Correct Prop

[duckhunter55]

Have a 1983 25hp Chrysler, with a 10 3/8x 12.5 in prop. Someone told me that this prop was for a 55hp chrysler. It does seem rather large compared to my 25hp johnson prop. My question is does anyone have a motor like mine and if so what sized prop are you running? Im pretty sure if i lowere the pitch it would go faster right, because it would allow my motor to turn faster.

 

[Frank Acampora]

Re: Correct Prop

An older 25 horsepower Chrysler should use a 9 X 10 inch pitch prop. On my '70 something 25 HP Chrysler I am using a 2 blade 9 1/4 X 11 pitch prop. This is on a 10 foot tunnel hull racer.

I'm not too sure about the '80s but the older Chryslers had a different sized prop shaft and the 10 3/8 prop would not even fit the 25. However, even if it did fit because they changed the shaft size, that's still too much prop unless you are pushing a VERY light boat--like a 12 foot aluminum jon boat with nothing but yourself, a 3 gal. gas tank, life vest, anchor, fire extinguisher, and paddle.. The thought also occurred to me that if your boat is rated for 25 HP, perhaps the previous owner changed the decals and you really have a 35, 45, or 55. So yeah, I would say the prop you are now running would usually be used on the 55.

Look inside the lower pan for an aluminum plate bearing the model number. The first two numbers of the model--not serial--will be the engine size.

If that is the correct sized hub and shaft, and if the engine is indeed a 25, a better choice would be a 10 3/8 X11 pitch prop.

You have really piqued my curiosity. Is it possible to post a photo of the engine? Thanks.

 

[Frank Acampora]

Re: Correct Prop

It just occurred to me--actually I was on the toilet--it's where I do my best thinking: In the early '80s before they were sold to AMF/Brunswick to satisfy Govt. demands for a bail-out of Lee Iococca, Chrysler re-rated it's engines from Crankshaft horsepower to Prop shaft horsepower. At this time, the 4 cylinder 105 was re-rated to 90HP. So: it is possible your 25 was a re-rated engine--which would probably be the old 35 block and leg which took a 10 3/8 diameter prop.

In any case, as I said before unless your boat is extremely light, I still think a 12 1/2 pitch prop is too much.

 

[duckhunter55]

Re: Correct Prop

Man Frank, you sure know your boat motor history! But i have looked the serial numbers up and it is indeed a 25hp motor. The motor is on a 2007 16ft. MV aluminum jon boat. Its kinda of light by itself, but once you add me 6'4'' 280, 1 or 2 hunting buddes, gas, 2 batte. dekes, guns, gear, it will get pretty heavy. I am quites surprised at how well it does already. With 3 people and all the stuff i can still get up on plane. But i was thinking about the prop and how someone told me if i lowered the pitch, i would get better performance. YOu wouldn't happen to know where i caould get a 10 3/8 x 11 pitch prop do ya? Thanks for your help

 

[Frank Acampora]

Re: Correct Prop

franzmarine@aol.com. Franz Buddenberg. He really knows his onions. Give him your model number and the size boat etc. He will have a prop for you.

Go over to Chrysler Crew if you are interested in messing with the engine or anything Chrysler. Lots of interesting photos in the albums section too.

 

[Frank Acampora]

Re: Correct Prop

I must stand corrected!

Just today I picked up a 20 hp Chrysler just like your 25. Imagine my surprise when I opened the cover and it was the old style 20, 25, 35 series block mounted on a 35, 45, 55 series leg, mounting clamps, and lower unit. It also came with a 10 3/8 by 12 1/2 pitch prop. That is probably more than coincidence. It was probably the standard general purpose prop delivered with the engine.

I still maintain that this is too much prop for that engine though.

Next step is to compare lower unit gear ratios and also to see if they changed the crankshaft splines. The old 20-25 had a smaller driveshaft and prop shaft than this one. I also need to see what kind of adapting plate they used because the two different series engine blocks used different mounting bolt patterns.

Learn something new every day.

 

[duckhunter55]

Re: Correct Prop

If you happen to change props on it let me know if you can tell any performance difference. Thanks