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Today at Atelier Kaz - Private NSX Enthusiast, ex-Honda R&D engineer with F1, Indy/CART background

Potential C32B Engine failure – Intake Valve guide

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I regularly have meeting with NSX specialist in Japan and recently, I was informed of quite scary engine failure mainly on C32B engine.

I spent more than a week to carefully consider whether I should share this information or not, as the cause of issue is still not clear.

Also, I didn’t want to cause too much concern for the owners and ending up keeping NSX off the road.

At this stage, the cause of this issue is not clear and even the running conditions or engine modifications are not exactly the same.

Not sure whether it happened in US or not.

At the same time, I thought it would be important for both the owners and the people working on the NSX to know the fact of this potential issue.

Knowing the fact may protect the engine and if the unfortunate happens while someone was working on the NSX, at least this information will support that things can happen without any symptom.

Also, I hope it will protect some of the people working on NSX in case the unfortunate happened while carrying out power check, engine tune and so on.

In Japan, there are only about 350 NA2 NSX on the road.

Out of these, 5 x C32B engines failed with the same issue of sudden dislocated/cracked Valve Guide only at the Intake side.

As none of them had any failure at the exhaust side, at this stage, it is very unlikely to be heat related.

All five engines were more or less used at continuous high rpm mainly at the track or similar running condition.

Some of them didn’t have any modifications at all to the engine or ECU.

On the other hand, there are several heavily modified C32B engines with aftermarket ECU and happily running on track for many miles without any issues so just running on the track is not the cause of issue.

There was one report of C30A engine failure with the same valve guide issue but not clear whether it was the same phenomenon or caused as a result of other failure.

The diameter of intake valve was changed for C32B compared to the ones on C30A so it is possible that something related to this (such as changes in resonounce frequency) caused the failire but not clear at this stage.

Unfortunately, because this issue is at the intake side, anything cracked there will enter the engine cylinder causing major problem.

By the time you noticed it, more or less the engine was damaged and the level depends on the timing on when you managed to stop the engine.

One of the failure happened recently was on track.

The cracked valve guide was trapped between the spark plug and the piston resulting in no gap at the spark plug.

This caused misfire and the engine was stopped immediately.

The compression check was fine and after replacing the spark plug, the engine ran fine.

It was suspected that the cracked piece hit the plug and reduced the spark gap and thus, decision was made to open the engine and found the broken intake valve guide.

The damage to the engine was minimum so could be repaired with reasonable cost.

For the other engine, it was not that lucky story….

The owner noticed something not correct with the engine but kept running it and eventually lost the compression due to massive damage to the cylinder wall….

Unfortunately, due to the FRM cylinder block of C32B, once you damage the wall, you are very likely to end up with replacing it with many other engine parts at the same time...

Not cheap and long lead time for some of the main components...

Will update this info once I have further information.

Again, I would like to stress that under normal driving condition, it is very unlikely to experience this issue and very unlikely to happen on C30A engine.

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