nigelt

iTrader: (10)

After blowing my turbo, I had the exhaust manifold off and figured I should do a leak down test. The results leave something to be desired.
Prior to the turbo grenade, the symptoms were burning some oil, as well as blowing some oil through the exhaust port breather. When the turbo went there were billows of white smoke and overheating, which I initially chalked up to a BHG, and then found to be a blown turbo.

To run the test I set each piston to TDC before testing. I found TDC by manually turning over the engine with a piece of dowel dropped down the spark plug hole. I checked for the exhaust valves to be open on the way up and then took it around another rotation to make sure I had TDC on the compression stroke. I used an off-the-shelf leak down tester set to 100 psi.

Results:
1 - 52 psi
2 - 80 psi
3 - 24 psi (WTF?)
4 - 50 psi

For 1, 3 and 4 I could hear and even easily feel the air coming out of the exhaust port.
Especially on 1, but also on 3 and 4 there was air coming out of the valve cover breather. On 1 I could feel the pressure pushing my thumb off when I put it over the valve cover breather hole. This confirms an issue I've been having with oil coming out of the exhaust side breather.

So, intuitively, it seems like this engine shouldn't run, right? Has anyone experienced anything like this? Sounds like I need some head work right?

Thanks!

Savington

iTrader: (31)

It will probably run pretty well. I've seen 70% leakdown caused by a lightly burned exhaust valve on a perfectly running engine. The raw numbers don't mean much unless you have a good tester (I spent about $90 for mine from Aircraft Spruce, the cheapest FAA-spec one I could find) but those differentials aren't great. If it's 24% and you're feeling air from the oil cap, then you may have broken or melted a piston.

For leakdown, I start by finding TDC#1 and testing. If I get a huge amount out of the valves, I rotate 360deg and try again until I get a reasonable reading. From there, you can go in firing order, so #3, #4, #2 in order, with 180deg rotation between them. That's the easiest way to know you're on TDC compression for each cylinder.

Bronson M

iTrader: (1)

I would think no matter what if you're getting that much air out of the breather hole you've got ring problems. I'm going to guess you've got a large portion of the ring land missing. It'll run but not well.

adryargument

iTrader: (1)

My car boosted like that for ages, but RPM graph dipped everytime the leaky cylinder fired and i had a shittonne of oil blowby
Car topped at 11psi. When i re-ringed it, it boosted to 15psi

ryansmoneypit

iTrader: (6)

Haha, similar here. Mine was at like 60% loss and still ran fantastic. Moved a lot of oil though.

DNMakinson

iTrader: (3)

Consensus: Put on a catch can and keep on driving.

Underlying trend: Build an engine on the side.

nigelt

iTrader: (10)

Thanks for the input everyone! I'll put together, dial down the boost, and work on my backup plan.