What should be replaced when replacing pistons?

[jnaarnold]

What should I replace when putting new pistons/rings in and boring cylinders? Here's what I have so far:
1986 Evinrude 50 HP ,VRO system has been removed.
- Piston/ring .020
- powerhead gasket set
- water pump kit

Do I need to any machine work to the cylinder head/powerhead block?

 

[Silvertip]

Re: What should be replaced when replacing pistons?

Are all of your posts about the engine you can't seem to get to run right? If so, it seems to me you are jumping around trying to resolve an issue without any thought about diagnosing the problem. You have several posts, all about the same engine, all about the same problem and it's getting very difficult to keep up with you. You are really running everyone around the farm trying to help but there doesn't seem to be any action involved on your part except for a new question. Why are you replacing pistons? Have you run a compression check? If so, what are the numbers? If compression is good there is no reason to install new pistons. Have you removed the head to look at the cylinder bores? If so, are they scored? If so, yes you need to have the block bored to the next oversize. You cannot put .020 oversize pistons and rings in a standard size hole. Ever tried to put a 1/2 inch bolt in a 3/8 inch hole? If you have not determined whether or not boring is actually necessary, why on earth did you buy .020 rings when it may be necessary to bore .030 oversize. The rings do you no good without the pistons.

 

[MikDee]

Re: What should be replaced when replacing pistons?

Has it been bored? if so, how much? next if it has been bored, you need matching oversize pistons, Your machinist should match all this up for you, if you're using one? before installation, you need to hone a crosshatch pattern in the bores, for break in. Then before all else, you need to set your piston ring end gap to specs. Finally, your rings go on the piston with the gaps opposite one, another, if you have 3 rings per piston, the rings gaps go on 1/3 of the way away from each other.

 

[jnaarnold]

Re: What should be replaced when replacing pistons?

Silvertip,
If you actually read the post you could answer your own questions.
John

 

[Solittle]

Re: What should be replaced when replacing pistons?

For what it is worth John I read your post and silvertips (& mikdees). I had the same questions that they did. You are getting good advice - Often we know in our mind what we want to say but sometimes it never makes it to the keyboard. Read what you wrote as if it were written by a stranger and you may see what we are trying to convey.

 

[jnaarnold]

Re: What should be replaced when replacing pistons?

I didn't want to come across rough, but I felt as if what he said was unfair. I have spent a lot of time on this motor. Sorry, I am just getting frustrated. I need an expert opinion, not a sarcastic one. Please forgive me.
John

 

[ondarvr]

Re: What should be replaced when replacing pistons?

To answer the question you asked above, everything.

The entire engine needs to be taken apart to change the pistons and/or rings. So if you plan to replace them, get all new seals, bearings, gaskets and whatever else looks to be worn or in bad shape.

Yes, the block needs to be bored for the new oversized pistons to fit.

The people here that are puzzled and asking you questions are pretty sharp, so give them the information they need to help you.

 

[MarkV_Deep6]

Re: What should be replaced when replacing pistons?

I didn't want to come across rough, but I felt as if what he said was unfair. I have spent a lot of time on this motor. Sorry, I am just getting frustrated. I need an expert opinion, not a sarcastic one. Please forgive me.
John

Them Seal Teams are Killer's

Ya need a good technician from the salvage divers!

 

[Silvertip]

Re: What should be replaced when replacing pistons?

Am I incorrect in that there are least four separate posts on this engine, all for what is apparently the same problem? when one jumps from one post to another it's terribly difficult to determine what has and has not been done to remedy the problem. In the other posts we are dealing with fuel system training. Now we have jumped to an overhaul situation. Without a logical approach to diagnosing the problem we (I especially) get more than a little frustrated. Remember that we can't see your engine, can't hear it, and can't touch it. That's where you come in. Service manuals, regardless who publishes them, generally have good descriptions of how outboard engines work. Unless you get into the new DFI and EFI engines, carbed two strokes are very basic and easy to understand if you put your mind to it. The long and short of it is that the engine needs fuel, air, compression, spark, and everything needs to happen at the right time. The only way you will get this engine right is to follow very basic troubleshooting techniques. When people offer suggestions, act on them, post the results and move on to the next step. Skipping steps because you don't understand what that step is supposed to accomplish or you don't have the tools or knowledge to perform means the project is beyond your skill level. At no time in this or other discussions do I mean any disrespect. All I ask is that you keep this series of posts in sort of logical order so we can keep up. Jumping around is not diagnosing -- it's called shotgunning and rarely does that hit the mark and result in a fix. I hope someone else can help you fix the problem.

 

[jnaarnold]

Re: What should be replaced when replacing pistons?

Again, you say you mean no disrespect, then go right in to being disrespectful. You are assuming I am not competent by saying things like, "training", and "you don't understand or have the knowledge". I have laid out my steps, I have followed advice. Everyone has been very helpful. Some people are not cut out to be teachers, I am not blaming you. You are just not being very patient or forgiving. If it frustrates you, then just don't post. I was getting a lot of information from others. It seem like you just chimed in because you wanted to rant. Sometimes it is best to leave things unsaid. I won't be offended at all if you choose not to help. I understand. Thanks
John

To the others, what I was originally asking in this thread was, do I need to have the head or the powerhead casing machined, as in surfaced, like you would an automobile engine? I know it has to be bored to put oversized pistons in, that wasn't even a question. I guess what I meant to say was, what other things should be replaced when boring and installing oversized pistons/rings. Like, do I have to put certain bearings in or wrist pins? Are there dowels that should be replaced, you know, things that go unnoticed? Sorry if it got confusing. Are there any special tools needed? I have every hand tools( ring compressor, hone-for cross hatching) and most specialty tools out there, so I should be ok, unless there is something you can think of.

 

[Solittle]

Re: What should be replaced when replacing pistons?

What you need is the OEM shop manual for your engine. It has detailed procedures and pictures to help you. The Parts manual gives exploded parts diagrams with part numbers.

 

[sankanother1]

Re: What should be replaced when replacing pistons?

I am a little confused if you have a ring compressor and a hone I would think you already know what you would need to rebuild an engine.If you don't I would suggest finding some one to do it for you.you can find some great prices on power heads as well,Sometimes it does not weigh to buy alll the parts and have it machined vs purchasing a rebuilt power head.ie bent rods scored or burnt crank deterioation of the block warped deck or heads bent reeds and so on.I am sure someone here can point you in the right direction.Just tell them the whole story and why.They are great folks on these forums they help me almost everyday.

 

[jnaarnold]

Re: What should be replaced when replacing pistons?

I was looking at what parts I might need or 'special' tools.....thanks anyway.
John

 

[iwombat]

Re: What should be replaced when replacing pistons?

I think we're all just scratching our heads here because the first post in the thread kind of starts in the middle of the story. What happened to the motor to cause a rebuild is an important part of determining what you're going to need during the rebuild. If it failed catastrophically you're going to have to determine what the cause was, and that may take some extra tools and parts too.


Did it overheat and fail? Plan on planing or replacing the heads and exhaust covers. Also, plan on replacing all the bearings.

Is it just worn out? Plan on closely inspecting all the bearings at the very least, replace the big-end bearings out of hand. No need to deck the heads or anything probably.

Did you break a ring? Don't buy your pistons yet. Have it bored big enough to remove the scoring first.

You get the picture. Take a couple of steps back, and tell us why you're rebuilding and you'll get some better answers.

 

[Silvertip]

Re: What should be replaced when replacing pistons?

If you have a cylinder hone, you would probably burn up the drill while attempting to "hone" a cylinder .020 oversize. Boring bars are used to "bore" a cylinder and make it round again. A cylinder hone will not do that. As for the training comment -- seems to me we are spoon feeding you information. Is not the definition of training -- the transfer of knowledge. I'm done here. You are free to put me on ignore.

 

[jnaarnold]

Re: What should be replaced when replacing pistons?

Silvertip,
Who said anything about boring the cylinder with a hone!?! WOW, I mean come on you are being comlpetely rediculous, I would put you on ignore, but I enjoy the humor.
Yeah, I kind of did start in the middle, I was hoping not to be confusing or get off topic, looks like it happened anyway. I appreciate all the help though. Will try and clear it up tomorrow. I am going back out on the water, I actually think I have the problem nipped. I will report back tomorrow.
J

 

[kanai8238]

Re: What should be replaced when replacing pistons?

Perhaps I can shed a little light on the situation,as a auto tech for 20yrs
with ford motor company,I beleive whats being asked is if anybody has
come across this and has any eye opening tricks of the trade sort of
speak.Goodluck and don't get discouraged.

 

[kanai8238]

Re: What should be replaced when replacing pistons?

ps.you don't have to replace the bearings when replacing rings and pistons
it's just a good idea while you have the pistons and rods out to give it the
full meal deal,I have rebuilt hundreds of engines and it just depends how the
bearings and crank look,remember you only want to do the job once.By the
way I have seen broken rings in a perfectly good engines before ,rings often
break from fatique and ring land fatique or por installation on a newly
serviced engine.hope this helps in some way,good boating.

 

[wilde1j]

Re: What should be replaced when replacing pistons?

If you are going to have the block bored, make sure the place that does it is outboard block machine shop, not a auto machine shop. Have them mike the bores and determine the OS to use, then tell the shop the brand of pistons you will use (it makes a difference). The parts to be replaced depend on your judgment as to whether or not the existing parts meet service requirements or need to be replaced. If you can't tell, take the block to a rebuilder to do, rather than make a major mistake.

The most important thing, however, is to determine exactly why the failure occurred, or it will likely happen again.

 

[jnaarnold]

Re: What should be replaced when replacing pistons?

Great advice guys!!! I just got back from going out today. Great trip, a little choppy for a 16' Jon. I am glad it's a wide. Motor ran very well. Started right up at the dock. Ran it idle up for about 3 minutes. Put it in reverse and backed up. Into forward and away I went!! Yesterday, while setting my link and sync and timing I noticed my fuel filter had some white milky stuff at the bottom. So, I examined my fuel tank and sure enough, about two inches was at the bottom of the tank!! I feel very positively this is where my problem was. I guess it pays to double check things sometimes. She still surges a little on top end, and I did notice my fuel bulb does not get as firm as before, even with the line unplugged from the engine. I replaced the ends on the line, now I will replace the bulb and line itself and try again. All in all I am VERY encouraged. My daughter really enjoyed cruising with me. I am also going to dissassembly the carbs again and make sure they are clean(maybe there is some of that water-liquid in them). As far as what caused the scoring in cylinders, I think the previuos owner had a reed valve problem as these are very close to brand new...he might of lost one in the engine...all I know is now it run like a sewing machine!! Thanks again.
J