3.3 Compression test. Suggestions please.

herman maire · 06:10 AM

I did a compression test on my 3.3l . This engine has not run for maybe 1.5 years now. Test was done on a cold engine since its not currently set up to run.

This first test was done at room 25c / 77f .
#1- 120psi
#2- 120psi
#3- 115psi
#4- 102psi
#5- 110psi
#6- 120psi

I was concerned about #4 results so did another test. The temp in the garage this time was colder, around 5c / 40f on a obviously cold engine. Results were worse. Also did a leak down.

#1- 110psi -Leak down- 4%
#2- 115psi -
#3- 115psi -
#4- 95psi - 9%
#5- 100psi - 5%
#6- 100psi - 3%

I ran out of time and was not able to do the leak down on #3 and #2. When doing the leak down test, in all cases I could feel and hear air coming out of the crankcase vent at the top of the motor. So air is getting past the rings.

What do you guys think. The engine is out if the car to install 964 camshafts, do you think I dig a bit deeper and check the rings on #4 or just hope that the poor reading is because it has not run in a long time and maybe the rings are sticking.

Also wanted to mention, this engine was supposed to have been rebuilt in 2009 with a set of good used pistons and cylinders ( not new) and has not had many miles put on it. Who knows for sure though, it looks a bit to dirty and corroded to be true.

Not quite sure what to do. Any opinions appreciated

Ronnie's.930 · 02-08-2012, 06:13 AM

Do you know how many miles were put on after the build? I ask, because it is possible that the rings have not seated . . . I'm not an engine building expert like others here, but I don't think that the 9% loss is something to be overly concerned with given the circumstances surrounding your engine . . .

herman maire · 02-08-2012, 06:26 AM

Ronnie,

Thanks for the reply. its hard to say how many miles... car was not driven last year and very little in 2010. I would just be guessing.

I also dismantled the waste gate. It has 2 wastegate springs

, one large spring then a smaller spring in the center. I am worried that it may been run with too much boost. From what I have seen on these forums, broken rings from too much boost seem to give similar compression results.

TT Gasman · 02-08-2012, 06:46 AM

If the engine is out of the car I would tear it down and investigate,

philip j · 07:19 AM

I have seen a stock wastegate with the extra spring which will bring the total to 1 bar. In this pic, the larger spring is a 1 bar, and the smaller which would fit inside and get me to 1.2 bar. I also have a .8 spring somewhere. If I can find, I can post a pic for you, maybe it will help identify what you have. Philip

mark houghton · 07:23 AM

Quote:

Originally Posted by herman maire

I also dismantled the waste gate. It has 2 wastegate springs

, one large spring then a smaller spring in the center. I am worried that it may been run with too much boost. From what I have seen on these forums, broken rings from too much boost seem to give similar compression results.

I think the springs are typically color coded (I think....at least that is the case with my aftermarket Tial WG, but not sure with a stock WG). Two springs generally means someone had it set up for more than the stock .8 bar - possible .9 or 1.0. I wouldn't be overly concerned with .9, but running more than that a person should have better air charge cooling (better intercooler) and some means of adjusting/assuring the proper amount of fuel on boost (adjustable WUR). Update: as I typed, I see where Phillip chimed in with some spring info.

Tough call on how to proceed from here. I too wouldn't be real concerned about a 9% leakdown on that one cylinder, give the car is cold and has not run for so long. Even if you do have a bad ring, the car will most likely still run fine and give a bunch more time and joy before having to crack into it. But the time it takes, the inconvenience of pulling the motor again, and the $$ associated with repairs all are personal choices.

jwasbury · 02-08-2012, 08:17 AM

Quote:

Originally Posted by mark houghton

Tough call on how to proceed from here.

Agree. I would be concerned that something is amiss with #4, but in my experience, your leakdown would be worse if something were seriously boogered.

See below examples

This piston shows signs of overheating. Top ring land is deformed. This cylinder was at 44% leakdown when tested...my engine:

Similar story on this one. I think leakdown was a little better (in the 20-30% range). Not my engine, this one is fellow Pelican "Citrus"

fredmeister · fredmeister's Garage

Before you took the engine out of the car did you notice if you were getting alot of smoke puffing out of the oil tank when running the car with the cap off?
Typically if the rings are gone on one or more cylinders you will get the tell tale puff puff of oil smoke out of the oil sump tank when you run the car at idle.
Its hard to tell you what to do, but would it be smart to buy a set of rings and remove the cylinders and check everything now that the top end is being rebuilt with a new cam? Worse case is you re ring it and reassemble if the pistons and cylinders look good.....your call.
I would not double up on wastegate springs but get the correct spring for your desired boost setting. Running more than 1.0 bar is pushing things unless you are making other mods and monitoring the engine carefully.

964 cams are a good mod.....let us know how they run compared your current set up.

willtel · 02-08-2012, 08:43 AM

Some more food for thought.

I had a PPI on my car and they found 4% leakdown across the board other than 14% on number 6. I bought the car and enjoyed it for ~20000 miles.

This is number 6. The top compression ring was in 3 pieces.

Broken Compression Ring by willtel, on Flickr

I can't argue with a teardown at least for inspection sake but keep in mind no one takes one of these apart and gets away with only replacing the rings.

Roby466 · Roby466's Garage

this engine has not run for over a year... Good advise if you are rebuilding the top end to just go beyond but if you are not, I would leave it. The numbers might get better once it runs for a bit and lubrication gets in there and the valves do their job. I'm not an expert at all but it might simply need an italian tune-up.

Jim2 · Jim2's Garage

Herman, while doing the leak down you need to listen to the crank case breather, intake port, and exhaust port then compare the amount leakage you hear from the bad cylinders to the good cylinders. At least you will be able to narrow it down to rings/not rings. If the air is escaping from your valves, remove the valve covers and give a few taps on the rockers to see if the leakage sound changes. Could be crud between the valve and seat.

Tippy · 02-09-2012, 08:50 AM

2 problems with the test IMO:

1. Cold engine
2. Hasn't ran in 1.5 years

You have results but can you hang your hat on the accuracy? No.

herman maire · 02-09-2012, 06:14 PM

Thank you all for the opinions and advice....

I had a little time to monkey around with the engine. I checked the leak down on #2cyl-4% , #3cyl-4% and rechecked #4-10%

This is my first leakdown test I have ever done. I have all the intake, shrouding, cooling fan ect... off the engine so its easy to hear where the air is leaking. I stuck my ear right up to the intake port and exhaust port on the cylinder head and no air is leaking there.

In all cases the air is leaking out from the crank case vent on the top of the case so the air is getting past the rings.

When I purchased this engine, I was told it ran ok with no blue exhaust fumes on cold start up or when up to running temperature. Also no strange noises.

These are the waste gate springs that I removed. I will buying a new .8 spring just to be sure.

This is roughly the reading I get for all the cylinders except for #4Cyl

This is #4cylinder

herman maire · 02-09-2012, 06:24 PM

Quote:

Originally Posted by Tippy

2 problems with the test IMO:

1. Cold engine
2. Hasn't ran in 1.5 years

You have results but can you hang your hat on the accuracy? No.

I most certainly cannot hang my hat up on these results..... thats why I am looking for advice. I dont want to overreact and start stripping a engine down because I can feel myself stepping out onto the slippery slope which results in the engine in a million pieces on a work table. Maybe all it needs is a good run .....

willtel · 02-09-2012, 07:12 PM

I would say drive it. My car ran fine and still made over 350hp to the tires with broken rings. I only pulled it apart because of excessive oil consumption.

herman maire · 02-10-2012, 04:32 AM

Quote:

Originally Posted by willtel

I would say drive it. My car ran fine and still made over 350hp to the tires with broken rings. I only pulled it apart because of excessive oil consumption.

Did you have any other cylinders with broken rings?

I do like the fact that you were able to still drive 20k miles.... thats a lot of miles.
I honestly would be happy with that. Its not that big of a deal for me to pull the engine later since I would be doing it myself.

Jim2 · Jim2's Garage

An observation: Even though you are hearing the leakage from the rings, the variance on your gauge between #4 and the other cylinders appears minor. Sometimes the compression ring gaps line up and this will affect readings.

Since the variance appears so minor I'd be inclined to run the motor as is and review it sometime in the future. Regarding your wastegate, maybe the single spring is producing less than factory boost.

willtel · 08:28 AM

Quote:

Originally Posted by herman maire

Did you have any other cylinders with broken rings?

I do like the fact that you were able to still drive 20k miles.... thats a lot of miles.
I honestly would be happy with that. Its not that big of a deal for me to pull the engine later since I would be doing it myself.

Yes. I had broken rings on 4 out of 6. Number 6 was the only one broken in more than one place. Of course I can't say when they all broke but somewhere during those miles I had some wastegate issues that led to too much boost. That could have killed a few. The car still pulled hard before I took it apart but it was using incredible amounts of oil. About a quart every 100 miles.

I didn't bother with a leakdown before I took it apart. Jacob's 930 was way worse than mine and was still running when he tore it down.
Jacob's rebuild thread

philip j · 02-10-2012, 08:51 AM

Heres a pic of the .8 bar spring I removed from my 87. If you need one pm me. thanks Philip

TurboKraft · 02-10-2012, 08:58 AM

Stacked springs is the old 1.2bar combination.

Another test to check when doing a leakdown: when testing a cylinder, the tap the rocker adjusting screw with a mallet enough to pop the valve open for a second. If there's some dirt or debris between the valve and seat, the compressed air in the chamber will blow it out. I can't tell you how often we see an engine that's sat a long time and has poor numbers, but a few taps to each intake & exhaust brings the numbers down to <6%.

If the numbers are still high, listen for air leaks coming out the intake port, exhaust port, or crankcase breather -- tells you where your problems are.