Is this engine OK?

Forgiven · Postby **Forgiven** » Fri Sep 25, 2020 1:20 pm

Can somebody please tell me whether these compression and leakage tests showing any issues:
135 psi with 5% leakage
145 psi with 25%
135 psi with 12%
135 with 8%
It's for a 1999 NB with 187K km.

93_Clubman · Postby **93_Clubman** » Sat Sep 26, 2020 1:03 am

Crikey Ted, you're a glutton for punishment! Comps seem a bit low to me.

Forgiven · Postby **Forgiven** » Sat Sep 26, 2020 10:01 am

93_Clubman wrote:Crikey Ted, you're a glutton for punishment! Comps seem a bit low to me.

Yep, I keep coming back to a MX5!
So, you see no issue with the leakdown figures?
A line on the invoice after the figures said "Leakdown test still in green until over a 40% rate". Test operator implies therefore that any result less than 40% is fine, and says that "There is absolutely nothing wrong with that motor." I said No to the car because of my caution with the condition of engines - but how does somebody like me know who to believe?

93_Clubman · Postby **93_Clubman** » Sat Sep 26, 2020 11:33 am

Forgiven wrote:So, you see no issue with the leak down figures?

Leak down testing tests certain elements, but not others, & compression testing tests certain elements, but not others, so best to do both as done to get as complete a picture as possible. However, those comp numbers still look low.

Forgiven wrote:...how does somebody like me know who to believe?

Unfortunately, that's the nature of information - there are no guarantees in life, apart from death, taxes, & politics!

ricky-pinky · Postby **ricky-pinky** » Sat Sep 26, 2020 12:58 pm

Hi Forgiven,

That engine is stuffed. I have an NB with the same sort of figures - 130, 123, 137 and 130 dry and 142, 138, 137 and 147 with a squirt of oil in the cylinders. I overheated it during a track day at SMP one hot January a couple of years back and subsequent lap times were down by about four seconds. An engine rebuild would cost more than the car is worth since I am unable to DIY that sort of thing anymore. The youtube link below is a compression test of a VVT NB. Dry compressions are over 180psi and wet compressions are over 220psi.

https://www.youtube.com/watch?v=tzLPx-E ... d-Collings

CrazyRacer · Postby **CrazyRacer** » Sun Sep 27, 2020 6:04 pm

Have to agree that it sounds pretty tired.

I did a compression test on my NB8A with 330,000km on the clock which while it still ran ok was using about a litre of oil a track day or in fortnight of daily use. It was still getting dry comp figures in the 170s.