Jet drive to prop drive conversion.

[arvo11]

I have an 2004 Mercury Jet80 model that has a cracked and damaged water pickup housing. I would like to remove the jet drive assembly and replace it with a prop drive lower unit. The data on the engine says that the year model is 2004, the max rpm 5250, and the max hp 115. Is this a reasonable swap? If so, what is involved? I have tools and a journeymans knowledge of automotive engines, but almost zero knowledge of marine engines. Thanks in advance for your help.

 

[79Merc80]

Re: Jet drive to prop drive conversion.

The conversion is as simple as getting a lower unit for that engine and installing it, then re-routing the shift cable. The problem comes in as to the type of boat you have. Usually, going from a jet to a prop also requires a shaft extention kit/spacer since with a jet, the engine is shorter shafted than if it were a prop. Best thing is to measure the height of the transom, then from the part of the engines mounting bracket that sits on the transom to the top of the jet portion of the engine (That will give you the shaft length of the engine). Then it's just a matter of doing a little math to find out how much of a spacer you would need.

Hope This Helps.

Craig

 

[arvo11]

Re: Jet drive to prop drive conversion.

Thank you Craig for your response. I was hoping it might be possible to replace the jet with a lower unit assembly. I plan on putting the motor on a 24 foot pontoon that currently has a Merc Classic 50 with a 20in shaft. My next plan of action now is to remove the old engine and mount the 04 engine and do some measureing. Any ideas what prop pitch to start with on this application? My assumption is that the power will be somewhere close to the 115hp mark with the prop drive assembly. Is that a correct assumption? Thanks again.

 

[canoemang]

Re: Jet drive to prop drive conversion.

Your correct on the 115 hp after propped, i know the prop to jet conversion took me 2 hours both times. I'm uncertain as to if there is going to be any difference going from a motor from the factory stock as a jet to prop.. i don't think there would be..

What part of the jet foot cracked?

 

[arvo11]

Re: Jet drive to prop drive conversion.

Thanks Canoemang for the info. The foot is cracked on the left front corner looking at the motor from the back. The crack goe's from the outside making a cresent almost all the way around to the front again, stopping an inch of two from the front of the pickup. The strainer bars are all trashed (bent badly, but not broken) and mashed together. I bought the motor from some duck hunters that whammed a huge rock just under the surface. They made it back to the dock under power. Then they went to a dealer and bought a bigger motor (150hp Merc) with a Jet drive on it. Said they wanted more power anyway. LoL. They offered me the busted motor at a good price and gauranteed the powerhead to be good with less than 150 hours so I took them up on it because I wanted more power for my pontoon. (More power is always needed, right?) My son is a machinist and welds aluminum as part of his job, so we may try to fix the foot, assuming the impeller and the rest of the jet checks out ok. Sounds like you know jets. Anything special to look for when checking this unit out?

 

[canoemang]

Re: Jet drive to prop drive conversion.

When i pieced my Merc 115 jet together the jet foot had a crack on it, i ended up buying a new one from Outboard jets and had my old one welded. I carry my old one with me for a spare.

If it is just the foot and not the volute that is damaged and you plan on using it you can always do what i did. You can have most machine shops make you custom intake grates for about the same price as ordering them also..

If you grease it and water comes out with the grease the seals are shot but with low hours on it the seals should be fine.Also make sure the clearance of the impeller and liner is within spec, i think it is .032 with a feeler gauge.

 

[Mi duckdown]

Re: Jet drive to prop drive conversion.

arvo11. Pics of the damage would help.