'71 25HP - Overheated, won't start now

[Bindernut]

I've got a 71 'rude 25HP. First trip out this year...the water pump impeller died and I overheated the motor. It didn't seize up, but was hot enough that wake spraying on the exhaust housing was sizzling off. I shut it down as soon as I noticed it and limped back on the trolling motor but after replacing the impeller she won't start any more.

What is an acceptable compression reading for this motor? I'm getting 70 & 75psi. That seems too low to me. I haven't pulled the head yet, but I'm guessing I'll find scuffed pistons.

Next question...rebuild or replace...

Rebuild--I'm pretty new to outboards, but am a big vintage sled nut so rebuilding an old two-cycle doesn't scare me too badly. Are parts still available and where's a good source to get em? (pistons and gasket set in particular).

Replace--The motor is on a 1980 14' Blue Fin aluminum v-bottom. It was a resort rental boat from Minnesota originally. Just a basic fishing boat, but the previous owner added a small platform/battery-compartment from the front bench to the bow along with a bow-mount troller. With just myself in the boat, it gets up pretty good with the 25HP, but it just doesn't come up on plane with another person in the boat. If I replace the motor I'd like to step up to a 30-35HP but I can't find any info on this boat to see what the max HP/weight is for it. The tag is all faded out, I can't read anything on it except the stamped serial #. Can't find any BlueFin info on the net except for their big offshore stuff either. Can anyone point me in the right direction? A friend has a newer 35HP Johnson that is only 20-25lbs heavier than this 25HP...what kind of trouble could I get into by stepping up to something that size?

Thanks!

 

[F_R]

Re: '71 25HP - Overheated, won't start now

Personally, I'd opt for the newer 35hp. I have an '84 on an aluminum 14' Lund and love it. It certainly doesn't sound like you are near being overpowered now. Disclaimer: I'm not familiar with your boat, maybe somebody else knows more.

 

[tashasdaddy]

Re: '71 25HP - Overheated, won't start now

you bluefin was made by one of the Brunswick (Mercury) boat companies, i went defunct in the early 90's i have and 18' center console. use the BLUE post reply, scroll down to manage attachments, clik you can upload pictures from your computer. let's see the boat. pull the head, could just be head or exhaust gasket. i reserve judgement on the increased Hp till i see the boat.

 

[Chinewalker]

Re: '71 25HP - Overheated, won't start now

70-75 PSI is way low on that motor. A good one will punch my gauge into the 120-130 range. If you're not willing to rebuild it yourself, it isn't really worth it to pay someone else to do it. Part it out on eBay and use that as seed money toward a newer/bigger motor...
- Scott

 

[Bindernut]

Re: '71 25HP - Overheated, won't start now

Thanks. I figured that 70psi was too low...I know that's way low for a sled motor.

Thanks for the Blue Fin info Tashasdaddy. I've seen a few other basic v-bottoms on ebay, but all have been 16 footers.
It'll be a few days until I get back to the farm to snap pictures. I'll post some down in the Blue Fin forum when I get em.

I'm also thinking that the 25hp might just have been getting tired before I overheated it and a fresh rebuild would help move it out across the water better.
Before, it would take 5-6 pulls to start but ran real nice when used at idle for fast trolling. It ran great at WOT too, but just couldn't pull the boat up on plane with two people on board.

 

[BF]

Re: '71 25HP - Overheated, won't start now

unless you've got lots more weight in your boat than I'm imagining, I'd say your motor was definitely weak/not right before. I have a '70 25 hp on a 16' boat that is rated for a 35 hp... It will plane out with 4 adults on board no problem. Mine has compression 120+. Not to say that your boat wouldn't handle more motor (?) but you might be happy enough if you had a healthy 25 on the back. Or maybe you've got way too much prop on it (?) I think 10" pitch was the "standard" one... Since the props for bigger motors may also fit, it is possible that someone has stuck a 13 pitch or something on it at some point. Maybe that was part of your problem.

good luck.

 

[Kevin W]

Re: '71 25HP - Overheated, won't start now

before I would call it quits on the 25hp I would pull the head.
the gasket may be toasted and leaking.
it may only need a head gasket to get the compression up.
It's also a good time to evaluate the cylinders.
If you get this one running again you could sell it and buy the 35hp.

 

[tashasdaddy]

Re: '71 25HP - Overheated, won't start now

doing a decarb will get them built up 35 year old crud out of it. 71 has just gotten broken in good. i like to run the 50's models.

 

[Bindernut]

Re: '71 25HP - Overheated, won't start now

All is well again. It turns out that I just cooked the head gasket and warped the head about 1/16".
I pulled the head this weekend and found nice clean cylinder walls with good crosshatch and only a couple small scratches so I surfaced the head and threw on a new gasket. Compression is up to 118 and 120 and she fires up on the second pull. I ran the engine a good half-hour on the trailer (yes, in the water too! ) and the cooling setup is working great.

I did the thermostat and also replaced the lower unit seals and a bent prop shaft while it was apart for the impeller. Just need to replace a slightly dinged up prop and keep this one for a spare.

Work dragged me away before I could take it out for a run though...we'll see how good she runs in a few days.

Tashasdaddy,
I decarbed the motor last year when I bought the boat, but never got around to doing a comp test on it before or after. It's gotta be an improvement now since it doesn't take 5-6 pulls to start anymore.
I'll post some pix when I get my camera unloaded...am still curious about the specs for the boat itself.

Thanks everyone!!!

 

[F_R]

Re: '71 25HP - Overheated, won't start now

Binder, listen up: If you cooked the head gasket and warped the head, you also burned the gaskets in the exhaust cover. That means that they will leak and very well might squirt water into the exhaust ports and ruin the powerhead. Consider yourself warned!

 

[Bindernut]

Re: '71 25HP - Overheated, won't start now

Binder, listen up: If you cooked the head gasket and warped the head, you also burned the gaskets in the exhaust cover. That means that they will leak and very well might squirt water into the exhaust ports and ruin the powerhead. Consider yourself warned!

I'll check them out. I didn't have any water leaking around the exhaust cover, but better safe than sorry...a couple gaskets are cheaper than a complete rebuild! Thanks for the heads up F_R!

What about the bypass port covers? A leak there could give me a lean condition and burn down a cylinder too right?

 

[F_R]

Re: '71 25HP - Overheated, won't start now

The worst that the bypass covers would do is make a mess and/or cause it to run poorly at idle. I can't see them leaking so badly that they burn a cylinder. Before that would happen, it would be running so lousy that you would be replacing them.

 

[Bindernut]

Re: '71 25HP - Overheated, won't start now

Sounds good F_R. Had her running and idling nice when I tested it on Saturday so they're probably okay...and I checked em by spraying carb cleaner around the covers looking for leaks but I'm gonna replace em anyway. I've lean-burnt a couple sled motors from intake leaks before so no sense in taking any chances. This is a great little powerplant!

If anyone might have info on the boat itself, I posted a couple pics of it down in the Blue Fin forum.
http://forums.iboats.com/showthread.php?t=196678