Prop for older motor

[keithmylum]

I have a 1971 2stroke 40 hp mercury. Can someone recommend a prop for this motor? Boat will be used for cruising/fishing. No skiing. It is a fiberglass 16ft deep hull boat. Thanks for any help. Everything I have seen says 1977 or newer.

 

[BonairII]

Re: Prop for older motor

Your prop choice is based on your motors correct operating range. You need to know your rpm at WOT. You'll need to hook up a tach to your motor(tinytach etc) and find out what rpm you're currently running.

 

[steelespike]

Re: Prop for older motor

Is there a prop on the motor?Size should be near the base of the blades or under the prop nut.
You will be under powered with a 40.try to get us the info needed in the stickys at the top of the prop forum.
A tinytach for rpm and a gps for speed.Some cells have a gps app.
If the prop is just damaged if you can't find a replacement you could see if a prop shop can repair it.

 

[keithmylum]

Re: Prop for older motor

It did not have a prop on it.a guy gave it to me in exchange for some air condition work. It was his mother in laws and does not know what happened to the prop.I did not mean to say deep hull, it has a v hull but not deep. Is there a way to tell by using my serial number? I do not have a model number. The engine is to old according to mercury.

 

[steelespike]

Re: Prop for older motor

A serial number might work.I have some numbers for early motors.Pictures of the motor will help.The color bands on the cover
can key the year.There is a 40 thats called a Classic 50 There is a Merc 400.

 

[keithmylum]

Re: Prop for older motor

A serial number might work.I have some numbers for early motors.Pictures of the motor will help.The color bands on the cover
can key the year.There is a 40 thats called a Classic 50 There is a Merc 400.

It is a 1971 mercury 400 2 stroke. electric start and pull start. says thunderbolt. I will take some pictures today and upload. Thanks for all your help! Serial number 3049291

 

[keithmylum]

Re: Prop for older motor

It is a 1971 mercury 400 2 stroke. electric start and pull start. says thunderbolt. I will take some pictures today and upload. Thanks for all your help! Serial number 3049291

 

[BonairII]

Re: Prop for older motor

Probably a good time to order yourself an OEM service manual. You'll be glad you did. The manual will list the "stock" prop and other optional prop sizes that were available for it.

Someone here will chime in with the "stock" prop size long before your manual comes in.

 

[steelespike]

Re: Prop for older motor

You might ask at Johns Old mercury Web site Someone there should have some ideas.

 

[keithmylum]

Re: Prop for older motor

You might ask at Johns Old mercury Web site Someone there should have some ideas.

ok thanks I will try there.