I was getting a Yanmar 3HMF started after not running for several years. One of the things I was told to do to prepare for starting the engine for the first time was to replace the seawater pump impeller. It was a good recommendation as the impeller was very deformed and degraded. Reassembly was going well until I was tightening the last of the 6 impeller cover bolts and it was just starting to strip. I went to the chandlery to get a replacement bolt to see if that might hold enough. As I’m using the bolt as a size gage I realized that it is a US standard size. A previous owner probably replaced the original bolts for some new shinny ones
- PLEASE Yanmar is a Japanese company, and like almost every other country in the world, uses the metric system!!!!
Lesson #1, don’t assume the bolts that were on the engine are the correct size if it has been apart before.
Lesson #2, if you have a suspect hole, mark it so you don’t forget which hole it is
Not wanting to buy a new pump, I bought a 4mm bottom top (not tapered) and carefully cleaned the threads. As the holes were compromised, I wanted to use just enough torque on the impeller cover but not too much. Finding out the spec for this was very difficult and the more I read the more confusing it became. The Yanmar shop manual doesn’t cover this – the smallest bolt I could find is M6 with a torque of 8-10Nm/71-88in.lbs. From
https://mdmetric.com/tech/Standard_tightening_torque.pdf
the M4 torque went from 0.75-3.6Nm, depending on the strength of the bolt. As the hole is brass I wanted to go to the low end of the scale, but as I tightened, it seem so light, that I ended up at 20in lbs (2.2Nm).
I didn’t have a torque wrench measuring in Nm/in lbs and bought one from harbor freight that could go as low as 20in lbs. It turned out not to really be usable at the low end of the scale and I ended up borrowing a “F.A.T” wrench from a gunsmith friend – highly recommend that tool. I will be getting an in lbs bar torque wrench as soon as I see one.
Put the pump on the engine and then started it up – then the water started coming out. I assumed that I didn’t tighten the bolts enough but when I looked with a mirror, the impeller cover was dry and the water was coming from the pump shaft seal opposite the impeller cover.
Lesson #3 – if you replace the impeller, you might consider changing the seal. It is not that much more work; some suggestions:
- take pictures as you disassemble, so you know the order and orientation of the parts. The shop instructions are not that clear
- the bearings stay on the shaft and slide out as a unit. You only need to take the bearings off if they need to be replaced.
In the end I disassembled and reassembled the pump 3 times, but you know what they say – the third time’s the charm; not a drop. That is from the engine, the shaft seal I’ll report in another post when I’m done with that.
- PLEASE Yanmar is a Japanese company, and like almost every other country in the world, uses the metric system!!!!
Lesson #1, don’t assume the bolts that were on the engine are the correct size if it has been apart before.
Lesson #2, if you have a suspect hole, mark it so you don’t forget which hole it is
Not wanting to buy a new pump, I bought a 4mm bottom top (not tapered) and carefully cleaned the threads. As the holes were compromised, I wanted to use just enough torque on the impeller cover but not too much. Finding out the spec for this was very difficult and the more I read the more confusing it became. The Yanmar shop manual doesn’t cover this – the smallest bolt I could find is M6 with a torque of 8-10Nm/71-88in.lbs. From
https://mdmetric.com/tech/Standard_tightening_torque.pdf
the M4 torque went from 0.75-3.6Nm, depending on the strength of the bolt. As the hole is brass I wanted to go to the low end of the scale, but as I tightened, it seem so light, that I ended up at 20in lbs (2.2Nm).
I didn’t have a torque wrench measuring in Nm/in lbs and bought one from harbor freight that could go as low as 20in lbs. It turned out not to really be usable at the low end of the scale and I ended up borrowing a “F.A.T” wrench from a gunsmith friend – highly recommend that tool. I will be getting an in lbs bar torque wrench as soon as I see one.
Put the pump on the engine and then started it up – then the water started coming out. I assumed that I didn’t tighten the bolts enough but when I looked with a mirror, the impeller cover was dry and the water was coming from the pump shaft seal opposite the impeller cover.
Lesson #3 – if you replace the impeller, you might consider changing the seal. It is not that much more work; some suggestions:
- take pictures as you disassemble, so you know the order and orientation of the parts. The shop instructions are not that clear
- the bearings stay on the shaft and slide out as a unit. You only need to take the bearings off if they need to be replaced.
In the end I disassembled and reassembled the pump 3 times, but you know what they say – the third time’s the charm; not a drop. That is from the engine, the shaft seal I’ll report in another post when I’m done with that.