Mercruiser (GM) 3.0L rod cap ? Is this normal fretting

[schiker]

So I have my boat engine out and the No. 1 piston is gualled pretty bad. I had hoped to hone and rering but I had better take it to a machine shop for second opinion. If I could just see cylinder marks I would hone but since I can feel one area it probably needs boring and hone for 0.030 over size. And I can get shop to fit new pistons to rods and I'll just save on assembly work.

I had also hoped to not do rod and main bearings due to low hours but the No.1 cap bearing looked a bitt worn and the No. rod too. I guess the No. 1 piston beat the snot out of rod bearing and adjacent mains. I ran out of time and will look at others tomorrow. The bearing did not turn in journal and just looks worn.

But is this amount of fretting on the rod cap excessive? Or normal?

 

[WarWagon]

Can't tell from the pic. Is the bearing shell actually missing here? Is it pitted from water/coolant corrosion? Does it have metal flakes slammed into the bearing?

Looks like coolant/water in the oil, lube failure, or metal fatigue flaking parts off.

 

[schiker]

First post is the rod cap only the bearing has scatch like fine lines like excessive wear but no gualling or metal flakes pitting or other. The crank rod surface looks good shiny, smooth, and clean looking.

Here is the bearing shell from the rod cap. When I see the other rods to compare it will be easier for me to judge. But the cap looks a bit fretted.

 

[schiker]

The back side of the bearing looks like a mirror image of the cap. It appears like the rod cap was starting to flake and guall to the bearing from hammering. That might be a better description than fretting.

I'll take another picture tomorrow of the back side of the bearing. And I hope to have other rods to compare also. I have not taken the main bearing out to look at the back side or main cap.

 

[3500GMC]

Big ends of the rods are starting to stretch. See the shiny edges of the bearing surface? That's from the bearing rocking side to side, hence the fretting on the cap and bearing shell.

I'd say resize the rods along with new bolts or new rods period.

 

[schiker]

Yeah, I was kinda thinking it needs a new rod. Here is the piston and suspect it was beating the rod pretty hard. I am actually a bit surprised the bearing and crank looked good. I should have said accelerated wear on the bearing instead of excessive wear on the bearing. I meant excessive wear for the number of hours on the engine.

I'll try to get another rod pic to show comparison. Not going to be able to start working on it til later today.

 

[schiker]

Well, surprised me a little all the rods seem to be fretted on the back side of the bearing fairly similarly. The mains don't have any fretting mark. I guess they don't fret because they are wider and distribute the load to 2 sides???

Here is another rod picture with similar marks. It might be hard to see in the pics I'll have the machine shop look at them too and see what they say.

Top left is No.2 rod, top right is No.2 main bearing cap and back of brg. Bottom is back side of No 2 rod brg.

 

[WarWagon]

The piston looks like the rod is bent. Is the rev limiter working on this engine? Stretched rod bolts can be from overspeeding.

 

[schiker]

iirc the WOT is around spec of 4700 or 4800 rpm. I haven't ran the boat in ~2 yrs I don't recall it seriously over reving but don't recall a rev limiter. Of course I don't know what previous owner did. It ran well until I screwed it up the first time out 2-3 years ago. Its been sitting since.

I remember my dad's boat early 3.0L taching up to 5200 rpm trimmed out and probably tickled 5400 rpm a time or two if the tach was accurate.

 

[schiker]

Here is the No. 3 rod. This is my first time looking at the back side of bearings and the appearance is not what I expected. I see lots of pictures of bearing failures on the ID but no real description of what backside should or should not look like.

Picture of the rod and cap with bearing out. Shows similar fretting marks? Is that what you would call them?

 

[schiker]

I think what limits the rpm is the coupler and outdrive isn't it not really an engine limit. I guess the engine limit would be due to balance and hydraulic lifters ???

 

[ak diesel driver]

it looks more like corrosion/erosion to me. send in an oil sample see what it says

 

[schiker]

iboat forum said it was staining and normal. Oil is mixed with recycle oil now. The interior of this engine is a nice pretty cast grey. A little carbon on the top of piston but pretty clean overall. It has sat in storage for a long time and way more hours than it has ran so could be corrosion especially from a bad winterization (sat with acidic oil for a long time). The first rod I was suspect due to damaged piston but after seeing all of them not so worried. I might try to polish them with some metal polish and see if appearance changes. Shouldn't remove any metal or change size. Its very fine polish used on plastic molds. I'll post back after I see what that does and see what the machine shop says too.

 

[WarWagon]

Yeah, I was kinda thinking it needs a new rod. Here is the piston and suspect it was beating the rod pretty hard. I am actually a bit surprised the bearing and crank looked good. I should have said accelerated wear on the bearing instead of excessive wear on the bearing. I meant excessive wear for the number of hours on the engine.

I'll try to get another rod pic to show comparison. Not going to be able to start working on it til later today.

This clearly is not a normal wear pattern on the piston. I recommend you replace this rod or at least check it for straightness.

 

[schiker]

Yes, I will get shop to thoroughly check rod if I reuse it.

I know (or think I know) what happened to the bad piston. I ran the engine hot with too many wot figure 8's with an old impeller that couldn't supply water in a tight turn. Not sure if they can new with really tight turns. Either when I straightened out and it flushed with cool water the front cylinder gets cool water and squeezed down on piston. Or when I shut it down and the water boiled off the cylinder it got really hot. I sat with engine off for 1-2 hours but wasn't enough and cool water flush on start up ruined cylinder. It was a bone head move on my part. Oh well live and learn.

 

[schiker]

I took some Congress Polish and cleaned the No. 1 rod cap and back of the bearing. The discolorization and stain came right off so I guess it was corrosion. To the naked eye it looked sorta kinda like a Damascus knife blade and would not have thought it would polish off.

Not sure why the rod bearings would stain and not the main bearings too but I guess they do. Machine shop said rod was ok and staining was normal. Here is the rod cap polished. Ole timer machinist said cylinder wasn't hurt bad and he would hone it and put a new std piston back it.

My plan now is 1 new piston, all new rings, and new bearings. I'll have machine shop hone and deglaze all cylinders and install new piston on rod. Hopefully can get back going for a little under half the price of a rebuilt crate engine by doing it myself. Fingers crossed.

 

[3500GMC]

I would be running a mic through the bid ends of those rods. Did the machine shop mic them?

 

[ak diesel driver]

x2 it wouldn't hurt to see if they're still round.

 

[schiker]

No he just looked at them. He said if it wasn't for number one piston and cylinder damage he would have said it was new. I'll ask him to measure the big ends next week before he puts the new piston on it. After seeing all the same stains on the other rods I really don't expect there to be a problem. It did worry me out at first though.

And he said the few small grooves (more like fine lines ) I feel in the cylinder were too far down to cause any sealing problems with the rings as the rings don't go down that far (plus I guess its at end of stroke too). The upper cylinder you can't feel anything just see them. I expect it to hone out nicely and not change cylinder size much at all.

It'll be 3 weeks before I can start assembly due to vacation and other honey do's though. Hope to be on the lake in July sometime if all goes well

 

[WarWagon]

Yes, I will get shop to thoroughly check rod if I reuse it.

I know (or think I know) what happened to the bad piston. I ran the engine hot with too many wot figure 8's with an old impeller that couldn't supply water in a tight turn. Not sure if they can new with really tight turns. Either when I straightened out and it flushed with cool water the front cylinder gets cool water and squeezed down on piston. Or when I shut it down and the water boiled off the cylinder it got really hot. I sat with engine off for 1-2 hours but wasn't enough and cool water flush on start up ruined cylinder. It was a bone head move on my part. Oh well live and learn.

This explains a lot. You scuffed a piston by oil failure from being too hot or simply ran out of clearance maybe both. Sudden cooling while hot will do this esp to the first cyl that gets the coldest coolant. This had to happen while running to score anything. Seen the same thing on my 1993 6.5 running way hot and the radiator cap popped off suddenly. Any hotter and your piston could have also cracked and/or locked up.

I doubt the turns were a factor - the old impeller was with too little or surging cooling water.