Pre 1979 B100 no compression

I recently bought a pre 1979 B100 honda outboard that doesn’t have any compression or spark. The motor looks really clean and doesn’t show signs of overheating. I pulled the valve cover and found that the outer valves have way more clearance than they should. I am thinking that this accounts for the lack of compression. Any ideas on getting the valves to seat properly without pulling the head? Any advice on getting the points set correctly? Thanks!

Hi Woodsguy,

I recommend that you first verify engine timing on this old gal. Simply remove the recoil starter assembly and completely expose the timing belt and flywheel. The flywheel has a "T" stamped in it. With #1 (top) cylinder on compression stroke, align the "T" on the flywheel with the stamped line on the starter support that is between the flywheel and cam pulley.

With the T correctly placed, the dot on the edge of the cam pulley should be facing the T and aligned with a dot mark in the engine case.

Once the timing is correct, you can adjust the valve clearance on #1 cylinder using the adjustment screws on the rocker arms.

After #1 valve lash is properly set, rotate the engine and bring #2 up on top center of the compression stroke and make sure the "T the line and dots are properly aligned. t
Then adjust the valves on #2 cylinder.

The adjustment requires a very small wrench to loosen then tighten the lock nut. I have always used a very small adjustable wrench to do this but care is needed to keep from boogering up the nut.

The clearance on all four valves is 0.002"-0.004". I try to set them all at 0.003" always keeping in mind looser is better than too tight.

If the timing is off or the marks won't stay aligned as the engine is rotated several revolutions then you may need to replace the belt.

I strongly recommend getting a shop manual. You can buy a new one here:

https://publications.powerequipment.honda.com/marine

Or you might find a good used one on ebay or other sites.

The no spark is always a concern for these older outboards because replacement ignition parts are no longer supported by Honda.

I recommend using the NGK spark plugs (DR-5HS) gapped to 0.024"-0.028"

Make sure the point set arms aren't bent or twisted and the contacts come together squarely when closed. The ignition timing 15° before TDC. This is indicated by the "F" stamped in the flywheel.

Align the "F" with the line in the starter case support post used for valve timing. The points should be just opening with the marks aligned and should be the same for both cylinders as they come up on compression stroke. The shop manual describes using a "timing tester" but that's nothing more than an ohmmeter to detect loss of continuity when the points open.

Sorry, forgot to say points gap should be 0.012"-0.016".

Other reasons for no spark and things to look for:

Open exciter coil

Open primary in ignition coil

The capacitor is 0.24 micro Farads. Make sure it isn't grounded or completely non conducting (open). Might need a capacitor tester. I believe that a Borg Warner BWD G610 might be adapted to use as a replacement.

Take the center cap off of the cam pulley and inspect the pulsar coil. Often, water gets in there and can cause problems.

I don't know if your outboard has one but many were equipped with a "neutral safety switch" that was really an ignition kill. It consists of a reed type electrical switch, a magnet and a plate that looks like a "Y" mounted to the horizontal portion of the shift lever at the top of the case. The plate upper "ears" come between the magnet and the Reed switch when the outboard is in either forward or reverse. The gap between the ears allows the magnet to effect the switch.

Things that go wrong with the neutral switch are:
"Y" plate loose or out of adjustment
Reed switch bad
Wiring to Reed switch grounded

The engine kill switch can also fail in the "kill" or closed position. Disconnect it and check for spark.

The kill switch wiring can ground to the frame or case.

The spark on these engines is VERY faint and hard to see at low rpm in sunlight. I like to use an induction timing light to simplify testing for spark but, in the wild, I've thrown a blanket over my head and the outboard to watch for spark. Obviously, a dark garage or dark night would work too.

I hope my ramblings might help.

Good luck.

Thanks for the Help! I am not sure I am going to keep this outboard so I have not purchased a manual for it. I adjusted the valve clearance on the #1 exhaust valve and it didn’t seem to make any difference. Compression is about 10 psi to 0psi. I have included a pic, let me know if timing looks right. Do you adjust the points gap with the flywheel at the F position? Any idea what coil resistance is supposed to be?

Hi,
No picture came through.

I see no logic in adjusting just one valve. Have you checked the lash on the others?

Many compression tests are "skewed" due to a faulty gauge. This happens because they aren't used often and then never checked.

How are you performing the compression test?
The correct way is:

Disconnect the fuel tank and drain the carb.
Remove BOTH spark plugs and install gauge in one cylinder
Hold or prop throttle wide open.
Pull the engine over hard 4 or 5 times.

If your gauge is working properly and pressures are still 0 try this:

Tilt the outboard UP to get it as close to horizontal as possible.

Squirt or pour about a teaspoon of engine oil into the cylinder. Rotate the engine a few revolutions very slowly to spread the oil around and, hopefully, get the oil out to the cylinder walls and piston rings.

Try taking compression again If the pressure comes up then the rings are either stuck or worn out and the cylinder wall probably is too.

Yes, the points gap is set with the F timing mark.

This outboard has two wound coil assemblies that need to work together to produce spark:

1. The ignition coil containing the primary and secondary coil windings and having the spark plug wires attached.
The secondary resistance is measured by putting the test lead ends into each spark plug cap. The manual calls for 8k ohms across the wires and internal coil windings but I have measured 31.5k ohms on running outboards.
The primary ignition coil winding resistance is listed at 0.56 ohms but I have measured 1.5 ohms on running outboards equipped with breaker point ignition.

2. The "primary" coil is located under the flywheel and produces the voltage to energize the ignition coil primary circuit. The coil resistance is listed as 2.0 ohms

There is a timing advancer assembly under the breaker points mounting plate. It can get corroded and stuck.

So last night after cleaning up the points with some fine emery cloth I set the points gap and checked for spark and viola we have spark! Thanks for your help on that! I blew some compressed air into the compression gauge and verified that the needle did move properly. I can't seem to figure out how to upload a picture to the forum but it may be because I am using a mac. I set the valve timing so that it is a straight line across the T mark through the starter mount mark and to the cam pulley mark. I have the motor on a stand so I tilted the motor up and put a liberal amount of 10w30 into the spark plug hole and then pulled the engine over several times. I then checked for compression and found none. I left the motor in the upright position and put more oil in the spark plug holes to see if oil sitting in there will make a difference overnight.

Lot's of people have trouble downloading photos to this site. It's usually because the file is too big. Try downsizing to see if that works.

It sounds like it's in time though. I don't know whats going on with the compression. I can't remember getting 0 psi on a test before although it probably happened. Even on a couple of cylinders that had holes in the piston top I got SOMETHING.

Again, are you holding the throttle WIDE OPEN? Are the valves going up and down with the rockers? No broken valve springs? It might be time to pull the head to see what's going on in there.It's very easy to do. I don't think soaking the piston in oil overnight will help but who knows?

You can sometimes see if there is excessive leakage to the crankcase by slipping a small balloon end over the end of the dipstick tube. If it inflates quickly as you pull the engine over that's usually a bad sign.

But, just remember, the fact that you have spark means that you at LEAST have a collection of valuable, no longer being made, parts.

And, if the reason for low compression turns out to be because the engine overheated badly and ruined the block then that's what you have. A parts outboard.

Good luck

Well I got to thinking about what is going on with this engine and the excessive gap on both of the exhaust valves when I started. I decided to put each cylinder at TDC and blow some air into the cylinder. I stuffed a clean rag around my blow gun and sure enough on both cylinders I got alot of air out of what I assume to be the exhaust on the lower unit. I verified that both rocker arms have clearance at this point. So…. Makes me wonder if something is gumming up the exhaust valves or??? Seems very unlikely that both valves are burnt and very suspect that they both had a large clearance to start with. Any Ideas??

Sounds to me like you've found the "smoking gun" and I DON'T mean a novelty crack pipe! ;>)

Your poor man's leakdown test indicates the exhaust valves aren't seating. Pulling the head is the only thing left to do to find out why.

That is, of course, if both the exhaust valve springs aren't broken.

Good luck.

Have you ever seen the exhaust valve springs break on these old engines? Do you think some seafoam might remove the gum? I am a bit hesitant to pull the head as it seems gaskets for this old girl are a bit hard to find.

If exhaust valves are bent you will see lots of clearance ( not closing ) and no compression.

No, I have never seen a broken valve spring on one of these.

As far as worrying about taking off the head, I don't think it's a big concern at this stage of the game. You have an outboard that won't start in it's present condition and, unless trying a "de-gunk" to seat the valves works (i don't think it will), what else is left?

Here's a link to a 1972 and the head gasket is available. If your block is the later type, those are available too.

https://www.boats.net/catalog/honda...o-bf100-1020309/cylinder-barrel-cylinder-head

The valves and rotators are also available.

However, if the valve heads are super carboned up because of worn valve guides, the guides are listed as being unavailable. There is probably a work around for that but, if you had to get some made at a machine shop, that will be expensive.

Good luck

racerone said:

If exhaust valves are bent you will see lots of clearance ( not closing ) and no compression.

Click to expand...

Well it seems that you are correct. I pulled the head, removed the rocker shaft, and removed the exhaust valves. I then cleaned one of them up a bit and cleaned the seat area up a bit. The valve still would not seat properly. I spun the valve around from the stem side and it does look like it wobbles a bit. On the other hand, it seems like the guides are good with very little side play. When I got the engine, it seemed like the timing was off 1 tooth. Any idea what would bend the exhaust valves? Maybe a broken timing belt at some point? Also there was a bit of rubber plugging the port where the water hose connects to the side cover so maybe they lost an impeller and overheated the engine, still a bent valve from overheating seems unlikely and a quick look at the cylinder walls makes me think it didn’t get too hot.