Been reading posts on determining the cause before rebuilding

[GatorMike]

I've been reading the posts about finding the cause of a problem before doing a rebuild and it makes great sense to me. I'm in the middle of a rebuild right now and am a little worried that I may not know the real cause of the problem. One of the posters made a comment on what he thought the cause might have been a week or so ago when I bought the boat. But at that time I am not sure that I gave an accurate description of the problem. I would like to post a detailed description of everything I have found and see if some of the experts might have some ideas.<br />--------------------------------------------------<br /><br />The motor is a 98 Johnson 115 model number J115TSLECM. A friend brought it over to me and asked if I would look at it for him. I'm not a mechanic but he knew I do my own repairs on my boat and thought I might help. He said it had been idling rough and took forever to get up on plane. I discovered he had low compression on the upper right cylinder, 118 lbs on 3 and 85 lbs on the bad one. He decided to trade it in but his dealer would offer him practically nothing for it. I bought it for slightly more than the dealer offered. Upon removing the head on the bad side I found the cylinder scored and the head badly pitted. Yesterday I removed the power head and upon closer inspection I noticed most of the dings in the cylinder head are around the outer edge where the head is flat. the piston also has some pits in the same area. The dome section of the piston and head have very few pits or dings in them. There is a small chip out of the edge of the piston about the size of a BB maybe a little smaller. I have been reading posts about burned or melted pistons and don't think this one is melted although I don't know for sure because I have never seen a melted piston. Is this enough info to get an idea what might have caused the problem?

 

[Dhadley]

Re: Been reading posts on determining the cause before rebuilding

Was the bottom ring was broke on the bad piston?

 

[WillyBWright]

Re: Been reading posts on determining the cause before rebuilding

That BB sized missing piece makes me think a ring locating pin failed. Is there a locating pin still in the top groove? It doesn't sound like a detonated piston. Sounds like a piston failure. To be safe, I'd go thru the carbs. That cylinder could've been running lean.

 

[GatorMike]

Re: Been reading posts on determining the cause before rebuilding

Dhadley sory it took a while for me to get back to you, I was waiting until I got the piston out. I have not been able to get the piston out yet because as I mentioned before I am tearing it down from memory waiting on my manual to come in and I can't get the crankcase halves to split apart and don't want to force it in case I am forgeting something. I did however take the inner and outer exhaust covers off and can see from inside the exhaust port that the piston ring nearest the head of the piston is broken. and much of it is missing. Does this tell us anything? I suspect so.

 

[Dhadley]

Re: Been reading posts on determining the cause before rebuilding

It sounds almost like typical damage from coking. Well see when you get it apart.<br /><br />Have you got the top and bottom bearing caps off? There are a couple of tapered alignment pins too. Drive them out from the rear of the powerhead. Dont drive them from the carb side toward the head side.

 

[reeldutch]

Re: Been reading posts on determining the cause before rebuilding

make shore that you take out 6 bolts (allan) there are 4 of them behind your reedvalves.<br />so take of the intake manifold, take the allan bolts out and puch out the taper pins as dhadley said from the back to the front.<br />take the crankcase head bolts out (upper and lower, Do not take the 4 lowerbearing retainerplate bolts out just loosen them.<br />now you should be able to split the case.<br /><br />check the waterflow restrictors for swelling and blocking the passages. especialy the middle ones.<br />the bottem ones are no poblem.<br />check for debris in the waterpasages.<br />and i defenetley would rebuild the carbs. running lean is bad for piston rings.<br />Make shore you are oiling propper to be shore i would mix before running on vro alone. use a good quality oil.<br />i use yamalube and do a decarb every season.<br />check for water leaks at headgasket and exhaustcover gaskets.<br />make shore the tstats are working and your overheat alarm works also.<br />make shore you are spinning the right prop overpropping does not make a piston a happy one.<br />and make shore your timing is set propper.<br />last and easyest make shore the waterpump works.<br /><br />anything else, ask dhadley<br />he knows more.<br /><br />reeldutch

 

[GatorMike]

Re: Been reading posts on determining the cause before rebuilding

Wow you guys are good. I think I've got it licked now, picked up a Clymer manual today to get me by until I get the other manual I ordered. Boy the procedure has changed since I did my old 89 rebuild. Back then they suggested removing the external parts before removing the powerhead now they recommend removing the powerhead with the parts on it then removing them. Guess it really doesn't matter. Looks like the allen screws behind the reed block was what I was missing. Helps to have a manual especially if you have only done this once before. No more questions for now. I imagine I will have a couple more when the time to reassemble comes.

 

[GatorMike]

Re: Been reading posts on determining the cause before rebuilding

I finally got the bad piston out. The lapse in time was because I didn't have the right tool to remove the rod bolts. Had to find a thin walled 12 point socket. (It sucks when you don't have the right tools) Anyway you guys were right as usual it looks as if the culpret was probably a broken ring. The outer ring was completely gone and a large piece was missing out of the piston between the two ring grooves. The other 3 pistons and cylinders looked fine, like I said before they all produced an identical 118 lbs of compression when it was toghther.................<br />Now I have a decision to make and I would like to hear some opinions. Do I bore and rebuild all 4 cyls or just the bad one? The only other rebuild I have ever done I did all 4 but it was on an older outboard. Right now I am leaning twards just doing the one mainly because it would save me 4 or 5 hundred bucks. This brings me to a question, if I reuse the 3 good pistons do I have to disassemble the wrist pins and needle bearings or can I just leave them assembled? (I hated that job the last time I did this)

 

[Dhadley]

Re: Been reading posts on determining the cause before rebuilding

The question of how many o bore will be answered by the person in charge of the dial bore gauge. <br /><br />The broken ring was most likely caused by coking. A sticky black substance that causes the rings to stick in the groove. Coking is promoted by combustion heat thats higher than normal. Too low top capable rpm, wrong fuel, wrong plugs or a combo. <br /><br />That same heat probably caused the cylinders to be out-of-round beyond the wear tolerance. The dial bore gauge will tell.<br /><br />Also keep in mind the pistons have worn some. By the time we hone the cylinders we've effectively "worn" the cylinders even more. Now the skirt to wall clearances are even bigger.<br /><br />Bottom line -- yes, you can bore only 1 cylinder. IF the others are in tolerence. It doesnt matter what they LOOK like. The difference is not 4 or 5 hundrd dollars between doing 1 and doing 4.<br /><br />As for the wrist pin bearings, use the caged style. They are much easier to handle and are stronger that the loose style.<br /><br />Youre doing great. Hang in there.

 

[reeldutch]

Re: Been reading posts on determining the cause before rebuilding

i agree with dhadley let the machinist decide if he needs to rebore al four he knows best.<br />hophely they will be in specs and probbebly they are.<br />and reboring all four cylinders should not be more than about 200 dollars and thats high.<br />but four new pistons will cost you about $380<br />so i would ig you dont have too only hone the 3 other cylinders out.<br />inspect the cylinders and bearings very carefully.<br />if you can save money on pistons thats great bud dont go cheap on bearings.<br /><br />reeldutch

 

[Dhadley]

Re: Been reading posts on determining the cause before rebuilding

Look at it this way --<br /><br />Boring a cylinder is about $40 which includes honing, chamfering and deburing. Hone, chamfer and debur only is about $10. That means each additional bored cylinder costs about $30 or $90 total.<br /><br />Each new piston lists for $89. Less the cost of rings at $28 each. And new retaining ring sets at $1 each. So each new piston costs $60 each or $180 total. <br /><br />The difference between doing 1 cylinder and 4 is about $270 total. Plus your time for cleaning the old pistons.<br /><br />Plus if you find a dealer willing to give a discount, thats more savings.<br /><br />On a 1998 motor the wear may well be very little. But just in case, its not really that much more to go all new and have 100% life left in the motor.

 

[GatorMike]

Re: Been reading posts on determining the cause before rebuilding

Thanks Dhadley, I think I will do all 4. I had mis calculated. Didn't take into account I would need to buy rings if I used the old pistons and I ball parked pistons at $100+tax. I talked to the machine shop that will be doing my boring and the guy there made many of the same statements you have. He said he will tell me all the info I need to do it right, then if I want to skimp somewhere it is my choice. Don't think I'll do that though. I cleaned it up after work today and will bring it into the shop in the morning. By the way the exhaust ports and inner exhaust cover were covered with a black gooey substance (this is probably this coke substance you spoke of?)along with a ton of carbon. I don't think the previous owner ever decarbed the engine. I got most of it cleaned except for right around a couple of bolts where I couldn't get clean. Overall this engine is incredibly clean though. The last time I rebuilt an engine I broke bolts and had all kinds of problems. This one had only 3 hard to get out bolts the 3 at the bottom of the outer exhaust cover and they only took a little extra torque than the others. I guess that is the difference between a motor that has been used in salt water and one like this that has been a fresh water engine.

 

[Dhadley]

Re: Been reading posts on determining the cause before rebuilding

You are correct, that is coking. We can be 99% sure thats what caused the damage. To cover the other 1% we will go over the ignition once its running.<br /><br />I believe we can assume (it'd be neat to actually find out) that the previous owner had it set up in the low 5000 range. And it stands to reason that, as you said, he didnt do any decarb.

 

[reeldutch]

Re: Been reading posts on determining the cause before rebuilding

if you rebore cylinders that dont need it , the next time you wil have to rebore will be .030 over or even more depents on the damage.<br />in my v4 i rebored the bottem cylinders .020 over and honed the top ones out.<br />puttet 4 new pistons in.<br />if i damage the top i can still rebore them 0.020 over<br /><br />but i'm not a mechanic<br />just my 2 dollars worth<br /><br />reeldutch

 

[GatorMike]

Re: Been reading posts on determining the cause before rebuilding

I thought of that too reeldutch but I don't think it's that big a deal. The guy at the machine shop was impressed, he had to show it to his helpers. He said we don't see many fresh water engines around here. He did say for a 98 it showed a little more wear than most. He said but due to the depht of the scoreing he would probably have to go .020 over so when we are through it will have 100% life back in it. He looked at the old piston and said "yup definatly a ring hung up". Between him and Dhadley I am pretty confident we have found the cause. I let the guy at the shop order my parts too...one stop shoping what I like.<br />Should get it back with the parts Monday unless this hurricane throws a monkey wrench into my plans. No more questions for now, thanks guys.

 

[GatorMike]

Re: Been reading posts on determining the cause before rebuilding

On second thought I do have a couple of short questions. While I wait on my parts I have a couple of things I plan on doing this weekend. A new waterpump impeller and rebuild the carbs, both I can handle myself. I also may install a tach, this boat doesn't have one and I can certainly use one. Any suggestions on how to install one? I'm sure instructions will come with it. Also since this freshwater motor will become a saltwater motor as soon as I get it running I would like to touch up my wrench marks and flaked off paint from separating parts. I would prefer to use a brush on paint for touch up if possible. What is a good paint to use for this purpose?

 

[GatorMike]

Re: Been reading posts on determining the cause before rebuilding

Got the boat project on hold for a few days thanks to hurricane Charley. Got more pressing issues right now, like removing the tree from my roof. We're staying with friends for a day or two. Hopefuly will be back at home and online a little later in the week. They are telling us one to five days before we can hope for power.

 

[GatorMike]

Re: Been reading posts on determining the cause before rebuilding

Back online thanks to all the good linemen from power companies all over the South. Considering the number of people Charley effected these guys are doing a great job. Picked up my cylinders from the machine shop today and am starting to put it back together. Just put the needle bearings and wrist pins in the first piston and feel realy foolish because I mentioned earlier how much I struggled with that job the last time I rebuilt one of these. The machinist at the shop that bored my cylinders told me how to do it. Seems a little vasoline petroleum jelly spread around the piston rod hole and those needle bearings stick right into position. <br /><br />Now I have a question. In the manual they mention a tool for holding the piston rod cap in place while the screws are tightened. I didn't use such a tool the last time I did this, I was just careful to line up all edges and checked them with my fingernail. Is this tool necessary? I don't plan on using one since I don't have one but if necessary I guess I will find one.