Low compression numbers on a 4k mile motor

[Spoolingaround]

So I figured I would move this discussion over from the turbo tech since thats where it started.

I put a rebuilt 6 OEM bolt engine in my car back in august and so far I have about 4k miles on it. Right now it is burning a significant amount of oil (a quart every couple hundred to a thousand miles and I have linked a video of it idling after warming up) and the compression is about 110-125ish across the board. After I put some oil in the spark plug hole and retried the compression test I saw 190 psi, which leads me to believe the rings are bad/never seated properly.

[ame=http://www.youtube.com/watch?v=H_t71mYTsJI]DSM burning oil on a fresh rebuild - YouTube[/ame]

I thought I followed the right break in procedure. I ran conventional oil and I basically ran no boost the first 500 miles, changed the oil, then ran wastegate pressure (10psi) for the next 500, then oil change, then 16 for another 500 and I kept bumping it up. I believe I switched to synthetic after about 1500 miles total of driving.

What I find rather interesting is that sometimes at idle there is a lot of blue smoke (like in the video), and other times there is none. Why would it vary?

I called the shop that built the motor, and the owner said they most likely used hasting piston rings. He also said however that the motor should only get about 150 psi of compression when new, which clearly contradicts what I have heard from the online community, that it should be about 170-180. He believes that the oil burning is coming from the turbo and that the low compression is because the rings haven't fully seated yet.

My main question is, is there any chance that the rings could still seat correctly after 4k miles? If so, should I remove the synthetic oil thats in there now and change it to conventional?

Also, when I did the compression test and put oil in cylinder #4 and cranked it over, I saw a lot of smoke coming out of cylinder #2. What would cause that!?

My plan as of now is to continue driving it for the next two weeks until i go home where I have a shop and resources to remove the engine and start the tear down process if necessary.

I really appreciate any help and input you guys give. I have to admit, probably one of the shittiest feelings ever to see a brand new motor go bad.

 

[92AWDHX40]

Was the head redone too, did you replaced the valve stem seals, sounds like something is wrong I would have the shop further inspect if if they did the job, if it was done right it shouldn't have issues unless something else is or have gone bad.

 

[boost97gst]

The wet test does point to rings. I dont, per say, blame the break in. It was not done correctly though. You should run boost on it the first drive.It takes pressure to seat the rings. I followed motoman method. Many many dsmers do that and swear by it. But hey, im in the same boat except im only low on one cylinder and not burning oil. I didnt learn the first time and went back to the same guy. DUMB. . Id say the machinist didnt do the job right or you REALLY babied it for the first 20 to 50 miles. Like highway-cruising, non-varying load type babying. Thats a sure fire way to not seat the rings. good thing is, you need a hone, set of rings, and you'll be back up n running.

Do a leakdown next and let us know the results on each cylinder.

2g compression(cold or hot from my findings) should be ~180-185

 

[Spoolingaround]

Id say the machinist didnt do the job right or you REALLY babied it for the first 20 to 50 miles. Like highway-cruising, non-varying load type babying. Thats a sure fire way to not seat the rings. good thing is, you need a hone, set of rings, and you'll be back up n running.

Do a leakdown next and let us know the results on each cylinder.

2g compression(cold or hot from my findings) should be ~180-185

Well its a 1g motor, 6 bolt. Ill see what I can do about the leak down test. I mean, I did baby it for the first 50 miles, but I definitely made it a point to vary the rpm and loads.

Big Question: Is there any way that bad rings/unseated rings could leak to failed bearings or any other damage?

 

[92AWDHX40]

Not exactly sure on that bearing issues could arise if improperly installed or lack of oil or contaminates. Bad rings if they were installed incorrectly. Etc

 

[boost97gst]

You would have to get a ton of blow-by to get enough gas down there to cause bearing failure. It would be very obvious. Also would have to be running pig rich. I just dont think rings or blow by could feasibly cause any bearing problems. The engine would be barely running if that were the case.

1g: Isnt that supposed to be around 155 on a healthy engine? Im not sure let me google then edit my post if necessary haha
edit edit: do a leakdown. Then see whats up. I misread your post twice. Im off tonight.

 

[Phantom DSM]

Aside from machining error or assembly. The compression will read better as the rings seat fully. The break in is different for everyone and some say to take advantage of first 50 miles to seat the rings by getting on it rather than babying it.
What pistons do you have and did you have to mill the head ? stock 1g 6 bolt compression max from fsm shows 164 psi (7.8 pistons). the 7 bolt had max of 178 psi (8.5 pistons)
Keep in mind these readings will fluctuate if rebuildng again with stock components.

 

[jayson427]

After 4k what is done to the motor is done. There's no more seating of the Rings as they have gone through enough heat cycles to form. So what you have is it unfortunately. Unless metal gets in the oil you won't have bearing issues or at least you shouldn't. I would hope you have some kind of warranty since it seems like you did a stock rebuild?

 

[Spoolingaround]

After 4k what is done to the motor is done. There's no more seating of the Rings as they have gone through enough heat cycles to form. So what you have is it unfortunately. Unless metal gets in the oil you won't have bearing issues or at least you shouldn't. I would hope you have some kind of warranty since it seems like you did a stock rebuild?

It is a stock rebuild with a metal head gasket, so I know that the metal HG could lower compression, but definitely not by the amount that I am seeing.

There was a warranty, I can't remember exactly how much it was for, however I probably voided the warranty by pushing more than stock boost (20-25psi on a 14b which I did not push until about 2k miles on the motor). Although I suppose the shop doesn't have to know that... Also I bought the motor and it sat for a year before it was installed. I have to check but I feel like the warranty starts upon receiving the engine. I'm not totally sure.

Also, on my way back from the gym this morning I noticed the CE light came on around 3.3k rpms as the turbo spooled to about 3 lbs. I can tell it was the knock setting on ECMLink as there was a sudden loss of power (pulled timing). I have Link set to display CE light at 3 deg of knock or more. This is new and sometimes it would throw a CE and other times it wouldn't when I repeated. Could this be related?

 

[JacksonAuto]

Break-In method will vary depending on the type of rings and the way the block was honed. There is no "one size fits all" procedure.

That said, most modern rings in todays engines will seat almost immediately if the block was honed properly. We do a leakdown test on all of our engines before they leave and they rarely have more than 5% leakage and that's before they're even fired up.

Proper diagnosis is key. You need to determine why the compression is low. Yes, the wet test suggests that the rings are to blame but you need to know for sure before you begin disassembly. Perform a leakdown test which will tell you where the compression is escaping. It could be the rings, but also could be the head gasket or valves. Low compression can also be the result of improperly timed cams.

 

[DSM_GSX01]

I agree do a leak down test. This will help you determine if its valve seals, rings, head gasket, bad leaking valves. Do this first before you tear it apart. Its better to make sure then not know.

 

[Spoolingaround]

So an update, I drove the car home (about 400 miles) and I noticed I was still getting pretty good gas mileage on the highway, about 22-25 mpg, which leads me to believe that the motor does have good compression.

I am getting a leak down test tool this afternoon and that will help me determine what is going on as well, but also...

I also changed the battery and the starter since they were worn and caused some slow cranking which I know can lead to lower compression numbers. I redid the test and I got exactly 120 psi across the board. I looked up the spec in the shop manual and the service limit is 120psi and the spec for a new motor is 164 psi. I know that I have a thicker full metal head gasket in there and I was wondering just how much a thicker head gasket can decrease the compression, does anyone know??

Also i checked the mechanical timing to see if it was off by a tooth and it was very difficult to determine. I threw in a couple pics of the cams, they seem to be in time but I wanted the community to give me some feedback if possible.

 

[BogusSVO]

The cams look good, with the cams like that, how do the crank marks line up?

 

[livedsm4g63]

Recommended Break In Procedure: Drive it Like You Stole It.
If you ever do another build.

+1 with Bogus. See where your crank lines up when the cams are aligned.

 

[Spoolingaround]

Recommended Break In Procedure: Drive it Like You Stole It.
If you ever do another build.

+1 with Bogus. See where your crank lines up when the cams are aligned.

Crank is lined up too. I'm at the mitsu dealer talking to a mechanic and he said if it was build with high tension rings they may just not be seated yet and to go drive the piss out of it and try to seat the rings.

 

[livedsm4g63]

go drive the piss out of it.

You talking Dirty to me?


I ran 25psi after the first oil change. I also would do a full pull, hit 6-7k, let off the gas, and then let the engine come all the way back down from 6-7k. From my experience, the rev downs work with seating the rings greatly.

Hope it works out.

 

[codym]

Noo no no. With over 4k on the motor the piston rings are as seated as they will get.

While loading the engine is imperitive to the piston rings seating properly, it is just as important to let the engine brake(let the rpms come down on their own. no foot brake)

Fail for mitsu dealer mechanic, unless he's getting you a new motor after pissing around town. A leakdown will tell you what you need to know.

 

[Spoolingaround]

Noo no no. With over 4k on the motor the piston rings are as seated as they will get.

While loading the engine is imperitive to the piston rings seating properly, it is just as important to let the engine brake(let the rpms come down on their own. no foot brake)

Fail for mitsu dealer mechanic, unless he's getting you a new motor after pissing around town. A leakdown will tell you what you need to know.

He knows I would not pay someone for an engine job so I would think he's not trying to get to to blow it up.

He has built dozens of dsms and said he has seen an engine take up to 20k miles for rings to full seat with the high tension rings. He also mentioned if they were low tension rings they could have been washed out if the car was running rich which I know it was.

 

[BogusSVO]

He knows I would not pay someone for an engine job so I would think he's not trying to get to to blow it up.

He has built dozens of dsms and said he has seen an engine take up to 20k miles for rings to full seat with the high tension rings. He also mentioned if they were low tension rings they could have been washed out if the car was running rich which I know it was.

20K miles to seat rings??? I have never heard anything like that before.

Do you or him even know what the difference is?

High tension rings fell out of favor some time in the early 70's with the OEs and the aftermarket, They can cause accelerated block wear, and parasitic HP loss.

I can not even think of an Asian Import that runs them now, or since I started machine work in the early 90's.

Look at the block wear in a 150K mile 4g and the wear in 140K mile 1970 something SBC.
You will see a huge difference in the cylinder wear.


What causes most ring failures in the DIY builds is the wrong grit stone being used for the ring type.

The 3 stone hone that is used on a drill comes loaded with a 180 grit stone, great for a domestic running a steel ring like a Hastings 139

But is way to coarse for a 4g with NPR rings that the top ring is a moly (silver face) that should be a 240 grit at a minimum.

 

[Spoolingaround]

Well, the leak down test confirms that the piston rings are the source of the lost compression :'( Well, here comes a build journal in the near future I guess :/

 

[livedsm4g63]

Well, the leak down test confirms that the piston rings are the source of the lost compression :'( Well, here comes a build journal in the near future I guess :/

Take it out and rip on it Whats the worse that could happen right?

 

[Spoolingaround]

Take it out and rip on it Whats the worse that could happen right?

Well its started misfiring under boost even on brand new plugs so I'm afraid that may be compression related. Also I need another vehicle to rely on before I risk making this one undrivable.

Also I called hasting piston rings and told them what was happening. They said they is absolutely no way the rings have yet to seat.

 

[shortydtp]

more boost.

 

[JacksonAuto]

They said they is absolutely no way the rings have yet to seat.

Unless:

Cylinders weren't bored accurately and are out of round.
Improper cylinder wall finish.
Improper piston-to-wall clearance.
Rings washed out during break in.
Cylinder walls have become glazed.
Wrong rings installed onto the pistons.

After only a few miles the rings should be seated. Our engines leave the shop with less than 5% leakage and that's before initial start up and break-in. His statement is accurate only if both the engine builder and installer/tuner have done their jobs correctly.

 

[Spoolingaround]

Unless:

Cylinders weren't bored accurately and are out of round.
Improper cylinder wall finish.
Improper piston-to-wall clearance.
Rings washed out during break in.
Cylinder walls have become glazed.
Wrong rings installed onto the pistons.

After only a few miles the rings should be seated. Our engines leave the shop with less than 5% leakage and that's before initial start up and break-in. His statement is accurate only if both the engine builder and installer/tuner have done their jobs correctly.

Correct. I should have clarified that there is no possibility that I will see an increase in compression and now I am going to have to pull the motor.

I have started a build thread, you can follow it here if you like http://www.dsmtuners.com/forums/dsm...i-awd-6-bolt-swap-take-two.html#post153397018