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Bad piston rings or damaged cylinder walls?

eric240sx
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eric240sx Contributor

eric240sx

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Bad piston rings or damaged cylinder walls?

Recently, I opened a discussion on my excessive oil burning that my rb25det does and thanks to the help of many enthusiasts we concluded that it is bad piston rings or a damaged cylinder wall... or can it be both?

Engine had a full upgraded rebuilt 6 months ago with it being bored over .020 over. It has been driven 1000 miles or 1609 kilometers since 

I have compression tested all my cylinders and it showed a psi of 50-70psi. When I did a wet test it shot up to 120-135psi

My rb25det has a 1.5 cosworth head gasket so compression will be lower than normal 

My hopeful prediction is that the piston rings have seized, been installed improperly, or the rings are worn out. The reason why I don't believe its damaged cylinder walls is because every cylinder shows the same sign of compression loss and piston rings go out together. Cylinder walls are unlikely to all be damaged at the same time

 

What do you guys think?

Birds Grand Master

Birds

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Why wouldn't they all suffer the same fate/damage? You're repeating the same process for preparation, installation and running in of each cylinder which happens all at the same time. If it was just one cylinder then you could put it down to a faulty part...

eric240sx Contributor

eric240sx

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3 hours ago, djr81 said:

Piston rings don't wear out in 1000 miles.  What does happen is people don't bed them in properly and they never work from the start.  How did you run the engine in after start up?

when i finished with the rebuilt, i would keep the car in high rpm when race on the street and events. But whenever I drove normally, i would try to have it at the lowest rpm possible around 2k-3k rpm 

eric240sx Contributor

eric240sx

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3 hours ago, Birds said:

Why wouldn't they all suffer the same fate/damage? You're repeating the same process for preparation, installation and running in of each cylinder which happens all at the same time. If it was just one cylinder then you could put it down to a faulty part...

The reason why i find it unlikely for all 6 cylinders to be wall damaged is because there needs to be something thats consistent throughout the cylinders thats causing the damage. If something exterior got in and scratched a cylinder wall it would only be on that one and not all of them. While rings go out together since all they do is seal and if they were installed wrong then they are all going out  

Birds Grand Master

Birds

Posted
Posted

Sorry, I think I misread your original post. I meant that they could all have buggered piston rings and not just one.

Though I guess there is a possibility the walls were not honed correctly? Tolerances are all matched up fine, I assume?

KiwiRS4T Grand Master

KiwiRS4T

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Doesn't really matter the head will have to come off and the pistons out. You can measure the bores and see if they are glazed. If they are within spec you may be able to rough them up with a suitable hone. Get a professional to look at your rings or compare them with a new set.

When the motor is rebuilt do not start it until you have an aftermarket ecu set for your injectors and get it tuned on the dyno with a load of mineral oil or special running in oil. By the time it has had a few full power pulls on the dyno it should be half way run in .(if you can't afford to buy and tune an aftermarket ecu - about $3000 - then return the engine to stock until you can) .

The head gasket will not have a significant effect on your compression ratio although I would be inclined to get a 1.2 Tomei gasket which you can reuse if (hopefully not) you have to pull it down again.

PS and don't keep starting new threads for the same issue!!

eric240sx Contributor

eric240sx

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15 hours ago, KiwiRS4T said:

Doesn't really matter the head will have to come off and the pistons out. You can measure the bores and see if they are glazed. If they are within spec you may be able to rough them up with a suitable hone. Get a professional to look at your rings or compare them with a new set.

When the motor is rebuilt do not start it until you have an aftermarket ecu set for your injectors and get it tuned on the dyno with a load of mineral oil or special running in oil. By the time it has had a few full power pulls on the dyno it should be half way run in .(if you can't afford to buy and tune an aftermarket ecu - about $3000 - then return the engine to stock until you can) .

The head gasket will not have a significant effect on your compression ratio although I would be inclined to get a 1.2 Tomei gasket which you can reuse if (hopefully not) you have to pull it down again.

PS and don't keep starting new threads for the same issue!!

This is exactly what I am going to do. I am going to pay an RB specialist to disassemble my engine and inspect my internals. I am going to be running an e32 ECU with nistune to tune the engine. "I have money, it's trust and character that I never looking for." -Han ?

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