Divemaster1
Well-Known Member
Following from my last work on one of our iron lumps ( http://www.ybw.com/forums/showthread.php?290687 )
For some time I've had some suspicion that my SB engine (approx. 2500 hrs on the clock) had some compression issues as she is slow starting (particularly when cold ... and boy does she smoke when firing on four, five then six pots)... makes Sabre's and AD41's look like lean, clean burning machines...
... and also sound a bit lazy when starting warm... sort of does not kick into life with same enthusiasm as the port one.... When warm she is clean as a whistle, and idle smoothly at 500 RPM ... so nicely in-tune, and performing well in principle... but un-sociable smoking when cold..
So suspecting a compression issue, I thought that I should do some prep work and do a visual cylinder inspection before even considering a compression test etc.,... or at least take the KISS approach and try to rule out more complex or work not required. For those un-familiar with Detroit Two Stroke diesels, you can visually inspect the cylinder, piston and piston rings, by opening up a airbox cover in the block of the engine and rotate the engine (with a 32mm socked & bar) until piston and rings are in a good inspection location .... it looks something like this (not my picture)
Anyway, armed with a 14mm spanner, small screwdriver, torch and glasses (annoying when you forget the last vital item and have to return..
), I crawled between my iron lumps around the front of the SB one and faced the block (see pictures in other thread) ... opened the covers and started the visual inspection... Liners, appeared nice and clean with no damage.... Piston rings were springing back nicely on four cylinders, but on two of the cylinders, the top compression rings (there are two compression rings on each piston) did not spring back when pushed, just appeared loose.... so guess I found the cause for the slow starting issue...(damaged / broken / split compression rings)
So there you have it ... it will be the return of the "Cheap cylinder repair company" this winter when I will do another cylinder re-build in situ..... but this time I plan to do all Six holes (so oil pan will have to be dropped)... my personal challenge will be to keep the cost of parts to about £100 per hole.... not too bad a cost I guess as this is the first major job we have done to this lump over the 9 years we have owned the boat... apart from the servicing and oil changes I have done myself...
Documented evidence of work performed and challenges met will follow in due cause ... in the mean time prep work has sort of started by removing soft furnishing, carpets etc.., no spanners spun yet ...
For some time I've had some suspicion that my SB engine (approx. 2500 hrs on the clock) had some compression issues as she is slow starting (particularly when cold ... and boy does she smoke when firing on four, five then six pots)... makes Sabre's and AD41's look like lean, clean burning machines...
... and also sound a bit lazy when starting warm... sort of does not kick into life with same enthusiasm as the port one.... When warm she is clean as a whistle, and idle smoothly at 500 RPM ... so nicely in-tune, and performing well in principle... but un-sociable smoking when cold..So suspecting a compression issue, I thought that I should do some prep work and do a visual cylinder inspection before even considering a compression test etc.,... or at least take the KISS approach and try to rule out more complex or work not required. For those un-familiar with Detroit Two Stroke diesels, you can visually inspect the cylinder, piston and piston rings, by opening up a airbox cover in the block of the engine and rotate the engine (with a 32mm socked & bar) until piston and rings are in a good inspection location .... it looks something like this (not my picture)
Anyway, armed with a 14mm spanner, small screwdriver, torch and glasses (annoying when you forget the last vital item and have to return..
), I crawled between my iron lumps around the front of the SB one and faced the block (see pictures in other thread) ... opened the covers and started the visual inspection... Liners, appeared nice and clean with no damage.... Piston rings were springing back nicely on four cylinders, but on two of the cylinders, the top compression rings (there are two compression rings on each piston) did not spring back when pushed, just appeared loose.... so guess I found the cause for the slow starting issue...(damaged / broken / split compression rings)So there you have it ... it will be the return of the "Cheap cylinder repair company" this winter when I will do another cylinder re-build in situ..... but this time I plan to do all Six holes (so oil pan will have to be dropped)... my personal challenge will be to keep the cost of parts to about £100 per hole.... not too bad a cost I guess as this is the first major job we have done to this lump over the 9 years we have owned the boat... apart from the servicing and oil changes I have done myself...
Documented evidence of work performed and challenges met will follow in due cause ... in the mean time prep work has sort of started by removing soft furnishing, carpets etc.., no spanners spun yet ...
