Rod Bearings for 90 300ZX 5sp

[gwb2709]

Hello, I have a rod bearing knocking on #2 pistion and I am going to have to replace the bearing, I plan on replacing all of the bearings. My question, can I do this by going in from the bottom of engine by removing the oil pan? I do not want to remove the engine..I would really like to here your expert advice. By the way the oil pressure is still good at idle and reving the enging the pressure gets close to 90. I am not going to replace the main crank bearings, just the rod bearings. I took your advice from another thread and when I unhook pistion number two, the clatter goes away. I took my car to Z1 in Atanta, and they agree, it is the rod bearing in #2. I hope the crank is not messed up, I will use an emory cloth to clean it up and do the fingernail test. I just want to make sure it can be done from the bottom by removing the oil pan. I have read the 300ZX online manuel and will follow the instructions reaging the removal of the oil pan. That will be a task in itself. Any tips would be appreciated!

[NISTECH]

you need to determine if it is the rod bearing or the wrist pin at the piston. get the car running to when its making the noise. pinch off both the fresh air hoses to the valve covers[pcv fresh air intake] they are the one inch hoses coming off the large intake hoses going to the throttle body. You will have 2 hoses on the drivers side. make sure you dont pinch off the one that leads to the back of the intake. That is your idle air control feed. But the 2 that go to your valve cover under the throttle body are the ones your after. Pinch both of them off and let it run at the knocking point. after awhile if the if the noise goes away you have a wrist pin knock and not a bearing knock on that cyl. If the noise doesnt go away then it is infact your rod bearing. The effects of pinching off those hoses wont be immediate it could take a min or so. What it does is allow pressure to build up in your crank case so it will put pressure against the bottom of the piston and keep it from sloping around on the wrist pin.

[gwb2709]

Thank you for some very good advice, I will try that! If it turns out to be a pistion top pin I will have to lift engine out to repair, correct? Also, if it is the rod bearing, will I be able to do the work from under by removing the oil pan?

[NISTECH]

yea but you will also need to remove the lower support and use something to to keep the engine in the car from the top. We have a cross bar at our shop from OTC to support the engine from the top.You may be able to loan or rent it form a tool rental place.

[s13sr20chris]

dropping the subframe while laying on the ground is a serious job. putting it back in is even more serious. just be sure you are up to it. wrist pins require the the heads to be off. at that point you really want to just pull the motor. pulling the motor is not as hard as dropping the subframe and pulling both heads in the car. just be ready for some downtime. i would recomend doing all the bearings and stuff if you pull the motor. if doing it in the car(rod bearings) then dont mess with the mains as they are a whole nother ball game. vg motors are funny about their mains and cranks. for one thing you cant turn the crank. that kinda sucks.

[gwb2709]

Hey Guys, thanks for all the advice!! Well my son and I got to it today and I have just quit working on it, calling it a day. You are right it is a very serious job . I have got to the point on dropping the oil pan, Under support off and engine is in place be aid of a rent engine lift. Took a while, was very careful and so far, going ok. My question is I am looking at the crank and no sludge or any obuvious signs of trouble. I know that it is pistion #2 that the rod is knocking. What is the best way to turn my crank so I can loosen the nuts to get to the bearings. Without moving some are impossible to get do. Do I turn the crank from the nut on the the crankshaft pully? Also do I replace one at a time? It it going to be fun getting the right size by reading the codes, any suggestions? What is the amount of foot pounds on the nuts when I put new bearings in? Any hints and help is greatly appreciated!! One last thing, what is the MM size of the nut on the cranksaft pulley, going to have to buy one, dont have on that big?

[s13sr20chris]

the crank bolt is a 27mm. go ahead and turn that to turn the crank. you want to do one at a time. put some assembly lube on the face of the bearing but keep the back dry.

[Q45tech]

Consider using one grade tighter clearance rod bearing than stamped to compensate for crank wear.........measure a few crank journals to be sure.

How many miles on engine?

[NISTECH]

plasti gauge works well to measure for proper bearing size. you will need a micrometer to measure it out. Do you have a service manual for the specs?

[gwb2709]

Hello, Again..

Thanks for all the great advice, I could not have come this far without the help. In answer to your question, the Z has 173K on it. It ran perfect before the knock and did not smoke at all. I thought is was worth trying this first before replacing the whole engine. I am using the online Z manuel that I found thru the 300Z forum. I guess measureing the correct bearing size is going to be a challegene. to you measure with the bearing in or out of the end of the connecting rod. The hints are a lifesaver!!

[gwb2709]

UDATE...... Hey guys, the job is done and the Z seems to be running GREAT! I want to thank all of you for some great advice. I could not have done it without it.

I told my son to keep it below 4K rpms for the first 500 miles. The engine is really purring and the knock is gone. However, we had a scare when we first started up after the install of bearings, I knock was still there and seem louder. it lasted for about 5 minutes and then it when away. The crank really looked good, the wear on the bad bearing had worn through the first layer, the the copper layer, starting on the last layer, the crank was smooth as silk and no signs of wear.

Thanks Again...

[s13sr20chris]

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[NISTECH]

awesome:thumbup:congrats on a serious job even most dealer techs wont take on[liability reasons]