Mark 55 project

Mercury Outboard general discussion
Zetta
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Mark 55 project

Post by Zetta »

Hi everyone, I’m new to the forum and have been lucky enough to have a friend ask me for help with her Mark 55. A local shop told her that there is no spark but before I tackle that I discovered a blown lower unit. I’ll add pictures but it looks like the engine wasn’t winterized at some point and the outer bearing and seal seats are cracked. Can the lower unit be welded and milled or is there somewhere that I can purchase a new lower unit? After that I will have to check out the internal components.

Thanks in advance for everything I expect to learn from this group.
Attachments
Mark 55 cracked lower unit
Mark 55 cracked lower unit
Mark 55 cracked lower unit
Mark 55 cracked lower unit
dave bernard
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Re: Mark 55 project

Post by dave bernard »

I have a long shaft lower for that. the spark should just be cleaning the mag. 914 310 7086
Zetta
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Re: Mark 55 project

Post by Zetta »

Sorry for the slow reply and also for my ignorance on this engine. My lower unit appears to be about 14” from where it would detach to the bottom of the skag, does that make it a long shaft or how would I tell? Thx
ctpdsr
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Re: Mark 55 project

Post by ctpdsr »

I recommend calling Dave B. as noted above.

With regard to shaft length, once you pull the case, the driveshaft for a MK55 Short Shaft service motor will measure about 17".

Chuck
IMG_2137.jpg
dave bernard
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Re: Mark 55 project

Post by dave bernard »

POST A Pic OF THE MOTOR I can tell from the Pic
Zetta
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Re: Mark 55 project

Post by Zetta »

Hopefully the photo will come thru. I’m assuming it is a short shaft but we all know how that can work out so please give me your opinion. Thank you.
IMG_5203.jpeg
Attachments
IMG_5169.jpeg
dave bernard
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Re: Mark 55 project

Post by dave bernard »

YES, Short shaft. If you can't find a SS lower, you can put the SS drive shaft in the long shaft lower. 914 310 7086
Michael
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Re: Mark 55 project

Post by Michael »

Zetta wrote: Sat Jan 27, 2024 2:29 am Hopefully the photo will come thru. I’m assuming it is a short shaft but we all know how that can work out so please give me your opinion. Thank you.

IMG_5203.jpeg
check your email.... I located a short shaft and long shaft....I was told they are both operational , shafts spin and shifts

I havent seen them but was told to assume they need a rebuild kit with seals
Zetta
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Re: Mark 55 project

Post by Zetta »

Thank you Michael, r u referring to the email u sent me on Tuesday?

Any thoughts on where I should go for a lower unit rebuild kit? As I stated this isn’t my engine so I need to gather all costs and get them approved by the owner before I can spend.
Michael
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Re: Mark 55 project

Post by Michael »

Zetta wrote: Sun Jan 28, 2024 2:28 am Thank you Michael, r u referring to the email u sent me on Tuesday?

Any thoughts on where I should go for a lower unit rebuild kit? As I stated this isn’t my engine so I need to gather all costs and get them approved by the owner before I can spend.
lower unit parts
https://www.oldmercs.com/category_s/683.htm
Zetta
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Re: Mark 55 project

Post by Zetta »

I decided to check out more of this engine while I wait for the new lower unit and I arrive. I pulled the plugs to check for spark and compression. Spark is good on all 4 cylinders which surprised me because the owner was told there was no spark?? From just a quick pull on the starter rope compression appears good on cylinders 2 and 3 but I have to get an angled adapter for my compression gauge before testing cylinders 1 and 4 because they are tucked in behind some of the housings. I’m feeling good about the internals of the engine but I do have some concerns about the condition of the spark plugs. This engine is pretty but has not been well cared for and didn’t run at all last year. I don’t know when it was last tuned but please take a look at the spark plug pictures and let me know if you think there could be an internal water leak causing the condition of plugs 3 & 4 or if this is just the effect of running an ethanol mix fuel. Thank you 194132.jpeg[/attachment]
Spark plug #3
Spark plug #3
Spark plug #4
Spark plug #4
I’m holding the spark plugs in sequence with #1 on the left
I’m holding the spark plugs in sequence with #1 on the left
dave bernard
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Re: Mark 55 project

Post by dave bernard »

Possible bad bottom seal.
Zetta
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Re: Mark 55 project

Post by Zetta »

Not sure if this is related but the upper drive shaft spline was rusty when I dropped the lower unit.
dave bernard
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Re: Mark 55 project

Post by dave bernard »

No not related.
mercaholic
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Re: Mark 55 project

Post by mercaholic »

Zetta wrote: Wed Feb 07, 2024 2:17 am I decided to check out more of this engine while I wait for the new lower unit and I arrive. I pulled the plugs to check for spark and compression. Spark is good on all 4 cylinders which surprised me because the owner was told there was no spark?? From just a quick pull on the starter rope compression appears good on cylinders 2 and 3 but I have to get an angled adapter for my compression gauge before testing cylinders 1 and 4 because they are tucked in behind some of the housings. I’m feeling good about the internals of the engine but I do have some concerns about the condition of the spark plugs. This engine is pretty but has not been well cared for and didn’t run at all last year. I don’t know when it was last tuned but please take a look at the spark plug pictures and let me know if you think there could be an internal water leak causing the condition of plugs 3 & 4 or if this is just the effect of running an ethanol mix fuel. Thank you 194132.jpeg[/attachment] IMG_2024-02-06-194249.jpegIMG_2024-02-06-194314.jpegIMG_2024-02-06-194132.jpeg
Looks like moisture got into the engine. Best to spin the engine with lots of WD40 or a strong oil/gas mix thru the carbs before taking compression tests.

Also, those are the wrong plugs for that motor. Best to replace with conventional NGK's suitable for the ignition when it comes time to start it.
CANADA
KD4, Mk5, Mk6, Mk15, Mk20, Mk25, Mk28, Mk30, KE7, KF7, KG7, KG4, KH7, Merc 200, Merc 250, Merc 300, Merc 500, KG4Q, KG4H, KG7Q, KG7H, Mk20H
Zetta
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Re: Mark 55 project

Post by Zetta »

What are the correct NGK plugs for this Mark 55?

Also, how involved is it to replace the lower crankshaft seal?
dave bernard
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Re: Mark 55 project

Post by dave bernard »

equivalent to champion J6J
ctpdsr
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Re: Mark 55 project

Post by ctpdsr »

NGK B6-S is the equivalent to a Champion J6J, but recently discontinued. If you can find some NOS, buy them. Denso W20S-U is currently available. The plugs you have are way wrong, intended for a newer style ignition system, and must be replaced.

viewtopic.php?t=21603

Be careful with a 1957 powerhead with repainted cowls. Might have been restored internally? Maybe not. Take a look at the attached thread regarding a rebuild of a very similar motor. Photos of your friend's powerhead minus the cowl wrap would help.

Chuck
Zetta
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Re: Mark 55 project

Post by Zetta »

Thanks for the heads up Chuck. I’m playing snowbird for a few more weeks but will be digging into as soon as I get home.
Zetta
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Re: Mark 55 project

Post by Zetta »

I’m finally back to the Mark 55 Project.

Chuck, I’ve included a couple of pics of the power head and based on the apparent age, I doubt any upgrades have been applied but I look forward to your opinion.

It is time to dig into the bottom crank seal. Does anyone know of a video or have advice on how to accomplish that before I just start after it all fat, dumb and happy?
Attachments
IMG_5399.jpeg
IMG_2024-04-02-105852.jpeg
Zetta
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Re: Mark 55 project

Post by Zetta »

Can anyone share with me how a Mark 55 power head is attached to the lower cowling and driveshaft cover? I’m trying to remove the power head so I can get to the bottom crankcase seal. Thanks in advance.
dave bernard
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Re: Mark 55 project

Post by dave bernard »

under the bottom cowl are 8 nuts 4 on each side. just to start.
1 914 310 7086 Dave.
Zetta
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Re: Mark 55 project

Post by Zetta »

Thank you. I had loosened those but didn’t want to put too much pressure on separating the two halves until I asked. It just took a little prying to get thru the gasket adhesion. Now it’s into the bottom crank seal and bearing. Whoo hoo, progress!
Zetta
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Re: Mark 55 project

Post by Zetta »

Turns out it was a great idea to pull the bottom crankcase end cap. The bearing still spins but clickity clacks like an old freight train and the inner seal was so stiff the rubber cracked when I removed it.

Any thoughts on a good source for these parts and the many others I expect to need soon?
Michael
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Re: Mark 55 project

Post by Michael »

you can get the gaskets and seals here and source the bearings thru the bearing numbers
https://www.oldmercs.com/category_s/670.htm
Tom Brockmeyer
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Re: Mark 55 project

Post by Tom Brockmeyer »

Zetta wrote: Wed Apr 03, 2024 11:49 pmAny thoughts on a good source for these parts and the many others I expect to need soon?
If you read a few of member ctpdsr engine build threads, he hands out the bearing & seal part numbers left & right... Here are a ton of engine rebuild threads and comments from Chuck ( ctpdsr ) and by the time you read them all, you can rebuild your engine by yourself... Maybe in your sleep, like Chuck!? viewforum.php?f=10
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dave bernard
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Re: Mark 55 project

Post by dave bernard »

you should split the crankcase to look at the insides. lower rod and crank throw may also be bad best to check before spending the $$$$$$$$$$$
Zetta
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Re: Mark 55 project

Post by Zetta »

Ok experts, what is the best way to pull the propeller shaft bearing and seals?
Tom Brockmeyer
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Re: Mark 55 project

Post by Tom Brockmeyer »

Did you get your hands on a factory service manual? It details this procedure and the tools needed pretty well.
Lake Lanier, 30miles North of Atlanta, GA
Old Mercury outboard fan... Especially the fast ones!
Mercury/MerCruiser, Evinrude/Johnson & VolvoPenta Technician (After my suit & tie wearing career was done!)
Zetta
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Re: Mark 55 project

Post by Zetta »

I have not. I originally planned to rely on the experts on this forum but I’ve gotten deeper into this engine than I had hoped so that has become a bigger ask than expected, so getting my hands on a repair manual makes more sense now.

Any suggestions? I’m old and prefer hard copy paper manuals or is there a good reason to download an electronic copy?

Any manual publisher or detail better than others?

Thanks for ur patience.
Toby Hall
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Re: Mark 55 project

Post by Toby Hall »

Real ones used to show up fairly regularly on eBay, for $40 or so. Try to find an original one if you can. The illustrations are way clearer than in the reprints!
The stuff you can't see - That's what's important.
mark 55
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Re: Mark 55 project

Post by mark 55 »

People in a hurry to get married should be trusted as much as people eager to get elected.
Locomotion
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Re: Mark 55 project

Post by Locomotion »

The factory manual will be the best $50 you ever spent!
The time and anguish it will save is hard to describe.
Ray
East Tennessee Born & Raised
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Mark 25
Zetta
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Re: Mark 55 project

Post by Zetta »

Just ordered a manual. Thanks for the advice guys!!
Zetta
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Re: Mark 55 project

Post by Zetta »

Back again. I have received my coveted factory service manual and have found several helpful tips. However I have a question about the bottom crankcase seal direction. My motor only has one seal but I forgot to take a picture of which way it was oriented in the cap. Would the metal part of the seal face the lower unit or the powerhead. TIA
Attachments
image.jpg
dave bernard
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Re: Mark 55 project

Post by dave bernard »

all crank seal lips face down. your pic is incorrect for bottom.
Zetta
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Re: Mark 55 project

Post by Zetta »

Thank u DB!!
white-merc
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Re: Mark 55 project

Post by white-merc »

Now that you have a manual, have the powerhead off and on a bench, have the lower endcap off and notice a bad bearing...

Do the right thing and take the whole powerhead apart. Take this advice from all the experience on this board.

Peter
Zetta
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Re: Mark 55 project

Post by Zetta »

Thanks for the advice White-Merc but since the compression numbers have tested good, I’ve been planning to avoid cracking open the power head. I’ve replaced the bottom crankcase seal and bearings and will be doing the same to the top seal next week. What is your reason for recommending that I open up the power head?

On another note, I’m reinstalling the rebuilt lower unit and have met quite a bit of resistance trying to close the last 1/2” of the gap by tightening the 3 bolts. Should I just muscle thru or could something be in the way? Both ends of the cooling tube are inserted properly, the shift rod is properly engaged and working, the driveshaft is engaged so I can turn the prop by turning the top crankshaft bolt. Am I missing something?

Thanks in advance for any advice.
dave bernard
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Re: Mark 55 project

Post by dave bernard »

the reason is to confirm the internal bearings condition
Zetta
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Re: Mark 55 project

Post by Zetta »

Makes sense. Thanks
Tom Brockmeyer
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Re: Mark 55 project

Post by Tom Brockmeyer »

Zetta wrote: Fri May 10, 2024 2:19 pmOn another note, I’m reinstalling the rebuilt lower unit and have met quite a bit of resistance trying to close the last 1/2” of the gap by tightening the 3 bolts.
NO!! Do not force it. It should install to all but the last hairline crack wtihout needing the bolts to force it. Something is wrong. If you disassemble it again, you'll likely see the issue. If the shift shaft splines don't align, you'll crack off a boss on the block and have a hole. If the waterpump tube isn't aligned, you'll wreck the tube or the waterpump housing. If the driveshaft isn't aligned, it will STILL turn the lower unit from the tight fit of you tightening those mounting bolts.
Lake Lanier, 30miles North of Atlanta, GA
Old Mercury outboard fan... Especially the fast ones!
Mercury/MerCruiser, Evinrude/Johnson & VolvoPenta Technician (After my suit & tie wearing career was done!)
Zetta
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Re: Mark 55 project

Post by Zetta »

Thanks for confirming my suspicion and fear. I’ll drop the LU and see what is binding it up.
Michael
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Re: Mark 55 project

Post by Michael »

I'd guess we have all had this issue at least once....check the rubber grommet at the ends of the water tube....that tube can come loose installing the lower and if the tube isnt seated in there proper it tries to crush that 1/2 grommet and cant the water tube needs to be seated proper
Zetta
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Re: Mark 55 project

Post by Zetta »

I think the water tube is the problem because I can’t remove it after dropping the LU so I’m in the process of separating the power head and the drive shaft housing. As Inigo and I learned from The Princess Bride, if you get lost, go back to the beginning. 🤣
Zetta
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Re: Mark 55 project

Post by Zetta »

I had the water tube installed backwards and there was room for the longer end to slide into the upper fitting. After changing that the lower unit slid into place. Thanks for alerting me to the cause of the symptoms.

Now another question. Does anyone know the size, length and thread of the GEAR HOUSING VENT SCREW? The old damaged lower unit had a sheet metal screw in that hole which buggered up the threads and probably contributed to water in the LU which then froze. The new used LU I received was missing that screw. I can order it online but I hate to wait a week to get it so if I can get the info maybe I can buy a brass screw to fit at Ace. It measures 0.184” diameter which is just under a number 5/64”, 10 screw. I can feel interior threads but it is hard to tell was the TPI would be. Thx.
Zetta
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Re: Mark 55 project

Post by Zetta »

Here is the screw from the buggered LU 🥴. I hate quick, unprofessional “fixes”.
image.jpg
AU52N
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Re: Mark 55 project

Post by AU52N »

Per the Mark 55 parts list the screw is 12-20262. I have these screws in stock along with the gasket. The originals were brass and the replacement ones are stainless. I have both. The Screw and washer are priced at $4.00 and shipping is $4.00. If interested please email me thru JOMS.
David
Aeroliner Race Boats, LLC
Zetta
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Re: Mark 55 project

Post by Zetta »

Thanks for the response and info AU25N but I found the stainless steel screw and washer at a local dealer.

On to the next part, does anyone know where I can get a prop nut and cone (part number 29825) for this Mark 55E? The old cone disintegrated when I tried to remove it.
Michael
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Re: Mark 55 project

Post by Michael »

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