Removing the top cover from 1958 Thunderbolt Mark 55?

[softdown]

Just bought a 14' Glass Craft with this motor. Getting into buying and working on older outboards for some reason, perhaps because working outboards are worth real money? The electric start will turn over the motor which has not been started in "7 years" per last owner. Yea. Needing a Mercury fuel connector, they seem to be about $20.

The manual start pull cord is fully extended and does not retract. I need to pull the top cover and work on the manual pull assembly. There is a 3/4" bolt with no interest in loosening. In the middle of the bolt is a slot though a screwdriver twist did nothing to it.

This motor looks like a 10hp size. The four cyllinders is contradictory to that assessment.

I'm in Colorado by the way...now owning ten outboards, four that work.

 

[racerone]

I would say it is a 1958 model.-----That nut may be a left hand.----Does not matter because you should leave it alone at this point.------Find the 4 nuts underneath , one in each corner.----Then lift off the entire assembly.

 

[merc850]

There is no such thing as a 1968 Thunderbolt Mark 55 - there is a Mark 55 built in 1955 a serial Nr. will help define it - do not keep trying to undo that bolt it holds the starter together; the reason the cord won't retract is because the spring or mechanism is broken or stuck. Do the nut back up and remove the top by undoing 4 bolts that hold the cover on to the powerhead then you can fix it. Watch out for the spring. You'd better replace the waterpump impeller before you use it.
These guys can really help http://johnsoldmercurysite.com/phpBB3/index.php?sid=0ab78df74659be5b9487a3cb640f3430

 

[softdown]

There is no such thing as a 1968 Thunderbolt Mark 55 - there is a Mark 55 built in 1955 a serial Nr. will help define it - do not keep trying to undo that bolt it holds the starter together; the reason the cord won't retract is because the spring or mechanism is broken or stuck. Do the nut back up and remove the top by undoing 4 bolts that hold the cover on to the powerhead then you can fix it. Watch out for the spring. You'd better replace the waterpump impeller before you use it.
These guys can really help http://johnsoldmercurysite.com/phpBB...87a3cb640f3430

Thanks to both racerone and merc850, I have not damaged my engine yet.

The donator advertised this as a 40HP motor for what this is worth. Seems too small to be much more than 20HP.

The serial # is 1028885. It is a Mark 55E. Wondering about the HP? That may help with water impeller search. You seem to be indicating that water impellers are an automatic replacement, at least on this engine. With 10 outboards to play with now, wondering about the "Commandments of Water Impeller Replacement".

Thanks again!

 

[DeepCMark58A]

If the motor has sat any amount of time it is a good idea to drop the lower unit and replace the water pump impeller and also check the lower unit fluids.

 

[racerone]

Post pictures of this --" seems to be 20 hp " -----4 cylinder motor.--------I am now curious as to what you have here.--------And yes waterpump impellers on that are replaced on a regular basis.

 

[merc850]

40 hp 1955 (40c.i.) https://store.oldmercs.com/category_s/130.htm they have parts and manuals

 

[softdown]

Post pictures of this --" seems to be 20 hp " -----4 cylinder motor.--------I am now curious as to what you have here.--------And yes waterpump impellers on that are replaced on a regular basis.

Here is your picture. Evening sun was unfortunate. Sure is a compact 40hp. My other 40's are back breakers to move around.

Seems that I need to read an idiots book for repairing outboards. Figured they were similar to auto engines, have rebuilt a couple of them, there are many differences.

I see a recommendation for gear weight 105. Hmmm.....things always seem to get a lil more complicated.

I have ten outboards. None have seen regular use for some time. I did replace the gear oil in the Johnson 175 in 2011. Most of these outboards were bought for parts or resale. Perhaps I should buy a gallon of good gear oil. My memory is that squeezing an automotive 80/90 bottle allowed me to refill the Johnson.


I really should replace the differential oil in all my old vehicles.......always something.

 

[merc850]

This is the gear grease you use not 90 weight https://store.oldmercs.com/product_p/92-24734-1.htm
Here's an ad from the day

 

[softdown]

This is the gear grease you use not 90 weight https://store.oldmercs.com/product_p/92-24734-1.htm
Here's an ad from the day

Thanks for the tip. Since the motor is about a 1958, I suspect the boat may be as well. It has a curved windshield like the ad, made of fiberglass. Would have been ahead of its time in 1958 I think. Wasn't wood the norm until fiberglass got going in the early 60's. The woodies called them "plastic" boats. Well.....most of the plastic boats are still around. Not so much so for the woodies.

 

[DeepCMark58A]

The plastics look good on the outside but suffer osteoporosis under the skin.

 

[racerone]

I have a MARK 28 motor.----Plastic emblem / face piece on the front looks as good as new.-----Not sure what they used but it is better than some of the plastic used on motors of the 1980's.

 

[Chinewalker]

Mark 55 was one of the best motors ever built. The basic 4-cylinder motor design was built from 1949 to the early 1990s. Real powerhouses for their size. They were originally rated at 25hp in 1949 as the Mercury KF9. Yeah right. They actually came with a spring-loaded deadman tiller throttle. Crazy fast! In racing trim, the Mark 55H could push a small hydroplane to speeds in excess of 80mph. Bottom line, yes, it's a healthy 40 horses.

As noted above, take care to do the water pump impeller, likely will need hoses and fuel pump kits (easy!) and the timing belt. Mercury made a manual for their pre 1965 wares that turns up periodically on eBay. Mercury had lots of quirks when it came to service (setting timing, reinstalling the lower unit after replacing water pump, plus need for special tools for several things, etc.) so the manual is a good investment.

Great motors once you get them dialed in!

 

[merc850]

Manuals and parts lists available at the link I posted - old mercs; finally someone has posted help for a real THUNDERBOLT motor, all the other ones have been reading the Thunderbolt Ignition on the faceplate.

 

[jbcurt00]

Chinewalker, check your PMs.

 

[softdown]

At $75, service manual at oldmercs.com.... that is an ouch price. Not a problem if I had one outboard to fix up, I have ten to play with.

On the other hand, I would love to have 40hp than I can carry in my hands. It is a classic motor and worth something. Persevere I shall...

I bought these motors hoping some starter fluid would bring life to a couple. That is doubtful given the value of working outboards in the 30hp to 65hp range....and the price that I gave.

Still learning to use this site guys....I am impressed at the level of knowledge and helpfulness!

Chinewalker....wow! Nice writing skills!

 

[DeepCMark58A]

Nothing worse for an old motor that has sat for years than spraying starting fluid and cranking or starting without lubrication.

 

[softdown]

Nothing worse for an old motor that has sat for years than spraying starting fluid and cranking or starting without lubrication.

True....I was keeping it simple. Of course you squirt 30W oil into the cylinders first....and make a good effort with fuel/oil mixture. If the carb jets are gummed up with ethanol, nothing will work of course.

I know a motor repair guy. He says that 100% of his work is caused by consumer problems with ethanol in the fuel system. I think he is exaggerating a bit.

I got six "complete" outboards and a parts motor for $750....plus a truck trip to Vegas to pick them up. One of the motors works....or it better. All 30hp to the big 65hp Merc....a backbreaker to move.

 

[Chinewalker]

Backbreakers indeed! After my guts tried to escape through my abdominal wall a couple years back, reminding me that I'm no longer 25 years old, I invested in a shop crane from Harbor Freight. Makes moving the big guys much easier!

I do try to get things from iboats (which doesn't carry the 1965 & prior manual) and OldMercs from time to time to support their efforts, but I've found the manuals on eBay for less. There are a couple there now, part number C-90-25500.

Thanks!

 

[softdown]

Backbreakers indeed! After my guts tried to escape through my abdominal wall a couple years back, reminding me that I'm no longer 25 years old, I invested in a shop crane from Harbor Freight. Makes moving the big guys much easier!

I do try to get things from iboats (which doesn't carry the 1965 & prior manual) and OldMercs from time to time to support their efforts, but I've found the manuals on eBay for less. There are a couple there now, part number C-90-25500.

Thanks!

You mean an engine hoist? Harbor Freight engine hoists seem quite good to me.....as is maybe half of their stuff. If only they would quit marketing ultra cheap crap to lure people in. Not aware of a shop crane though that means almost nothing.

OldMercs wants $75 plus $20 to ship the manual....so off to Ebay for roughly half price. Who cares about some shop usage.

Just found out that iboats carries a lot of stuff. The prices have been good so far.

If they could make a small 40hp over 65 years ago, why are they so huge now?