- Joined
- Sep 4, 2010
- RO Number
- 32322
- Messages
- 164
Hi, All,
I'm wondering whether to redo (or not) the head on my Onan/Kubota 8.0 MDKD diesel genset (3 cylinders). It appears original to my boat, so vintage 1968.
After the genset would barely crank and not start, my mechanic found a bent pushrod and a seized valve, along with a pushrod that had jumped off its rocker arm seat.
I am comfortable with wrenches (rebuilt a car motor some years ago), so I pulled the head myself. Sure enough, the middle cylinder was the culprit, with rust on the valves and some on the piston top – enough to seize one of the valves but not looking too terrible on the piston. The other two sets of valves and all three cylinder walls look ok, no apparent scarring, no rust. When I bumped the starter, it moved the pistons smartly, fuel pumped from the lines, etc. (kind of a DUH on that, I know, but I had worried that the starter might have been shot, too). So the starter appears ok. Crankcase oil looks good, too – good, solid black, no milky appearance.
I'm puzzling whether the problem was a blown head gasket or whether I may have back-flowed seawater from over-cranking. It's an academic question maybe, but I am leaning toward the head gasket, since I found a problem in only one cylinder.
Anyway, I am thinking that having a machine shop refurbish the head, with new valves as needed, etc., might be the ticket to revive my genset. I'm willing to try that first, especially compared to the cost of pulling the genset and buying a new/newly rebuilt one.
I have the tech manuals and know the order of tightening the head bolts and the torque settings. (Also, don't I recall that I will need new head bolts, that the old ones won't hold proper torque?)
Am I off base? Thank you very much for your thoughts and suggestions. All are most appreciated.
V/R
I'm wondering whether to redo (or not) the head on my Onan/Kubota 8.0 MDKD diesel genset (3 cylinders). It appears original to my boat, so vintage 1968.
After the genset would barely crank and not start, my mechanic found a bent pushrod and a seized valve, along with a pushrod that had jumped off its rocker arm seat.
I am comfortable with wrenches (rebuilt a car motor some years ago), so I pulled the head myself. Sure enough, the middle cylinder was the culprit, with rust on the valves and some on the piston top – enough to seize one of the valves but not looking too terrible on the piston. The other two sets of valves and all three cylinder walls look ok, no apparent scarring, no rust. When I bumped the starter, it moved the pistons smartly, fuel pumped from the lines, etc. (kind of a DUH on that, I know, but I had worried that the starter might have been shot, too). So the starter appears ok. Crankcase oil looks good, too – good, solid black, no milky appearance.
I'm puzzling whether the problem was a blown head gasket or whether I may have back-flowed seawater from over-cranking. It's an academic question maybe, but I am leaning toward the head gasket, since I found a problem in only one cylinder.
Anyway, I am thinking that having a machine shop refurbish the head, with new valves as needed, etc., might be the ticket to revive my genset. I'm willing to try that first, especially compared to the cost of pulling the genset and buying a new/newly rebuilt one.
I have the tech manuals and know the order of tightening the head bolts and the torque settings. (Also, don't I recall that I will need new head bolts, that the old ones won't hold proper torque?)
Am I off base? Thank you very much for your thoughts and suggestions. All are most appreciated.
V/R