Possible blown head gasket Honda BF45A

[EricR]

Hello all-

A year ago I bought a used BF45A with controls for a screaming deal of $650 to run on my 15' Glasspar runabout. It has been a really good motor until this problem-

I overheated it running on the flusher, the impeller bit the dust. I was busy washing down the boat and did not notice the tell tale wasn't putting out water until the exhaust sound changed. I shut it down, but it was pretty hot to the touch.

I pulled the foot, and installed a new water pump kit complete as my wear plate was grooved up. I reasembled, it ran and pumped well on the muffs.

I took the boat out and ran 10 min below 2000 RPM, then got it on plane and ran up to cruise. After two to three minutes, the horn went off, and heavy steam came from the exhaust idle port. I thottled back to under 2000 and the horn quit. I idled back in. None of my lights on the control (Honda side mount) lit at the time, I later found they do not work when tested per the Honda service manual.

I later tested the temp switch and the oil switch, they both function to set the horn. I pulled the thermostat housing, the 'stat was very corroded and broke in my hand. The plunger so to speak was stuck- I figured the thermostat was stuck just barely open and did not open enough to deliver the volume of water at higher speeds/loads. I replaced the 'stat and gasket.

Took the boat out this afternoon, same thing, 2-3 minutes on plane, got the horn and the steam cometh. Idled back in.

Did a compression test at home- first off. the bottom plug is whitish, the other two are sooty. Compression with the throttles closed (yeah, I know the book said to unhook the linkage etc) was 115-120-115 psi. Even enough for me.

My guess is a warped head causing a blown gasket, and until the thermostat opens it does not effect it. No evidence of water is found in the oil.

I have experience on two stroke outboards, and am a marine tech by trade on inboard diesels, but have not touched on OHC four stroke outboard yet.

Anyone agree on the head gasket diagnosis, and have any advice on pulling the head, tips-tricks?

Eric in Savannah

 

[Skinnywater]

Re: Possible blown head gasket Honda BF45A

Hard to condemn the head gasket at this point.
A cylinder leak down test would be worth the effort.

Suppose you removed the water jacket plate and picked out all the old waterpump debris, bits and pieces of obstruction.
That would be an excellent place to hear any escaping air being applied during the test.

Curious what year it is, how many hours?

 

[EricR]

Re: Possible blown head gasket Honda BF45A

Ahh, yes there was impeller debris when I replaced the thermostat that I dug out of there. I will pull the plate and hopefully the gasket will survive.

Only one Honda dealer near me, and they stock very little. I had to order the gasket and thermostat. Wish there was a place online (or is threre?) where I could look up parts on an exploded view, then order direct.

I can rig a leakdown adaptor too.

I have no clue the hours, I was told it's a '96 model, Honda's infinite wisdom to rivet a corrodable aluminum serial plate to the clamp bracket wasn't the best, it's gone. I was on a rental skiff and does have I would guess some hours on it. It ran perfectly last year for me.

 

[EricR]

Re: Possible blown head gasket Honda BF45A

Well crap- I broke two screws off trying to take the plate off and the rest all feel like they are going to go. I knew I took a gamble with this saltwater engine, and I am mad at myself for not catching the impeller failure right away.

I assume the "water jacket plate" to be the plate on the exhaust side of the block, below the T stat housing?

 

[Skinnywater]

Re: Possible blown head gasket Honda BF45A

Ahh, yes there was impeller debris when I replaced the thermostat that I dug out of there. I will pull the plate and hopefully the gasket will survive.

Only one Honda dealer near me, and they stock very little. I had to order the gasket and thermostat. Wish there was a place online (or is threre?) where I could look up parts on an exploded view, then order direct.

I can rig a leakdown adaptor too.

I have no clue the hours, I was told it's a '96 model, Honda's infinite wisdom to rivet a corrodable aluminum serial plate to the clamp bracket wasn't the best, it's gone. I was on a rental skiff and does have I would guess some hours on it. It ran perfectly last year for me.

Do a thorough search on this, our hosts site for the parts you need.
If iboats doesn't have what you're looking for email me direct, I'll send you a link to a online Honda dealer I use.
bachelor@stormnet.com

Get the remaining bolts soaking, and get prepared to drill and tap like your motors life depended on it.

 

[EricR]

Re: Possible blown head gasket Honda BF45A

I don't think soaking will even get down to the threads, the bolts have a shouldered head. I can forsee broken stainless steel bolts in an aluminum engine block. Oh joy. In any case I may have to pull the head to get in there and see what obstruction there is. I know when I take out the thermostat, and trickle water down that opening, it runs out the prop hub.

I wonder since it holds even compression if there is a small crack in the head or something that opens up when it is hot under load. I am thinking of taking out the temp sensor, and rigging a nipple into that hole to backflush water through the powerhead. I can also do this while applying air to cylinders.

I am going to pull the lower unit and take a coathanger through the tube to the powerhead and see what comes out. I'm pretty bummed right now, thought I had it fixed with the thermostat and now there does not seem to be a way I will have this running for memorial day weekend.