Driveline question

[Rickairmedic]

OK I'm the new guy just picked up a 1974 larson 1700 shark with a 120 HP mercruiser I/O . The boat will go just fine at idle but at any higher RPM's it wont move . The guy I bought it from said he thought it needed a throwout bearing ? . I am quite versed in auto mechanics but havent torn into a boat before anybody got any ideas on the issue . I will be ordering a manual tomorrow but if they are anything like most Hanes or Chiltons auto manuals it may not be alot of help.


Thanks for any help Rick

 

[boatguya1]

Re: Driveline question

Motor off shift lever in forward can you turn the prob backwards? If the prop will turn but not the pro shaft you have a spun hub in the prop. Jump up and down and shout yahoo because it's cheap and easy. New prop or get a new hub installed at the prop shop. If the shaft turns with the prop it's either the engine coupler or a drive problem. Put face in hands and wimper/cry it will be $$/work.

James No throw out brg on the boat

 

[Rickairmedic]

Re: Driveline question

James thanks for the quick reply I had done a little looking around and saw the coupler listed in the parts breakdown . I will try the prop deal tomorrow and also order a manual for it .

Rick

 

[windsors03cobra]

Re: Driveline question

Factory Service Manuals available for download among other valuable information pertaining to your MerCruiser stern drive at the top of this sub-forum in the "ADULTs ONLY" sticky post. I would say you need #2, much better than an aftermarket like haynes manual, which yes is unhelpful rubbish.

Probably needs a gimbal bearing, bellows,lower shift cable, etc, etc.... Every old boats laundry list. B.O.A.T=Bust Out Another Thousand.

So you say it moves and idles fine but "won't move" but when you increase the revs, does the prop speed increase ? Perhaps the prop hub is spun, when you increase the revs does it feel like a slipping clutch ?

 

[Rickairmedic]

Re: Driveline question

Windsor I havent actually had it in the water yet just picked it up last night but yes the guy I bought it from described a feeling like somebody pushing a clutch in when he reved it up. I havent had a chance to do much checking on it yet but will do some checking this afternoon. He said when it happened it felt like he hit a sandbar and then wouldnt move he had to idle it all the way back to shore so who knows maybe I got lucky and he actually did hit a sandbar and spin the prop . Thanks for the info on the manual I am downloading it now to my garage laptop.

Rick

 

[Rickairmedic]

Re: Driveline question

Well I just got home from work and put the boat in forward gear and tried turning the prop backwards and it wouldnt move backwards but spun freely forwards so I am leaning towards the engine coupler . I will download the manual tonight on my desktop as I am wireless out here in the garage and its a laaaaaaaaage file hopefully I will be able to play with it some more tomorrow . I am pretty well whoooooped at the moment I own an HVAC company and have spent the better part of an 80+* day in an attic . Thanks for the help so far .


Rick

 

[boatguya1]

Re: Driveline question

Assuming you turned it hard towards backwards with the shifter in fwd and it wouldn't move it sounds like you may have to run it in the lake some to get it to act up then do the same test. There are 2 ways for the coupler to fail, 1 the splines give out and you should be able to turn the prop for this one,2 it has a rubber hub just like a prop if this is the problem it may have to run under load for a while to start slipping. Same with the prop hub you might have to run it some.

I've also had people pick up some debris on the front of the lower unit causing the prop to airate with the same symptoms. A good blast of reverse many times clears this.

At this point I think you need to run it and see what you have, uptill then you're relying on the sellers description. Make sure your oil levels are good and watch your temp closely. Don't bring the family just you and maybe one experienced boater if one is available.

James

 

[Rickairmedic]

Re: Driveline question

Thanks James probably not a bad idea and yes I will have to take an experianced boater with a second boat . I dont live close to a lake but am 2 miles from a ramp on the Ohio river so will need a backup boat just in case I need to be towed back .


Rick