Prophylactic exhaust elbow maintenance revisited

[RichardS]

Over a year ago I posted that I had removed the stainless steel exhaust elbow from my port Yanmar 3YM30 because I could see evidence water leakage from it in the form of some rust stains on the engine block below the elbow. On inspection I could see a hairline crack in the weld on the outside of the elbow. I repaired the elbow with a "fillet" of Milliput epoxy but I didn't take a photo. I had a couple of PM's asking for more details.

Anyway, 100 hours later the port elbow is still fine so today I removed the starboard elbow.

Although the stb elbow showed no signs of leakage, it was evident that the weld was giving way as there were some rust bubbles in it which had clearly originated from the inside. So this time I took preventative action and sanded the weld with coarse sandpaper until the entire weld was back to shiny metal and did another epoxy fillet.

Hopefully this will be good for a few more years.

 

[vyv_cox]

My exhaust elbow leaked after about 2000 hours, 3GM30F. I replaced it and examined it, finding a crack somewhat like yours but not exactly the same, mainly on the front face of the flange. These cracks are not corrosion related, although there may be a corrosion influence, they are due to thermal fatigue. Each time the manifold heats and cools the different thicknesses of metal expand at different rates, causing large stresses at the welds, where restaint is greatest. Over time, dependent on the number of starts and stops, a fatigue crack will develop. Fatigue happens more readily where corrosive media are present, although there is not a lot of evidence of salts deep inside the manifold. Hence the material used is not too critical: I see that one of the USA after-market manufacturers uses 304, probably not a factor.

 

[RichardS]

The port engine elbow weld referred to in my first post on this thread was "fixed" with a fillet of Milliput over 3 years ago and the starboard elbow shown in the photo above was done similarly 2 years ago.

Anyway, the port elbow has just started to weep seawater around the weld again after 3 years although the starboard one is still holding firm. I decided that the port elbow had reached the end of its useful life so I decided to investigate a replacement .... and these two lovely puppies arrived this morning:

Stainless steel, all the way from the USA, so I decided to replace both elbows as I had a choice between buying these two or, for the same price, buying one Yanmar elbow in the UK. A bit of a no brainer really.

Richard

 

[charles_reed]

My experience similar - Yanmar elbows distort and fracture (about 2000 hours life) the US ones seem to be far more effective. Engine is a 3YM20 and the US one seems to still be good after 1136 hrs.

 

[RichardS]

Removed the old elbow and fitted the new shiny one this afternoon.

After 3 years the epoxy seal had clearly failed against the elbow flange. Presumably the weld under the epoxy has corroded to the point where it couldn't stick any more. Anyway, a 3 year extension is not to be sneezed at.

It took me a couple of hours to remove and replace the elbow back in 2015 because the exhaust hose had "welded" itself to the elbow and the water trap and the manifold gasket had welded itself to the manifold so had to be scraped off. When I replaced it I copper greased the manifold gasket and the studs and plastered the elbow and trap with silicone grease.

This time the exhaust hose was loose as soon as I undid the clamps and the manifold fell into separate pieces as soon as I loosened the nuts and I just lifted the old gasket off without any of it being stuck to either mating surface. Total job this time about 15 minutes.

Richard