3.0L Mercruiser 1987

[rmyauck]

Hi,

Engine seized on a person after he shut it down, it wouldn't turn over or barely would. After checking for flooding
I pulled it and found it would turn over very stiffly with diesel and engine oil, but loosens up nicely when piston pairs are at TDC only. Maybe 200 hrs on it and cylinders look & measure like new thanks to Mobil 1 20W50 for last 130 hrs.

Tore it down & found every bearing is badly scuffed (had heated up) but crank looks fine! Piston rod end pins on #2 & 3 are super tight and #1 is a bit tight. #4 is normal!

I had told that person few years ago not to engage heavy throttle till warmed up to operating temp (water) , but never listened as impatient type. I imagine pistons got too hot with non expanding cylinder wall (too cold) and big load from my reading.

I found Speed-Pro Hypereutectic Pistons H896CP in std. size that look the same for maybe a worthwhile upgrade at under $100 US a set. Plan to reuse old rings as they look great and I won't have to get it honed.

Does anyone know if these pistons or any std. size piston would weigh the same as the old ones?

Thanks very much for any info or thoughts!

Randy

[rmyauck]

Forgot to mention it has an oiling problem by the looks of it so will have to find it!

[modok]

It does not matter if new pistons weight the same as old, as this is a four cylinder engine.
I THINK, this is basically four cylinders of a chevy 250....right? I've seen a few.

Running heavy oil and not letting it warm up, I am not surprised the bearings are hurt.
Why 20-50? does the manual say that's ok? Will have to be built extra loose to make that work; clearances .0015 per inch range.

[roc]

It does not matter if new pistons weight the same as old, as this is a four cylinder engine.
I THINK, this is basically four cylinders of a chevy 250....right? I've seen a few.

Running heavy oil and not letting it warm up, I am not surprised the bearings are hurt.
Why 20-50? does the manual say that's ok? Will have to be built extra loose to make that work; clearances .0015 per inch range.

I agree with everything, with small exception: the marine 3.0L (181") also has 4" bore like the 151" (but with a stroked crank). The 250 is 3-7/8".

I'm guilty of using 20W-50 oil on everything in my young days... wished I knew better.

[mag2555]

Is that not a Version of the Pontiac iron Duke motor?

[rmyauck]

Mercury factory engine manual calls for 20W40 (their oil) or other heavy oils like 30W. I figured synthetic would flow much better as it rated to pretty cold temps to flow properly, and we used it since 93 with no problems. Will have to try 10W30 synthetic! I put 5W30 in my car and 0W40 XD-3 synthetic Esso/Exxon in my 93 Cummins 5.9. Maybe that 0W40 or Mobil's Diesel 5W40 would be better as they seem to be rated for gas industrial use also.

I always put on GM's high performance oil filters with the magnet in them and the latest one was a K&N as I had them.

The people at Federal- Mogal Motorparts in St. Louis were very helpful and gave me tech. line to call 1-800-325-8886 where they
told me the H896CP std. size Hypereutectic Pistons weigh 724 grams +/- 7 with the pin.

I remember reading a Merecedes Benz shop manual years ago (had a beater 220D) for their 4 cyl Diesel saying to keep the parts within a few grams for best life.

Just have to figure out how to get pins out ( heat method looks best) without a Sunnen tool! Maybe a propane torch or hotplate would be safe? I believe I should just get the rod end hot enough for it to easily slide out without a press?

Thanks!

Randy

[In-Tech]

Just have to figure out how to get pins out ( heat method looks best) without a Sunnen tool! Maybe a propane torch or hotplate would be safe? I believe I should just get the rod end hot enough for it to easily slide out without a press?

Thanks!

Randy

Why are you afraid of the press? Heating is not the answer

[rmyauck]

I thought it was the proper way and is mentioned in old manuals and even the mercury factory manual. I read it's easier to damage parts and I don't have the tools to keep from damaging the parts.

[rmyauck]

I believe it is part of that engine family (Iron Duke).

[Hrdlx62]

Aren't those engines like overgrown 153 Chevy II power plants?

[roc]

Aren't those engines like overgrown 153 Chevy II power plants?

Sort of. It's more closely related to the 151" (shares 4" bore, with longer stroke).

[ProPower engines]

Mercury factory engine manual calls for 20W40 (their oil) or other heavy oils like 30W. I figured synthetic would flow much better as it rated to pretty cold temps to flow properly, and we used it since 93 with no problems. Will have to try 10W30 synthetic! I put 5W30 in my car and 0W40 XD-3 synthetic Esso/Exxon in my 93 Cummins 5.9. Maybe that 0W40 or Mobil's Diesel 5W40 would be better as they seem to be rated for gas industrial use also.

I always put on GM's high performance oil filters with the magnet in them and the latest one was a K&N as I had them.

The people at Federal- Mogal Motorparts in St. Louis were very helpful and gave me tech. line to call 1-800-325-8886 where they
told me the H896CP std. size Hypereutectic Pistons weigh 724 grams +/- 7 with the pin.

I remember reading a Merecedes Benz shop manual years ago (had a beater 220D) for their 4 cyl Diesel saying to keep the parts within a few grams for best life.

Just have to figure out how to get pins out ( heat method looks best) without a Sunnen tool! Maybe a propane torch or hotplate would be safe? I believe I should just get the rod end hot enough for it to easily slide out without a press?

Thanks!

Randy

No you don't heat the rod to remove the pin you press the pin out of the rod by supporting the piston and use a driver that will fit the pin but slide through the piston and rod small end.

Heating the small end of the rod to assemble the piston onto the rod will work as long as you don't overheat the rod which will cause the pin to stick part way through thus needing to be removed and the process done over again.

By the time you get enough heat in the rod you will have heated the pin as well and it will never come out.
Oil for marine engines such as yours need the correct oil and the oils you are suggesting have no high pressure anti-wear additives in them for use with a conventional flat tappet cam or lifters as well as no anti foaming or anti corrosion additives either. the oil filter is a good choice but I would not recommend the oil choices.

[rmyauck]

I was just looking at the merc. manual and your right about just heating the rod end to install it!

There is no rust in the engine and it's super clean inside. I and others think the Mobil 1 saved it from "blowing up" or really bad damage to the major parts!

I just pulled the cam and everything looks like new there I think again that oil helped. Maybe a lighter grade will be better and they do say the 0W40 has more ZN to help the cam and tappets. This engine has hydraulic lifters also.

Thanks all!

Randy

[modok]

I thought it was the proper way and is mentioned in old manuals and even the mercury factory manual. I read it's easier to damage parts and I don't have the tools to keep from damaging the parts.

May need to forget some of these things you "know"

The pistons on a four cylinder engine need to be balanced to each other, they all weight the same. If you replace ONE piston, it needs to match the other 3, but if you replace all pistons then you just make sure they are all the same.

You PUSH the pin out, supporting the piston so as to not bend the rod. To install the pin, the rod is heated and you slide the pin in, in less than 1 second. If you have not done this before take it to a shop that has the tools to do it, as making the tools will end up costing you more.

Far as oil the cummins should have no thinner than 10-40 synthetic IMO, as they are built LOOSE, this I know well.

and the boat I might drop down to 15-40, IF it's built on the loose end of the range. If the bearings are same as for a car and mid spec or tighter you'd be better off to ignore the manual and put some 10-30 in there if your boy won't let it warm up.

There really is a DIRECT relationship to bearing clearances and what oil wight you can use. Trust us, I bet most of us learned the hard way, I know I did

[modok]

Aren't those engines like overgrown 153 Chevy II power plants?

yes

Is it an "iron duke"? I don't know. They named two different engines that, and so I figure the name is like vortec or eco-tec and all that, as in it means nothing, but I could be wrong.
If you know the story, of why two engines have that name, let me know!