Blowing sound from intake valves

MLUNGISI

MEMBER
2018 NISSAN NAVARA
2.5L
4 CYL
4WD
MANUAL
100,000 MILES

I recently did a top-end overhaul on a Nissan YD25 engine, Tested the vehicle for 190 km. Then later heard a blowing sound from the inlet valve.

I removed the cylinder head and I noticed that the one inlet valve was partially closed and was running tight, took it to the engineers to confirm. They repaired the cylinder head. After fitting it the same problem recurred after driving for 40 km.

What could be the cause?

8 Replies

KASEKENNY

MECHANIC
18,907 POSTS

Just to be clear you have valves hanging open after running the engine?

If this is the case, then the cause of a sticking valve is normally heat but this would take longer than a few miles. So, what it sounds like is the valve guides are too tight and it is causing the valves to stick and hang open.

You can confirm this is happening again by running a compression check before you remove the head again. Here is a guide that will help with this:

https://www.2carpros.com/articles/how-to-test-engine-compression

So more than likely the valve guides are the issue, or the head is damaged in ways that I am not sure yet.

What is the history of this vehicle? Why did you originally do the top end overhaul? Did you have an issue prior to this, and did you replace the guides?

Let's start with this info and go from there.

Thanks

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Saturday, March 5th, 2022 AT 5:35 PM

MLUNGISI

MEMBER
8 POSTS

The reason for doing the top-end was after one overhead cam broke, resulting in a bent valve, the engineers say they have replaced all the valves and buckets. I inspected my bottom half, and all seems fine except for the head, it only happens after running when the engine has reached optimum temperatures.

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Sunday, March 6th, 2022 AT 12:54 AM