Bravo XR Drive Rebuild - Page 3

jwalker · 12 October 2021, 18:27

Matt, rather than a shower you might find this interesting. I'm not overly familiar with the Bravo drive but from your pics it looks similar. Water is tapped off the side of the exhaust water injection before it enters the exhaust gases and it's plumbed into the side of the drive case so the case runs flooded with a constant flow of water, albeit a bit above sea water temp. The top of the case has a hole about 25mm dia so the outflow pours over the drive as it exists.

Matt · 12 October 2021, 22:48

Yeah, the Bravo doesn't have a fitting - but I have a cap that goes on top of the finned top bearing cap that douses it in water - and I could source that either from the cavitation plate or from cooling water, am sure both could be made to work.

jwalker · 13 October 2021, 00:24

The Volvo didn't have a fitting either, you have to drill an 'ole.

Matt · 13 October 2021, 12:02

Ah, I get you. On the merc, drilling an 'ole anywhere near there would let water into the oily bits.

I've got a "shower cap" for it in the stores - but need some bits (longer bolts) to make it fit, which are on order. I quite like the idea of using cooling water though rather than pickup off the cavitation plate, that's tidy. It's part of a bigger question WRT to how to quieten the thing down a bit though.

jwalker · 13 October 2021, 19:21

Quote:

Originally Posted by Matt

... It's part of a bigger question WRT to how to quieten the thing down a bit though.

Aye, it's tricky. If you've got the back pressure right you'll be reluctant to mess with it. I'm fortunate not to have neighbours so no issue flushing it though i do miss the quiet of the through prop exhaust when travelling. It's reasonably quiet in the cabin but it used to be quieter, however, the improved performance is worth the increased volume.

Are your exhausts straight out the back with no turbo?

Matt · 13 October 2021, 20:45

That’s right, naturally aspirated with the whole induction system quite carefully designed. And all built by me - I'm sure you've seen the pics?

I’ve not run it for 2 years!!!! Going to see if I can get it all going this saturday though to check the drive is all OK before the winter. If all goes well, Southampton will hear it.

I’ve been working on a plan. I think if I put a crossover pipe in, along with a pair of large exhaust poppet valves (like they did on early emissions control), and if needed, an air pump that pumps air in at idle via the valves (which is easy to trigger off the Megasquirt ECU), they I can hopefully get enough airflow through the exhaust at idle to prevent reversion. Then I can start adding some water and baffles to the tailpipes and we'll be OK. If it goes well this weekend, that might be a winter project. I've already bought the TIG welder for it....

jwalker · 13 October 2021, 21:20

So your exhaust is dry open pipes? It's possible I've seen it but I'm now an old bloke and can't remember what I had for breakfast!
Post some pics again.

Matt · 13 October 2021, 22:25

I was 28 when I joined rib.net and had just bought my first house at the time. Now I'm err....quite a bit older....

jwalker · 14 October 2021, 12:24

Aha, I see, they are wet. Very short though to quieten them significantly. You're a bit tight for space, are you thinking your cross pipe between the rubber? You could link them externally and pick up more water to cool the gasses and have a big, badass central exit.

Just thinking out aloud.

Re age, I wasn't sure but reckoned you'd be passed mid forties, it passes fast and faster as you age! My advice, forget second career teaching unless it gives you a worthwhile pension. Get your pension pot as big as possible and retire early and stay as healthy as you can, every day will be a holiday but it's easy for something to put a spanner in the works - the older you are, the more likely that may happen.

Keep us updated with the exhaust...and get those trumpet flares into a full circle, lots of the air will come from the rear and sides of the trumpet and it's better guided in.

Matt · 14 October 2021, 13:13

Actually dry - the silicone is just the outer carrying the cooling water.

The inner is a 3.5" bore stainless pipe that runs to the tip.
But yes, crossover pipe as close as possible the the collectors, still dry until after the crossover is the plan. I'm actually even thinking maybe no crossover and just pump more air through the valves - we'll see.

Teaching - you read my mind.

Especially re. health with the way I'm limping around at the moment.
What age group & subject(s) did you teach? It's is something I would love to do - 6th form and upwards age groups though.

jwalker · 14 October 2021, 17:03

Oh, so the dry pipe runs through a water jacket. You could have silencers instead of an open pipe. Stainless stuff is readily available for manufacturing silencers, perforated pipe, sound absorbing filling etc. I made a couple for my motor bike last year. It's not usually marine quality stainless but provided the outer case is you should be ok. You can even buy stainless silencers ready built to length which you could sheath. Ooo...all sorts of winter planning to do! And a new tig welder too...

Matt · 14 October 2021, 17:23

Yup, tig welder it all sorted, I've got a Parweld one. It's nice.

I've tried silencers. I bought the biggest (length & diameter) I could find - made almost no difference, though I might already be deaf. So what I've done is taken those silencers and put a block in the middle - which forces the exhaust gas through the perforations and sound padding now. It's almost quiet now, adequate for running on the hose at home anyway. But far too large for proper use.

I still think water is the answer. On the first run of the boat, I had some GGB inserts and water @ the tip, with flappers. Just through the reversion effect, enough water was going back up into the GGB inserts to make it quiet. Really quiet, actually. But I could tell water was going back up the headers too....I couldn't let it idle for long without blipping the throttle to clear it's throat. And the lambda sensor was soaking!

So if I can get enough positive airflow through such that it doesn't suffer from reversion, then I can add a bit of water in along with the GGB mufflers and I reckon we'll be good. I hope. We're on Mk2 exhaust system now, already. Mk3 will be along over the winter maybe.

So far, I've mostly used 304 stainless anyway. It's internal, so I don't care about a bit of staining.

Matt · 17 October 2021, 13:44

Put a couple of hours on it yesterday. All went well, except it looks like there's a bit of a leak on a sump gasket that I'll attend to over winter.

Rebuilt drive all worked fine though and boat performed very well.

jwalker · 17 October 2021, 14:17

Cool,

paulbrown22 · 17 October 2021, 20:58

Great news that the rebuilt drive performed as expected.

I'm sure you'd like a little Winter job anyway :-).

Matt · 17 October 2021, 22:19

I have enough other winter jobs. Like installing an interior and some scatter cushions

Don't really want to have to pull the motor if it's the sump gasket - feels like I need some velcro mounts.

Quote:

Originally Posted by paulbrown22

Great news that the rebuilt drive performed as expected.

I'm sure you'd like a little Winter job anyway :-).

Tim M · 05 January 2022, 15:37

Now my turn......with the boat finally out of the water, running them up on a hose they sound very similar to the video above with considerable whine. However I'm convinced the drive showers have helped over the course of the last season and they don't slip anymore even without the recommended 50 hour oil change.

Also discovered both of the steering arm/gimbals are very loose/worn. Hopefully the local Mercury dealer who doesn't speak a word of English will drum some new life into them!

Matt · 05 January 2022, 15:46

The XR is not a quiet drive at the best of times, owing to the straight cut gears

If it's the trim & tilt bushes on the gimbal rings with play in - that's not too bad.
If it's the tiller pin and steering arm into the gimbal ring - that's a bit more work. Possibly engine out - but can't remember and it depends on your install.

If it's all coming apart, it's worth considering upgrading to external hydraulic assist (the imco kit is lovely). That takes all the load off the internal tiller arms, it only uses it for position reference then, so you'd never have to worry about it again.

Internal tiebar only at the moment yeah? Don't be persuaded to put an additional external one on as well. The internal & external inevitably fight and end up prematurely wearing the gimbal ring/pin/tiller arm again. Either internal or external only.

Tim M · 05 January 2022, 15:52

Thanks for the info. It's certainly the pin/arms that are loose. And yes it's engine out to replace them! The steering on each drive is independent so no tie bar; we've got the Mercury DTS / Axius / skyhook system so both are electronically actuated with their own ram on each drive.

Given how much oil one of them is using and the relatively high hours I think a full rebuild is the only way to ensure peace of mind for this year.

Matt · 05 January 2022, 16:01

Oof! Afraid I have no familiarity with that steering system at all. But I do know external hydraulic assist is pretty decent without the cost of full hydraulic.

I guess he might try to wind you into new gimbal rings (Hopefully not transom assemblies) - they're usually
the bit that wears. The pin itself is harder than kryptonite. It's possible it's the tiller arm - but IIRC they're steel, so unlikely.

If the gimball rings are worn where the riller arm passes through, but otherwise in good nick, the trick is to shim them. So make up some shims for each gimball ring, tight enough that they need hammering in (not too hard, mind). The ali ring itself will of course need some dressing to do this. and then do up the u-bolt on it nice and tight. With a bit of preload from the shims, plus doing the bolt up - this should minimise any movement.