So I just bought a Mac X....

[opie]

[Drifter]

Replacing parts I can keep doing but when it comes to skimming aluminium heads and holes in the engine, that's beyond me.

There's no sign of water in the engine oil, which is good, but usually the clue for a blown head gasket shows up in the coolant. Can't really inspect that on an engine that constantly replaces the water from outside.

For some reason I was thinking/hoping that the very fact it's constantly replaced meant the water cooling system on an outboard is not under high pressure, like it is on a self-contained car engine where pressurization increases the boiling point of the water? So was thinking a blown gasket was unlikely - but reading the things are so vulnerable they need skimming every time they're opened changes that.

If at any point in the last 25 years the OO ever changed the piston rings then it may well have a warped head, by the sound of it.

Well I guess the only thing to do is follow the basics. Seems I can't really test it under load in a tub.

• Change back to 3 blade prop - done
  Change the thermostat - done
  Find the time and enthusiasm to change the impeller
  Flush the engine with Saltaway
  Fill all water and fuel containers, icebox and full crew, launch and after warming up, give it WOT for 5 mins and see what happens

If it does still overheat, see if I can find the exact point it does (previously told 3500 rp). Might be able to squeeze one river-only fishing season out of it as a very slow boat, while saving up and trying to source a replacement engine.

If it doesn't, then fine, I'm happy to baby and care for the little Honda, which seems a lovely engine if it doesn't do the overheating thing.

Back in the UK or maybe even mainland Malaysia it would be possible to try taking the engine to an engineering company and asking them to skim the head. I had to do that once for a high performance Audi, after some rally-driving fun created a mud/bush covered radiator and overheating.


As an aside, the most likely local alternative engine would be a Yamaha 80hp 2-stroke. In terms of weight, it would probably not be any heavier, but obviously more powerful. Think the transom could take it? Obviously Roger would say no, though I do hear of people fitting 90hp engines?

[OverEasy]

Hi

I figure your somewhere out in the bush of sorts and havin had to make do in primitive conditions a time or two there is a trick if you are desperate enough that I used a couple of times on two-stroke racing heads that were warped beyond what the head gaskets could handle.

“Modern” marble counter tops are ground pretty flat.
You can check it with the edge of a good machinist’s square ruler several places in an overlapping asterisk pattern and a strong flash light.
Take the finest grade wet/dry Emory paper (400 grit or better for the finish, 200 grit to do the rough work) and using thinned contact cement apply it grit side up on to the cleaned marble surface. It helps to have a clean smooth cylindrical (check flatness with machinit’s ruler edge) marble pastry rolling pin to apply the Emory paper and flatten it out.
If you do it right you have a proto lapping table to manually level your warped head.

Emory surface should be roughly 2x your head contact surface area.
Wet the Emory and use a figure 8 motion to evenly level down the head contact area.
By figure 8 I mean take the head with one hand on either side and make a sideways 8 motion with the head about 1-1/2 times the length and width of the head seal contact surface area.
Don’t force it!
Just mainly let the weight of the head and the figure 8 motion do the work.
Keep the paper wet and periodically rinse the paper and head to clean away accumulating debris.
Occasionally rotate the head 180 degrees for an increment and continue the figure 8 pattern.
As your witness marks become uniform across the entire surface change to progressively finer grits using the same process.
Yes, the process is laborious and time consuming but if you’re in the middle of nowhere it’s a way to get the job done.

Alternatives surfaces are things like thick plate glass or a thick mirror on a solid smooth level surface.
The more stable the surface the better.

Another option is my preference which is to contact engine machine shops in a more developed area or country, talk to them and see if you can mail them the head. You’re not limited to what happens to be nearest to you locally.

Alternatively you might be able to find a new head via the internet and have it shipped to you.

Parts is parts. Keep an open positive mind and pleasantly surprise yourself!
(I’ve spent a career or two pleasantly surprised! )

Hope this was of some help.

[Drifter]

Well OverEasy, I suspect you're making things sound... over easy?

While trying to stay positive and while waiting for the shop manual, anyone know the specs for the tilt/trim oil?

I've found this:

https://shopee.com.my/1LT-AIMALUBE-POWE ... 7355844556

Nope, scratch that, "West Malaysia only". Wouldn't want to blow up the whole planet by shipping a liter of fluid to East Malaysia; that would be terrible.

But if I were to find some dastardly scoundrel willing to break all the rules, what fluid would a criminal like me be looking at smuggling?

Any old ATF or...?

[Russ]

I believe it's just any old ATF.

Here's an old thread (missing photos because hosts went out of biz)

viewtopic.php?t=26236

[Drifter]

Wahoo! I feel somewhat confident I can do this bit

Cheers!

[Be Free]

Just remember that 5th bolt that holds the leg on. It’s either under the trim tab anode, or it’s under the intake screen; I just don’t remember now, but it’s in there somewhere. I put a floor jack under the leg when taking the bolts out, just so it can’t drop, but any stack of scrap wood will do of course. Or do it while it’s tilted all the way, but be careful it doesn’t drop. It’s not heavy, but it is somewhat delicate, being aluminium and all.

The fifth bolt is under the trim tab. Re: an earlier question - the trim tab will be turned a little bit clockwise (a degree or two, maybe three). It will not be straight to the rear.

I've never had one fall off but I don't doubt it could happen. I usually have to give it a light tap or wiggle to get it to come off the locating dowels.

[Be Free]

The shift rod won't fall down when you disconnect it on this engine. When you put it in reverse to be able to reach the nuts it's already as far down as it can go.

The stream in your video looks a little weak to me. You may have a damaged impeller in the water pump. It's easy to change. See my previous post. Change the impeller before you mess with the heads.

The easiest test for a blown head gasket is a compression test. All you have to remove are the spark plugs. I don't have a manual handy. Does anyone know what the correct pressure is for this engine?

5000 RPM in neutral is pretty fast. You probably did not hurt it but I would not recommend doing that again. Also, running it in gear at full throttle without the prop WILL allow the engine to exceed red line. That is also a very bad idea. Engine damage is very likely.

I'm not concerned with the scale in your thermostat passage. It won't hurt to clean it but it's probably making your engine run hot. If you are confident that the thermostat did not open at the right temperature just go ahead and replace it. The pointy end goes up, the longer, round end goes down. I don't think you can even get the cover on if it is in wrong.

I suspect the information you saw regarding adjusting the tachometer was setting it for the correct number of cylinders. If you have a Honda tach it will be matched to the engine. If it is aftermarket it might be wrong but it would be off a multiple or a fraction of the indicated value. If you were reading 3500RPM at or a little above half throttle you probably don't have a problem with your tach.

[Drifter]

I thought I replied on my phone but seems not...

First, thanks again for all the great replies

Regarding gripping the selector shaft, that video was a for a 75/90 and watching again it seems the shaft is pulled out of the top end, so the Molegrips are to maintain the same place and stop it dropping out of adjustment. Seems on the 50 you unbolt the shaft so it separates into 2 parts, OK, understood.

I think my phone didn't do a great job of capturing the pee stream, which is pretty powerful and any increase in revs (on idle in the vid) immediately creates a stronger flow. However i think we all agree the impeller needs changing, if only so I know exactly how old it is.

Although I have a bunch of spare impellers and a couple of gasket kits I have ordered a new one...

Why?

Because I've tried ordering this:

https://www.amazon.com/gp/product/B00BDXRXWQ/

It's the complete kit, with a new housing, new steel plate etc. The whole thing. For less than $70 inc shipping I figure it's worth doing.

One thing I did notice with the thermostat is it was lightly covered in sand. Couple that to the fact the OO has so many spare impellers suggests that the engine has often been beached or used in shallow water with sand kicked up, and perhaps a history of sand wearing out the frequently-replaced impeller?

If so, then it may have also damaged the housing etc. So changing the entire thing will give some peace of mind and eliminate the impeller from suspicion... presuming the kit does actually fit, does arrive OK and I do manage to fit it correctly - but I'm being optimistic here

Regarding a compression test, I read on a different forum somewhere it should be crazy high, like 199 PSI? That's way, way higher than I'd normally be looking for with a big 2-stroke, where anything over 100 is OK and 130 is considered good. I guess little 4 strokes are different from big 2 strokes.

I do actually have a compression tester kit. Not 100% sure if any of the adapters will fit the tiny Honda plug holes but I can try.

In my tool box i have some things you fit into the spark plug caps, so that the electronics are not damaged by a lack of spark. Is it however correct that just not using the safety lanyard will prevent it sparking and also prevent causing any damage?

It won't hurt to clean it but it's probably making your engine run hot

You skipped the word "not", right?

[Russ]

Regarding a compression test, I read on a different forum somewhere it should be crazy high, like 199 PSI? That's way, way higher than I'd normally be looking for with a big 2-stroke, where anything over 100 is OK and 130 is considered good. I guess little 4 strokes are different from big 2 strokes.

I do actually have a compression tester kit. Not 100% sure if any of the adapters will fit the tiny Honda plug holes but I can try.

In my tool box i have some things you fit into the spark plug caps, so that the electronics are not damaged by a lack of spark. Is it however correct that just not using the safety lanyard will prevent it sparking and also prevent causing any damage?

A quick search turns up "Normal compression for the 50hp is 199psi at 500 rpm."

More searching shows this with a warm engine and throttle at WOT. And yes, apparently wires grounded so not to damage somethings.

One thread showed an owner spoke with a dealer who said 180psi is okay. Others seems to say it's more important that there be little difference in PSI between cylinders. My guess is the heads are fine.

Another thought is that it might be a faulty sensor. I had a Seadoo that kept overheating. It's cooled from the jet pump so no cooling impeller. It was the sensor. Quick and easy fix.


Great idea to replace the whole impeller housing parts. Maybe even look up if possible to see if there are any old broken bits of old impellers in the channel.

You got this.

[opie]

My Honda 50 BFA works fine for me even though compression is less than specfied.
Opie

[Be Free]

Yes, I missed the word "not".

I've used that water pump kit before. It works great.

There are three things that are rough on water pumps.

• If you run them without water at all they will overheat and begin to melt the impeller blades to the inside of the pump housing.

• If you suck up sand the additional friction will quickly erode the rubber.

• If the boat sits for a long time (many months) the rubber dries out and the impeller blades break off when you start it. Even if you don't let it sit a long time you should still replace the impeller periodically. I do mine every other year. Some do it every year; some wait longer. I prefer scheduled maintenance to unexpected repairs.

Around 200psi sounds about right from memory. I did not want to quote that last night since I have not looked it up in a long time. Since you are dealing with an older engine it may be lower but all of the cylinders should be close to the same (lower) number. If one of them is significantly higher or lower then there is a problem somewhere. Put a small amount of oil into any cylinder(s) that are reading too low. If the reading rises then the problem is rings. If it stays the same then it is probably the head gasket (might be valves).

Another preventative maintenance item you should not neglect is the timing belt. Your engine is an interference design. That means that if the timing belt breaks the piston can, and almost certainly will, make contact with any open valves. That will be a multi-thousand dollar repair. Inspect the belt each year. If it is cracked, missing teeth, or in any way looks suspicious you should change it. While you have the cover off make sure the tensioner is still working. It is not self adjusting but is very easy to adjust. Your belt should not be loose at all.

[opie]

Be Free is +1

Also, for filling the tilt, make sure you are fully tilted up before removing filler nut.

[Drifter]

Quick question regarding the compression test, why is it necessary to remove the throttle linkage, and then open the throttle?

Oh... because it won't turn over in gear, right? But if you have to hold the throttle open manually anyway, and it's going to be in neutral anyway, then why not just, you know, hold the throttle open manually, without dissembling it?

Especially when it says "carefully", like I might break something?

Regarding the timing belt, I see this:

https://www.marineparts.eu/spare-parts/ ... 0-zv5-014/

Mine is a 96, so was there a difference, does anyone know? I've read somewhere the BF50A are all identical up until 2006, but that "Years: 1997 >" is making me nervous...

[opie]

Drifter, you may have a point. I don't remember. Can the throttle can be opened by hand without disconnecting the rod?

But, the rod snaps off and on.

In any case, the reason for opening the throttle fully on a car or boat engine during compression test is to allow unrestricted full air into intake.

(Edited to ask the above question)