The story of two motors - 75 Johnsons

[Moserkr]

Hello everyone! Been hanging out in the starcraft rebuild forum with the mob for most of the last year. Not sure if I put the cart before the horse, but the boats looking good and my motor is having issues….

Link to boat rebuild here: https://forums.iboats.com/threads/1979-starcraft-16’-ss-refresh.740894/

Lets introduce the twins first!

On the boat currently is a 1983 J75TLCTE. She is in rough shape. Back up to the previous owners…. got her a year and a half ago from a friend who drilled two holes in the side of the housing to get to the bolts that hold on the exhaust manifold. She got water into the #3 cylinder and he replaced all those gaskets. #3 cylinder has scaring. Prior to that maintenance is unknown and probably poor. The gas tank she came with was an old rusty 18g tank with a hole. Needless to say her carbs are bad. Also, her threads were stripped on the cylinder head cover for the spark plugs. When I got her, I ordered a full gasket kit for the top and bottom. I swapped the other motors’s cylinder head cover onto her since the spark plugs holes were toast, and i butchered rethreading them…. Replaced all seals in the lower unit except the prop shaft seal (now leaking), put in a new water impeller kit, and changed the lower fluid. So… the good news - the 75tlc does run. She has a lot of trouble starting on the water, more now than when i got her. A guy yesterday said my carbs have a flat spot when firing. On the muffs she fires quick and can idle all day (roughly), she has a little shake. Im also at 4000’ at home and boat at 5000’ elevation. After she runs on the water for a bit though, Im good the rest of the day when shes warm. Runs great at WOT where i normally keep it, unless Im trolling where she will idle rough but all day long (last year at least). Recap: Needs carb rebuild, prop shaft seal replaced. Fuel system is completely new - new fuel/oil, lines, tank, and a water/fuel separator. I use semi-synthetic oil and she seems to like it, smokes a lot less, runs smoother.

Next up is the “twin” sister - a 1978 75 Johnson Stinger - J75ELR78C. This motor was found barely hanging on to the back of the 1968 SS minnow from gilligans island (not literally). A lady was giving away her husbands forgotten project - it was an eyesore in a nice neighborhood in the nevada desert. I drove 2 hours from the CA sierras to the NV desert and picked up the boat to get the motor. Its lower prop shaft had sunk into the dirt it looks like and leaked all the lower fluid out. The rubber inside the cowl covering wires etc looks good, but the cowl seal and any rubber outside was destroyed by the desert sun/heat. I borrowed the cylinder head cover off of it for the other motor so I can see inside the cylinders. They are clean and smooth so thats good news. Also there is zero gas/oil/debris under the cowl. Someone took good care of her until she was put away, and sat outside for at least 3 years until I got her. Now she is sitting on a motor stand in my garage, waiting to be brought back to her former glory.

Now, my thoughts on what to do…. This is the story of 2 motors - the ugly duckling (tlc) and the stinger (elr). Ideally, Id like to get the ugly duckling running enough to keep me on the water while I rebuild the stinger top to bottom. Then swap em, run the stinger while I rebuild the ugly duckling top to bottom.

So where do I start and what tools do I need? Is my fix up, rebuild, swap, rebuild plan smart or do we need more info? I admit that Im not a great mechanic so all the input is appreciated and welcomed. From reading previous threads I know @racerone is going to say “what are your compression numbers?” Well, I do not know…. But i have a tester that just needs the right fitting to check them.

For the ugly duckling, which Ill refer to as UD from now on, current plan is to rebuild the carbs, and replace the prop shaft seal, as well as check compression.

Open to suggestions. Id like to get a manual too for these motors. I believe i need a special tool to help with the removing the prop shaft too. Again, please help!! Thanks everyone. Looking forward to the roller coaster ride of working on old boat motors. Hoping for 2 good runners in the end, but would be happy if that stinger runs great and the UD ends up as a parts motor.

Stinger pics first. Next post UD pics.

 

[Moserkr]

Pics of the UD. Oh yea, i forgot the PO2 was a duck hunter and hit a submerged log with the boat in the sloughs. Ran it over and it hit the skegs/prop of the UD. Broke fins, prop, and did other damage im sure too. The friend I got it from, PO, had our other friend weld up the skegs so they are semi-fixed lol. I usually use a trolling plate on the motor and his welds have held fine. Still has a chunk missing and a crack though…. She was also painted bright green so you can see why the name ugly duckling is appropriate! The cowl is now spray painted white for the time being so I dont have to look at the ugliness…

 

[ct1762@gmail.com]

prop shaft... to replace the seals the prop shaft stays in the gearcase. you yank out the carrier and put new seals and an 0-ring in it. when its out, clean the crap out of the inside of the gearcase so as not to damage the fresh 0-ring when reinstalling. i use a dremel and soft wire wheel.two 5/16-18 (NC) 10'' long screws into the carrier, and a flywheel puller is all thats needed there.
for the exhaust: did you check surfaces with a staitedge? id replace head gaskets, and while the heads are off, replace the pressure relief valve grommets, and of course the t stat and water pumps. then check spark. gotta jump 7/16''-1/2''.

 

[Moserkr]

Thanks @ct1762@gmail.com . The prop shaft seal looks easier than I thought to do - found a good video of it on youtube from “brandon’s garage”. Now just need to acquire the tools for the job.

For the exhaust, I did not do those gaskets, that was the PO. Not sure if he checked with a straight edge but I can ask.

Head gaskets have been changed when I swapped heads from the stinger to the UD. I did not replace the pressure relief valve grommets or t-stat so will look into doing that. Motor seems to be stay plenty cool, ran her hard all last year and she never skipped a beat. Water pump was replaced last year. Never checked a spark before so will add that to the list of tools to acquire.

Any recommendations on proper tools are always welcome. Need to find a good tutorial on carb rebuilds - recommendations welcome there too! Thanks again!

 

[SHSU]

Joining the thread instead of using your rebuild thread

You can test head gasket seal by doing a compression test of all the cylinders. Should be ~120 PSI per cylinder or within 5% of the three. Also to clarify I am not aware of an official PSI standard for these older motors.

Once you clarify Cylinders are still good, then you can test your spark plugs. Use a gap tester to make sure it jumps the 3/8 - 1/2 gap with a bright clean spark.

With that side of the head done, then it comes to carburetor cleaning, which I am guessing you already have kits and such. Make sure to give them a good soak. Also not sure if the jets were adjustable on your model, so make sure you count how many turns in you have to make to they are.

The lower unit, since you are going to be redoing the prop shaft seal, might as well do the other ones as well (Drive Shaft/Shift lever/new oil screw seals). Good time to just replace them in one go.

That is top of mind, if you have other issues then we can go from there.

SHSU

 

[ct1762@gmail.com]

agreed. the driveshaft seal and shift shaft cover seals are in the kit. common places for water to creep in!

 

[Moserkr]

Thanks @SHSU ! When I was at the lake of course someone said I should just buy a new motor…. Not giving up on these 2 for a while lol. I bought the lower seal kit last year and did every seal in the lower except the prop shaft seal…. Newtons law lol. Going to forgo the others since i dont have to drop the lower for the prop shaft seal and they were done last year. Hoping they arent a yearly thing…. I will change the fluid and replace the oil screw seals.

Will stop by napa tomorrow and see if they have the right fitting for my compression tester. Assuming they do, then can check that. Will pick up the spark tester too, as well as a puller for the carrier of the lower so i can do the seals.

It would surprise me if I have good compression numbers within 5% with the scaring in my #3 cylinder. Someone tested the motor back in the day and wrote the compression numbers on the head - they were in the 150-160 range. Ill be happy if they are just close to even. Hope to have some news tomorrow!

 

[Moserkr]

Alright, compression test is done. Numbers are as follow and I repeated each cylinder 3 times, with each cylinder showing 0-1 psi change.

Averages:
#3 - 99 Bottom
#2 - 100 Middle
#1 - 107 Top

So numbers are not great and Im not surprised. The hour meter that came disconnected on the boat read in the thousands, though Im not sure if it was all on this motor. She fired right up when I started her to bring her up to temp before the tests. Idled for around 30 min with the occasional rev every now n then. Ever since I got this motor she has had trouble starting at the lake, but runs strong once going. Starts easy on the muffs in 2 clicks.

Will go get a spark testing kit now. What do you guys think? My thought is the compression numbers are low, and she needs a rebuild. Could be shes just tired or i did not do a good job on the head gaskets that I changed last year when I swapped the cylinder head covers from the stinger to UD. But my goal is to be on the water while I rebuild the stinger. So move on to the next trouble shooting steps? I know the UD will run, and low compression definitely has something to do with her poor starting capabilities. I even warm her up prior to going to the lake to help…

The help is much appreciated. Working on old motors is becoming a lost art and Im stoked to be learning about it with the hope of reaping the rewards on the water. Thanks! Oh yea, im guessing those compression numbers in the pic below were from the factory given that its how high they could come from there, according to some reading I did.

 

[racerone]

I would pull the head now.----Inspection of cylinder walls in needed.

 

[Moserkr]

I would pull the head now.----Inspection of cylinder walls in needed.

Thanks @racerone I can already tell you the #3 cylinder is scored, the top 2 cylinders looked great. I did not take pics of it unfortunately when I pulled the head cover last year. Only ran her for a one week trip after that then the motor was put away until now. Would you still recommend pulling the head then? What are my options already knowing I have a scored cylinder? And in doing so would I need a new gasket since I replaced both last year? Wondering if I need to order one, assuming that keeps the UD alive to hit the water this season. Sorry for all the questions, just learning here. I see your advice on many threads and figured you would chime in when I took compression numbers - took 7 minutes . Thanks.

 

[racerone]

Not sure why folks do not understand.---Scored cylinder means that motor must come apart for repairs.

 

[Moserkr]

Understand that I have zero knowledge of motors. Wasnt raised around them so I ask a lot of questions to understand what Im doing and why. Ive read enough posts to know many people skim over your advice which Im not trying to do. Just learning…. Old man raised me to make money to pay people to fix things. I prefer to do it myself and have to learn the hard way.

Anyway, what do you mean by repairs? I need to know what im looking at cost and time wise, then weigh my options. I have two motors, and parts are interchangeable so could rob peter to pay paul. I could also scrap them and get a new one although id prefer not to. What repairs and how much do they typically run? Can i do them myself with basic tools?

 

[SHSU]

To start, I have never done a cylinder rebuild

That being said, not something I would undertake lightly. You are cracking that case open, getting new cylinder sleeves, honing, fitting new pistons, balancing the drive shaft, etc...

SHSU

 

[flyingscott]

To start, I have never done a cylinder rebuild

That being said, not something I would undertake lightly. You are cracking that case open, getting new cylinder sleeves, honing, fitting new pistons, balancing the drive shaft, etc...

SHSU

Why are you re sleeving? Why are you balancing the crankshaft?

 

[racerone]

When a piston is scored the aluminum material smears and jams piston rings in their grooves.----They can no longer work as a seal.----Now the rings and pistons on a 2 stroke do double duty.-----They control pressure on top in the cylinder and underneath in the crankcase.-----Damaged pistons and rings allow pressure to leak past them.-----So fresh air fuel mix can leak out and combustion gasses can leak into the crankcase.----Piston and ring condition are very , very important in a 2 stroke.----Many novice boat owners today do not understand the concept of 2 stroke engines.-----Many folks do not understand the concept of how mixing gas and oil works in a 2 stroke !!!

 

[racerone]

On more than one occasion have I shown folks damaged pistons and broken piston rings .----Told them the motor needs a rebuild / new pistons.-----People looked at me in disbelief and questioned my opinion / honesty.-----So now I refuse to help folks locally and just chuckle when I hear of folks struggling with simple motors.

 

[flyingscott]

If you knew how easy it was to rebuild those motors you would do it. You could probably rebuild that power head for less than $1000 and it would be new. I dont know why more people don't.

 

[flyingscott]

To start, I have never done a cylinder rebuild

That being said, not something I would undertake lightly. You are cracking that case open, getting new cylinder sleeves, honing, fitting new pistons, balancing the drive shaft, etc...

SHSU

Sorry why are you balancing the driveshaft?

 

[SHSU]

If you knew how easy it was to rebuild those motors you would do it. You could probably rebuild that power head for less than $1000 and it would be new. I dont know why more people don't.

The original thought was to use this motor while he did a tear down of the new one. He doesn't want to use it long term, unless I missed something. So the amount of time, effort, money may not be something he is willing to invest.

Sorry why are you balancing the driveshaft?

Its something that might need to be done. Won't know until he cracks the case.

SHSU

 

[Moserkr]

@SHSU That is correct. Id like to stay on the water for a few months until the end of the season. The ugly duckling is not worth rebuilding - yet. She has so many issues, and the UD would need balancing of some sort the way she shakes too…. Was told that by a guy at the docks who knew a lot more than me. The stinger IS worth rebuilding since I have the head off and she looks great internally, also looks great externally.

Ok, thanks for the information guys. Looks like the powerhead (assuming now thats at minimum the head and pistons) needs a rebuild, and the cost is around $1000. Im guessing more people dont do that because its a lot of money to put into an older motor - a labor of love, not wise spending. Thats a decent down payment on a brand new motor but I get it.

Two motors, two options.
1- Rebuild ugly duckling, cant say I want to polish a turd.
2 - Cannibalize the UD as needed and rebuild the stinger from scratch - more inclined to go with this route.

So… heres the plan. Going to clean the carbs and change the seal/oil of the UD. That should (barely) keep me on the water and it preserves future parts for the stinger. I get it - not great for the UD, but shes called that for a reason. The Stinger is the motor worth building from the ground up and doesnt need a full powerhead rebuild (from the looks of it) - she just needs a revival. Once the stinger is revived, I will look at rebuilding the UD’s powerhead.

My question now is, where do I start with the stinger? I have almost complete gasket kits, minus what ive used, for these motors and the stinger had been sitting in the desert for years. Id be surprised if any of her gaskets are still good. Ill get started on her as soon as the carbs and seal are done on UD. Just dont know where to start. My previous experience with these motors has been bolts break easy and are hard to get out - so tips and tricks to make life easier and not cause bigger issues would be appreciated.

I did borrow the head cover off of the Stinger for the UD so I will find, a hard to find, replacement for the Stinger. Need another anyway to have 2 motors.

Side thought - a guy was selling a boat and trailer with 2 running 75’s and a parts 75 for $1500 obo…. For that powerhead rebuild cost I could have a fleet of motors lol.