Piston examination...1973 70hp Chrysler

[nathanhooper]

So here is a slight continuation, but new subject in the same. Took the pistons out last night. When removing the first one, top, I thought that I might be wasting my time doing this. It was in real good shape. But then again this is my limited knowledge speaking. This would be why I am bringing it to the board for examination.

The middle piston, the one with the worst cylinder, was messed up pretty good. When I pulled it I was glad I was doing this after all. The rings are stuck on it from the metal on the edge of the ring grove "binding" the rings.

The bottom piston is in decent shape also, best I can tell.

My questions, desire for opinions/advice, is about the rings themselves. I am pretty sure, although you can correct me if I am wrong, that the pistons themselves are good to go with a little clean up. There is no cracks, chunks missing, holes or anything like that wrong. Seeing how the rings are what keep in contact I would assume they are the critical point.

So as far as the rings go, what classifies them as being "unfit for service"? It there a way to put calipers on them and decide if they are too worn? There is no sign of any breakage or anything to that extent. In fact they look like they have only been in for a little while.

It almost looks like the motor had been rebuilt, then something got caught in the cylinder and made this happen. Or maybe because of all the sand I found in the exhaust cover(thats another subject), it over heated, which I know has happened sometime in the past because of the discoloration, and when it overheated it caused this damage to happen.

Either way, I need some advice from people that have seen and dealt with this before, and opinions on what to do. Also I will attach a picture of what looks like some molten aluminum on that middle cylinder, on the edge, in the water jacket. I can tell its aluminum because it is not magnetic.

Thanks guys! If you hold your mouse over the pictures it will tell you what piston it is and so on.

 

[perculator]

Re: Piston examination...1973 70hp Chrysler

i'd trash it.

 

[jerryjerry05]

Re: Piston examination...1973 70hp Chrysler

You need to show the tops of the pistons(thats where they show oversize) and the cylinder walls for all the pistons..
If I was gonna rebuild I might use #1 and #3 piston again but not #2.
I have rebuilt a lot of these chrysler/Force motors.You might get away with using old rings but I wouldn't.
Then the most important thing???? Why did it go bad?????
Usually, if the oil is right(cheap or TCW 1or2 both bad) and the temp is right and the air crews are set.If the block isin't clogged.Or if the reeds are good then you won't have a carbon build up.Poor water circulation on that side of the block etc.Look for these problems.J

 

[BuzzStPoint]

Re: Piston examination...1973 70hp Chrysler

That # 2 piston is the worry here.

Why is it scraping the cylinder?
Could be the rings failed due to lack of oil.
Or could be the rod/bearing or wrist pin.

 

[bkwapisz]

Re: Piston examination...1973 70hp Chrysler

That "Middle Cylinder Slag" picture looks like someone tried to weld up the edge of the cylinder and then ground it down. I'm not sure how well that works on an outboard, but I'm sure someone else will comment on it. My uneducated guess is that someone made a repair, warped the cylinder and the clearance was too tight on that side. Does that coincide with the rub marks on that piston?

The middle piston is toast.

 

[nathanhooper]

Re: Piston examination...1973 70hp Chrysler

I'll get pics of the tops on later tonight. They are in great shape. you can see a little indention from spark and all, but they are in real good shape. You can also see them in my first post. I have some pics of the cylinders with me so they will be attached now.

I put calipers on the pistons and they are right on as far as size. They are out of round, but i thought I read somewhere that they are a tad bit oval shape. I will write down measurements tonight.

Reed valves are in perfect condition. I can post some pics of them also. I think that the major cause of this is lack of water flow. I am wanting to say that the thermostat is not functioning the way it should, combined with the sand and corrosion I found in the exhaust, show me it has been rough ridden. I will do a complete system flush after I am done with this to make sure the block is not clogged.

That is the major issue, why did it go bad. There is not much telling it. I plan on being meticulous putting it back together, so I will know for sure that there is not any foreign object in there. That is what I think happened. I think the over heat issue came first, and then someone just did what they had to to get the motor running again to sell it. That is where I think the poor sucker ended up with it before me.

I believe that the person who overheated it(it has been for sure), melted the pistons(maybe the "slag" on the out side of the cylinder?). Then they put new pistons in it(the pistons in it look good, head wise) and did a rough(very rough), hone job. Hence the "sos" pad looking scours along with the deeper groves toward the back that are definitely not fresh. I don't think that it has had very many hours on it since the job took place. I believe that they left something in the cylinder and after noticing the mistake decided they had enough.

That is why I am wondering if the rings could be re-used. Who knows though. The only way I could see knowing for sure if the rings could be re-used, is if I had the specs on what a new ring measures at, then I could tell the wear on the ones I do have.

Now, if only I could say all of this is true, and then be able to prove it, I would play the lottery tonight. lol

 

[nathanhooper]

Re: Piston examination...1973 70hp Chrysler

Yes, the "slag" does coincide with the marks on the inside. Very nice intuition on the warping causing the binding, which would in turn cause the damage we see.

I answered my own question on the rings though. Kind of that is. I still would like some specs on some new ones if anyone has a way to get them. I also need the end gap clearance that they are supposed to be at.

The best way I guess in determining if they are fit is if you stick them in the cylinder and measure end gap. This also might lend to the problems we see, because IF someone did over heat it, warp the head or at least "narrowed" a part, then if they did not check the proper ring clearance it would not have been allowing enough oil through to properly lubricate the cylinder.

Sound plausible?

Also attached is a picture of the opposite side of the cylinder. You can see the deep scars in it, but they look a lot older(in person) than the ones on the opposite side. They are also not visible until you pull the piston out. Does that ring any bells with anyone? Or does it indicate the out of round from the opposite side?

Thanks for the advice guys, keep it coming.

 

[nathanhooper]

Re: Piston examination...1973 70hp Chrysler

I do not want to argue with people that know what they are talking about, but humor me if you would.

If the piston rings are what keep in contact with the cylinder walls, and not the piston, then why could a person not "smooth" out the rough areas on the skirt itself? Again, not trying to argue, just trying to learn. The rough marks are not all that deep, I will attach a picture of them at an angle. The image in the picture is of the worst "scars", where they are "holding" the rings.

I will also post the pictures of the piston heads tonight. Looking down on them you cannot tell that the skirts are even damaged.

I am going to test the piston pin for "play" along with over heating discoloration. But I am going to bet 5 to 1 that there will be no signs of over heating, I seriously think these are new pistons and rings. But a person has to know facts before they proceed, and that is what I will do.

FYI. the "grit" or little pieces of "dirt" and such, in the pictures of the cylinders, is a combination of carbon and dust/lint. They are much cleaner than that when you take a rag to them. I am not too worried at this moment seeing how I will do a thorough wash down of the inside of the motor.

 

[bkwapisz]

Re: Piston examination...1973 70hp Chrysler

Well, again, I'm no expert, but if that middle cylinder is ok with the repair there I'd get it bored and honed and replace at least that piston. To me, the piston looks a little too damaged to repair it but I'm sure someone who has been this route before will chime in to give you the expert info you need.

I don't know enough about the shape of the pistons to comment on whether or not they're oblong or not. I've only rebuilt automotive engines, myself, and those are defintiely round. If I were you, and since you already have this disassembled as for as you apparently do, I'd do my own rebuild with the proper new parts and then you'd at least know you have a new engine. But that's just me (I'm a "might as well" type of guy.) I do know that proper cylinders have a very smooth appearance and also have a "crosshatch" appearance when you hit them with light the right way so they hold oil film.

If you can, post some pics of the crank journals.

 

[Frank Acampora]

Re: Piston examination...1973 70hp Chrysler

OK, Nathan. You asked for it!

The middle piston is junk and the center cylinder needs to be overbored. While it is true that the piston rings take compression and combustion pressures, the skirt of the piston seals the crankcase. This allows it to induct a fresh charge and pump it through the bypass ports to the cylinder. With the skirt as badly scored as yours, pumping efficiency will be affected and horsepower will be lost. In other words, the engine will run like crap.

As far as the other two: Outboards do not generally get the same wear as auto engines and rings generally do not wear out. If the cylinders are in good shape, the rings probably are also. Besides, I don't think new rings are available for those older style three ring pistons.

The apparent welding is just that: The aluminum chipped off (manufacturing defect?) and without its support the head gasket blew out. The P.O. had the repair welded in. It is so small that it is doubtfull that it affected the cylinder in any way. The scoring came from other causes (perhaps a lean running carb?).

So now, you can rebuild by boring one cylinder and buying a new oversize piston--about 200 bucks. Pistons are available from Sierra (cast--cheaper) or Vertex (same) or Wiseco (Forged--a bit more expensive but stronger and complete with wrist pin and rings)

Your options are to rebuild or try to find a cheap short block to replace yours.

It would be nice to know your location, because HINT--HINT--Frank has parts. I wish it were a forum requirement that all posters give an approximate location. Believe me: If you just give a state, no one is going to stalk you.

 

[nathanhooper]

Re: Piston examination...1973 70hp Chrysler

yes, yes I did ask for it frank. lol. Sometimes the truth hurts, lol. I live in Arkansas. I am not sure what I am going to do. I know I do not have the money to do the rebuild like it should be done. Some times you just got to get along with what you got. So the dilemma will be if I try to limp along until I get the money, then do the rebuild. Or if I just let it sit until I get the money. Either way, I am not going to try to pass it off on someone else, and I am not going to just junk it. Multitudes, multitudes, in the valley of decisions...

 

[Frank Acampora]

Re: Piston examination...1973 70hp Chrysler

Oh, yes--forgot to mention: Pistons are cam ground with a major and minor diameter to account for uneven heating due the bypass and exhaust porting. They approach round when hot.

 

[jerryjerry05]

Re: Piston examination...1973 70hp Chrysler

The cylinders might be honable.I couldn't FEEL the walls from the pics. The piston is and has melted aluminum on it it's clogging the rings.It's not re-usable.
There was a company I used years ago. It was called Flint Piston,Flint,Mi. and they could get you pistons and rings for almost everything.
You can use the newer style piston with the 2 ring set-up.
There are lots of graveyards where you can get some older parts.
Lots of old stuff here.Valley Sales3896 East Houghton Lake Drive, Houghton Lake, MI 48629-8337 989) 366-8178 J

 

[nathanhooper]

Re: Piston examination...1973 70hp Chrysler

Ok, humor me yet once again if you would please. What could happen, what would be expected to happen, if I did reuse the piston? Again, this is just a "what if" senerio. Let's say that I did that, cleaned up of course. What would I expect to see if I opened it back up in, let's say, a year? Or would that in and of itself be stretching it too long?

I completely understand this would be a unwise descision as far as good engine mechanics go. But are we just talking reduced horse power, or something else?

Ahhh, the questions that are racing through my mind. Lol. I am new to this, but it has sucked me right on in. I have to say that even though this is not the best of circumstances, I have rather enjoyed the process. I think I know what I am going to do when I retire.

 

[nathanhooper]

Re: Piston examination...1973 70hp Chrysler

Just to throw out another question here, why did they go from a three ring piston to a two ring one?

 

[bkwapisz]

Re: Piston examination...1973 70hp Chrysler

I would think that if you put that piston back in there the engine would probably run, albeit not well, and it would continue to chew up that cylinder to the point that it would render the whole engine block useless. The only reason to put that back in there would be to purposely completely ruin the rest of the engine, so if your intention is to destroy what's left then that's the right course of action.

If these guys who have experience think you can just replace that piston and get the cylinder bored, then I'd do that and get some enjoyment out of summer with that motor.

 

[perculator]

Re: Piston examination...1973 70hp Chrysler

Ok, humor me yet once again if you would please. What could happen, what would be expected to happen, if I did reuse the piston? Again, this is just a "what if" senerio. Let's say that I did that, cleaned up of course. What would I expect to see if I opened it back up in, let's say, a year? Or would that in and of itself be stretching it too long?

I completely understand this would be a unwise descision as far as good engine mechanics go. But are we just talking reduced horse power, or something else?

Ahhh, the questions that are racing through my mind. Lol. I am new to this, but it has sucked me right on in. I have to say that even though this is not the best of circumstances, I have rather enjoyed the process. I think I know what I am going to do when I retire.

as i said earlier........i'd trash it. spend 500 for a decent used one. you'll save money.

 

[waterwilly]

Re: Piston examination...1973 70hp Chrysler

Ok, humor me yet once again if you would please. What could happen, what would be expected to happen, if I did reuse the piston? Again, this is just a "what if" senerio. Let's say that I did that, cleaned up of course. What would I expect to see if I opened it back up in, let's say, a year? Or would that in and of itself be stretching it too long?

I completely understand this would be a unwise descision as far as good engine mechanics go. But are we just talking reduced horse power, or something else?

Ahhh, the questions that are racing through my mind. Lol. I am new to this, but it has sucked me right on in. I have to say that even though this is not the best of circumstances, I have rather enjoyed the process. I think I know what I am going to do when I retire.

after reading your post and seeing your pictures its obvious you have probs but if it were me i would clean it up and put it back together who knows 50-50 chance it will run or 50-50 it wont and if not you will have learned a hell of a lesson.

 

[jkoppe73]

Re: Piston examination...1973 70hp Chrysler

Plain and simple from any person with any mechanical experience of any kind and common sense, the two pistons in question are trashed. they both need to be replaced, THEY CAN'T POSSIBLY BE "CLEANED UP", THEY ARE JUNK, SCRAP, FRIED, TOASTED, as stated in a previous reply, if your goal is to destroy the engine, then yes put them back in. you will get what you deserve, a completly blown engine. TRASH THE TWO PISTONS. HAVE THE CYLINDERS BORED AND HONED, BUY TWO NEW PISTONS TO REPLACE THEM. It can't be said any clearer. Comprende'??

 

[nathanhooper]

Re: Piston examination...1973 70hp Chrysler

Yea, I am just glad I found all of this out before I started work on the boat itself. I mean after all it did run, just one thing led to another and here is where I am. The absolute only reason I had in pulling the heads was to check the thermostat. There were no other problems I could see. But I am not complaining it is better I caught this than to be out on the lake and the engine sieze.

I know this other guy, he has a funny name for a boat "The F.S. Bounds", he is spending a lot of time and money in the boat itself without doing anything about the motor. Who knows, he said it ran last year, just like mine did, so he is satisfied with it. I would hate to be out on the water with him if it went down for a simple reason that he didnt check out before getting out.

But, I am not going to judge. I am just glad that I found this out before hand, not after the summer got into full swing. I will let you guys know what I decide to do.