How to Revive a 1958 Merc Mark 78 Super Marathon?

[jagans]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

Hey Guys,
We made it out on the water Saturday & stayed overnight on the boat until Sunday afternoon. The boat ran well all day Saturday but it started to overheat on Sunday so we shut her down hopefully before any damage was done. I've watched a few videos on Youtube & apparently if the impeller fins are in decent shape & not broken it still might need to be replaced because the fins have taken a set? Anyhow I was wondering if anyone had a good source for an impeller or full impeller kit for this 1958 Merc Mark 78 Super Marathon? We got a lot of positive comments & questions about the boat & it's history. I have enclosed a link to a real short clip of the boat underway. Thanks for any help you might have!

1955 Lone Star "Cruise Master" powered by 1958 Kiekhaefer Merc Mark 78 Super Marathon - YouTube

Hi Steve, I just read your post, and I do not know half as much as most of these guys, but the first thing I would have said is STOP! Do not even attempt to start this motor until you pull the lower unit and replace the impeller. Even if the rubber the current impeller was made of was good, the chances of the vanes sticking to the cup are about 85-15 When that happens they will tear off if the motor is not stuck in a tank for a couple of days with a little surfactant in the water. Hopefully your drive-shaft is not rusted solid into the power head. I had one of these direct reversing engines, and it was really a PIA not having a neutral, but I had a slip with fast moving water. The motor ran very well though, and would pass everything but a gas station. Man was that thing thirsty (80HP) OK way back then, not too cool today. I think you should think about completely rewiring the engine in the off season.

Quite a find though, Have fun.

 

[Stevum]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

Hi Steve, I just read your post, and I do not know half as much as most of these guys, but the first thing I would have said is STOP! Do not even attempt to start this motor until you pull the lower unit and replace the impeller. Even if the rubber the current impeller was made of was good, the chances of the vanes sticking to the cup are about 85-15 When that happens they will tear off if the motor is not stuck in a tank for a couple of days with a little surfactant in the water. Hopefully your drive-shaft is not rusted solid into the power head. I had one of these direct reversing engines, and it was really a PIA not having a neutral, but I had a slip with fast moving water. The motor ran very well though, and would pass everything but a gas station. Man was that thing thirsty (80HP) OK way back then, not too cool today. I think you should think about completely rewiring the engine in the off season.

Quite a find though, Have fun.

Jagans,

If you look at post #8 you will see that I have dropped the lower unit & inspected the impeller. It turned freely without any rough spots & all the fins looked good. What I have discovered watching some You tube videos is that can be deceiving & it might not cool properly at a higher RPM. Fortunately we shut it down in time (I hope) & the motor will turn freely when the pull rope is pulled. I have yet to pull the lower unit again & inspect the impeller since it was driven on a lake at full throttle. Enclosed is a photo of the impeller in the water pump housing.

 

[emckelvy]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

Mercury Mark & Kiekhaefer MARK 75A - 60 HP, 78, 78A - 70 HP GEAR HOUSING ASSEMBLY, COMPLETE (LEFT HAND ROTATION) Parts

The impeller is NLA from Mercury, but there are some sites that still carry left-over stock.

Here's one place, but gotta tell ya, it ain't cheap! WATER PUMP IMPELLER

The old original # for the impeller is 47-26203, in case you run across some old stock somewhere.

Be sure to carefully inspect the (2) check valves, these ensure water flows properly when the driveshaft rotates in either direction. If the "check" feature doesn't work, pumping efficiency will suffer. The rubber "duckbill" valves should be pliable and seal in one direction, & allow flow the other way.

This site is rumored to have the check valves if you need 'em: Laing's Outboards | New Parts

Another good source of NLA and just plain Old parts is Seaway Marine in Seattle. I've used them for years and they always seem to be able to come up with those oddball parts you can't find anywhere else:

Sea-Way Marine-your source for Marine Parts - Johnson Outboards, Evinrude Outboards, Chrysler Outboards, Mercury Outboards, OMC & Merc Cruiser Sterndrives

HTH...........ed

 

[Stevum]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

Ed,

Once again I want to thank you for all the helpful info you've taken the time to provide.......I'm almost out of the woods with this old gal!

Thanks again!

 

[Stevum]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

OK,
I tore down the lower unit again this morning & the impeller definitely needs to be replaced. It has taken a set so badly that with the cover removed you can see that the vanes don't even come in contact with the sides of the pump housing at times. I can't seem to find any check valves that Ed mentioned so I don't know if they're completely gone or what? I will probably have to bite the bullet & shell out $70.00 for a new impeller if I want this to cool properly.....small price to pay as I only have $1300.00 invested in the boat, motor trailer & licenses so far. I'll keep you posted. Ed if you read this please describe the location of the check valves if you have a moment. Thanks to All!

 

[matt167]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

This guy rebuilds impellers. Water Pump Impellers

 

[emckelvy]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

It's been so long I can't remember, but if you look at your stainless pump plate you'll see 2 rather large holes at the rear of the plate; as I recall the rubber flappers are under the plate.

See parts 32, 33, 34, and 35 on the parts diagram I posted previously. The flapper (33) is fastened to the adapter (32) by clamp (34) and the adapter has various thicknesses of shims (35) under it to make it sit flush where it's pressed into the gearcase, so it'll seal properly against the pump plate.

That's the best of my recollection, of course if I were looking at one I'd remember right away (as soon as those dormant brain cells woke up!).

Anyhow, if you're still cornfused, post a good pic of the lower unit, water pump area, without the pump plate installed. I think the (2) flapper adapters will be very evident.

HTH........ed

 

[Stevum]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

Matt & Ed,

Thanks for the advice....I believe somewhere along the line the 1 previous owner probably had the lower unit apart & failed to replace the check valve gasket as there is no sign of it except for a ghostly outline in one of the photos I have included. This is what probably contributed to the motor being shelved for 26 years. I'm still doing some research on the check valve placement but the lower end diagrams are so faded it's hard to tell what goes where. I did locate an impeller source on Ebay for a little more reasonable $35.00 including shipping. Here are the photos of the top of the lower unit, the bottom of the water pump housing (where I believe the check valve goes) & the middle plate. I did purchase some good gasket material from the local automotive outlet & hopefully I can fabricate some new gaskets with some patience.

Thanks again for the advice & I'll keep you posted, Steve

 

[Stevum]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

Guys,

I was able to obtain a clearer & more blown up version of the exploded view & now I realize I was looking for the check valve in the wrong location. I see that it's mounted vertically under the pump housing. I'll look into it tomorrow as it's getting late here in wonderful South Dakota. Thanks!

 

[Stevum]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

Ok,
I received the over-priced impeller in the mail, installed it & everything worked great. Water pumped great, exhaust manifold was cool to the touch etc. Went outside tonight to test it again & it will only run in reverse. When disconnected from the motor the control housing & cable that house the shifting mechanism move freely with no binding. However, when the shift cable is disconnected from the motor the distributor cap won't rotate back to the forward starting position even by trying to move the vertical rod that rotates the distributor manually. It got dark on me & I didn't want to try & force anything so I just quit for the evening. I'm hoping it's something real simple that is making this get hung up & I'll be able to see it in the daylight. I was just wondering if anyone else had encountered this problem with their Mark 78 Dockbuster?

Thanks again! Steve

 

[turtles11756]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

the impeller was priced right. are the rubber "duckbill" vavles ok they must be installed right ? $8.00 each. marineengine.com for a good parts diagram and parts.call jeff at laings outboards for parts. the lower unit looks to be in good shape ! it's something simple try holding shifter in a different position when rotating dist. to forward ?

 

[Stevum]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

Ok, Got to look at the motor again after work in the daylight....it turns out that when I was putting the recoil assembly back on the flywheel one of the washers had slipped off & was lodge in between the teeth of the distributor cam mechanism. It was a easy fix with a needle nose pliers to remove the washer & everything works fine now. Took the boat up to the lake on Saturday....this was the second time I had it on the water & the first time with the new impeller installed. The boat started right up & we set off on our journey, with the motor running real cool & steady. The boat was pretty sluggish but it would get up on plane. As the day went on it seemed to improve in performance, I'm guessing that it was just getting some fresh fuel running through it. It still didn't seem to develop the RPMs that it should be capable of. We experimented with the pitch & it needed to be on the highest hole to perform at it's best. Also, if we got it up on plane & then my girl friend & I would move all the way to the front it would plane out even better with the motor building RPMs & stay there even if I moved back to the wheel. At one point in time it really started to run @ about another additional 500 RPM (just guessing) & we thought maybe it had come out of hibernation. Turns out it was just leaning out as we were about to run out of gas on the 1st tank. Switched tanks & it ran as it had before by not developing RPMs. I would think that this should run between 4500 & 5000 like most OB motors? Anyhow, we took it back up to the lake on Sunday & it was really finicky & seemed like it wanted to load up unless you were running it a WOT. I was very careful to mix the fuel consistently at the 50:1 ratio & I'm using 91 octane in it so the fuel itself shouldn't be the problem. I'm going to look around for some info on adjusting the high speed jets if possible in the hopes I can get a little more out of her with blowing it up. Things are improving!

 

[Stevum]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

I forgot to mention in my last post that this motor has been in our area it's entire life & we're at approximately 5000 ft above sea level.
Also, if I were to install a whale tail & drill 4 holes in the cavitation plate would this greatly decrease the value of a classic motor such as this? Thanks!

 

[Stevum]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

Does anyone have any suggestions on what size main jet I should be running in this motor at the 4000 - 5000 ft. elevation range? I see that they are available in many sizes ranging from. 057 to .067 in 2 step increments. I would like to find a happy medium as I'm trying to get just a little more RPM's out of the old gal. I haven't had the time to do a compression check of the 6 cylinders but that's on my to do list also. Here's a real quick video of the boat on Pactola Reservoir in the Black Hills of SD.

1955 Lone Star Cruise Master on Pactola Reservoir - YouTube

Thanks again! Steve

 

[emckelvy]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

Does anyone have any suggestions on what size main jet I should be running in this motor at the 4000 - 5000 ft. elevation range? I see that they are available in many sizes ranging from. 057 to .067 in 2 step increments. I would like to find a happy medium as I'm trying to get just a little more RPM's out of the old gal.

According to the parts diagrams, the stock main jet size (for sea level operation) is .063". You'd want a smaller main jet to lean out operation at higher elevations. One thing you can do until you rejet would be to lean-out the idle mixture screws. You'd need to do this with the motor warmed & idling in Fwd. Obviously you'll need a helper to steer the boat! Run 'em as lean as you can while still having a good hole shot, if it bogs upon application of throttle, it's too lean.

Adjust one carb at a time and don't make extreme moves (maybe try 1/8-turn increments).

Back to the main jets, I see that the .059" jets are only $4.50 each and they have 10+ in stock, so maybe that would be a good size to start with:

Mercury Quicksilver 1399-1459 - Jet -.059, Nla @ MarineEngine.com

One other thought, older motors (Mark 75, Mark 55, Mark 30, for example) had adjustable high-speed needles. If you can get hold of 3 of those needle assemblies, you can make your mains adjustable.

The needle assembly screws into the carb in place of the main jet plug. Since your motor has removable jets, you'd need to use a counter-sink or similar tool to drill a chamfer into each of the main jets, that the end of each needle will slide down into.

The racers modified their carbs to adjustable mains, doing the very same thing. In fact, Merc sold as a racing accessory some special jets which were modified at the factory in a manner similar to what I described. The hole in the jet was greatly enlarged, along with the chamfering, to flow a lot more fuel for racing.

In your case, you don't need more fuel, only less, at altitude. So, all you'd be doing is "clamping down" on the fuel flow thru the jet, until you got a mixture that makes the motor "happy" at altitude.

The advantage of this setup is that it's immediately adjustable for changes in altitude, up or down. The adjustment is a bit complex, since you have to get the motor up to full rpm and "tweak" on each high-speed needle for best operation, but becomes easier with practice. And once it's set for a specific altitude, you shouldn't have to change it unless you go to a lower or higher elevation.

The really difficult part is finding the correct "bits" for the mod. You might find a few old scrap Mercs on your local Craigslist, you only need (3) sets of the needles, so if you were to find a Mark 75 parts motor it'd be a Home Run!

Meanwhile, might be simpler to just order the smaller jets and give 'er a shot. It'll only cost $13.50 + shipping!!!

BTW you might get a better hole shot if you move the tilt-lock pin one hole down. In the video the motor is tilted up quite a bit, if this is how you've been running it at speed, it might be too much of an up-angle for best performance. Every hull wants something different, best thing to do is give it a shot and see what happens.

HTH............ed

 

[Stevum]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?



Ed,
Thanks once again for your wealth of knowledge! Tonight when I get home I'll pull one of the jets & see how it's marked for size. If they are the .063 I will go ahead & order a set of smaller jets as it's a small price to pay. I'm not real worried about a big hole shot...I just want to be able to go a little faster than the current 14 mph at WOT. I have also just purchased what looks to be a higher pitched 2 bladed prop for a very reasonable $50 including shipping so that is an option also.

 

[Stevum]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

I spoke with a mechanic at the local Merc dealership & he told me to only change the main jets in 1 step increments to avoid burning up the motor. When I got home I pulled the middle jet (easiest to get to) & found out it was a .061 so I went ahead & ordered 3 of the .059 from MarineEngine.com. Hopefully this will make a major improvement on performance. I'll have this old gal running right - hopefully before the snow flies & the lakes freeze over.


Thanks again for all the help,............That means you ED!

 

[Stevum]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

BTW, that's a very nice-looking boat and I think it's gonna need a Pirate flag!

And here's some good info from the FAQ section on awakening your mighty Tower of Power:

http://forums.iboats.com/engine-fre...kening-sleeping-outboard-boatbuoy-158086.html

Cheers..........ed

OK,
I got the new .059 main jets installed along with the higher pitched 2 blade prop & took it up to the local reservoir (10/26/13) & it ran real well but I think that I will go back to the original 3 blade shallow pitched prop as it wasn't developing the RPMs I think it could. Unfortunately this will have to wait until the end of April as the "Cruise Master" has been put into indoor storage for the winter at a local fairground building. I have included a 1 minute clip of the Mark 78 running for the last time this season. I want to thank ED for all the great advice & suggestions! I did get that pirate flag that you suggested & you can see it in the video flying below the "Stars & Bars". I would have gotten on the water sooner but we got our butts handed to us in a Oct. 4th fall blizzard that knocked down trees & knocked out power in some places up to 5 days, I had to spend a couple of weekends cleaning up property.
The writing on the flag says "The Beatings Will Continue Until Morale Improves" Thanks for all the help! I'll keep you posted

1958 Kiekhafer Mark 78 Super Marathon - YouTube

 

[merc850]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

I would suggest buying an alternator driven tach to get a line on what you are doing ( + or - ), that motor should be @ 5500 rpms at full throttle.

 

[Stevum]

Re: How to Revive a 1958 Merc Mark 78 Super Marathon?

I would suggest buying an alternator driven tach to get a line on what you are doing ( + or - ), that motor should be @ 5500 rpms at full throttle.

Merc 850,

Do you have a source for such tach you mentioned?

Thanks!

Stevum