Tayana Owners Group messages about exhaust hose size
.... A good point was made regarding my quoted engine price and whether it included a tranny. But I will check. In discussing my options, one mechanic intimated the 4 cylinder Yanmar 4JH4E may require a 3-inch exhaust versus a 2-inch for the 3 cylinder 3JH. Anybody have an opinion on that? … Even if I ran 3-inch, my thru-hull exhaust is only 2-inch, so even though the internal resistance may be less, I'm going to be limited somewhat by the stainless exhaust diameter. Both engines appear to have the exhaust coming off the port side, and all my exhaust is currently plumbed off the starboard--probably not a big deal to run it to starboard.
Thanks, Rudy Heller March 2006
Hi Rudi –
When we replaced our 4-108 with a Yanmar 4JH3-TE in our Tayana 42, we were also told we need to up-size the exhaust, which we did. Also upsized to a 4-inch Chrome exhaust nozzle. The new exhaust involved a lot of extra cost and hassle (ever try to work with exhaust hose that size?), but I didn't want to go to all the expense of purchasing and installing a new engine and not adhering to mfg specs. We've very pleased with our new engine.
Bill March 2006
The mechanic who walked us though the installation of the 4JH3 advised us that the 2-inch exhaust would be adequate even though the installation specs called for 3-inch. After 250 hours of engine run time, we've not experienced any problems with excessive back pressure. I can't recall seeing any repowered boat in our HP range that ever went to 3-inch hose. Would be interesting to ask Tayana factory what size hose they are using in the new T-37s. 3-inch hose would take up a lot of space in the engine room. Regarding the starboard side exhaust fitting, ours is that way too; it is no big deal to run the hose the extra 3 feet to reach the fitting.
Dayton Eckerson T-37 MISTRESS (#215) March 2006
Mark Eller, Maraj, V-42 CC hull # 40 or 42 (1 of ours) repowered from a 3QM30 to a Yanmar 56. He had the same questions & concern about increasing the size of the exhaust. He pressed the engineers at Yanmar about exactly how big the exhaust needed to be for the health of the engine. They were reluctant to depart from the company standards that all of their smaller engines use the larger exhaust hose. He finally got them to admit that the smaller hose was fine for that particular engine and installation. He installed the engine and had no problems.
That's my best recollection of the details. If you want further info I would recommend contacting Mark, or better yet, the experts at Yanmar. So far, I'm sticking with my 3QM30.
Harry & Melinda Schell Sea Schell, 1981 V-42 CC #41 March 2006
After reading the above thread, I saw that nobody noted that increased exhaust size may require a new waterlift muffler. I have experience with 3 different mufflers.
Having owned my V-42 center cockpit since 1982 when it was new, I have had the original stainless steel Tayana muffler which was quite adequate and fit snugly into the corner of my engine room. When it corroded after 10 years, it was replaced with a rather small Vetus plastic waterlock, probably the wlock50s model, see http://www.pridemarine.com/Vetus.htm. I didn’t use a muffler with it as shown in the diagram. The engine noise did not seem louder than with the Tayana muffler. Although I experienced no problems, I did not like the thin plastic muffler. I considered it a fire hazard if the water pump failed and it always seemed too flimsy and small. It was hard to secure and I just had it hanging in line and supported by all the hoses.
I finally decided to change to a more substantial waterlift muffler. A mechanic recommended that it would be a good time to increase the diameter of my exhaust hose from 1 ½ to 2 ½ inches. I agreed and ordered a custom muffler from Naqualift that I designed to fit very much like the original factory unit but with an angled bottom. It wasn’t overly expensive and was very well built. Just draw it – they build it! It has the standard-sized exhaust input connection for a Perkins 4-108 - two inches. The exhaust output is 2 ½ inches.
A custom transom exhaust connector was fabricated out of stainless steel to handle the 2 ½ inch hose. The original inline check valve was not included. The custom exhaust connector was expensive! Better alternatives are offered by Naqualift or Vetus.
Was the larger diameter exhaust required? Well, the engine ran OK for another 2500 hours before reaching 6000 hours and finally requiring overhaul due to low compression on 2 cylinders and excessive oil consumption. I really can’t say whether the larger exhaust helped at all. Oil analysis still showed excessive soot. If you are replacing the muffler anyway, an exhaust hose size upgrade could be accomplished for the cost of the hose plus around $120 for a stainless steel transom connector from Vetus or as little as $30 for a 3-inch outlet made of Primex by Naqualift.
See the accompanying pictures of the installed muffler in my V-42.