?'s on rebuild

[Robert Harris]

Just got my 1980 Johnson 115 powerhead tore down to block.Lucky for me the crank looks good.Just a few questions I need some answers on.<br /><br />1) Had piston meltdown which caused damage to cylinder wall and head.Will be taking to shop to bore all four with new pistons.What has to be done to the intake and exhaust ports if anything? Also what about heads..one was chewed up pretty good from the bad piston.<br /><br />2) Is there really a difference between Wiseco or genuine OMC pistons as far as quality or performance.Will not be running that hard(it's on a bass boat).Is there a way to find out if these pistons are original by the part number on them?<br /><br />3) Crank bearings all look good from what I can tell.Should I replace anyways or just the seals and o-rings?<br /><br />Also, it was recomended by a dealer that I go up one size on my main jet and get the thicker head gasket.Can someone explain this to me?<br /><br />Thanks for the advice.I'm not experienced at all with this outboard stuff, but I'm elbows deep in it now.

 

[ShawnQ]

Re: ?'s on rebuild

I'm jumping out on a limb here...<br /><br />But, when I used to race Karts (2 strokes), we would run a thinner head gasket to raise compression just a notch. I assume that a thicker gasket would lower compression, causing less stress.<br /><br />Also, the bigger jet allows more fuel, thus more oil (if it's a 2 stroke). That means less wear...but also more carbon if the fuel is un-burned.<br /><br />Correct me if I'm wrong, I'm just a youngin'<br /><br />Shawn

 

[Hooty]

Re: ?'s on rebuild

First thing is find out what caused the original melt-down. That's probably why the dealer said to go up in jet size.He thinks the problem was lean running. I would suspect a plugged main jet. Find out for sure.<br />The Wiseco pistons are forged pistons and the stock pistons are cast. I like the Wisecos but the machinist boring your block really has to know his caca or they'll sieze. Consider cast pistons.<br />You shouldn't have to do anything to the ports but be sure when honing after boring not to use a ball hone as this will ding up the edges of the ports. <br />Bearings should all be fine, just replace gaskets, "o"rings, seals, etc. I'd use the stock thin head gaskets.<br />I think that covers all your questions, but if you have anymore, ask away.<br />If you don't have a shop manual for that engine, I'd sure get one.<br /><br />g'luck & c/6<br /><br />Hooty

 

[dpminc]

Re: ?'s on rebuild

Go ahead and run the bearings, if the journals look good, and measure out, the bearings should be fine. Given the age of the o/b, bearings will add cost to the point the overhaul might not be worth it. Wisco pistons are very high quality, and should work well. Keep in mind that the forged wiseco pistons require strict adherance(sp) to warm-up time. The reason for upsizing the main jet, is to richen the mixture, slightly, at WOT. This has a number of effects. First, it helps to lower combustion chamber tempratures. The oxygenates found in modern fuels (ethanol,methanol,mtbe) chemically add oxygen to the combustion process to raise the temps for better emission control in automotive engines. By adding fuel to counter this oxygen, we bring the temps down closer to design temps, and help stave off detonation, the number one cause of two-stroke failure. Secondly, since the lubricant is carried with the fuel,we ar getting a little more oil at WOT as well. <br />The purpose of the thick head gasket is to lower compression, and allow the use of lower octane gasoline(very low). I know these kits have been available for some time, but I question their value(unless buying mexican 84 octane). These thicker gaskets change the "squish area" when the piston is at TDC, and lower compression.However, keeping the squish tight increases intake charge turbulance, which promotes stable combustion(no detonation). You will see a barely noticeable power decrease when using these thick gaskets. <br />You should, also, decrease the timing advance at WOT by 2 degrees.<br />Be sure to check your ring gaps, and wash the bores with hot, soapy,water, not solvent when you get ready to assemble your motor. Also, make sure that your machine shop uses a blind hole tool when boring,as the design of these blocks makes it hard for some boring bars to get to the bottom of the sleeve. Machine shops will sometimes try to cover this up by just blending the uncut area with the hone. This can lead to piston failure, be sure to measure the bore from top to bottom, after it gets back from the machine shop.<br />Oh yeah, use new rod bolts too!<br />Good Luck

 

[Robert Harris]

Re: ?'s on rebuild

Thanks all for the good advice.<br /><br />The only thing I still have a question on is the heads.I'm sure the damaged one will have to be replaced, but do the heads also need to go to the shop for milling or is there enough clearance to seat a .30 over piston.<br /><br />Also, where can I find out if these pistons are stock.I got the part numbers off them. There is a couple set of # on each. 470-99 , 322969.<br /><br />Thanks for the time.

 

[dkondelik]

Re: ?'s on rebuild

Mornin' RH,<br /><br />As to your question Re. p/n on pistons, oem or not. Sorry, not versed on this subject but several on this forum are. Stick around for a while. I'm sure that someone here can respond accurately.<br /><br />To the HEAD. Pitting and dents can and will produce hot spots. This will lead to/cause detination/pre-ignition. THis can be a BIG problem resulting in another rebuild. I haven't seen the head but from the description, play it safe. Replace the head.<br /><br />Good Luck<br />HAVE FUN!

 

[Joe Reeves]

Re: ?'s on rebuild

RH..... As Klondike has stated, replace the damaged head as it will cause pre-ignition due to the many small fragments embedded within it.<br /><br />The cylinder heads would not need any machine work unless they have a warped surface. That can be checked with a straight edge. As you know, the oversize pistons pertain to the diameter, not the height, and they do not come close to contacting the heads so there is no need to machine a head just because of having oversize pistons installed.

 

[clanton]

Re: ?'s on rebuild

The thicker head gasket is based on the fuel you are using. There is a service bulletin with chart that details which engines need thicker head gasket, and which engines need timing change to use 87 octane fuel. Your engine does not appear to need any changes. See SB 2155, SB2159, and seems like should be one more SB, but coulc not find it. The rebuilder should have excess to these bulletins, and they are indexed by subject.

 

[Dhadley]

Re: ?'s on rebuild

When you change the damaged head make sure you get the matching one to your good one. There are many styles of V4 cf heads. The casting number will be one number different from side to side on a cf by 1 number - ie ***502 & ***503 are a set as are ***504 & ***505. The port head will be the lower number. Match to the GOOD head. On older motors the heads may have been changed at some point. I would go with a newer set and avoid all the thick gasket issue. <br /><br />As for the pistons either the OE or Wisecos will work well. The important thing, as stated, find the cause of the problem. A damaged piston is a result - not the cause. Set the rig up to turn 5800 with an average load and it will last for years.<br /><br />Good luck!

 

[Robert Harris]

Re: ?'s on rebuild

I plan on rebuilding carbs and waterpump with new impellar. The problem would have to be either fuel or water , right? If there is any thing else or any ideas I'd appreciate while I got the thing apart.<br />Just a note, the bad piston had both rings broken.I don't know if this was the cause or effect.I have not torn into the carbs or waterpump yet.<br />Thanks for the info on the gasket and jet, but I'm still not getting it.I'll just have to trust the wisdom of the experienced. It just seems to me if you up the size on the jet for more fuel/oil mix plus put on larger head gasket for less compression that you will have unburned fuel mix unless running at WOT. Which is not what I plan on doing.It's just a 16' bass boat.I don't need to be doing 65 mph on the small lakes around here.<br />Thanks for the time.

 

[Dhadley]

Re: ?'s on rebuild

Sounds like coking. Whats the top rpm? In the low 5000 range? What spark plugs? What was the WOT timing set at? What fuel? How old was the fuel? What oil? Is it the starboard piston? <br /><br />Lots of questions, huh?

 

[Robert Harris]

Re: ?'s on rebuild

Those are all very good questions, unfortunately I don't have the answers except I beleive it's the #3 piston. Lookin from back, bottom right.<br /><br />I bought the boat this fall, and paid for what the boat & trailer was worth knowing the motor had problems on one cylinder. So here I am not knowing much of the history. I do know the previous owner was smart enough to shut it down and not run it anymore after the problem because I see no evidence of any more damage to other internal parts. Unless he got lucky and all the bits and fragments went out the exhaust.<br /><br />So, I'll just plan on replacing all the likely culprits of piston damage.<br /><br />Thanks

 

[Dhadley]

Re: ?'s on rebuild

Its very common for starboard pistons to coke up first. #3 piston has the broken rings. I would bet the #1 piston has at least the bottom ring stuck or starting to stick. I would also not be surprised that when the machine shop measures the cylinders you will find they are out of spec for roundness. All this comes from combustion temps being too high. <br /><br />You are on the right track. A rebuild and then on to fine tuning the set up. It'll be fun and very rewarding.<br /><br />Good luck!