bryanlow

iTrader: (10)

I'm doing some maintenance stuff before the turbo install and I got these numbers for Dry/Wet Compression & Leakdown:

CYL.--DRY/WET---LD

1-----176/200----28%
2-----174/195----35%
3-----154/177----50%
4-----180/195----30%

Leakdown numbers look really bad, but I'm using a shitty Harbor Freight tester that is calibrated at about 15psi. The point is, I see this test as relative and I'm not too worried about # 1, 2 & 4.

I'm having a hard time listening for the leakage since the pressure is so low.

My gut feeling is that the #3 rings are fucked, but if they were wouldn't i see a different pressure variation from dry to wet? All of the cylinders increased 20psi+- which makes me believe the rings are all worn about the same.

I'm hoping it's something in the head because I'm willing to pull it and get a valve job since I wanted to do the timing belt anyway.

Opinions?

Background info:
'95M
135,000 miles, about time for a timing belt.
Runs fine, power seems pretty good
Idles perfectly at 900rpm
Smokes a little if I wind it up really hard; drips a little, probably from the rear main. Oil usage is otherwise not noticeable

patsmx5

iTrader: (16)

So, your running 15PSI for a leakdown test? I would suggest getting a better guage and doing it with the standard 100PSI.

bryanlow

iTrader: (10)

I should have gotten a better tester, but even a snap-on tester would probably tell me the same thing...#3 cylinder fucked.

urgaynknowit

iTrader: (5)

my numbers as of friday were like this

1-158
2-142
3-155
4-155

mine suck too :/

patsmx5

iTrader: (16)

Borrow, rent, buy, or steal a better gauge and run the numbers again. You need accurate data, plus doing it right you'll be able to pinpoint where all the leaks are. No sense in us going through two pages on here making random guesses until you get fed up and then buy a better gauge anyway.

bryanlow

iTrader: (10)

I'm sure the gauge is accurate in that the #3 is leaking more than the others. Seriously, what is a better gauge going to tell me?

Anyways, I plan on running the compressor directly into the cylinder w/o the gauge and see if I can hear anything.

samnavy

iTrader: (7)

I agree you probably want some better equipment... but assuming the numbers are accurate, you've got a couple options.
There are some products you can run through your oil that are designed to help with blow-by... maybe a Slick50 treatement or something? You can also run a can of SeaFoam through your gastank and Seafoam the motor... might help get a little carbon off the exhaust valve seats and get them to bed a little tighter.

Swap in a used motor... 2 for sale now on m.net classifieds.
OEM rebuild for cheap... almost all of the online rebuild kits come with new pistons/rings for about $350, but you'll need to re-use the water pump, oil pump, and timing belt. If you want those parts new, the rebuild kit goes up to about $800... plus the tank/hone/labor for another $500-$800. A core swap head rebuild is about $350.

You can do a search for "mild build" and you'll discover that it takes about $2500-$2800 to fully build a motor that will reliably hold 300whp.

mrtonyg

iTrader: (1)

If the car is not missing from the issues at #3 cylinder or burning oil, just slap on the turbo and run it as is!!!

Sure it's going to be down in power a bit, but just use that engine as a learning experience for the tuning. If you want more power then get a hold another engine and build it up with some rods and pistons and boost away!!

Tony

patsmx5

iTrader: (16)

Oh I dunno, maybe WHERE THE LEAK IS!!! Jeezus, come on now. I'm also willing to bet you get different numbers too. I would have very little faith in a 10 dolllar HF knockoff guage that only uses 15PSI. Sorry.

Go get a decent gauge and do a real leakdown test.

timk

Just beat on it until it blows!

When you are blowing smoke then swap it! I have 285,000km on my engine so I bought a spare, but it still runs nice as. Now that I've said that it will probably die on my way to work this morning.

bryanlow

iTrader: (10)

Have you ever actually used one?

Please, do tell... Exactly how does a leakdown tester tell you where the leak is?

As I understand it, the only way a leakdown test will tell you where the leak is is by listening to the areas thru which leakage occurs, i.e. oil filler, radiator, intake, exhaust. The gauge itself doesn't tell you where the leak is coming from.

If I was trying to find out if my cylinder was leaking by 48% or 52% I could understand spending $300 on a gauge, but I already know one cylinder is out of spec because I've tested it relative to the other cylinders. What I'm trying to determine is whether the rings or the valves are bad. If it turns out to be the valves, I'm going to have a valve job done, but if it's the rings, I'm going to run it until it explodes.

When I get a chance I'll run the compressor directly to each cylinder at 100psi and listen.

04 Miata

Also the HF unit says it has a gauge from 0-100 psi so I doubt it works at 15 psi.

http://www.harborfreight.com/cpi/cta...emnumber=94190

bryanlow

iTrader: (10)

It also works on vehicles with low clearance! WTF does that mean?

Trust me, this POS gauge calibrates at around 15psi. I am not denying the gauge is crap, but I'm not going to spend a load of money on a gauge that will tell me basically the same thing. I trust this gauge enough to know cylinder 3 is bad.

patsmx5

iTrader: (16)

Oh my. Suppose your engine is not new. Perhaps it has a lot of miles on it from daily use. One day a grain of sand found its way into your crossover pipe after changing air filters. It was sucked into the intake and fell directly on the valve seat right before the intake valve closed. Then the valve smacked it with around 70 pounds of seat pressure, enough to score the seat and face of the valve slightly.Then the grain of sand was sucked into the engine where it lodged itself between the cylinder wall and the piston. Here, it proceeded to bore a scratch in your cylinder wall as the piston moved up and down. Eventually the piece of sand deteriorated or came dislodged and exited the cylinder on the exhaust stroke.

Now, you have a slightly damaged seat, valve, and a scratched cylinder. The scratch in the cylinder is filled with oil by the oil control rings, causing the engine to smoke a little at high RPMs. The intake valve has a nicked area where it leaks under high pressure, similar to a cracked valve but with less effect.

At a mind blowing 15PSI, the oil that resides in the scratch on the cylinder is enough to seal up the gap between the piston rings and the cylinder wall, therefor not revealing itself to your low pressure test.

A leakdown tester is a tool. It doesn't 'tell' anything directly. If used properly, it can be used to indicate if one or more areas of suspect are leaking, and indicate the percentage of leakage. You can get a decent leakdown gauge for like 80 bucks.

bryanlow

iTrader: (10)

OK , I went down the street to the Boeing store and got another leakdown tester. The sales guy told me they do leakdowns on jumbo jets and fighter aircraft with it. Fighters! So you know it's accurate! So Here are my numbers:

CYL.--DRY/WET---LD

1-----176/200----28%
2-----174/195----35%
3-----154/177----50%
4-----180/195----30%

Any ideas?

04 Miata

My guess would be that they mean it doesn't need a lot of room to attach to the engine. As in an old Ford or Chevy where the plugs are hard to access because of their location behind suspension arms.

mrtonyg

iTrader: (1)

Is this post for real...if it is, that salesman gave you one hell of a sales pitch...jumbo jets and fighter aircraft of today use turbine engines...you don't run leakdown tests on turbines!!

Tony

wes65

iTrader: (7)

oh god i hope thats a joke.

patsmx5

iTrader: (16)

So, you went and got a compression tester from your local Boeing across the street. Yea.... Looks like you copy and pasted those numbers to me. Besides, it's HIGHLY unlikely your gonna run that test twice and get the same exact numbers to the pound.

bryanlow

iTrader: (10)

For those who thought I was being serious about buying another tester, STOP POSTING NOW!


For those who want to know, it is an exhaust valve in the #3 cylinder. I will take some pictures and post how I know this later.

FWIW, I took samnavy's advice and ran some seafoam thru the motor. Very interesting results:

CYL.--DRY/WET

1-----180/227
2-----179/235
3-----160/214
4-----181/229

As compared to my original test results:

CYL.--DRY/WET

1-----176/200
2-----174/195
3-----154/177
4-----180/195


The dry numbers went up across the board. The wet numbers are not really significant as I used much more oil this time around.

Maybe it was an anomaly, but the seafoam certainly didn't hurt. Made the car feel a bit stronger too.