1978 John/Evinrude crankshaft difference

duckmn56

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Hello,

I am still working on the same project I was a while ago. Anyway update from last time. Found out the old engine was shot. Low comp and pistons and cylinders were in bad shape.

I ended up buying a replacement which I thought would be a drop in... Anyway the fun has started now. It looks like the replacement motor is actually model# 25852C, a 25 hp model, and the old one was model#35R78R, 35 hp. I have done quite a bit of research and everything shows these a nearly identical... I have also heard the hp difference is due to the carb?

Anyway I ran into a bit of a problem last night. The crank shaft splines are different. The original motor has many more splines and a larger diameter. Not sure but maybe around 9 or so splines. Whereas the replacement, the 25 hp, has a smaller diameter and less splines maybe 3 or 4.

I see from boats.net and other parts websites that there was an old crankshaft that was obsoleted. Obsoleted was # 0323000, and the replacement is 0323533. Does anyone know if this accounts for the differences I am seeing between the two shafts?

I noticed the lower units between the two motors are different and the drive shafts are also different. Not sure what all the differences are.

Would swapping a drive shaft or lower unit be a possibility? I would rather swap the cranks if I can since I have all the parts, and do not need to put more money into this project. What is the best path forward?
 

SparkieBoat

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ok both of your motors are 1978. your motors may look similar but you probably have the larger gearcase on your 35. I would recommend getting another 35 that would fit. you can cross reference part numbers at most boat parts sites. like boats dot net or the evinrude/johnson site. I cannot tell you for sure but swapping the cranks may be an option, my guess is that drive shaft spline may be the only difference between the 2 cranks. you could pull them both out and measure them to make sure. but if you were going to do that you could have just honed out your 35 and put in new rings unless you warpped the cylinder holes from over heat. or if they have heavy grooves or something. you can cross reference the connecting rods between the 2 motors, they are probably the same, you could also cross reference the bearings and seals, probably all the same. but just so you know there are porting and exhaust differences between the 35 and 25, it is not just the carbs. you can put your 35 carbs on that 25 but you will probably just hurt your gas mileage and not boost your HP much at all. I think your 25 pistons will work in your 35. is the 35 block too far gone?
 
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duckmn56

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Thank you for the reply. Almost every part of me wants to write a sarcastic smart ass response to most of what you have said. I am trying to resist that, because I do appreciate the effort. I was hoping for specific answers. Not just guesses and assumptions.

I have already cross referenced the parts numbers as I had previously stated. Both crankshafts were used in both the 25 hp and 35 hp motor. One was obsoleted and replaced with the other PN. I wish I could confirm the only difference was the spline. If anyone has any pictures of either PN it would be most helpful.

Additionally I have confirmed every part in the piston/crankshaft assembly is the same. I am not too worried about the crankshaft interchangeability. They seem fine.

As far as the gearcase goes yes the 35 hp is larger, and the two assemblies do not share drive shafts. What is confusing to me is that even though the crankshaft changed, a PN was obsoleted, and replaced with a new PN. The drive shaft does not have an obsoleted PN or a new one. This would have had to change as well to accommodate the different spline coupling. I guess I should have asked if anyone can confirm the drive shaft is different now. Has a square instead of 12 tooth spline. Also I was curious how much work it would be to swap drive shafts. As in remove old and buy a new one and replace. With the correct coupling design, but a shaft made for the 35 hp setup.

Not sure what you're talking about for porting being different. I mean I see the exhaust manifold was different, but I do not know if that affects the engine or if they're different because of the lower unit design. However, I can see the exhaust ports are both the same. Cant see the intake well, but they look the same too. Pistons and displacement are the same... It appears everything is the same on both motors. Well there is a vacuum line that is different on the reed valve cover, but if that causes me problems I can drill and tap the other location. Do you know if your statement is accurate, or is it another thing you are guessing on?

Looks like I am moving forward with the crankshaft swap.

The 25hp motor was bought to avoid rebuilding the engine. The 35 cylinder wall probably could have been machined, but I wanted to get back on the water faster. This should have been a drop in replacement, but it appears there was a mid-year change to the crankshaft design. Now I am $275 into the 25hp motor. Its not like these things grow on trees and I have not been able to find a 35 hp motor I wanted.
 

gm280

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According to a boat site I just went to, to see the part numbers, both the '78 Johnson 25 HP and 35 HP engines use the exact same crankshafts with a part number of 0323000. However that part number is now obsolete and the other part number is 0323293 for either of those HP engines. And the Evinrudes uses the same part number crankshafts for the same HP engines as well. Don't know where you got the 0323533 part number from... I also seen a few listed on EBay as used for around $45 dollars with the part number 0323293... Hope that helps some....
 

F_R

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The way I see it, the 25hp and 35hp motors use different lower units, the 25 having the old split case unit. That would explain the 4-spline drive shaft in the 25.

The crankshaft numbers I come up with are 323293 for the 25 and 323000>327591 or 328212>328376 for the 35. I haven't figured out the reason for the changes yet.

EDIT: It seems the original question is can you put a 35hp shaft in a 25hp powerhead. It looks like you have done your homework on that, concerning mating with other parts. If everything else truly is the same, it should be a go. But I still don't know the reason for 4 different shafts in a 35. Looks like ordering one might be a crap shoot.
 
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SparkieBoat

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I was just trying to be helpful. I am sorry that I cannot answer your questions more specifically. I am fairly positive about the porting being different, I know with all the other motors I have messed with they are. I mostly deal with v4 and v6s. but I do have a 40 and a 35, I just have never torn the motors down or tried any parts swappping. So I tried to help. sorry I do not know everything. but if it were me, I would try to rebuild the 35 if the cylinder walls are honeable. the 25 pistons would work if your pistons are bad. I mean changing the crankshaft is tearing your motor down anyway. Just take it all apart and see what you got. that would be the thing to do.
 

duckmn56

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WOW thanks for all the information guys.

I guess I was snappy because I am frustrated with this project. I appreciate the help and don't mean to discourage your response. I just prefer they are correct if I am going to use them to make decisions. Not based on conjecture. The way you wrote your statements I had a hard time evaluating your knowledge.

gm, I must have messed up a PN, when I was typing this I was looking through lots of pages and diagrams.

I am seeing the 323000>0323293 for both the 25 hp (25852C) and the 35 hp (35RL78R).

I will let you all know how it goes. No plans on going to a dyno tho, so well see. I guess if a 25hp motor is better than a malfunctioning 35hp we will be fine. Old motor was going out all of last year.
 

SparkieBoat

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sure. I just wanted you to understand that putting 35 hp carbs on a 25 will not make it a 35. If you want to keep the extra 10 HP then you should rebuild the 35, if you are going to be removing the crank shaft, you have already torn the motor apart and can evaluate the cylinder condition. the pistons and rings from the 25 may work and save you some money. If you just need honing and new rings rebuilding your 35 would be the better option if the extra HP means anything to you. If it does not then I guess you could swap the crankshafts, but that is a lot of work and some expense in gaskets and seals. IF the midsection is the same for both gearcases, you may could find the smaller gearcase shaft and that might be easier and cheaper, but I am not sure if the midsections are the same. or possibly the drive shafts are interchangeable. I just am guessing at these last 2 options, but I would at least look into it before I went tearing a engine apart.
 

ttankmoran

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Im pretty positive there is not any porting differences between the 25 and 35 hp engines. The extra power lies in the intake manifold and carburetor. Feel free to look more into it if you like but many have performed the 25-35 hp mod.

You have the engines side by side by the sound of it, take the intake manifold off (between carb and reeds) you'll see the bore is noticeably different along with the bore of the carb.
 

duckmn56

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  1. Its in! No issues at all. Used old crankshaft in new/old motor. Pics to come some time.
I have to get new gaskets for the reeds and intake cover. However, I wanted to note ttankmoran that the intake manifold is exactly the same on both of these. I dont have the old carb to compare. Hope to have it running soon.
 

SparkieBoat

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I am glad that it worked out. I thought that he said the intakes were different. but you had it in your hand, so you would know. good luck and thanks for posting your results. this could help someone else in the future.
 

SparkieBoat

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that is great. I know that a lot of guys have tried that with larger v4 and v6 motors and found out that there are porting and other block, intake and exhaust differences. I guess with such a small motor they just used a smaller carb to reduce HP. Have you got it running yet? I hope it works out well for you.
 

duckmn56

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It runs!
Well kind of. Currently it is misfiring at high rpm..

Checked plugs and for some reason I set them at .030. Set to .040 per the repair manual.

That seemed to help but still missing sometimes. Manual says to adjust spark advance. Going to try that next.
 

duckmn56

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Hmm there is a wire with a small nick in the insulation. I was hoping it wasn't deep enough. Maybe I'll just get new wires for the heck of it.

Could I just tape the nick with electrical tape though to test the theory?
 

SparkieBoat

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yes electrical tape will work fine. also you could try it with the cowl off and see if that makes a difference.
 

duckmn56

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Thanks for the help so far guys.

So I took it out on the water to test under load. It ran great for about a half hour. Then at full throttle the motor bogged down. I reduced to idle and it died. I re-started after a couple minutes and tried adjusting the carb. It ran great for another 15-20 minutes when it started to bog again slightly. I knew what to expect and so I reduced throttle to idle. After a minute or so of idle it died.

I felt the motor to check for overheating and I was able to touch without issue. It was warm but not boiling hot or anything. I noticed the water was kind of sputtering out at idle and a low pressure stream with any amount of throttle. Didnt notice a big difference from 1/2-full throttle in terms of output though. Looking at videos online I was expecting the amount of water at idle that I get at full throttle.

I am suspecting the water impeller or something is going wrong with the cooling system. I am thinking my bogging issue was related to overheating? Any ideas?

I also need a new prop the old one has some dings and rolled metal on the edges of the blades. Maybe the motor had to work too hard or the prop was out of balance?

Thought and opinions welcome!
 
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SparkieBoat

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Well you need to change that out for sure. I run dinged up props on my smaller motors a lot, so long as they are not too out of balance and shaking my gearcase. I also installed an overheat alarm on my 35. sometimes if you wait until the motor starts acting up it is too late. you might want to do another compression check on the cylinders to make sure you didnt get warpage.
 
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