converting a johnny 115hp to a rude 140hp

[cdoliver]

I have a good complete great running motor from a 79' johnny 115hp and a 81' 140hp rude with low compression. Is it possible to take parts off of the 140 and put on the 115 to make it a 140? I'm guessing heads, intake, carbs??? Anything else? Thanks for the input.

 

[tashasdaddy]

Re: converting a johnny 115hp to a rude 140hp

that really sounds like a great way to ruin a good running motor.

 

[Dhadley]

Re: converting a johnny 115hp to a rude 140hp

Yep, everything will swap. Will you see any difference? Yep, if you have a performance hull like an Allison or Hydrostream and are over 6000 rpm. It'll never be like a 140 looper though.

 

[redfish10]

Re: converting a johnny 115hp to a rude 140hp

DHadley you have a PM

 

[cdoliver]

Re: converting a johnny 115hp to a rude 140hp

I have a skeeter wrangler. I paid 200 bucks for the 140 thinking I could do the swap, and maybe gain a little more performance from this old boat and have a little fun turning the wrench at the same time. So you guys think it's a waste of time? could I gain anything from doing this? If not I'll just rebuild this motor and sell it. Thanks for the quick replies.

 

[tashasdaddy]

Re: converting a johnny 115hp to a rude 140hp

i would rebuild it, and try it after the rebuild, rather than possibly screw up a good running motor.

 

[cdoliver]

Re: converting a johnny 115hp to a rude 140hp

maybe that's what I'll do. I also have a 79' 100 hp powerhead that I replaced a piston in (this is the origional powerhead from the 115). Maybe I'll use that powerhead with the rest of the parts from the 140 and make a whole other motor. that powerhead is compatible isn't it? thanks again

 

[mikesea]

Re: converting a johnny 115hp to a rude 140hp

I may be wrong and would like correcting.But,I tought the intake ports and the exhust config.(bubbleback)on the 140 were different

 

[ezeke]

Re: converting a johnny 115hp to a rude 140hp

Most likely the ports are different. You can have them milled. You would want the bubbleback exhaust system.

 

[cdoliver]

Re: converting a johnny 115hp to a rude 140hp

ok here's an update.
we took the heads off of the 140 (it's a '83 not an '81) looking for the damage of the cylinder with low comp. I couldn't find anything of suspect, but the walls were very dry. I sprayed it down with lubricant and let it sit for a while. I'm guessing the carbs need rebuilt. Now all cylinders are at 132psi. So I'm thinking I'll just put the 140 powerhead on my lower unit. My lower unit is from a '79 100hp johnson. Is there anything else I need to change over or will this 140 powerhead bolt right on the 100 LU? the 140 has a broken skeg. Thanks again for the info.

 

[slikciv99]

Re: converting a johnny 115hp to a rude 140hp

Sounds like you are picking up on this rebuilding thing. I'm not sure if there is anything different about the lower units. From my limited exposure to these, i've only notice a few differences, i.e. 1 extra exhaust port and a grease fitting towards the prop. The splines from the shaft and the input box from the powerheads seem to be the same though. All mounting brackets seem to be the same and recomended prop sizing is similar. Makes you wonder though, why someone would say that one cylinder has low compression and you find it not to be true.

 

[ezeke]

Re: converting a johnny 115hp to a rude 140hp

SkegGard would repair the skeg for slightly more than $100. A good aluminum welder could probably do it for less. Some prop shops will repair skegs.

The critical thing when working with your series of motors is that the length of the driveshafts is the same. You have three possible variations, so called 15", 20" or 25".

You also need to know the gear ratios so that you can make sure that the propellers will perform the same.

 

[jimmbo]

Re: converting a johnny 115hp to a rude 140hp

exhaust tube is different. gear ratios are the same

 

[Chinewalker]

Re: converting a johnny 115hp to a rude 140hp

Actually exhaust tubes are the same (#323255). Exhaust manifolds are different, though. The 140 uses a "bubble back" exhaust tuner manifold on the back of the block, while the 115 is a "flat back", like the 85/90. The 115/140blocks both have the same "big" porting, which is larger than that of the 85/90 models. Adding the 140 carbs and exhaust tuner will essentially make the 115 a 140 (also need to knock out some of the webbing between the exhaust cavities). But, as pointed out, unless you really have a high performance rig, you won't notice much of a difference in speed, but you will in fuel consumption.
- Scott