Outboard Gearcase Pressure Tester

In this video I put together a simple tool for pressure testing outboard gear boxes. This is done to test the lower unit seals around the prop shaft, drive shaft and shift rod.

Dangar Marine

About Dangar Marine

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Outboard Gearcase Pressure Tester – Video Transcript

Hey there, Dangar Stu here. Today's video is about making a pressure tester for an outboard gear box and is proudly sponsored by MarineEngine.com.

I did a video ages ago back at the house about making one of these using a bicycle pump and a pressure gauge and a few bits and pieces make it from scratch. But I don't really use that one anymore. I use sort of a slightly upgraded version. I don't use that one anymore because it was a little bit cumbersome and it didn't work that well to be honest with you. I often get questions about the one I do use, though. So, I thought I'd do another video on it. Sort of upgrade the old videos. There's a lot of old videos that are pretty dodgy to be honest so I'd like to sort of replace them with some updated ones. So, bear with me for covering a bit of old ground again but I do think this is worth showing. So, what I use as the main part of the tool is one of these. You've got the pressure gauge, it actually does pressure in vacuum you can swap like this and it's a single unit hold and you can just pump it all in one hand. So, it's nice and easy to use. It's quite good economically. This is actually sold as a brake bleeder. I'll put a link in the description to an example on eBay, pretty much exactly this unit.

So, the unit I got comes in a kit. It's got a little reservoir so as the brake fluid comes through just drops in and you can use it for bleeding brakes, obviously. But because it's got the gauge it's actually really good for testing lower units as well. The missing ingredient obviously is just a hose to go into a lower unit and it's a slightly expensive way to go. I think they sell for maybe twenty dollars or something, but what works really well it makes it really easy is one of these. I really like this unit because it comes with a metal screw cap that goes onto the hose and then it comes with an adapter here. So, the adapter pretty much does every Japanese model and the metal version does pretty much every American model. So, it covers all outboards really nicely. This kit's actually designed to go onto a bottle of oil so you can put gearbox oil into a gearbox. That's what this is sold as and they're great for that. I use one for that as well. But, by taking everything other than the pump section, you can make yourself a really good pressure tester. So, basically about a hundred dollars.

I think the pump was about eighty and this is about twenty, so comes out give or take roughly in that vicinity. Making actual tests drop is dead simple. Making it up is easy. Opening the package, not so easy. Sorry I was wrong before. The actual plastic unit that comes on it is the one for the American outboards and the adapter is the one that adapts it to the Japanese outboards. Marineengine.com sell a Sierra equivalent of this sort of pump so I'll put a link to that in the description as well. At the pump end here it's just got one of these little spring clamps. I'm just gonna pop that off. So, this is the bit we're going to keep for the pressure tester. But these pumps are really handy for refilling the gearbox afterwards, so if you can really kind of get two of these and keep this. That's ideal, but unfortunately comes in the kit together. So, all I'm gonna do now is simply put this outboard adaptor straight onto the brake bleeder and then put the hose clamp back on. And literally now that is all I use and I found it really effective.

It's not a tool you're gonna use all the time at home, but if you are doing your own servicing it's just a great thing to do. You drain the gearbox oil. Check for leaks. If you find them, fix them. Then put new oil in. By testing that each time, you're never gonna get in the situation where you've actually run with water in your gearbox for a long period of time. Done any damage. So, you might actually find this sort of tool ends up saving you more than it costs you in the long run. Obviously, it'd be a pretty short video if I didn't give you a demo of it. So we'll go over here to an old gearbox I've got on the stand, drain the oil out and give it a run. This gearbox came off an outboard that lost drive and it turned out was because the drive shaft had sheered completely. It's a pretty rare thing, so I'll show you what it looks like. Here you can see the top of the drive shaft has just basically snapped not too far from the elbow pump. This section of the drive shaft runs on a little bit of a bushing just up inside the leg in the midsection. So, that may have been a part of what caused this. It could also have been because of maybe hitting a rock or something and putting a shock load through it. But anyway, what we'll do now is drain the oil out.

I'll take this water pump off so we can see the drive shaft oil seal and then we'll do a test. Just take this top drain plug out just so air can get in it'll drain more quickly. Obviously, another big clue as to whether you got a problem, before you even start, is if there's already water the gearbox. A seal is already gone. But the pressure tester can be a great way of finding out which seal it is. Because the oil pan on this stand needs to sit sort of half on the rim that's the base of this stand, I've just put a wheel here. But it's made me realize I might actually weld a plate there for an oil pan to go on just as a bit of an improvement to this stand. I'll have the design perfected by the time I retire. Now this is pretty much drained. I'm going to put the bottom plug back in and we'll put our pressure tester into the top one. You can pressure test from either hole, but the top one is easier access so that's what I use. I'm not expecting to find any leaks because the oil looks pretty good. So I'll show you that. So here you can see it's pretty black. No water in it, so that's a good start.

One other thing I've noticed with these pumps is that this yellow part actually spins inside the clear tube, which makes it much easier to thread in without twisting up the tubing itself. Because this is Yamaha and a Japanese motor, I'm gonna leave the adapter on. Once I got the adaptor way onto it until the o-ring is seated so it seals, I'm just gonna pump it until we get 10 psi in the gearbox and we're gonna see how well it holds that pressure. So, there we go sitting on 10 psi. The specs in most manuals say that it only has to hold this pressure for 10 seconds or something. Not very much. This has now been 30 seconds and the needle hasn't moved at all, so I'm pretty confident all the seals of this gearbox are in pretty good shape. I'll quickly zap this water pump off just to show you the drive shaft seals as well. That way we can just run through all the seals that this pump is actually testing.

So usual routine. Pump housing and impeller then I'll just get the pump base plate off. There's also the little woodruff key just stuck into the driveshaft, so I'll grab some pliers and pull that up. Alright so I'll just bring over quickly and show you the three seals that this pressure test is checking. This white housing here is the oil seal housing for the drive shaft. So if those seals had failed, we'd have this air escaping up past those seals. Up past the drive shaft. So there will be one area. The other area is a little sort of o-ring seal here around the gear selector. And the most common one to go wrong, because it gets the hardest life and gets a lot of fishing line around it etc., are these seals in here around the prop shaft. So this needles now dropped two psi, but it's been about 10 minutes so that's more than good enough. It's well within spec. If that was dropping really quickly, though, you'd need to find out where it's from. And by taking the pump off you can then have a listen and, if you can't hear anything you could even just spray a bit of soapy water on. It'll start to bubble where it's leaking from.

So, check the gear selector, your drive shaft and your prop shaft. But because this one didn't drop very quickly at all, we can now unscrew it and put you all in pretty confident that it's gonna be fine for another season. So, as you can see, it's a pretty simple tool to put together. Cost you about $100, but it's really useful. It's a great way to give yourself heaps of confidence that your gearbox is good to go and it'll also really help you diagnose it if it's not. So, I know this was going over a little bit of old ground and I know it's a bit of a short video. That's mostly because the one I was filming didn't go so well and I'm gonna need to finish it next week and you know the story. As I was saying before, I'll put links to the two parts of this tool in the description. So, if you want to build one up you can sort of go and grab those and then just put them together and get going.

I'd like to cover a little bit more about tools down the track too. I don't think I've ever done one of those you know 'what's in the toolbox kind of a thing' because they're definitely a handful these sorts of tools. They're really good if you want to do a bit of outboard maintenance yourself. Some of them are bought. Some of them are homemade. But one day, when I get a bit of time, I'll go through the whole set and show you the things that I commonly use. Well thanks for watching. Take care.

Next week I'll show you the video I was filming today, which is about the manual tilt mechanism from a Mercury outboard. Those mechanisms are reasonably complicated and they do fail. I see a lot of outboards where they're not really kind of working properly. So, I think it's worth seeing the basic idea about how they work. Unfortunately, they're different for different brands of outboards. So, I can't sort of do one video that shows you how they all work, but we'll sort of slowly build the catalogue up of the different brands. So, if you do have trouble with your sort of manual, shallow running, trim tilt sort of bracket, hopefully you'll be able to find the one that suits you and sort it out. Alright well take care and I'll catch you soon.