Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead???

[vcaptain]

Hello everyone,

I bought a jon boat and trailer the other day from a guy for a song, it came with a 15hp honda, the serial number is BAAL-1204740, so I think it's a 1997, but not positive. The gear case oil looked good, motor oil looked good, and it will turn over with the electric start.

With the difference between the two being about 30psi, am I looking at a big problem? I know it should be within 10%, but before I sink any money into it (needs fuel pump for sure), I'd really like to hear from one who owns on of these or works on them frequently.

Thanks guys!

 

[MattFL]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

First check the valve clearances. With any luck, the low cylinder just has a valve that has no clearance and is hanging open. In this case it is possible a valve adjustment could put you back to normal. If that doesn't do it then you need to look further.

 

[vcaptain]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

First check the valve clearances. With any luck, the low cylinder just has a valve that has no clearance and is hanging open. In this case it is possible a valve adjustment could put you back to normal. If that doesn't do it then you need to look further.

Thank you for the quick reply, I'll be happy if it's something simple. I've never done a valve check, but some searching I found this set of instructions on another site...is this the right way to do it? To move the flywheel to align do I take off the recoil starter?

1) Make sure the engine is COLD.

2) Move the flywheel so that the T markers line up. Makes sure you turn it in the direction of the arrow on the flywheel.

3) Remove the valve cover checking that the gasket is in good condition. If it's cracked replace it.

4) Adjust the valve to the gap as prescribed in your manual and close it up.

correct? What do you use to measure the valve gap? spark plug gap sizer?

 

[MattFL]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

More or less. Get yourself a manual like a clymer brand, it will take you step by step. You will likely want a new valve cover gasket, but make sure the valve adjustment fixed it before you spend on the gasket. You will need a feeler gauge to measure the clearance.

 

[vcaptain]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

More or less. Get yourself a manual like a clymer brand, it will take you step by step. You will likely want a new valve cover gasket, but make sure the valve adjustment fixed it before you spend on the gasket. You will need a feeler gauge to measure the clearance.

I have been referencing this manual - Boatinfo - Honda Service Manual for BF99A and BF15A

I got the cover off and access to the valves, but I'm stumped on where to check clearance. am I supposed to check where the rocker arm comes in contact with the camshaft?

 

[MattFL]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

Most typically you check where the rocker contacts the valve. If the timing marks line up but the valve is being held open then rotate the crank 360 degrees and the valve will be closed. Start with the smallest allowed clearance and see if you can push the feeler in. Some small resistance is OK, but it should slide in pretty easily.

 

[vcaptain]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

Most typically you check where the rocker contacts the valve. If the timing marks line up but the valve is being held open then rotate the crank 360 degrees and the valve will be closed. Start with the smallest allowed clearance and see if you can push the feeler in. Some small resistance is OK, but it should slide in pretty easily.

Thanks, I got the wrong set, way too thick.

 

[vcaptain]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

I am searching for the right feeler gauges and am confused. The manual I found said the intake should be .010-.037mm The smallest I found is .020mm, any advice on where I can get a .010?

 

[vcaptain]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

Ok, I got the wrong info, found a new manual and it says IN .12mm +-.02, and EX .20 +- .02 and it needs to be in neutral. Which ones are IN and which are EX? There are 4 from top to bottom, I'm just guessing, is the top one intake? then ex? and so on?

 

[MattFL]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

Intakes are going to be on the same side of the motor as the carburetor(s). Exhaust are on the opposite side. Most likely the cylinders fire alternatively, which means you'll have to measure one cylinder then spin the crank 360 degrees and do the other (assuming 2 cylinder).

 

[vcaptain]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

Intakes are going to be on the same side of the motor as the carburetor(s). Exhaust are on the opposite side. Most likely the cylinders fire alternatively, which means you'll have to measure one cylinder then spin the crank 360 degrees and do the other (assuming 2 cylinder).

All the springs are one side, two per cylinder, top and bottom, carb and exhaust are on the same side.

 

[MattFL]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

hmm... follow the intake plumbing, it should more or less line up with the intake valves. You can also shine a light into the sparkplug hole (or carefully partially insert a long pencil) to see which way the piston is moving and see which valve opens while the piston is on the way down, that will be the intake valve. Also the manual should tell you which is which.

 

[vcaptain]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

OK, did the pencil trick, and I think I've figured that part out. Both pistons are at the top at the same time, is that right? I always have believed that they would alternate.

 

[MattFL]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

It depends on the motor. I would expect most boat motors to alternate, though they may move together but fire alternatively.

 

[vcaptain]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

ok, thanks!

 

[vcaptain]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

I was thinking about it, and the valves do alternate when the they lift per cylinder as I rotate the flywheel. It must alternate firing.

 

[vcaptain]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

Success! I adjusted the valves to specs, and the top cylinder is 125, bottom 125 on a cold test. Now to order the new fuel pump and gas lines and I hope to catching some lunkers soon.

 

[MattFL]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

Great! Keep an eye on the valve cover the first time you run it to make sure you don't have an oil leak, and enjoy!

 

[vcaptain]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

Great! Keep an eye on the valve cover the first time you run it to make sure you don't have an oil leak, and enjoy!

Thanks for the help!

 

[vcaptain]

Re: Honda BF15A - compression tested, 95psi on top 125 on the other - problems ahead?

FYI - The manual still does not really specify which valves are which. The top one of cyl. 1 is EX, the bottom of cyl. 2 is EX. The other two are obviously IN. My manual says adjust cyl 1 first, then rotate flywheel 360 and do cyl 2. both IN and EX at same time on each cylinder. .12 IN, .20 EX