Mercury Mark 40-H

[John (Taylor) Gabrowski]

Some one said that some racers went that far that would make on really oversquare racing Merc with some real power extras to think about.

Would they have used Turner pistons for such an adventure at that time or used what for pistons if not Turners?

49 cube Merc 4 would make for one neat FE or SE engine if such things were legal.

[Mark75H]

It might be legal, I'd have to look closely at the restrictions on 44's in 850, there aren't many.

I have no idea who made the big pistons. Might have been from some other motor of the day.

[Aeroliner]

Thought you would enjoy seeing inside. All 4 cylinders used the same basic crank except for the taper. Mark 40-H engines had the smaller taper cranks. The inside of a 40 H was very restrictive and we opened it up quite a bit. The real hard part was taking the heads from a 44 that were from a power dome and puting them on the engine. Hope you enjoy the photos. We will be posting a video on our website soon so you you can hear it. We ran a stock 44 just before this engine and it really hurts you ears. If anyone else is intrested in engine work you can try Doug Kay. His info is on our web page at www.Aeroliner-Boats.com
Alan

[Aeroliner]

As you can see the bore size for the 44 cubic inch mod came right up to the pins so it seems impossible to get 49 cubic inches unless the stroke is changed. Don't think the crankcase will let this happen.

Alan

[John (Taylor) Gabrowski]

I love those pictures, that is really cutting it close to the locating pins alright! Putting on power domed heads must sure envolved some neat welding skills too to get them just right. Nice porting that would make it sing. That motor at 44 cubes must have stung a few when they saw the cowls fly by!

I had 2 KG9s and 2 40Hs and one resleeved Mark 50. One KG9 and one 40H had Hubbell reed valves installed on the intake transfer port areas. The ports too were stock height but squared. Here they allowed the KG9s unaltered as class Ds for hydro but for runabout that was a bit too hard so they allowed the Hubbell reed valved KG9s and 40Hs into D runabout where they enjoyed a but more success with the added breathing. I would run them on that (lightened and bottom revamped) Asburn D Alky runabout I had and could run 2nd or 3rd against 55H stockers with them by sure force of being able to turn that runabout so tight it was a corner catcher against the 55Hs. I got a first for seasons points for a couple of years before I could afford 55Hs just from running 2nd or 3rd all the time consistently in D runabout. There is a picture of that big Asburn banana runabout on the website here under the historical threads with a big CP144 numbered on its sides where it was with a 40H on her and she did cook for her time. I wished I still had her for posterity sakes.

Please keep up the pictures and the write ups on the work, it is all a pleasure to see all that.

[Aeroliner]

As soon as it gets warm we will break the engine in on a hydro. I will give you the speeds as we go throught the testing. I expect that we will see close to 80 mph , hopefully more, if all goes well. Doug Kay dose all my 4 cylinder work and I have to say I have found no one better. I hope to make a few D's wonder how an old mark 40-H could run like that,

Alan

[Mark75H]

As soon as it gets warm we will break the engine in on a hydro. ... I expect that we will see close to 80 mph , hopefully more, if all goes well. ... I hope to make a few D's wonder how an old mark 40-H could run like that

[Aeroliner]

The engine is setup with KC6A cards and big read blocks to help it on the induction side. Then the interior of the block has been opened up to increase the flow to the intake ports. Both intake and exhaust ports have been reworked to allow for more flow. These are done to the Harry Brinkman specification. I have to note that the block had been ported with a file before we started the conversion. The largest changes have been making the engine into a 44 cubic inch engine using current flat top pistons. The cylinder domes were replaced from a Mercury power dome engine. The compression was also increased during this operation by installing them lower. The engines has 190 psi on a check of the compression after its first tank run. I expect this to come up a little. We are intrested in how the segmented exhaust is going to work in that the devider was left in from the standard 40H block. I beleive the engine is more capable than the current 44XS engine, but I guess we will see when we do some on water testing. The photos show some before and after shots of the build process. Have added some closeups of the ports.

[Aeroliner]

We have completed the 40-H and hope to test it on a hydro soon. We now have the "D" cones and bearing carriers in stock. See aeroliner-boats.com for photos and pricing. Have sold a number of them allready but we will always have them in stock. Have attached photo of the engine plus the 1959 55-H that Doug Kay has just completed.

Alan

[Aeroliner]

Hope you like them