Question about changing a rod bearing on my 87 GN

[syclone98]

I know that pulling the motor and rebuilding it would be the preferred solution, but due to time and budget constraints I just need to get a little more life out of the motor for the time being.

Anyway, the 87 GN that I recently bought (with 105K) has a rod knock. The guy who sold me the car stopped driving it after it suddenly developed an oil pressure problem. I put in a Melling kit last week and although I get 80psi when the motor is cold, I'm only getting around 5psi when it's hot and idling in park.

I ruled out loose torque converter bolts because I disconnected the spark plug wires one by one until the knock went away (it's most noticeable at around 2500rpm).

I've decided that I'm going to pull the pan and if the crank is okay, I'm going to swap out the bad bearing.

The questions I have are as follows:
- How do I determine which size rod bearing to use?
- Since I'm going to rebuild the motor soon anyway, do I need to worry about the other rod bearings and/or the mains right now?
- Is there anything else I should do while the pan is off?

I've done a similiar thing with my 70 Chevelle (many years ago) when I had to swap out a bad piston so I'm not afraid to tackle the job. My biggest question was just trying to determine which size bearing to use because I noticed that the parts places sell them in several different sizes.

Thanks in advance,
Christopher

 

[Blown&Injected]

measure the crank.

Has it been turned before that you know of? If not just get a standard rod bearing.

It might last for a tank of gas but what caused the problem? I have seen engines last forever after just cleaning out the pan and slapping in some bearings but that seems like luck.

 

[syclone98]

To the best of my knowledge the motor's never been apart.

I don't really know what caused the problem unfortunately so there is a certain 'shot in the dark' element to this whole thing.

 

[bison]

Changing rod bearing wont help the pressure. You have clearance issues somewhere else. Some good places to look are the front cam bearing, the oil pump clearances, the front main bearing, and the remaining mains. If it had a knock then the engine will need to come apart or it will be knocking again real soon. Id be the the crank needs to be ground also. Not to mention the metal particles floating around the engine and oil cooler circuit. Pull it know and save yourself a lot of future headaches.

 

[A2000RICH]

I know that pulling the motor and rebuilding it would be the preferred solution, but due to time and budget constraints I just need to get a little more life out of the motor for the time being.

Anyway, the 87 GN that I recently bought (with 105K) has a rod knock. The guy who sold me the car stopped driving it after it suddenly developed an oil pressure problem. I put in a Melling kit last week and although I get 80psi when the motor is cold, I'm only getting around 5psi when it's hot and idling in park.

I ruled out loose torque converter bolts because I disconnected the spark plug wires one by one until the knock went away (it's most noticeable at around 2500rpm).

I've decided that I'm going to pull the pan and if the crank is okay, I'm going to swap out the bad bearing.

The questions I have are as follows:
- How do I determine which size rod bearing to use?
- Since I'm going to rebuild the motor soon anyway, do I need to worry about the other rod bearings and/or the mains right now?
- Is there anything else I should do while the pan is off?

I've done a similiar thing with my 70 Chevelle (many years ago) when I had to swap out a bad piston so I'm not afraid to tackle the job. My biggest question was just trying to determine which size bearing to use because I noticed that the parts places sell them in several different sizes.

Thanks in advance,
Christopher

chris--------i have seen quite a few TR motors come into my shop with rod knocks---------about half of them have left repaired with only replaced rod bearings--------the real difference is how quickly did you turn it off when you heard the knock-------i know of one car where the driver was at the track and heard a nasty knock and immediately let out of it and turned the engine off and had it towed to the shop----------removing the rod caps showed that the #5 rod had excessive wear resulting in too much clearance-------a light lapping of the journal with a tape of 600 grit and installation of +.001 bearings gave it a new lease on life and believe me that car doesn't have an easy life------belonged to a college student that runs the devil out of the car-------i've had this kind of luck several times with this symptom-------my advice????-----you should have checked the bearings before doing the pump and starting the car------with the clearance that causes knocks you don't want to be running the car at all!!!!------serious damage comes quickly----if the rod cap is hammered out of round its over with--------remove the caps and visually check the bearings and journals----------if they don't look too bad it can't hurt to polish the crank and reinstall a set of standard bearings and do a simple plastigauge check for clearance--------if its a half too much you can put in one half of a +.001 bearing shell and and if its more you can always put in both halves and see what it measures--------you can usually get by with as much as .0025----------------RC

 

[syclone98]

Unfortunately I didn't know about the rod knock until after I fixed the pump and had driven it for a while.

I think I'm still going to give it a shot this weekend to see if I can hopefully fix the knock by replacing the bearing. It's a project car that I'm doing with my son so I figure at worst we've spent a few hours learning something.

Thanks for all the input.

 

[bison]

chris--------i have seen quite a few TR motors come into my shop with rod knocks---------about half of them have left repaired with only replaced rod bearings--------the real difference is how quickly did you turn it off when you heard the knock-------i know of one car where the driver was at the track and heard a nasty knock and immediately let out of it and turned the engine off and had it towed to the shop----------removing the rod caps showed that the #5 rod had excessive wear resulting in too much clearance-------a light lapping of the journal with a tape of 600 grit and installation of +.001 bearings gave it a new lease on life and believe me that car doesn't have an easy life------belonged to a college student that runs the devil out of the car-------i've had this kind of luck several times with this symptom-------my advice????-----you should have checked the bearings before doing the pump and starting the car------with the clearance that causes knocks you don't want to be running the car at all!!!!------serious damage comes quickly----if the rod cap is hammered out of round its over with--------remove the caps and visually check the bearings and journals----------if they don't look too bad it can't hurt to polish the crank and reinstall a set of standard bearings and do a simple plastigauge check for clearance--------if its a half too much you can put in one half of a +.001 bearing shell and and if its more you can always put in both halves and see what it measures--------you can usually get by with as much as .0025----------------RC

Usually on an engine that was otherwise fine develops a knock it is for a reason. That reason is usually severe detonation on one or more cylinders or oil starvation. When the detonation is that severe the rod is distorted and needs to be straightened, re-sized, or replaced. Rod and main bearings are not wear items in an engine. They dont wear out like other components do. When they fail there is an underlying cause. They will fail again if the problem is not isolated and corrected. Chances are in his case he has a big clearance issue somewhere because he has low pressure. Probably oil pump/front cam bearing wear.

 

[Blown&Injected]

I have had engines that sounded perfect but oil pressure gauge said something is wrong and the crank could not be saved so if you already are hearing the knock...stroker kit time

 

[syclone98]

Any suggestions on where to purchase a stroker kit from? Or is it something you piece together by yourself?

 

[A2000RICH]

Usually on an engine that was otherwise fine develops a knock it is for a reason. That reason is usually severe detonation on one or more cylinders or oil starvation. When the detonation is that severe the rod is distorted and needs to be straightened, re-sized, or replaced. Rod and main bearings are not wear items in an engine. They dont wear out like other components do. When they fail there is an underlying cause. They will fail again if the problem is not isolated and corrected. Chances are in his case he has a big clearance issue somewhere because he has low pressure. Probably oil pump/front cam bearing wear.

i agree with you 90%-------But sometimes the bearings do wear under extreme conditions and the rods aren't damaged--------- AND i have had good luck doing this about half the time-----the first i can remember was over 5 years ago and that particular car is still running well and strong------large turbo, front mount, 60 lb inj etc-----and i've done several since--------to me its worth a try------i believe its all in what the root cause was and more importantly how much/hard the engine was run when the knock started------all it costs is a few dollars for bearings, pan gasket and oil------------chris--------i recently purchased a stroker kit from full throttle-------crank, rods, pistons------it looks really nice-------can't remember how much it cost but it wasn't much....................RC