doctur

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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

if 3 & 4 I`d be worried about the manifold or riser dumpin water in the motor.when you pulled the head were any of the pistons devoid of carbon?A sure sign of water in a cylinder.If you beat a piston down on the pin from water ingestion it will appear to be a seize issue but caused by water.
 
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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

Update:

I took the advice to test the manifold for leaks. There are none.

There is also no water mixing with the oil.

We pulled the motor and took it apart with the rebuilder.

Turns out, Pistons 1,2 & 3 are all made my Hastings and are all burnt up. Number 4 (furthest from the water pump and most prone to overheating) was made by Federal Mogal and is perfect.

So we have a piston problem. This one brand of pistons once they get hot and expand, are seizing, breaking up, and cuffing the wall.

So needless to say I won't be getting the same brand pistons installed this time.

I am going to reuse the manifold because I see nothing wrong with it and cannot justify another $400 after all these expenses.

So hopfully we will get this thing going for one real boat ride before winter.

Will keep you posted.
 

Buttanic

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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

Incorrect ignition timing can cause high temperatures and piston failure. I would not be too quick to blame it on the brand of piston. Each piston manufacture provides specifications for piston to cylinder wall clearences depending on the type of metal used and application,auto, marine, racing, etc. Forged aluminum pistons require much more clearence than cast or hyperutetic pistons. Also generally piston ring end gaps need to be larger than normal in marine engines. I would look more at the engine builder not following manufactures specification especially if he is not familar with the special needs of marine engines.
 

whywhyzed

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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

jeez- this summer I ebayed an awesome running 2.5. I got a whopping $200 for it... It had 115 psi on all 4 cyls. I even posted a video of it running on the auction.
Are you sure it's smart to rebuild these.....
I have a line on more....
Get a 3.0.
 
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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

kjdkjd said:
jeez- this summer I ebayed an awesome running 2.5. I got a whopping $200 for it... It had 115 psi on all 4 cyls. I even posted a video of it running on the auction.
Are you sure it's smart to rebuild these.....
I have a line on more....
Get a 3.0.

Where were you when I bought this thing 2 months ago? I searched everywhere high and low for a motor. Sure enough you are in Ontario as am I.

The rebuild cost me $800, with a 1 year warranty. They specialise in Marine rebuilds.

This was the best deal I could find after calling everyone, scouring the web and literally driving around with the block in my car to every rebuilder out there.

As far as getting a 3.0, the 2.5 and 3.0 GM are the same block, only difference is the bore and piston.

I am going to get the electronic ignition coversion kit this time round.

We'll just have to wait and see.
 

Don S

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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

The rebuild cost me $800, with a 1 year warranty. They specialise in Marine rebuilds.

Sounds to me like they specialise in taking your money, not rebuilding your engine.
Did they rebuild YOUR engine or is this a short block, long block, complete engine?
I would worry about an engine that siezes wrist pins and pistons in cylinders then to find 3 Hastings pistons and 1 FM piston.Didn't they have enough spare parts laying around on the floor to use all the same kind. Where did the rings and bearings come from. Junk bin at JC Whitney?
Think about the price of labor these days for a competent rebuilder. I can rebuild you a great engine, but we get almost $100 an hour labor, so that means I have 8 hours to rebuild an engine if no parts are used. NOT.
Even at $50 an hour, and 16 hours, you will NOT get a quality rebuild. Perhaps they use minimum wage labor with no experience and hope the engine makes it a year.
Oh, have you checked out the price of parts lately, check the prices of pistons, rings, all bearings and gaskets for that engine.
Switching over to electronic ignition is NOT going to cure your problem, either way you go, they have to be set properly and working.
 

whywhyzed

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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

Where were YOU?
Some guy drove from Montreal to pick it up and complained that the alternator was rusty, then handed me $100 less than the winning bid and lost his ability to speak english while I counted the money... It was weird....I have another 2.5 if you tire of throwing money into that one...- hystat@hotmail
 

lilmandavis

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Mar 9, 2006
Messages
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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

im with don on that one. sounds like the rebuilder dont know jack shoot. but weve all been there. the best thing is to get either a remaned one from a REPUTIBLE builder or do it your self with a manual. start with all new and all good stuff. id throw it out the door into that guys garage and say you really want your money back. id take that jerk to small claims and get my money back. at my shop we are usually the forth or fifth guy to come out. when everyone else has hacked into it. WE FIX THE PROBLEM thats what were paid to do. period. i would of slapped him up side his head if i was standing there when it all came apart with different stuff inside. thats a win win case in court.
 

Buttanic

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Re: GM 2.5 L OMC engine rebuild 3 X - NIGHTMARE

I rebuilt a 2.5 mercuiser myself several years ago. New pistons, rings, bearings, lifters, etc. and the parts alone were more than $900.
 
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