2 Years ago I bought a JDM B18C ITR motor off a guy on Craigslist. I was getting around to cleaning up my parts bins and thought I'd share this with you guys.

Here are the results of the previous owner's decision to use the stock JDM P73 ECU on California 91 Octane.

Note 2 things:
1) The discoloration on the crank to rod bearings is from detonation
2) The crank bearing scoring from the bent rod - I'd say the previous owner was very very close to throwing a rod and killing this motor. A testament to Honda's over engineering. Thank you Honda.



2 Simple Lessons:
1) Tune you motor if it's been significantly modified. If the previous owner would have spent $200 on a USDM ITR ECU he wouldn't have almost blown this motor.
2) If you are thinking of buying a JDM motor and or built motor, and the previous owner offers you a JDM ECU, or non-tuned ECU. Say "No Thanks" or ask for a significant discount, and explain why you will be rebuilding their motor due to their stupidity.

Here's the rebuild of my ITR:
https://honda-tech.com/forums/honda-civic-del-sol-1992-2000-1/my-project-1999-ex-coupe-b18c-r-swap-2717816/

 

Thanks for sharing your observations... It's always nice when someone takes a minute out of their day to share their experiences..

However, I'd have to disagree with the ignition timing changes in the ROM on the JDM ECU vs. the USDM ECU causing the damage. (It may not help when combined with lower quality gasoline, but most likely not the cause of the damage). First to note, the bearings that you indicated are the MAIN bearings, not rod bearings. All of the rod bearing halves that I can see on the left look like normal wear (possibly a little dirty oil or low pressure) and the two towards the right look reasonable. Where are the other two halves? It's hard to decipher, but it looks like they may be still in the rod in the picture...

From what I can see, it looks like simply low oil pressure caused main journal contact with the main journal bearings on one or two journals. (possibly the bearings indicated along with the lower bearing just to the left of them were the outer bearings, and thus ran lowest on pressure??) As far as the rod getting bent, I have yet to see minor detonation cause a rod to bend. It usually shows up on rod bearings or on extreme cases pistons melting.

Please take no offense, I appreciate your efforts, but think you may be overlooking the actual diagnosis.

 

Great feedback. I appreciate being corrected by someone who know's what they're talking about. It's good to know what actually happened. I've been trying to wrap my head around it for a while now. The fact that he was using his JDM ecu is all I could come up with. It's good to know that the JDM tune is not the cause. I never considered he ran the motor out of oil, the thought that someone could be so negligent, giving him the benefit of the doubt was a mistake...

The other halves of the bearings are still in the rod as you guessed, they look very similar to the bearings on the left.

The machinist said he's never seen a rod come out of a Honda motor quite like that. I guess it's either catastrophic failure, or everything is okay. No in-between states. It was the machinist who suggested detonation as the cause of discoloration. I guess it was the only explanation for both the rod and the bearings, but you are suggesting they are the result of separate events. Low oil could have contributed to the bent rod as well. Under the right conditions anything is possible I guess.