Mercury thunderbolt 50 hp

[ETA]

Hello all,
I just inherited a 1975 Astroglass bass boat with a 50 hp mercury outboard (1975 also I suppose)
I have never had a outboard and don't know
anything about this one, there is no model or
serial sticker in the transom mount and the only
thing I see on the motor is the word Thunderbolt
and a casting number of some sort, Is there any
way to findout what the model number is for this
motor and does this engine require a gas/oil mix
and if it does what is the mix 24:1/50:1 or what?
Thanks in advance. All help greatfully appriciated.
Sincerely,
Edward
Added Photo Below (even though the bands around the cowling look blue/green as does the boat they are both blue in color. ).)
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Also how can I tell if there is a power trim or not (I see no Hydrolic lines to any cylinder likes on my sterndrives)but the remote control has the trim button (may or may not be original controls) and I haven't started the engine or any thing as I had it delivered to the local Mercury dealer to have the compression checked and the lower unit readied for winter before I took possesion of it. Was told by dealer that compression was great in all 4 cylinders and yes it is an inline 4. I am planning on doing my own maintaince but I have only worked on the mercury stern drives so this outboard stuff is really new to me. But at $68.00 hr @ the local dealer I know I can learn to do it. Once again Thanks Everyone...

 

[roscoe]

Re: Mercury thunderbolt 50 hp

Yes, 50:1 fuel mix, using TC-W3 rated 2 cycle Outboard oil.

Sorry, can't help you with the model number.

 

[tmcalavy]

Re: Mercury thunderbolt 50 hp

Look on the front of the transom clamp, up close to the bottom of the engine cover/cowl. If it hasn't been removed, that's where the ID plate should be. Is it a blueband Merc? Is the band around the cowling blue? If so, probably an early 70s Merc 500 50 hp, inline 4 cylinder. Great engines. I had a 73 on the last family boat we had. If you can post a photo, that will also help date it. Once you ID it, you can easily find a factory manual or after-market manual for it...highly recommended if you're going to do your own basie maintenance.

 

[TriadSteeler]

Re: Mercury thunderbolt 50 hp

If the plate above the transom clamp is missing, then take off the front cowling (The plate that says "Thunderbolt Ignition" then underneath that remove the wrap around cowling, and the serial number will be stamped on a flat area between #1 and #2 cylinders on the starboard side of the motor.

 

[TriadSteeler]

Re: Mercury thunderbolt 50 hp

Also, If a power trim unit is installed, then there would be 4 hydraulic lines (2 on each side) pushing two cylinders that straddle the transom swivel assembly where the OB is mounted to the transom. Since you see no hydraulic lines, I'm betting that you just have the absorbers.

 

[Texasmark]

Re: Mercury thunderbolt 50 hp

If you had power trim you'd know it by looking at it. In those days the pistons were obvious and I don't think the 50 had shocks (that look like PTT cylinders without the 4 hyd lines); bigger engines (I6) did if they didn't have PTT.....as I recall.

Mark