Johnson 115 powerhead swap

[jeepzj94]

I recently bought a boat that came with an 81 johnson 115. It has a melted piston but I'm sure could be rebuilt. However, the guy included another johnson 115 that he got on craigslist that doesn't have a lower on it. He was going to swap the lower from the damaged motor but it wouldn't bolt up on the other johnson. I don't know what year the spare engine is as I cannot find any model info on it anywhere. It is definitely newer than the 81 that is damaged just based on looking at the motor. It has a newer type of ignition system than the 81. My question is what years are interchangeable as far as powerheads?? Can I swap the newer powerhead onto the 81 mid and lower units?

 

[emdsapmgr]

Re: Johnson 115 powerhead swap

Many of these V4 crossflow engines will swap. They used the same powerhead mouting gasket up through 1995. There were a few changes, including the shift mechanism under the lower carb and the mouting for the trim box on the back of the engine. Would be helpful to know what the model number is off the replacement block. There is a quarter-sized casting plug on the top of the block which may have a factory serial/model number on it. ...Post it if you can locate it.

 

[GatorMike]

Re: Johnson 115 powerhead swap

I can't imagine a lower unit not matching up. I have a late 70s model lower unit on my 98 115 and it matched up just fine.

 

[jeepzj94]

Re: Johnson 115 powerhead swap

I'll take some pics of it tonight after I get home from work and post them up for you guys. Maybe that will help. But that silver plug with the serial #'s on it seems to be missing from the spare motor. I know the location its supposed to be in, as it covers a freeze plug on top of the block, but it is missing and all that remains is the freeze plug. Also, did Johnson make a 115 that might have had a smaller mid and lower size?? I haven't personally tried swapping the lower to the spare engine, but the man I bought it all from said he did and that the spare engine mid section was too small and didn't align with the 81's lower. But maybe he was wrong, and I should try it for myself.

 

[Dhadley]

Re: Johnson 115 powerhead swap

The V4s started using the later model gearcases in 78. The 77 140s had them too. The shift was different until 79. A gearcase from 79 and newer will fit the 81. The earlier ones will not bolt up.

Since the lower unit is old enough it will not bolt up we'll assume the powerhead has the old style bolt pattern. The old style will not bolt up to the 81 properly. Powerheads with the newer bolt pattern can be retro fitted to work on the earlier mid sections but not old pattern to new mid section.

 

[jeepzj94]

Re: Johnson 115 powerhead swap

So, sounds like it might be easier and less of a headache to just tear down the 81 and hone the cylinder and replace the ruined piston?? Since it is a complete upper and lower unit. Or, should I try and find out which year the spare is and try to track down a good lower that will fit it?? What do you guys think? And, I will still post some pics tonight of the 2 outboards to help you form opinions lol.

 

[Dhadley]

Re: Johnson 115 powerhead swap

If it were mine I'd rebuild the 81. Once you measure the cylinders you'll know what needs to be bored. (Any cylinder you're going to buy a piston for should be bored)

 

[demon1]

Re: Johnson 115 powerhead swap

you gotta take it apart anyway .I would try to put the newer motor on .that would be a lot cheaper!

 

[jeepzj94]

Re: Johnson 115 powerhead swap

Ok, here are a few pics I took real quick last night. I also took the head off the cylinder that had a melted piston. I expected more damage from what the previous owner had told me. but nonetheless, damage is damage. Also, the more I look over the spare motor, I'm thinking that it is older than the 81. It has a manual choke on the motor, where the 81 has an electronic choke controlled by the ignition switch and key. But I dunno. I've included pics of both engines. the 81 is white, and the other is dark gray. First 2 are of the spare motor. The rest are of the 81 that is already complete and setup for the boat.

Hmm, I wonder if that .030 written on the block means its already had work done once??

 

[G DANE]

Re: Johnson 115 powerhead swap

The 81 115 should have bobble back exhaust. That powerhead is a 85 or 90 HP. All could mean all bored to 0.30 over, but one can never know. Speedmarkers are cheaper than machine work.You can get up to 0.60 over, so no worries. Pouple cheat eachother all the time, sad. Two guys at our marina glad showed me a motor they bought at a good price, an evinrude 140 dark blue from the late eighties, they were told. Dark blue started around 90, and the motor was obviously repainted. Lifted the hood and it had an old green flatback powerhead. Sad people are like that.

That being said, the Johnson looke nice and clean.

 

[emdsapmgr]

Re: Johnson 115 powerhead swap

Looking at the pictures is certainly confusing. The white engine you state is an 81. In 1981, the 90 and 115 were both flatbacks. (The 140 that year was the bubble back model.) However, your white 81 engine has the low compression bathtub heads of a later engine-typical of engines in the mid 80's. You almost got a good picture of the model tag on the top of the engine. The model/year is identified on that round, shiny aluminum disc in your picture. Would be helpful to have you post it. It is possible that it is .030 over. When you pull the pistons, check them. Factory pistons (most mfg'r's) are visibly marked .030 over. You are right, the other engine is at least a 72 or older. You should be able to also find the model number on that same disc on this engine-to help clarify the years. There is not much that will swap between those two powerheads. Also, the powerheads themselves won't interchange.

 

[jeepzj94]

Re: Johnson 115 powerhead swap

Looking at the pictures is certainly confusing. The white engine you state is an 81. In 1981, the 90 and 115 were both flatbacks. (The 140 that year was the bubble back model.) However, your white 81 engine has the low compression bathtub heads of a later engine-typical of engines in the mid 80's. You almost got a good picture of the model tag on the top of the engine. The model/year is identified on that round, shiny aluminum disc in your picture. Would be helpful to have you post it. It is possible that it is .030 over. When you pull the pistons, check them. Factory pistons (most mfg'r's) are visibly marked .030 over. You are right, the other engine is at least a 72 or older. You should be able to also find the model number on that same disc on this engine-to help clarify the years. There is not much that will swap between those two powerheads. Also, the powerheads themselves won't interchange.

Thank you for clarifying if parts or the blocks themselves would be interchangable. That helps a lot. All the numbers match on the white one and the model number is J115TLCIM which is how I found out it was an 81 115. The silver disc and all other identifiable model numbers are missing on the dark gray one. I can't find numbers anywhere on it? Which sucks cause it kind of leaves me stuck as far as what I can/should do with it since I don't even know the year so I could try to find a lower for it. So, just to clarify, If the gray one is indeed a 72 or older, than I cannot strip it down to the block, and swap the block over to the 81 chassis and put all the 81 accessories on it correct? So what I ultimately have is 2 engines that can do nothing to help each other right?? And my options are to repair the cylinder/piston damage on the 81, or find a lower for the gray one?

 

[jeepzj94]

Re: Johnson 115 powerhead swap

Ok, sorry for what might be all dumb questions to some of you, but I've never worked with outboards before. So based on what we know, that the 81 lower will not bolt to the gray one, (the 81 is too big) do you think this lower from this link would work for the gray one?? Also, How is there a for sure way to tell if the original lower from the gray one was electric or manual shift?? There are 2 wire leads I found on the gray one to which I can not find anywhere for them to go, and all the 69-72 lowers that I have found seem to have electric shift. Also, the gray motor does not have what I can find to be any type of lever for a cable to even hook up to for manual shifting?? Again, sorry if this is all redundant but Forums like these are generally good places to pick experienced peoples brains! Thanks guys!

http://cgi.ebay.com/ebaymotors/John...8443603QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear

 

[emdsapmgr]

Re: Johnson 115 powerhead swap

You are correct, there is nothing really that will swap back and forth. The blocks are different, changed when the blocks went from one thermostat to two. Even if they are both 99.6 cubic inch blocks, the rod length and piston pin heights and crank journals are different between many of the older (pre 1973) and newer engines. The lowers are not compatible either. Up through 1972 the lowers were electric shift and require a special control box. The ignitions are different-the newer block has cast supports to hold the timer base and stator. So-you are relegated to overhauling the 81 or: what shape is the older engine in? Getting some of these older V4's going is a job and many parts are no longer avail, but-maybe it's in good shape. Have you checked the compression and spark? I think the 81 has had the heads replaced, perhaps when the prior owner had a powerhead failure and had to bore it to .030 over.

 

[jeepzj94]

Re: Johnson 115 powerhead swap

Yeah, I decided I am just going to rebuild the 81. Its going to cost me a lot to get the older one going as it is missing all of the steering bracketry and brackets to even mount it on the transom. Not to mention the controls I'd have to get to operate the electric shift, and the money spent to even buy the lower for it. So in the end, it'd probably cost more to get that old one ready than to rebuild the powerhead on the 81.

Couple q's on that though....Aside from the machine work I will be doing everything myself. I have plenty of experience with automotive engines, but not the machine work side of things...so in searching for parts for this motor, the biggest pistons I can find are .030. Being that this motor is probably already bored .030, what do I need to look for? Or I suppose it all depends on how much machine work is needed to repair the damage to the cylinder right?

 

[emdsapmgr]

Re: Johnson 115 powerhead swap

OMC only makes factory oversize up to .030 over. If you use up to .030 over pistons, you don't have to rejet the carbs. Other manufacturers make larger oversize pistons. If you go with a larger overbore, I'd watch the plug tips to make sure the new powerhead is not running lean after the overhaul. A machine shop can measure the bore on the block. Even though the pistons are in need of replacement does not mean the bores are bad (out of factory spec.) You might be lucky and need only a hone on all 4 holes, then put new .030 over factory pistons/ringsets back in it. A good marine machine shop can measure the cylinder taper and determine if the bores are oval shaped and out of spec. You need also need to determine the reason for the current failure. Was the timing too far advanced? Was there a restriction in the high speed jets which ran the engine lean? Was the engine running hot-causing a lean condition? Was there water in the fuel tank? Even check to make sure you have the right carbs on the engine....

 

[mamm7215]

Re: Johnson 115 powerhead swap

I'm doing the same as you, just rebuilding an '81 140. Here's a rebuild kit I found you might want to look at if you haven't already...http://cgi.ebay.com/ebaymotors/ws/e...0158025678&viewitem=&sspagename=STRK:MEWAX:IT
And yeah, check the carbs...(thanks emdsapmgr)

 

[G DANE]

Re: Johnson 115 powerhead swap

I stand corrected about the bobble back, sorry. However the drawing in the 81 parts listlooked like a bobble back, I now realize it is the 140 cover that is pictured. The freeze plug solved it.

 

[jeepzj94]

Re: Johnson 115 powerhead swap

Well bad new guys....tore more of the block down today and found the following:

In case the pictures didn't do justice, the rod put 2 nasty holes through the cylinder wall. Luckily I just found a running, complete motor on CL for a good price..gonna go see it tomorrow!