Johnson 235

Bign0703 · Sep 15, 2021

Hey guys,
New here and have a question! I recently acquired a 1990 ASTRO bass boat with what I thought to be a 1985 johnson 150 gt. Well turns out it is a 85 johnson 235 under a 150 hood. Didn't check numbers when buying it but I have $75 in everything including gas to go get it. Anyhow after getting it home and doing a compression test the sorrow began! Number 6 cylinder was dead. Pulled the head and the piston top is melted!!! Good news is the cylinder isn't scored at all. Actually looks as good as the other walls with 120 pounds of compression. I work on boats on the side. Usually keep it simple as in I don't tear into power heads! Well after seeing this I figure why not jump into it! So my theory is to atleast replace the one piston and rings and possibly hone that cylinder a little. This is going to be a semi budget build so I know I should tear I completely down and rebuild it but the wife is not going for that cost!!! So if I replace that piston and any other parts needed for that cylinder along with both head gaskets, thermostat, new seals as broke down, rebuild carbs, fuel lines, vacuums ect. Do you think it could be worth it and salvageable? The outside of the entire motor looks amazing for the year! Just wondering if this could work or if I just need to part it out. I've seen the parts go considerably high around my location and super hard to find. So if I do have to let it go I can easily make my money back.

What are your thoughts?

MrGiggles · Sep 15, 2021

Do your best to evaluate the rest of the motor. Power trim work well? Motor and pump sound good, how long will it stay up? How's the lower unit? Clean oil, shifts good?

Got spark on all 6? Does the charging system work? Won't know that unless you've had it running though.

I wouldn't be scared to throw a piston in it, but I wouldn't order any parts until you get it on the bench in pieces. Make sure the lower end and the bore is in good shape before you spend any money. If by chance you find more damage, you're already halfway to parting it out.

I'm sure that I don't need to tell you that a replacement 235hp isn't going to be cheap.

Of course you'll also want to figure out why it hurt the piston on #6, and get it fixed.

wmk0002 · Sep 15, 2021

Is that a normal lower unit for that particular motor? I'm not familiar with the larger HPs but that nose almost looks like some of the low water pickup ones. Probably showing my ignorance here though.

On smaller parts motors I typically keep track of parts and parting out pricing in my head but for something this size I would make a spreadsheet or get a notebook and starting listing out the parts you have with their part number, aesthetic condition, working condition, and avg used price for it off Ebay. Once you get a list of some surefire good parts to sell then make decisions from there. If making money is the goal then I'd probably just go ahead and part it but if you want to actually personally use it you will have to weigh your options. I would probably try to estimate the cost to rebuild assuming you needed to bore and get oversize pistons all the way around and replace all bearings, gaskets, etc while its apart. Then see if the rebuild were to run into a roadblock issue that I would be in less or even than if it gets parted out. It's basically a risk assessment of breaking even parting it out after starting to rebuild with the alternative of the rebuild going well and ending up with a good motor for the rebuild price OR selling it for parts right away and putting that money towards another motor (which introduces a new risk if you try to stay cheap or get a fixer upper).

Pappy · Sep 15, 2021

Stock lower unit with a nose cone added.

Bign0703 · Sep 15, 2021

MrGiggles said:
Do your best to evaluate the rest of the motor. Power trim work well? Motor and pump sound good, how long will it stay up? How's the lower unit? Clean oil, shifts good?

Got spark on all 6? Does the charging system work? Won't know that unless you've had it running though.

I wouldn't be scared to throw a piston in it, but I wouldn't order any parts until you get it on the bench in pieces. Make sure the lower end and the bore is in good shape before you spend any money. If by chance you find more damage, you're already halfway to parting it out.

I'm sure that I don't need to tell you that a replacement 235hp isn't going to be cheap.

Of course you'll also want to figure out why it hurt the piston on #6, and get it fixed.

Your absolutely correct. There is alot of I don't knows so far. I am definitely going to tear it down. I work on boat motors locally and my business has picked up tremendously lately to the entire west tn range, even though it's been just something for fun on the side, and I have never done major jobs like internal motor work on an outboard. I've done alot of small engines like atvs, dirt bikes, motorcycles, and cars and trucks. Just never had a boat to do it to myself until this one. It will be a winter job for sure and I plan to completely disassemble it and make sure the motor needs nothing else. I plan to ohm out everything on it and check resistance to make sure parts are good. My only issue is the wife will not let me do a full rebuild. So if it isn't where I can keep it under 1k or so it will end up parted out. If I can get away with the one piston I am going to try since all other cylinders look great with great compression. The head gasket appeared blown on that one cylinder and I'm not sure if it could have been the carb went down and got it hot and that caused it to blow or if it blew and melted the piston. Lots of its. But if it is capable of being fixed in my budget I am going to try.

If all else fails I've done alot of part outs on boat motors, atvs, and jeeps. I will source out all major components and get a good base value and post it. I parted out my 98 wrangler a couple years ago and ended up making 4,800 off of it and I still have the axles and all suspension. I even gave some of it away when others bought larger items haha. But I just wanted to get others input on it

Bign0703 · Sep 15, 2021

wmk0002 said:
Is that a normal lower unit for that particular motor? I'm not familiar with the larger HPs but that nose almost looks like some of the low water pickup ones. Probably showing my ignorance here though.

On smaller parts motors I typically keep track of parts and parting out pricing in my head but for something this size I would make a spreadsheet or get a notebook and starting listing out the parts you have with their part number, aesthetic condition, working condition, and avg used price for it off Ebay. Once you get a list of some surefire good parts to sell then make decisions from there. If making money is the goal then I'd probably just go ahead and part it but if you want to actually personally use it you will have to weigh your options. I would probably try to estimate the cost to rebuild assuming you needed to bore and get oversize pistons all the way around and replace all bearings, gaskets, etc while its apart. Then see if the rebuild were to run into a roadblock issue that I would be in less or even than if it gets parted out. It's basically a risk assessment of breaking even parting it out after starting to rebuild with the alternative of the rebuild going well and ending up with a good motor for the rebuild price OR selling it for parts right away and putting that money towards another motor (which introduces a new risk if you try to stay cheap or get a fixer upper).

Honestly I'm not real familiar with them either. It appears to be the original from what I can tell and everything works on it flawlessly thus far. Except the running haha