Mercury Mark 58s. What is their attraction, technically speaking?

[John (Taylor) Gabrowski]

I keep hearing people talk about the Mercury Mark 58s all over the place over the years and even have a complete hardly worn standard bore long block myself that was electric start but what is really the attraction from a technical standpoint??? The basic message that they make a good basis D-Mod or E-Mod motor depending whose sanctioning body isn't much of an answer. Seems everyone knows they are 44 inch and they had KA carbs and a different piston casting from the underside that the lastest model small wrist pin versions pistons hung on Merc's 600-4 connecting rods and large brass/bronze reed blocks and that they go like mad too but why the desirability the way people speak of them they are legendary for some reasons??? Why? I haven't heard a technical explanation yet in all these years! I just talked a person into buying one because it was in excellent shape and could still run good even though it was still factory sealed.

[Bob Rusnak]

I keep hearing people talk about the Mercury Mark 58s all over the place over the years and even have a complete hardly worn standard bore long block myself that was electric start but what is really the attraction from a technical standpoint??? The basic message that they make a good basis D-Mod or E-Mod motor depending whose sanctioning body isn't much of an answer. Seems everyone knows they are 44 inch and they had KA carbs and a different piston casting from the underside that the lastest model small wrist pin versions pistons hung on Merc's 600-4 connecting rods and large brass/bronze reed blocks and that they go like mad too but why the desirability the way people speak of them they are legendary for some reasons??? Why? I haven't heard a technical explanation yet in all these years! I just talked a person into buying one because it was in excellent shape and could still run good even though it was still factory sealed.

The MK 58 was a 44 ci engine and the 4 ci over the origionl 40 was noticable. From what I was told by many old time racers and mechanics is the 44 ci engine just had a better balance, (right combination) for the 4 cylinder engine. They do make great D Mod engines as I made one from a Merc 500 base enngine. I am looking for a MK 58 block right now as I had a wrist pin keeper come loose and distroyed a cylinder. It could be bored but will have to chande the rod assembly's and if I was going to do that I would make another D Mod powerhead. If you know of a block available, please let me know. As far a being legendary, I think the Mark 55 (40 ci) engine is more in demand.

[John (Taylor) Gabrowski]

I had a Speedliner and a Swift hydro that I donated to a local rat who was supposed to start a marine museum from all the donations he got in boats and motors for developing a privately owned, open to the public museum in Kenora, Ontario (Lake of the Woods) only to split with his wife and by all the sounds of it, she took him to the cleaners and he had to sell off all the donated stuff to stay afloat while the whole scene got sucked bone dry. There are a lot of people really pissed at him!!! I love your, that picture!

In any case, I will stop raving about that screwing everyone got when he was the pres of the local AMOCI chapter back then! ......

John R what your saying??? is that Merc's oversquaring the Mark 55 into redesign to a 44 cube Mark 55A, Mark 55A (electric start) and the big carbed Mark 58s and later engines is the basic reason??? I thought it was something way more complicated than just the increasing of the bore and carb sizing etc. size to change power development???? The first 44 engine I put quad Quincy pipes on was a basically stock blocked with bigger carbs (KA-7As) (has AJs stock from factory) Mark 55A 44 cuber and almost killed myself in an end over end flipping a Swift Big D in 1971. I could not bring myself to think 44 inch anything for a decade after that. Your right, I liked the 55H 40s more too for a long while after that and still do, but look ma? no available pistons anymore!

The Mark 58 I am sitting on seen little use up here with a loose .0035 tight .004 pistons clearances. You can still see the factory finish hone and groves on the rings and it was scrapped because it could not be tuned any more by a local Merc shop?????? It was just old and barely even used. Excuse to sell the guy a new engine? I had it for sale a while back, nobody wanted it so from all the talk over the last while I decided to keep it, sold off other salvaged 44 blocks and do something with it because people added all this mystique to Mark 58s!! I will ask my Kenora restorer/collector contact to see if there is some more Mark 58s around. He seems to be able to smell out old OMC and Merc motors out good or bad when asked, so I will ask him.

[John (Taylor) Gabrowski]

I hooked up with my contact out at Lake of the Woods, Kenora and he will check out what there is for Mark 58s over there. There is the odd old Merc 400s and 500s here that are in one to many sections/pieces. If its in one piece and runs, the prices for complete engines go to $700.00 for Mark 58s, Merc 400s and 500s to where its really a dusty junker and they are under $100.00 but for every good block you will run into 3 that are into serious bore and related problems not worth going into generally unless you really out to spend.

*Interesting point on magnetos on Mercurys. In the past year I salvaged and put back into good operating condition about a dozen and showed a few people how to do their own and keep them up. Out of that dozen 8 of them had points that did not have even a smear of lubricating grease on the cam follower pivoting arm post. All those points failed when the post hole got so dry from use that the fiber hole became oval and brought on uneven points closure and burn out. Thing is that the Mercury boxed points I got by the dozen for everyone up to the early 1980s and I just ran out, had a capsule of grease with the spring locked points for the purpose of lubing that point pivoting post hole. Eight non-lubed dry holes?? What a way to do business??

[John (Taylor) Gabrowski]

The magneto stuff about no lube was one thing but 3 engines that fried/scored pistons skirts and in one case burned a quarter coin sized hole right through the combustion chamber through to the water jacket without frying off the piston crown are rediculous right through pathetic.

In one case, the engines top carb fuel filter was so clogged the engine leaned out and the top two cylinders pistons self destructed. In the other case it was the bottom carb fuel filter was clogged frying the bottom 2 cylinders. The amounts of mud and sand seemed bizzarre yet their counterpart filters on the other carb(s) were perfectly clean?? Go figure, these were serviced engines from customers of a now defunct dealer from Lake of the Woods.

The 3rd engine is the most humorus or pathetic even. Someone deliberately knocked off the flywheel to then used a fine chisel to destroy a quarter inch of seal and its housing. The tool bite mark is remarkable in its clarity and the result was the top cylinder burning a hole right through the combustion chamber into the waterjacket without destroying, but minorly damaging the piston. Another remarkable feature on the block was a piece of masking tape, pretty dried up saying "compression on all cylinders about 120 and all cylinders good"??? That was a real wild statement.