'96 Johnson 115hp FastStrike - rebuild mess-up

[billwpg]

To make a long story jut a bit shorter, I accidently ran my motor low on oil, alarms failed me, caught it quickly but at least some damage was done. So off to the shop to get it rebuilt. Cylinders bored, pistons replaced, new rings, new lower bearings, used crank (not all of these parts were damaged "but while it is apart...." sort of argument. BUT......the another long story....the guy really messed up the rebuild somehow. At least 1 or more cylinders were overbored with the wrong (smaller) pistons use, so it "rattled" VERY bad when returned. Back it went. Now he tells me that they have placed a "sleeve" in the cylinder(s), all is fixed and he is now reassembling. I have lost ALL faith, to say the least. May never enjoy this motor again!<br /><br />Questions:<br />1) Just how concerned should I be about this motor, assuming it was done right this time? Is it badly compromised?<br />2) What questions or concerns should I explore with him before I take it back?<br />3) What is the desired piston clearance? I want to know so I can ask him what he has done then compare with your advise.<br />4) What steps should I take to break it in?<br /><br /><br />Many thanks....this has not bee fun and I have not seen my boat for 9 weeks now

 

[R.Johnson]

Re: '96 Johnson 115hp FastStrike - rebuild mess-up

When reboring, you don't have to do all cylinders, But! I always do. The factory reccomends that you go exact over-size. Let us say that your engine is 3.500 bore size. The OMC piston ( If that is what you use) will be .030 over size, thus, the bore size would be 3.530. If you put a 3.500 piston into a rebored 3.530 hole, (If this is what you say happened) I would expect a lot of scuffing. With possibly more damage, and certainly, the engine would have to be taken apart again. This has been brought up before, but I will say it again. Boring a 2 cycle block, with it's intake, and exhaust ports means an interuptded cut ( chatter) This become's worse on the loop charged engines. You need a good solid set-up, plus a good machinist with the proper tool's to do this. Honing a block is meant to take out the last .002-.003 , not take out deep chatter marks. If you go to a shop that has not done two cycle engines, ( Run! don't walk away)

 

[billwpg]

Re: '96 Johnson 115hp FastStrike - rebuild mess-up

Thanks for the reply....sorry for the delay....I have been traveling.<br /><br />Well it has been a few more weeks and no boat yet. Season is over just about over in any case.<br /><br />Can I get a bit more information or advise on the "sleeve" idea that I have been told they are adding in to the messed up and oversized cylinders to "bring them back to spec"? Any idea what the heck that means, and should I be concerned?<br /><br />From what I understand, when they dissaseembled the head again after the first mess up, the cylinders were in fact scored from the sloppy piston clearance that existed after rebuild #1. Hence the overboring and "sleeve" to bring them back smaller. <br /><br />You mentioned that boring a 2 stroke was tricky. I was told by the boat mechanic that the machine shop he uses does "dozens" a month.....but then how could they screw up so bad? No explanation offered.<br /><br />Thx,<br />Bill

 

[R.Johnson]

Re: '96 Johnson 115hp FastStrike - rebuild mess-up

The problem you have here is one man doing the machine work, another doing the assembly. Where I get confused here, if he put the standard piston, (pistons) in the over-bored holes, Where did he put the over-size pistons. I'm taking for granted we're talking four new pistons here. Those new pistons should have been taken to the shop doing the boring, or come from the shop doing the boring. On a rebuild, common practice is to replace all pistons. If not! trying to save a little money, can cost a lot of money. As for resleaving, this can, and is done. A point not often brought up about boring OMC engines, if you look at the cylinders with the head off, they just kind of hang out in mid-air. There is no support until that cylinder meets the cylinder head. That makes it important that the cylinder block is decked after reboring, and the heads are properly torqued. This last statement will probably bring a response, or someone saying Oh!Oh!

 

[seahorse5]

Re: '96 Johnson 115hp FastStrike - rebuild mess-up

R.Johnson,<br /><br />That 60 degree 115 block is a closed deck design. The cylinders are not hanging out in the open like the old crossflow motors.

 

[Dhadley]

Re: '96 Johnson 115hp FastStrike - rebuild mess-up

Resleeving is a common pratice although a bit expensive. Most likely the shop had the block bored and it ended up at .030 over but the assembler got .020 pistons. Believe it or not, the motor will run but wont idle well at all. And yes, it will be noisy. <br /><br />Perhaps the block was bored to .030 and marked .020. That happens more than you'd think. It really doesnt matter how it happens, the assembler has the responsibility of checking the bore, ring and piston size upon final assembly. Even if it was bored correctly, who's to say the pistons and/or rings are packaged properly? Things happen.<br /><br />Once things are checked and a problem is found then the assembly stops. That wasnt the case here. It does sound as if your assembler is trying to make it right. I'm sure he realizes now this was the reason it didnt idle right.<br /><br />As for the piston clearance, all we look at is the finished bore size (measured with a dial bore gauge at room temp). Its way too difficult to accurately measure a cam-ground, taperd, barrel shaped piston with most standard shop instruments.

 

[billwpg]

Re: '96 Johnson 115hp FastStrike - rebuild mess-up

The feedback and information you guys have provided has been very helpful and educational.<br /><br />I still do not have the motor back, but the season is over so not a big deal....if the extra time helps prevent another screw-up.<br /><br />FYI, I have now confirmed (helped by you) that the machine shop who did the boring also installed the pistons etc and the assembled head was returned to the mechanic for final installation. So one place did it all, as someone suggested was the right approach......... and screwed-up. But that does NOT explain why my boat guy did not pick up the fact that it ran rough abd was VERY noisy.....still no explanation provided and not worth talking about again!<br /><br />All four cylinders were done, to answer one of the questions (some at +0.20 and some at +0.30, it what I understand it).<br /><br />Final question (I think): what should be the clearance between the pistoin and cylinder wall....the mechanic says if is 3-5/1000. You agree?

 

[Dhadley]

Re: '96 Johnson 115hp FastStrike - rebuild mess-up

Dont be too concerned with the actual clearance. Its too difficult to measure a tapered, cam-ground, barrel shaped piston accurately. Expansion rates are different between cast and forged pistons. It also depends on the material make up. <br /><br />Stick with the finished bore size (measured at room temp) of the cylinder that the piston manufacturer recommends. <br /><br />And we're sure they mean .020 and .030. Its really going to be noisy if its bored .20 and .30 over.