Outboard Valve Clearance Adjustment
In this video I check and adjust the valve clearances on my Honda 40HP four stroke outboard. This involves removing the valve cover and using feeler gauges to measure the gap when the piston is at top dead center.
Outboard Valve Clearance Adjustment – Video Transcript
Hey there, Dangar Stu here. Today's video is on adjusting the valve clearance on a four stroke outboard and is proudly sponsored by Marine Engine.com.
So, we're working on the outboard that is on the green machine it's a 40 hp Honda 4-stroke. I've already got the cowling off. This outboard normally has a flywheel cover that I've lost. I don't know. The first thing I do is take the sparks plugs out. So, I'll just pop the HT leads off and then we'll pull the spark plugs out. The reason to take the spark plugs out is because we need to rotate the flywheel to do this job and we need to position it quite accurately. With the spark plugs in, it will start to build compression above the piston. So, as you get towards top dead center on that piston, the pressure will sort of build up. It'll be hard to turn the flywheel. Then as soon as it passes top dead Center, that compression is going to want to push it down the other side. So, we get rid of all that affect by taking the plugs out. Of course, being a Honda, one of the hardest things in this whole job is getting the spark plugs out. I ended up using one of these little tube sockets like this. The 18 mil one. Because they're so recessed into the cylinder head that it's really tight. A thick-walled socket just won't fit. Alright, last one out.
Now we're going to disconnect a couple of hoses from the valve cover. We've got a couple hoses attached to this valve cover. The top one here is just a breather. So, it's sort of a crankcase breather that comes back into the airbox. So, we'll just pop this one off. Then this bottom line is just an oil return so oil can come back down into the sump. Now, to get the valve cover itself off, there's just a hole lot of 10 millimeter flange fasteners. So we'll undo those. It looks like there's four port side and three on the starboard side as far as I can see. So there we go, valve cover. And I'll give you a sneaky peak inside. So inside here. I'll get some light and show you. We've got our camshaft that runs down here. These little sort of rockers here run on the camshaft and they open our valves. So we've got cylinder one intake manifold and the exhaust. I assume is number two intake and exhaust. Cylinder number three intake and exhaust. So, that's the configuration we've got. Out of interest, not really related to this video directly, but we've got the fuel pump here that has a little plunger that runs off the camshaft here. And down the bottom here is the oil pump that runs directly off the end of the camshaft.
What we need to do now is rotate similar number one to top dead center of the compression stroke because that's when both valves are closed. And when both valves are closed, both of the little rockers here are relaxed because they pushed open the valves the springs closed the valves naturally. Their natural position is they want to be closed. So, when the valve is closed, these Little rockers are doing their work. And that's when there's a gap. When they're doing work to push down on it, there's no gap to measure, there's no clearance to measure. It's only when the valve closes and that little rocker comes away a little bit, that you've got a little gap there you can check. So, now we've got cylinder number one on top dead center. There's a little bit of play in these. I'll show you that up close. So, hopefully you can see probably higher maybe you can. It's just a little bit of movement there. If we move down now to a cylinder that's not at top dead center, there's no play at all. Because this is pushing down the spring to partially open this valve.
Because this is either drawing air in Letting exhaust out, whatever. But the top, both valves are closed simultaneously. If they weren't, you couldn't get compression because the air would just escape. In order to get cylinder number one on top dead center, the instructions are to rotate this cam pulley until T1, which is a mark I'll show you in a second. It lines up to another mark on the crankcase. So, it's pretty straight forward. The instructions say to put a 56 millimeter socket directly on to this cam pulley that they call a pulsar rotor, in Honda speak, and rotate around. I don't have a socket that big. Even my (unknown) doesn't open that big. I actually just rotated the crankshaft, which the timing bolt just turns the camshaft, until those marks were lined up. In this case, Honda has four bolts on the crankshaft. So, there isn't a single center bolt. But, I could just get a shifter onto those four bolts and rotate them around anyway. Gotta to make sure you turn the motor the right way. You don't want to have cam lobes running the wrong way and you don't want to turn your impeller vanes around inside out. And in this case Honda's run counterclockwise, which isn't very common most motors run clockwise. This particular job is easy because we took those spark plugs out. So you can see these valves closing at the moment as the spring comes up.
Then you'll see this valve here, which is intake valve, start to open. Then we can see here the exhaust valve Opening. And so as we do that for all three cylinders going to go through its cycle of induction, compression, combustion, and exhaust. What I'm going to do though is stop now with cylinder number one at the top of its compression stroke. With this particular motor I know this because of this marker here which is one of the timing marks the other one is lined up with a little arrow there. Hopefully you can see with the shadows. You'll see a little T or an arrow on the engine block which is down here and that little T and arrow is lined up with the T and the arrow on the camshaft pulley. Here we go you can see them both together there. And that's how we know cylinder number one's at top dead center. So those markings are obviously Honda specific, but if you look at the service manual for your motor it will tell you what markers you are looking for. If an outboard doesn't have any markings or any engine does have any markings; what you're looking for is the cam lobe, which is sort of a teardrop shape, you're looking for that flat part not the peaked part to be touching on the lifter. If that's the case you know the valves closed. When you're in a situation with both the intake and the exhaust are closed. You know you're at the top of that compression stroke. You can also even put a little pencil or a straw or light straw into the spark plug hole sometimes and you can feel as the piston comes up and down. There's lots of different ways to do it. What we're looking for ultimately though is where both these little rocker arms have the pressure off them because the valves are closed and we've got that gap to measure. That wasn't probably a bit too clear so I'm going to try and make it more confusing with one of my diagrams.
Now, okay, it's not great but you probably get the idea. So, if you imagine you're looking lengthways along the camshaft. You've got these cam lobes and they're sort of egg-shaped. So, if you imagine as this cam rotates. This little rocker arm gets lifted up as the peak of this camshaft contacts with it. When it does, it lifts this side up which then pushes this side down. So, valves sort of look like this. It's up through the inside of the cylinder and this spring here is then pushing that valve up to seal against the inside of the cylinder. This little rocker here has got a small threaded rod that comes down here with a nut on the end and that is actually what pushes against the end of the valve. So as this cam lobe comes up, this rocks down. It pushes the valve down and as the valve goes down it opens and air can either come in or exhaust can go out. Then, as this rotates around to this flatter section here, this arm lifts up again and the spring closes the valve. So that's how it works. So, what we're looking to do is get to the stage where this is rotated around so that we're actually at the flat side of the cam. That cams pointing down, which means this arms lifted as far up as the cam, and we're measuring the gap between this little threaded pusher here and the top of the valve. That's the clearance we want to measure. To measure this we're going to use something called a feeler gauge and these just come as a set of all different thicknesses. So they're all marked with different thicknesses and you need to know the specification for your motor.
You also need to know whether this should be checked when the motor is cold or when it's hot. In the service manual for this Honda, it specifies that the intake clearance should be .13 to .17 of a millimeter and the exhaust clearance should be .21 to .25 of a millimeter. It also specifies that these should be tested when the motor is cold. So, just to show you those two things quickly. One of the first things it says is with the engine cold this motor and then here are the valve clearances for this Honda. To make this a little bit easier I've just used two sets a feeler gauges. That way I can have one with the correct sort of gauge for the exhaust extended permanently and one where I've got the correct gauge for the intake extended. You can do a single set, but they're not very expensive. So the other tools your going to need is a screwdriver, because there's a slot on the end of that threaded sort of push rod, and we then need a ring spanner to undo the locking nut as well. You can buy a special tool that is a combination of the ring spanner and the flathead screwdriver specifically for doing this job. I just haven't got one. Alright, so before we go any further I guess I've got to go say this probably is something I don't recommend you doing unless you're pretty confident in what you're doing.
You've sort of seen it before, maybe your just practicing on a motor your not so worried about, you're just looking to get your skills up and have a go. You'll hear if you've got it sort of right and wrong. If it's too loose, the gap is too big the motor will be noisy. Often you'll hear people say that a motor sounds a bit tappety. You know, it needs to be have those tolerances tightened up a little bit. But if they're too tight, you can end up sort of burning valves out. They end up being open. They never actually closed properly if they're too tight. So, you do have to kind of get this right. The tolerances are quite fine. So, if you're not super confident, I think I'd just consider this a sort of a fun video to give you an idea how these things work. Not saying I'd really highly recommend you sort of run out and do on your new four-stroke motor just because, you know, watch this video. I hope that doesn't sound a bit sort of, I don't know, negative or whatever, but it just does need to be right. Now, feeler gauges are called feeler gauges because it's all about feel okay.
Sounds a bit obvious, but really they're a bit of metal. You know it's like when you say are looking at some poking facilitation device and actually go look mate "It's just a stick" you know and that's kind of what these are. they're just a bit of metal. But the thing about them is the gap. When you put a feeler gauge between two things you need to feel a certain amount of resistance. It shouldn't be wedged in so it's tight and it shouldn't be flopping around. It is something that's very hard to show in a video, but hopefully it's easier to describe. Which is you're looking for a bit of resistance like it's fitting just relatively snugly between two surfaces. It's not pinched and it's not just really, really loose. So, that's really what you're looking for and that's why they're called feeler gauges. So what I'm going to do is start over here on the intake side. I know it's the intake side because I got my carburetors and my intake manifold here and I know my exhaust is coming out this side. And I'm looking to put the gauge between this little threaded rod and the top of the valve. So here we've got the arm, the locking nut, this little threaded rod here and the top of the valve. And what we're looking to do is get this feeler a gauge in between here. So, this particular one is feeling pretty good. I can definitely feel resistance in there. It's not getting wedged in there, but nor is it kind of really flopping around loosely.
So, we'll go over and we'll check; I'll use the other feeler gauge the larger one, and we'll check that exhaust side. So here on the exhaust side it feels pretty good too. You probably noticed these are two different styles. This is a sort of a bench style and a strait style and there's really long ones, whatever, there's a million different types. I personally quite like these sort of bent ones because often you are trying to get in somewhere. But, once again, it's really motor specific. On my motorbike you've got to go almost into 90 degrees. On this boat, you could easily use a straight one. So, it depends a lot on your motor what style is going to work best. Also, be aware that not all of these valve adjusting screws are just a flat head. This, for example, is the tool for adjusting the valves on my little Suzuki motorbike and it's actually like a little square head on them. So, sometimes, you will need a bit of a custom tool for adjusting them. Okay so cylinder number one's pretty good. So I'm going to rotate the crankshaft until the camshaft lines up for cylinder number two being a top dead center.
And I do that by simply bringing the marker for number two around to line up with the marker on the crankcase. Once again, because it's a Honda, turning counterclockwise. We also get this confirmation we're in the right place because both these little lifters are loose. So, using the thinner gauge on the intake side and the thicker one on the exhaust side; I would actually say the intake sides a little bit loose on that so it's good it gives us one to adjust. To begin making the adjustment on this intake valve I'm going to put the ring spanner on to the locking nut then I'm going to put the screwdriver on to the adjusting screw. Now what I need to do is undo this nut a small amount, but I need to make sure my screw driver holds that adjusting screw in the position it's in. I find that before you undo the adjusting screw it's probably good just to give yourself a bit of visual clue. I'd say that sitting at about two o'clock heading up this way. So, you sort of know where it was initially. Just in case you do accidentally bump it a bit. So, holding the screwdriver steady. now what I'm going to do is just move it to about three o'clock. It's not a huge change. Now I need to hold it steady at that three o'clock position while I just nip the locking nut up a bit.
Now I'm going to grab that feeler gauge and see what it feels like now. So, putting that feeler gauge in there that's actually too tight. I can't fit that in properly anymore. So it goes to show how small an adjustment it really needed. To be honest, if it wasn't a video, I'd probably left it where it was but you know. I'm going to go back hold it under the locking nut. Change this to 2:30 That'll go. So that's pretty good now. Pretty comfortable with that. That feels much more like the top one did originally. There is a torque setting for these locking nuts. I think it was about 23 newton meters, but I'll check that for you. Alright, I'm happy with that. Actually think that is better than it was. Still feel this little gap, but it's not too big now. One thing I don't do that might seem like an intuitively right way to do it is, if the gap is too big, put your feeler gauge in, wind screw in until it touches the feeler gauge and then lock it off because there's too much potential to sort of pinch it. You're much better off saying right it's a little bit loose. I'll make a very small adjustment, lock it off, test it again. Maybe back it off, maybe go further. But putting the feeler gauge in when you adjust it never works. Okay, now I'm going to rotate again to cylinder three and I'll check that one.
So, the clearance on the intake seems fine and the clearance on the exhaust seems fine with this one as well. So, I think we can kind of consider this done. As you can see, it's not really rocket Science. It's just a small gap you're Checking, but you definitely don't want them too tight. If they do, you can burn up valves, etc. So that's a problem. Why is there a gap at all, you might ask. And it's my understanding it's there to compensate for heat as the motor expands as it gets warm. I might be wrong, but that's just a recollection I can remember I heard that but I believed it to be true. One of the things that's really important to get right is to have that lucky nut tight again. If you don't, it can just vibrate off and then you'll have no closure or then suddenly that adjustment screw will just start winding itself out. And depending on the motor, that can actually almost fall back down some oil returns, back into sumps. You know all sorts of things can go wrong. So that needs to be tight. In this case, the spec for that is 23 newton meters. The other thing to pay close attention to is that when you do that locking nut, that you don't drag the adjusting screw with it. You need to hold the adjustment screw still whilst you pull the locking nut tight. Otherwise, you will actually be closing the gap as you do the locking nut up. Alright, now we know we're alright. We've made one adjustment.
The rest are fine. I need to put my valve cover back on. You may also be wondering how do I know if I need to do this. The motor bike I've got, for example, specifies checking the valve clearance every 5,000 K's. It's a really short interval. I'm not sure why they think it's going to change, but it's on the service schedule to check it really regularly. So, often it's just a service check. If a motor is really noisy you might look if they haven't opened up too large giving you that clutter. And if you find you've got a burnt valve; I would put a new valve in, but then I would also check my clearances to see if they were the reason it burned up in the first place. Alright, now we're going to put the valve cover back on so I'll just quickly head over to the bench. Before I put the valve cover back on, I bought a new valve cover gasket. So pretty much there are one use thing usually. You can probably get away with it in some cases if the motors not that old, but I figure you know why not change it it's off. First thing I do is also just check it's the right one. Now this does look to be the right one. We've got our four screws down one side three on the other. We lay it out and it's looking to be on the money. The reason I check is because if you need to use the motor you've got much more chance of this old seal resealing properly if you don't pull it out and go it's not the right one. My new ones not right let's put the old one back in. That's probably a bit dodgy. So now we know it's right I can lift this old one out.
Looks like it might have been sealed in in the four corners. I think this is some sort of sealant. It's quite flexible still, but I think I'm just going to press this one in. The nice thing about this is it actually sits inside a channel so it's not going to flop around and get dislodged when we go to put the cover back on. Alright we've got our new valve cover gasket on now so we'll go and throw the cover itself back on and recheck those hoses. I'm just going to run around these fasteners now make sure they're all done up evenly. There's no compression gases being contained by this gas cover or the valve cover gasket. It's just to stop oil leaks, but the more your going through this the more that seal will sort of do its job. Just put this bottom oil return hose on and then we've got our crankcase breather hose here as well. Now I'm just going to pop spark plug back in and pretty much job done.
So I hope you enjoyed this video. I hope it gives you a few ideas about what this job involves. As I said, I don't want people sort of rushing out and killing they're motors by doing it incorrectly, but it's not rocket science. It just does need to be right that's all. I mostly actually did this video because somebody commented we done a lot two-stroke stuff recently and be nice it's a four-stroke stuff so I thought I'll do this. I'll probably change the timing belt on the green machine as well. So we might go through that soon. I also want to do a few sort of more basic things to the green machine. I want to add a bimini cover to it and put a hydrofoil on the outboard. So we're probably doing those pretty soon as well. Alright, well take care and I'll catch you next week.