# Merc 402 40hp?



## Texas Prowler (Dec 1, 2015)

How do i find out what year it is? Hasn't been titled yet. Thanks. View attachment 1
View attachment 2


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## lckstckn2smknbrls (Dec 2, 2015)

Your motor looks just like my 1973 402. The serial number will give you the year it was built.


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## Texas Prowler (Dec 2, 2015)

Thanks!

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## onthewater102 (Dec 2, 2015)

https://www.iboats.com/basics/serial_number_year.html


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## Texas Prowler (Dec 2, 2015)

Thanks! Exactly what I needed.

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## Texas Prowler (Dec 2, 2015)

lckstckn2smknbrls said:


> Your motor looks just like my 1973 402. The serial number will give you the year it was built.


Hey would you mind posting some pictures of your 402 so I's can compare mine to yours? Mostly engine pics would help. Mine is missing the controls. Does yours have controls or is it a tiller?

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## Texas Prowler (Dec 5, 2015)

Anyhoo looks like the motor will be getting a rebuild. I figured so once i saw how bad the power wires to the ignition coils were corroded. Bottom cylinder reads 110psi top reads 40psi 60 when wet. I'm looking at the cost of parts vs paying a shop to rebuild the short block. This will set things back but make for a more reliable maiden voyage later...

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## Texas Prowler (Dec 5, 2015)

Would you guys just replace the rings and call it good or go in with more parts?

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## Texas Prowler (Dec 5, 2015)

I'm looking at just rings, honing the cylinder and replacing the needed gaskets. So far looks like it will cost $140 with the service manual from https://www.marineengine.com/parts/mercury-outboard-parts/402/3336258-thru-4117709-usa

If you guys think Img need to get anything else please let me know. I've found a parts motor to get the controls and steering from and other parts as well.

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## lckstckn2smknbrls (Dec 5, 2015)

Texas Prowler said:


> lckstckn2smknbrls said:
> 
> 
> > Your motor looks just like my 1973 402. The serial number will give you the year it was built.
> ...



It uses remote controls.
I can't do pictures at this time.


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## Texas Prowler (Dec 5, 2015)

Yea mine does to. I found a parts motor with controls that I can put on mine. This thanks though

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## Texas Prowler (Dec 5, 2015)

Pappy can you give me some advice please? Thanks!

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## Texas Prowler (Dec 7, 2015)

Anyhoo no help needed... I'll just start reading this manual and dive into rebuilding the outboard. Guess no one rebuilds motors around here.

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## JMichael (Dec 7, 2015)

Texas Prowler said:


> Guess no one rebuilds motors around here.
> 
> Sent from the dust in front of you!


There just aren't many of them that work on or have mercs. If you can't get the answers you need on a mercury here, you might want to try asking the mercury guys over at Iboats. https://forums.iboats.com/forum/engine-repair-and-maintenance/mercury-mariner-outboards


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## Texas Prowler (Dec 7, 2015)

Thanks man.

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## onthewater102 (Dec 7, 2015)

Sorry - the work you're getting into involves a machine shop unless you have the tooling yourself - which I do not. Living in CT once you get a professional involved in a project the cost skyrockets to the point it's likely not viable from a financial perspective. It's just easier to find a lazy idiot with a dirty carb that wants to sell his "non-running" motor for $50 than it is to dump that kind of time into a motor.

Power to you though, if you go that route you'll have a motor that you know inside & out which should be bullet proof for a long, long time.


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## Texas Prowler (Dec 7, 2015)

Yep reliable is what I'm going for I have a service manual and I've read through it. Guys I'm really into rebuilding things auto engines, electrical, hvac, plumbing, so I feel this would not be to difficult to take it apart and rebuild. I'm thinking of having a shop clean,bore and clearance the piston bores. This way I'll have a solid foundation to build from. This will also give me a better idea of what size pistons and rings to buy. I'm positive that I can rebuild this motor.

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## Texas Prowler (Dec 7, 2015)

Just found a shop (Texas Machine Works) that will bore the cylinders for $45 a piece. Not bad at all. He even offered to supply the parts if need be. I'll start tearing down the motor this weekend after buying some big Ziploc bags. Since he is going to bore the cylinders over I'll have to get a complete power head rebuild kit. I've found one on https://www.maxrules.com/fixphead_merc.html#mmu40

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## onthewater102 (Dec 7, 2015)

Are you sure this is worth it though? Why this motor? 

Points I see against it:

1.) It's a crank-rated 40hp motor, meaning it makes less power at the prop than a more modern 40hp motor whose power output is measured at the prop.
2.) Its age - maintenance parts will become scarce for it at some point
3.) Total cost to build it up - if you're going deep into the motor you should be putting more than $140 into it - you should be replacing the bearings & seals & just about anything else that moves so that you get the end result you're after - an engine with as close to brand-new reliability as possible.
4.) Value when you're done - what will the realistic sale value of that motor be? I'm willing to guess it won't be more than $500 which is likely below your total project cost by the time you're done.

Points for it:

1.) You own the motor already
2.) ???


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## Texas Prowler (Dec 7, 2015)

1.) I just want to get out on the water and have fun. Buying a newer motor just cause the prop hp isn't justifiable in my case.
2.) maintenance parts will be bought along the way little bit by little.
3.) The total cost has gone up because I've found a complete rebuild kit for $308. So motor$125, shop machine work $90, paint $30 for a total cost of $553 so far which could go up. I'm willing to pay that for a reliable motor that I can say I know what's going on internally.
4.) I'm not really concerned with the value because I don't plan on selling the motor as it will stay in the family.
Thanks for your input and please don't take what I've said negatively.

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## onthewater102 (Dec 7, 2015)

Not at all - I've just found myself too far down the rabbit's hole to get out without realizing it on far too many a project not to ask the questions I wish others around had prodded me with.


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## Texas Prowler (Dec 7, 2015)

Thanks for asking me those questions. I'm just glad to have some feed back on this.

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## Texas Prowler (Dec 8, 2015)

I figured I'd try to fire the motor before i tore it down and couldn't get any spark. I cut back the wires on the stator and found more corroded wires. Looks like I'll be buying another stator... One more step to reliability. Looks like i might just have more time off the water with this tin than i thought. All i have that works is a 4hp merc And I know that wouldn't push the tin without struggling.

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## JMichael (Dec 9, 2015)

I know you've already stated you didn't intend on selling it so care so much what it's worth when you're done. But FYI, I cleaned up, tuned up, and painted this 20 horse of the same vintage and then sold it for $650. With yours being a 40horse, and all that work done to it, I can't imagine it not being worth quite a bit more than what my 20 was.


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## Texas Prowler (Dec 9, 2015)

That 200 looks good man! Im all about reliability. I'm going to do mine in a red and black two tone. It should look real nice once finished.

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## Texas Prowler (Dec 15, 2015)

Little by little it's coming apart... I've already broke one exhaust bolt last week. Sucks...



View attachment 1


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## JMichael (Dec 16, 2015)

Yea, those pics are looking familiar. 





:lol:


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## Texas Prowler (Dec 16, 2015)

Yep that's what mine will look like soon enough lol.

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## nowgrn4 (Dec 16, 2015)

I assume the gasket set has new top and bottom crank seals?


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## Texas Prowler (Dec 16, 2015)

Yep any seal needed is provided in the kit. Needle bearings and all. 

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## Texas Prowler (Dec 17, 2015)

And let the scoring begin...


























What do you guys think about the scoring?

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## onthewater102 (Dec 18, 2015)

Just confirmation of what you already knew - compression loss. once you pull the pistons and can take measurements of how deep they run you'll be able to figure if honing/re boring is still an option.


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## Texas Prowler (Dec 18, 2015)

Yep. I should have it taken down completely this weekend.

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## onthewater102 (Dec 21, 2015)

The scoring was in the cylinder with the lost compression right? At least it lined up with the port opening so you could see it and confirm that as the cause & not that something warped from over heating.


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## Texas Prowler (Dec 21, 2015)

True. I didn't think about it like that. It does look like some trash made its way into the engine.

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## onthewater102 (Dec 21, 2015)

You did check the lower unit right? Oil is nice & clean & it shifts into fwd gear cleanly & into reverse? Now that you've got it off the powerhead you should be able to tell that the gears turn cleanly too.


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## Texas Prowler (Dec 21, 2015)

Yep the lower end is in great shape. Forward neutral and reverse work smoothly oils good as well.

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## wmk0002 (Dec 22, 2015)

I'm late to this thread, but I rebuilt my 70hp Force this past summer. It's a 3 cylinder and the machine shop charged me $160 to bore/hone all cylinders plus they pressed out my wrist pins for me and pressed on the upper main bearing on the crank. I think the press work was only $10 and the machine work was $50/cylinder. So for a two cylinder you may be looking at $100 from your local machine shop.

Also, I bought my rebuild kit from https://www.powerheadkit.com/mercury-mariner.htm. They have good customer service and it seemed to be a great deal once you start pricing all of the individual parts off of parts websites.


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## Texas Prowler (Dec 22, 2015)

wmk0002 said:


> I'm late to this thread, but I rebuilt my 70hp Force this past summer. It's a 3 cylinder and the machine shop charged me $160 to bore/hone all cylinders plus they pressed out my wrist pins for me and pressed on the upper main bearing on the crank. I think the press work was only $10 and the machine work was $50/cylinder. So for a two cylinder you may be looking at $100 from your local machine shop.
> 
> Also, I bought my rebuild kit from https://www.powerheadkit.com/mercury-mariner.htm. They have good customer service and it seemed to be a great deal once you start pricing all of the individual parts off of parts websites.


Hey your not too late. Thanks for the heads up on the parts source. They seem to have more parts for less $$$. I'll give them a call to see what's in the kit compared to the other site I was considering. How was the quality of the parts? 

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## wmk0002 (Dec 22, 2015)

Texas Prowler said:


> wmk0002 said:
> 
> 
> > I'm late to this thread, but I rebuilt my 70hp Force this past summer. It's a 3 cylinder and the machine shop charged me $160 to bore/hone all cylinders plus they pressed out my wrist pins for me and pressed on the upper main bearing on the crank. I think the press work was only $10 and the machine work was $50/cylinder. So for a two cylinder you may be looking at $100 from your local machine shop.
> ...



I was satisfied with everything it came with. The pistons were Vertex brand which are good quality. I know you can upgrade to Weisco too if you want. Some of the gaskets seemed a little thin but the main ones (the head, exhaust, and spacer plate gaskets) were up to OEM standards.


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## Texas Prowler (Dec 22, 2015)

Awesome thanks! Anyone know if there is a benefit of running forged pistons in a outboard?

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## Texas Prowler (Dec 26, 2015)

Ugh!!! So neither cylinder has any scoring. Both are smooth as silk. BUT the bottom cylinder has dimples in it...ugh! Should i be worried? See pics.









If you remember the top piston had scoring and low compression. The bottom had 120psi.

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## Texas Prowler (Dec 26, 2015)

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## Texas Prowler (Dec 28, 2015)

Well I spoke with my outboard shop and he says he can repair the damage by welding and smoothing it back to shape. I'll go that route if the block doesn't need sleeves.

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## onthewater102 (Dec 28, 2015)

Detonation damage.


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## Texas Prowler (Dec 28, 2015)

Yep the wot timing looked like it had been tampered with by the P.O. I figure since the top cylinder was not firing the po tried to advance the timing thinking it would help. But it just messed things up bad. 

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## onthewater102 (Dec 29, 2015)

Odd that it occurs in one cylinder and not the other.


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## Texas Prowler (Dec 29, 2015)

The other cylinder wasn't firing. At least that's what the plugs look like.

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## onthewater102 (Dec 29, 2015)

Sounds like you've got an electrical issue there too - did that motor have a switchbox on it or was it earlier than that?


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## Texas Prowler (Dec 29, 2015)

Oh yea the stator is toast. I'll take pics when I get home. The wires were toast. Both ignition coils check out good. But the wiring to them was also toast hints the no firing ugh. I'll be so happy once this thing is fixed up

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## Texas Prowler (Dec 29, 2015)

This is what I found under electricians tape. The ignition coil wires were the same.

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## onthewater102 (Dec 30, 2015)

A clue!


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## Texas Prowler (Dec 30, 2015)

[emoji17] 

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## onthewater102 (Jan 5, 2016)

Any progress? Or did the electrical issues put the financial nail in the coffin on this project?

https://www.boats.net/parts/search/Merc/Mercury/1973/1402223/FLYWHEEL%2C%20IGNITION%20COIL%20AND%20SWITCH%20BOX/parts.html

is that your motor? if so there is a stator listed as part #5255 in the diagram as component #9 which appears to be miss-listed for $7.29.


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## Texas Prowler (Jan 5, 2016)

Yea this merc has it me beat. The reed block is trashed which means it needs upper and lower bearings, stator cheapest i found is 168 before ship. Shop fees $150, power head rebuild kit 300... I'm gonna just trash this one and find me an OMC of some sort. I could replace all those things and still not have a reliable motor...ugh

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## DaleH (Jan 5, 2016)

Texas Prowler said:


> Yea this merc has it me beat. The reed block is trashed which means it needs upper and lower bearings, stator cheapest i found is 168 before ship. Shop fees $150, power head rebuild kit 300... I'm gonna just trash this one and find me an OMC of some sort. I could replace all those things and still not have a reliable motor...ugh


Ouch ... sorry to hear that ...


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## Texas Prowler (Jan 5, 2016)

No worries man... Just more time off the water and more time to paint the boat. 

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## Texas Prowler (Jan 5, 2016)

Lesson learned...

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