The Specifics:
1994 FZJ80
approximately 215,000 miles
serviced at the dealer and babied its entire life
motor completely stock
The Background:
The past few times I started it I noticed that the oil pressure seemed low and then would come up as it warmed up. This is odd and opposite of normal behavior in my experience (usually the pressure is high when cold and comes down a little as it warms up). I had been planning to get a mechanical gauge on it to check it but hadn't gotten to it. On a recent drive (interstate speeds) to a neighboring town, about 45 minutes in I noticed the oil pressure was just below the lowest tick mark on the gauge. I thought that seemed low and out of the ordinary. I watched it for a few miles and revved the motor a bit to see if it would come up with the RPMs but it didn't. Shortly after that the pressure started falling so I got off at the next exit. I got out and looked for leaks but found none and heard no funny noises. If I recall correctly, at idle, the pressure was about halfway between the bottom of the gauge and the first tick mark which is a lot lower than I am used to seeing. I turned it off and let it sit for a minute and then checked the oil level which was fine. I turned it back up and heard a knocking noise right off the bat but then quieted down. I put it in gear and gave it some gas to move and heard a knocking. At this point I shut it down and had it towed to town.
The next day I changed the oil and filter. I had a Wix filter on it and replaced it with a Toyota filter. When I turned it on the oil pressure gauge hit the third tick mark like I am used to seeing but the motor knocked. I used a stethoscope and narrowed it to the middle of the oil pan. Since it seemed like the bearing was just beginning to go I decided to pull the pan and see what it looked like. Once I got the pan off I pulled the connecting rod caps one by one. I found that the third and fourth (if counting the cylinders from the front of the motor) rod bearings were bad. When I was removing the cap for the sixth rod the passenger side nut seemed very loose. Not finger tight but definitely not at proper torque.
I measured all the connecting rod bolts as per procedure and found them all to be within specifications. Even the one with the loose nut, although that one was thinner than the rest. I'm in the middle of replacing the bearings now but when I torqued the cylinder six connecting rod bolt (the one that was loose when I removed it) it wouldn't tighten up.
The Question:
Can connecting rod bolts be replaced with the piston and rod in the block? If so, what is the procedure? I looked through the FSM and can't find anything about actually replacing the connecting rod bolts. All I found is that it says that if the bolts are out of spec they should be replaced as a set (bolt and nut) but doesn't have a procedure for it. I tapped on the rod bolt lightly with a hammer and it didn't seem to move. I also found that the head of the bolt had broken off. If I had to guess, I broke it when I tried to torque it down. As clarification, it didn't break when I did the 90 degree torque, it wouldn't even take the 35 ft lbs initial torque so it must have been pretty weak.
Another question I have is why was the connecting rod nut loose in the first place? I wonder if it would have continued to work loose and then I would have had a catastrophic failure sometime down the road.
tl;dr Low oil pressure; changing connecting rod bearings; one rod bolt wouldn't take the recommended torque and broke; How do you change the connecting rod bolts and can it be done without pulling the piston and connecting rod from the motor?
Richard.
1994 FZJ80
approximately 215,000 miles
serviced at the dealer and babied its entire life
motor completely stock
The Background:
The past few times I started it I noticed that the oil pressure seemed low and then would come up as it warmed up. This is odd and opposite of normal behavior in my experience (usually the pressure is high when cold and comes down a little as it warms up). I had been planning to get a mechanical gauge on it to check it but hadn't gotten to it. On a recent drive (interstate speeds) to a neighboring town, about 45 minutes in I noticed the oil pressure was just below the lowest tick mark on the gauge. I thought that seemed low and out of the ordinary. I watched it for a few miles and revved the motor a bit to see if it would come up with the RPMs but it didn't. Shortly after that the pressure started falling so I got off at the next exit. I got out and looked for leaks but found none and heard no funny noises. If I recall correctly, at idle, the pressure was about halfway between the bottom of the gauge and the first tick mark which is a lot lower than I am used to seeing. I turned it off and let it sit for a minute and then checked the oil level which was fine. I turned it back up and heard a knocking noise right off the bat but then quieted down. I put it in gear and gave it some gas to move and heard a knocking. At this point I shut it down and had it towed to town.
The next day I changed the oil and filter. I had a Wix filter on it and replaced it with a Toyota filter. When I turned it on the oil pressure gauge hit the third tick mark like I am used to seeing but the motor knocked. I used a stethoscope and narrowed it to the middle of the oil pan. Since it seemed like the bearing was just beginning to go I decided to pull the pan and see what it looked like. Once I got the pan off I pulled the connecting rod caps one by one. I found that the third and fourth (if counting the cylinders from the front of the motor) rod bearings were bad. When I was removing the cap for the sixth rod the passenger side nut seemed very loose. Not finger tight but definitely not at proper torque.
I measured all the connecting rod bolts as per procedure and found them all to be within specifications. Even the one with the loose nut, although that one was thinner than the rest. I'm in the middle of replacing the bearings now but when I torqued the cylinder six connecting rod bolt (the one that was loose when I removed it) it wouldn't tighten up.
The Question:
Can connecting rod bolts be replaced with the piston and rod in the block? If so, what is the procedure? I looked through the FSM and can't find anything about actually replacing the connecting rod bolts. All I found is that it says that if the bolts are out of spec they should be replaced as a set (bolt and nut) but doesn't have a procedure for it. I tapped on the rod bolt lightly with a hammer and it didn't seem to move. I also found that the head of the bolt had broken off. If I had to guess, I broke it when I tried to torque it down. As clarification, it didn't break when I did the 90 degree torque, it wouldn't even take the 35 ft lbs initial torque so it must have been pretty weak.
Another question I have is why was the connecting rod nut loose in the first place? I wonder if it would have continued to work loose and then I would have had a catastrophic failure sometime down the road.
tl;dr Low oil pressure; changing connecting rod bearings; one rod bolt wouldn't take the recommended torque and broke; How do you change the connecting rod bolts and can it be done without pulling the piston and connecting rod from the motor?
Richard.
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