scout-j-m
Chief Petty Officer
- Joined
- Jul 31, 2009
- Messages
- 641
I have a fully disassembled Yamaha 25hp motor I am about to dive into rebuilding. I bought it as part of a parts lot which primarily included motors with "bad crankshafts". The man I bought them from had bought the parts lot himself and really never got to working on them so it's kind of second hand information there on what the original issues these all had. The lot included this torn down 25hp as well as a similar year model one. All of the parts to put both back together are included even a pair of *what appear to be* new oem crankshafts.
This 25MSHB motor I am working on first has already been bored over at some point as it has 0.5mm stamped oversize pistons. Luckily the pistons and the bores look great (not so much for the other motor) in terms of no scoring or other damage. I have a cheap set of micrometers/calipers and a cheap bore gauge so I plan on mic'ing both to ensure they are in spec and it has acceptable piston to wall clearance before getting too far ahead of myself. Like I said they are cheap tools but I do have access at work to some quality calibrated tools I can at least measure the pistons with and some gauge blocks I can check and adjust my tools against. Right now the main thing I will have to address before doing anything else will be to clean up the rust on the bores.
This will only be my second full outboard rebuild and its been a few years since I did my first one. I started this thread mainly to help me stay organized throughout the process but also to get a few tips. The first thing I was wondering from those may know is if the factory service manual for a late 80s/early 90's motor, like I have, will suffice for this particular model? I know they have slightly different ignition setup in the later years but to my knowledge almost everything else is exactly the same. My next question is how I should address the rust on the cylinder bores? It appears to just be a lot of flash rust and is only covering about 20% of each bore. Best to remove it with something mechanically like light scrubbing with a scotch brite or maybe just use vinegar and a rag? Like I said, they seemed to be in good shape I just need to clean them up so I can get good measurements before moving forward.
This 25MSHB motor I am working on first has already been bored over at some point as it has 0.5mm stamped oversize pistons. Luckily the pistons and the bores look great (not so much for the other motor) in terms of no scoring or other damage. I have a cheap set of micrometers/calipers and a cheap bore gauge so I plan on mic'ing both to ensure they are in spec and it has acceptable piston to wall clearance before getting too far ahead of myself. Like I said they are cheap tools but I do have access at work to some quality calibrated tools I can at least measure the pistons with and some gauge blocks I can check and adjust my tools against. Right now the main thing I will have to address before doing anything else will be to clean up the rust on the bores.
This will only be my second full outboard rebuild and its been a few years since I did my first one. I started this thread mainly to help me stay organized throughout the process but also to get a few tips. The first thing I was wondering from those may know is if the factory service manual for a late 80s/early 90's motor, like I have, will suffice for this particular model? I know they have slightly different ignition setup in the later years but to my knowledge almost everything else is exactly the same. My next question is how I should address the rust on the cylinder bores? It appears to just be a lot of flash rust and is only covering about 20% of each bore. Best to remove it with something mechanically like light scrubbing with a scotch brite or maybe just use vinegar and a rag? Like I said, they seemed to be in good shape I just need to clean them up so I can get good measurements before moving forward.