skipjack27
Petty Officer 3rd Class
- Joined
- Oct 6, 2009
- Messages
- 79
I'd be interested to know if anyone has any bright ideas on how to deal with this problem. I have a 200 HP Volvo AQAD41A driving a Duoprop 290 leg. The boat is a 27' fibreglass flybridge launch, weighing around 3 tons. The engine is 23 years old and has around 1400 hours on the clock. As far as I know, it has never been rebuilt.
There are no problems running at modest revs (e.g., 2700rpm or so), but when the engine is pushed up to max revs (about 3500+) the crankcase breather starts venting oil in significant amounts. By significant, I mean that there is a continuous trickle into the bilge and the engine probably loses something like a couple of litres an hour - possibly more.
The local Volvo service mechanics suggested that the most likely cause was gas escaping from the cylinders under load and pressurising the crankcase to the extent that large amounts of oil were being blown out of the breather. They tested compression and checked the cylinders with a borescope. Compression is down - as much as 100psi on one cylinder - and there is evidence of glazing and vertical scoring. This appears to confirm the diagnosis.
The obvious solution - a rebuild - was quoted at around US$23k. I'm most reluctant to pay this, because the engine otherwise runs beautifully: starts instantly in the coldest of weather, doesn't smoke (once going), idles smoothly, accelerates vigorously, and uses practically no oil (other than in the problem full-load condition, of course). But for the breather problem, I would never have guessed that the engine was in anything other than the prime of life.
The alternative solution suggested by the mechanics was to install a housing adapter that would collect the oil and direct it into a container, allowing it to be returned periodically to the engine rather than collect in the bilge. But, this is a somewhat awkward and unsatisfactory arrangement (even dangerous for the engine if I happen to misjudge the need for decanting collected oil back into the engine), and definitely not a good look for the boat when I come to sell it.
I'd be extremely grateful for any comments/ideas from members of this forum.
Jeff
There are no problems running at modest revs (e.g., 2700rpm or so), but when the engine is pushed up to max revs (about 3500+) the crankcase breather starts venting oil in significant amounts. By significant, I mean that there is a continuous trickle into the bilge and the engine probably loses something like a couple of litres an hour - possibly more.
The local Volvo service mechanics suggested that the most likely cause was gas escaping from the cylinders under load and pressurising the crankcase to the extent that large amounts of oil were being blown out of the breather. They tested compression and checked the cylinders with a borescope. Compression is down - as much as 100psi on one cylinder - and there is evidence of glazing and vertical scoring. This appears to confirm the diagnosis.
The obvious solution - a rebuild - was quoted at around US$23k. I'm most reluctant to pay this, because the engine otherwise runs beautifully: starts instantly in the coldest of weather, doesn't smoke (once going), idles smoothly, accelerates vigorously, and uses practically no oil (other than in the problem full-load condition, of course). But for the breather problem, I would never have guessed that the engine was in anything other than the prime of life.
The alternative solution suggested by the mechanics was to install a housing adapter that would collect the oil and direct it into a container, allowing it to be returned periodically to the engine rather than collect in the bilge. But, this is a somewhat awkward and unsatisfactory arrangement (even dangerous for the engine if I happen to misjudge the need for decanting collected oil back into the engine), and definitely not a good look for the boat when I come to sell it.
I'd be extremely grateful for any comments/ideas from members of this forum.
Jeff
