165 Rebuild died, need info

My father-in-law rebuilt the motor in our boat earlier this summer (1987 Four Winns 190 Horizon with the Mercruiser 165 (I4)) after 1 of the 4 pistons gave up the goat in the oil pan (piston skirt broke right off, the other 3 were getting ready to do the same). It was determined at the time that the last time the motor was rebuilt (due to the dreaded wrist pin breakage), the shop over-bored it (.025 instead of .020), allowing too much piston slop.

The motor was bored to +.030, head and block were both decked, valves were done, and the crank was turned to +.010. Essentially, it was a brand new motor.

While out tooling around, we hit a shallow spot and had to get up on plane, and the motor topped out around 5000rpm, at which point it started to make a really BAD noise. We limped it home, pulled the motor, and removed the oil pan and found pieces of copper. The bearings were SMOKED.

The crank has now been turned to ".020, and is ready to go back in with new bearings. The problem being, we want to figure out WHY they got cooked so that we don't have a repeat performance.

Currently, the theory is this: We put a new oil pump on, as well as replaced the o-ring/seal between the pick up tube and the pump. It was noted that when we removed the pick up tube, it was extremely loose (we were able to pull it right out with no problems without removing anything other than the main bolt holding the tube to the block. We believe that the o-ring was not the correct size, even though it was ordered specifically for the motor.

So, after much rambling, I'm asking you this: WHAT type/size of o-ring should be there? We ended up with a standard round o-ring when the seal/ring we removed was either square or an x-ring originally.

I've found one site that gives me the dimensions for the o-ring, but I really don't have anything to compare it to, so any information would be greatly appreciated.

Thanks in advance!

Re: 165 Rebuild died, need info

Do you still have the failed bearings and know which main/rod they were paired with? If so, take detailed photos and post them so I can take a look at them. Be sure to label the bearings 1, 2, 3, etc., and main/rod bearing. The best thing to do is set them out on a piece of cardboard and write on the cardboard just underneath the bearing which number main/rod the bearing is. Then take close up photos of each. Also, take apart your lube pump and check for damage. Use the macro setting (looks like a flower) on your digital camera to take close up photos. The macro setting will take the best closeup photos.

I have analyzed alot of bearing failures over the years, so hopefully I can see something in them that will shed some light on the root cause. Often times the bearings that have the least amount of damage provide the best evidence as to the cause of the failure, so be sure to take photos of both hte bad bearings and the "good" ones.

Re: 165 Rebuild died, need info

I don't have any pictures like that, and the boat's all back together. We finished the rebuild last Fall, right before storing it.

We inspected the oil pump and found nothing out of place. The only thing that didn't feel quite right was the o-ring where the pickup tube goes into the pump. That was extremely loose. We believe that it sucked some air and foamed up the oil which starved the bottom end, as there was no sign of top end damage.

Re: 165 Rebuild died, need info

Difficult to determine the cause without seeing the kind of damage you had. But when you run an engine the first time the oil pump/passages need to be primed, if not and you try to start it you'll have instant bearing damage. I've seen this happen where there wasnt enough rebuild bearing grease on the bearings too. Crank could have been cut wrong, oil pump blockage or failure etc... Could have been many things

Re: 165 Rebuild died, need info

The damage boiled down to the bearings being destroyed. Some were worn right through the outer coating, and through the copper as well. I can't recall which ones were worse than the others. I ended up giving the bearings to one of my bearing design professors so that they had some hands-on "touchy-feelies" to pass around class to show what happens when there's not enough oil.

My father-in-law's a mechanic, and we went through and did everything by the book. Plenty of lube grease, primed everything prior to running it, used the plasti-gage to check bearing clearances. Everything was good. It ran fine for about 6 hours, then we over-revved it a bit too early, and that's when things went south in a hurry. We're pretty sure it wasn't so much the time that was on the engine, but that bad o-ring.

Re: 165 Rebuild died, need info

Bubba1235 said:

Bad combination. I think red line on a stock 250 is 4600 RPM or so.

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Bubba - his 165 is the 4 cylinder - not the inline six 250. Now 5,000 may still be too high - but just making sure everyone is on the same page.

Re: 165 Rebuild died, need info

I believe redline for the 165 is 4800. I say about 5000 because I wasn't driving, so I didn't have a good view of the tach.