I’m in the middle of a major service of my Yanmar engines. After coolers, oil coolers, turbos, and exhaust risers all removed and serviced. Plus the regular oil, filters, raw water impellers, plus valve clearance check. Unfortunately my exhaust risers are shot. They’re custom made and apparently made from cast steel. It looks like I caught them just in time. The new ones will be stainless, and I was wondering about ceramic coating the new ones to manage the heat. Is this viable, and will it last?
I was just reading that ceramic coating may only last 2-5years. If this is the case I’ll get an exhaust blanket made for them. The originals were wrapped in a fibreglass material. FWIW, the hot side of the turbo on my old boat was coated and it seemed to do a good job of reducing its surface temperature.
You know the old saying if it’s not broken why fix it ,the wrapping has been used for decades for a good reason it works,you could buy some heat shield and wrap over it but then you don’t see what’s going but as it’s all new you would not have to check for a long time.
ceramic coating works wonders on car custom exhaust headers
Exhaus twrap can cause thermal cracking in stainless headers and i have had this occur, i then replaced them like for like and the cracking did not occur again.
mates with the same headers who ceramic coated didnt have the issues i had of melting components around the engine bay
Car headers would be a lot thinner material though
Thanks Steve. I appreciate your feedback based on personal experience. I’ll talk to some local ceramic coaters and get an idea on price.Originally Posted by stevej
I am looking at getting new risers/mixers in the next year or so for my yanmars. Existing ones are stainless, but are deteriorating where the water mixes with the exhaust. Yours almost look like the wrap has made them rust?? Failing from outside??
Talking to experts (well, they know better than my nothing) even stainless ones don't last forever, maybe 4-5yrs at best.. The fabricator recommends ceramic coating for heat, but he deals mostly auto stuff. Maybe for looks?? although he reckons it really helps with heat and stops the external corrosion.
Yours are a bit different to mine, I have 2" riser into a 3" elbow. Is your water inlet shaped like a "s"? Almost looks like salt water could trickle down to the turbo?
That’s disappointing to read only 4-5 years out of stainless. I was hoping for a lot more than that. Once those risers are in place, the outlet points down slightly, and there was no mention of water getting back to the turbos by my mechanic, so I’m guessing they’re ok. Mine were definitely rusting from the outside, but the worst is those pics looking inside the pipe, which is the mixing area. It’s nearly closed over, so I was very lucky to catch it before it was too late. I spoke with Thermal Edge Coating in Brendale today, and he said he does quite a few boat risers. Their website has several options, with one in particular being recommended for heat control. Then they have all the nice colours, but they aren’t as effective for heat control, so I’ll be going the best for the heat.
I picked up my new 316 stainless risers today, and dropped them off for ceramic coating, which will be another couple of weeks. I can’t wait to get the boat going again as it’s been a while now.
They look great. What thickness is the pipe that you used? Looks heavier than regular exhaust tube. Also could you let me know roughly what they cost you. I think one of mine is just about knackered and tossing up whether to get custom made, or buying the cast stainless elbows and just getting new risers made.
I've been through all this on a commercial boat, and classic bikes as well. Getting the custom car thing out of the way, those which are internally coated are to stop heat discolouration of the header. Also popular on air-cooled bikes. And it does work, the heat doesn't transfer to the outer service. I actually tried the poor mans' version, coated the inside of the Norton headers with UHT exhaust paint. It worked, after a fashion.
As for wet exhausts, the point where the hot exhaust gases and the cold seawater mix is where you get the corrosion, and this is unavoidable. I took over a boat (6V92T GM) with stainless fabricated exhaust, light gauge, single outlet model, failed in the first year. Replaced with cast iron bends and heavy steel tube, lasted for 5 years and was still going when engine replacemnt gave me the twin-turbo model, needing two outlets. The exhaust was fabricated from cast stainless bends and heavy tube, and was till going over 10, 000 hours later when I changed boats.
The shape of the exhaust was mentioned above. I have something to add on this, from bitter experience. S-shaped risers are OK, sort of, as long as you have the headroom to get a really big rise, and a lot of boats don't. Thge best arrangement is to have an end stop, with the exhaust coming in overhead and downstream. Your major risk is having seawater rush into the riser when shut down, due to boat roll and pitch. And it won't dribble, it will fill the pistons which have their exhaust valves open. Can cost you a motor if you try to start it and hydrauliclly lock up, bending one or more rods. With a stop end, any water shooting up the exhaust should just hit the end stop, then run back out. I have included a rough illustration below.
Whilst 316 is marine grade it is not a good high temp stainless steel and prone to heat cracking.
Gr253 is a high temp grade with decent corrosion resistance.
Gr410 is another very high temp grade stainless with ok corrosion resistance.
So if your header is prone to cracking opt for one of the other two.
I did several fire tubes in bitumen tankers in 410 with no failures over the life of the tankers....304 and 316 fire tubes would crack at about 2 years of service. 410 stainless fire tubes lasted the 15 to 20 years service life. Not a corrosive environment but high temp.
Jack.
Sorry, but not sure of material thickness. I know this doesn’t help, but they were quite heavy. Certainly a lot thicker/heavier than your average stainless 4WD exhaust. Cost was $3300 for the pair, then I got custom exhaust jackets made, which added another $1000. For what I’ve spent, I’m hoping they last a while! If in doubt with your current ones, don’t delay. I was lucky I got mine when I did.
mixingelbow.jpgThese were the ones I was thinking, sort of similar to what's there but 2 pieces instead of mixer and riser combined. I might just patch up the ones I have until I work out what to do re engines
Have a look at these https://hdimarine.net/product/gm-sta...-mixing-elbow/ they get good reviews from a Yanmar FB group I’m in. Have you seen Mick n Jill on FB? Currently replacing engines in a Scimitar. They’re from Yeppoon, but getting the work done down here. Massive job by the looks, cutting the sides out of the hulls to get the engines out and back in.
I’ve got decent sized wet mufflers which should do the job of the stop end you’ve described. Plus my riser is about 500mm high, and the exit of the muffler rises above the water line, then slopes down towards its exit at the stern, so any water in this section runs out the back. Hopefully my engines are well protected.I've been through all this on a commercial boat, and classic bikes as well. Getting the custom car thing out of the way, those which are internally coated are to stop heat discolouration of the header. Also popular on air-cooled bikes. And it does work, the heat doesn't transfer to the outer service. I actually tried the poor mans' version, coated the inside of the Norton headers with UHT exhaust paint. It worked, after a fashion.
As for wet exhausts, the point where the hot exhaust gases and the cold seawater mix is where you get the corrosion, and this is unavoidable. I took over a boat (6V92T GM) with stainless fabricated exhaust, light gauge, single outlet model, failed in the first year. Replaced with cast iron bends and heavy steel tube, lasted for 5 years and was still going when engine replacemnt gave me the twin-turbo model, needing two outlets. The exhaust was fabricated from cast stainless bends and heavy tube, and was till going over 10, 000 hours later when I changed boats.
The shape of the exhaust was mentioned above. I have something to add on this, from bitter experience. S-shaped risers are OK, sort of, as long as you have the headroom to get a really big rise, and a lot of boats don't. Thge best arrangement is to have an end stop, with the exhaust coming in overhead and downstream. Your major risk is having seawater rush into the riser when shut down, due to boat roll and pitch. And it won't dribble, it will fill the pistons which have their exhaust valves open. Can cost you a motor if you try to start it and hydrauliclly lock up, bending one or more rods. With a stop end, any water shooting up the exhaust should just hit the end stop, then run back out. I have included a rough illustration below.
yep the pic I posted is the same one they list for JH3-DTE. wish that was in au$ haha
Yes, I am on that scimitar page, got a bit of a shock when seeing how they are doing the engine swap. I guess it's the only way to fit the new engines without dismantling them. Much quicker and 20yr old Scimitars could mostly do with a hull respray anyway.. time saved would maybe pay for the repainted sides.
It's got me thinking a bit, whilst my engines are still good, they have almost 1700hrs on them. It would be $100k job, but I would have brand new more modern engines, shinier sides, and I could probably get 100k more if I was to sell it in next few years.
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