McCrea hydros

[Mark75H]

300 is a 40 like a 35A

[John (Taylor) Gabrowski]

Mark 35A is a 40 cuber? no different than a Merc 350 with AJ sized carbs,. your probably right. I have had several Merc 350s salvaged for their blocks and cranks.

Mark 55A is not a 40 cuber but a 44 cube engine with AJ carbs. It was the earliest 44 cuber.

Merc 300 is a 30 cube engine. I had two and still have one and its a C-Mod now with a Mark50 crankshaft in it with LeBanco pipes and KC6 carbs on it and pictured here on BRF because of the older NOS Mk50 crank it fit.

[Mark75H]

Correct on the 35A, 300 is still a 40. Merc didn't make a 30 after the 30H. Correct on the 55A, its a 44 like the 58A that came out simultaneously. Neither was first.

[John (Taylor) Gabrowski]

Merc did make uo 30H-1s and well as 55H-1s. I used to have half a dozen 20Hs, 30Hs and 55Hs of which there were 2 - 30H-1s and 2 - 55H-1s. It could be that they were what you called "parts" motors from Mercury with their newer block style and squarish top wide shieve easy pull recoil starts but they came with their original Merc ID plates so that is what they were.

[Mark75H]

I think that most people would understand "30H" to include the 1959 Mk30H-1 sub-variant, which was the last 30ci Merc listed anywhere. I did not say there were no 30 ci motors after 1956. I will say no 30 ci motors after 1959 other than the few 1962 30H's.

[John (Taylor) Gabrowski]

I still have one Merc 30 cubic inch C Modified made from a Merc 300 out of the 2 I used to have. Maybe Merc did something different in Canada like sending Mark 55E blocks sometimes with and sometimes without serial numbers to replace Mark 55H blocks which was also done more than once. Next Merc 300 I lay my hands on his going to have its disassembly pictorial posted here on on BRF.

[Roy Hodges]

was a 40 inch motor with electric start AND alternator . I had one ,bought new in summer of 1957 , serial # 1091992 . A mk 55 S was electric start without an alternator. I calculated that a 40Cube block, to be made into a 30 cubic inch block would need VERY thick sleeves , about .1094 inch THICKER than the stock 40 in sleeves . ( Wall thickness ).......Mark 55E was a fishing motor,as was ALL the 30 & 40 inch motors , except those "H" motors .

[John (Taylor) Gabrowski]

I agree with your clarification on the Mark 55s in particular the Mark 55E. Evidently they sent them out here as substitute for use as Mark55H blocks because the porting was near identical.

I sure would not want to resleve a Mark 55 - 40 inch block down to the bore of a 30, who knows what irregular heat transfer problems would arise.

[Mark75H]

.060" different

[Puddleduck]

Blimey! I only asked a simple question and you guys are off on a bigger one than McCain Vs Obama! Amazing in-depth knowledge - many thanks for the feedback, especially on the throttle hook-up. Ref the propeller I've been given a nice 2-blade quicksilver 23587 A2 - 13. It needs a birthday but otherwise OK - more chance of finding rocking horse poo than racing props for non- through hub mercs here in the UK!