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Honda BF20- no compression in 1 cylinder

R

Rickles

New member
Need some help... Was out on the lake running at full throttle and all of a sudden the motor cuts off instantly. Has electric start and I can crank it over but the engine would not start. Get back to shore with the trolling motor. The motor has fuel, and spark but no compression in the top cylinder. Verified it with a compression tester. Any idea of what could have happened? Blown engine? burnt valve? etc... Is there anything I could check by looking at the valve body for a quick diagnosis, is there something I could check to see what possibly could have broken? What would cause compression on the bottom cylinder and 0 compression on the top cylinder? Any help would be appreciated. I just want to get pointed in the direction of repair or replacement. The motor is 12 years old. The motor always started up fine with zero issues, and idled fine, with no other issues except for what just happened. I change the oil yearly and use the boat about twice a month in the summer months. The water pump works fine. Not sure if the motor just blew up or what. Thanks for any help.
 
Hi,
Sounds bad.
First thing I would check is the timing and timing belt to see if it jumped time.

Take off the valve cover and watch the rocker arms to see if they're moving and opening the valves as you slowly pull the engine over with the recoil starter. I would NOT continue to crank it with the electric starter until I knew what happened. That could just cause more damage.

If the valves were never adjusted, there's a distinct possibility that they got tight and there may have been contact with the piston.

I have one of these 20 BFD's and the manual but I can't tell you if this is an interference engine or not.

Good luck.
 
jgmo said:
Hi,
Sounds bad.
First thing I would check is the timing and timing belt to see if it jumped time.

Take off the valve cover and watch the rocker arms to see if they're moving and opening the valves as you slowly pull the engine over with the recoil starter. I would NOT continue to crank it with the electric starter until I knew what happened. That could just cause more damage.

If the valves were never adjusted, there's a distinct possibility that they got tight and there may have been contact with the piston.

I have one of these 20 BFD's and the manual but I can't tell you if this is an interference engine or not.

Good luck.
Click to expand...
I opened up the case and found that the timing belt jumped off of the sprocket. I did find a small circular piece of plastic and was able to determine it was from the top of the sprocket. I attached pictures of what I found. It seems like the sprocket piece broke and it moved down on the shaft and the belt slipped off the top. Makes sense now why the motor cut off instantly. If I buy a new sprocket, is it as easy as removing the old one, installing the new one, putting the engine back in time, and installing the belt? Thank you for all the information so far.

20230720_191306.jpg

20230720_191328.jpg

20230720_191344.jpg

20230720_191350.jpg
 
Well, I wish I could assure you that replacing the cam gear (I would also replace the timing belt but that's up to you) would make everything ok but I just don't know.

You might just want to try putting the belt back on and doing another compression test before buying anything.

Don't try to start it!

Just replace the belt and, at first, turn it over slowly to see if there's any hard resistance to rotation or noises like metal to metal contact. If there is, don't force it as that will just create more damage.

If it seems to rotate without noise or binding and the #1 valves open and close smoothly and evenly, then do the compression test.

If that goes well, I think it would be safe to order your parts and give it a go.

I wish you good luck.
 
jgmo said:
Well, I wish I could assure you that replacing the cam gear (I would also replace the timing belt but that's up to you) would make everything ok but I just don't know.

You might just want to try putting the belt back on and doing another compression test before buying anything.

Don't try to start it!

Just replace the belt and, at first, turn it over slowly to see if there's any hard resistance to rotation or noises like metal to metal contact. If there is, don't force it as that will just create more damage.

If it seems to rotate without noise or binding and the #1 valves open and close smoothly and evenly, then do the compression test.

If that goes well, I think it would be safe to order your parts and give it a go.

I wish you good luck.
Click to expand...
I did what you suggested. I put the belt back on, made sure the timing marks were lined up, turned it over by hand slowly, and did not hear any noises out of order. No metal-to-metal contact sounds. The valves look like they are opening and closing normally but I have nothing to compare it to. I did a compression test and had compression on both cylinders, but it was hard to hold the tester up against the sparkplug hole and rotate the engine. My compression tester does not screw in but has a rubber end that makes a seal when you press it into the engine. The timing belt fits super tight when attempting to put it back on the cam gear.
 
Sounds promising!
I don't know what you used for reference to align the timing marks but I hope it's accurate.

Anyway...
You DO have something to compare #1 cylinder valve travel to......
....#2 cylinder valves!

#2 Had compression BEFORE so we know that they're probably sealing. So, if #1 and #2 valve action are very similar....there's your proof.

Although....if you're going to be doing this type of work, get yourself a decent compression tester screw in adapter.
Barring that, get someone to help you while you make do with that 1960's rubber (probably hard as a rock) tipped thing.
That's for lawnmowers FGS.

Spec is around 200+psi but what is VERY important is that both are VERY close to being the same. You really need to measure them to verify that.

And while you're there, don't forget to AT LEAST check the valve clearances. Adjust if not right.

That's an ABSOLUTELY FABULOUS OUTBOARD MOTOR. One of the BEST twins ever built IMO. So don't scrimp and don't shortcut the repair on something that can last you a lifetime.

Good luck.
 
I installed a new cam gear, new timing belt, checked valve clearance, changed the oil and filter, and made sure the timing marks lined up when putting everything back together. It starts up instantly just like before, idles great, and has full power on the water. The Honda gods must have been smiling down upon me when the gear slipped down and the belt came off. Thank you jgmo for the guidance, it is much appreciated.
 
Oh man! That's GREAT NEWS!

I was definitely worried about how it was going to turn out for you but you....

....GOT 'ER DONE!

Good JOB!

Now.....

....Drain that fuel chamber AT LEAST once a season and keep the carb drained anytime you're not using it.

Always fresh, non ethanol fuel (if possible). If you're forced to use ethanol, drain the carb every time you park.

Fresh plugs (NGK only) periodically....as it makes sense to you.

Regular water pump service. 2-3 years max.

T-stat 4 years max

Zincs

Oil changes ....more the merrier.

Gear oil changes

Behind the prop inspection for fishing line and....

....Replace the thrust washer when it's no.longer smooth.

Adjust the valves every three or four years.

Sounds like a lot but it's not really for an outboard that will last and be trouble free for a very long time if you give it a little love.

That cam gear failure was something I've never seen so I believe it was just a freak event.

Thanks for the Thanks and taking the time to update with your SUCCESS!

.
 
Have the same problem. When replacing the camshaft pulley, how do I know which timing mark on the cam pulley to align? Is #1 the upper cylinder?
 
Hi,

BF20D? Do you know what year? Or do you have the frame number?

Yes, #1 cylinder is the upper or top cylinder.

The top of the cam pulley is marked #1 and #2.

On the outer edge of the cam pulley there's a rectangular mark that's near the #1 stamp.

Find the "T" mark on the cylinder head near the edge of the cam pulley.

When the piston is at TOP DEAD CENTER on the COMPRESSION stroke, the rectangle on the cam pulley must align with the "T" on the head.

Are you saying that your cam pulley broke like the one in the photo above?
 
Yes, exactly the same break, and the belt walked off the pulley. Plan to replace the belt and pulley and then check the compression. Hoping to be lucky and have good compression.
 
Yeah, no problem.

Makes me nervous though. I have a 2006 BF20D. I never heard of this happening before and now, two cases in a row!
 
Parts arrived today. Installed new pulley and belt. It fired right off and is running smooth as ever. Thank you for your assistance.
 
That's awesome! I guess this proves that the 20D is NOT an interference engine. Otherwise you probably would have had a bent valve or two as well.

Good to know that since it looks like the crappy plastic Honda used on that pulley is prone to failure.

I have a lot of history with those outboards and have loved them for many years. This is the only "weak spot" (besides the Keihin carb) that I know of.

Thank you for the update and posting the excellent photos.
 
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