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1G DSM blow by/ piston ring seating

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all black 4G63

Proven Member
254
43
Aug 5, 2019
Chicago, Illinois
Hello,

Recently I started and ran my freshly rebuilt engine that was put together 17 years ago...yes, 17 years ago i had it bored and installed JE pistons (8.5:1) and crower rods, etc. Back then all I did was assemble the complete long block and monthly poured oil down the cylinder and rotated the engine around a couple of times, never started and ran it until now.

What is happening now is I finally reached about 500-550 miles running it moderately trying to break in the motor. When I finally reached the 500 mile marker I did some red line hard pulls and my dip stick flew out and doused my engine in oil.....

My compression is cyl #1 175 psi, cyl #2 152psi, cyl#3 175psi, cyl#4 164psi - this was taken at moderate cool down, probably 100° ECT. If i do the compression test at engine off operating temp around 195° all cylinders are lower but cyl#2 in like 145psi and cyl#4 is 155psi. #1 and 3 are around 165spi. Cylinder leak down is all crank case. I am using the stick PCV system. The car is totally stock as fare as bolt on mods.

My question is how long does it normally take to wear in rings? Am I screwed here or is there anything I can do other than remove the engine and do it all over again? I mean is there a possibility these rings will seat?

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Thank you for your input,
sorry if it sounds like i am in denial. ha i do mobile diag for a living, but i just don't want to believe this motor is f***ed.
 
You could drive it for a little while longer and see how much oil it is consuming, but as a engine builder, I'll tell you that you probably had some rust buildup after the years and it ate into the rings. I would rehone it and put a new set of rings in, checking the crosshatching the end gaps to make sure they don't exceed .028-.030" (which is a lot) and you should be just fine. I know its a lot of work but I don't think there is anything you can do to get rid of it. No "secret" that I know of but not a lot of money either, just labor.
Marty
 
It took my 420a 3000 miles to be fully broken in. The compression readings kept getting higher and higher all the way to that 3000 mile mark. And I could feel a difference in how the engine ran as I ran it more, I also noticed my vacuum readings were getting slightly higher. Obviously the 420a is a different monster than the 4g, but the concept is still the same.

500 miles is just that point when you need to change the oil & filter to get out all the metal shavings.

Some rings will take longer to seat based on their shape and material, and also how well you crosshatched the cylinder. One good way to get an engine broken in quick is high vacuum situations. Like letting off the throttle while going down hill with it in gear. And letting off while on the highway in gear.
 
I agree with @BLACK'98DSM's statements. It is a reason I said you "could" drive it a little while longer. If you babied it TOO much, it needs some backpressure on the rings as much as compression, so do some engine braking and see if what Solomon said may help out your situation also.
FWIW, I broke my last 4g motor in on 33lbs of boost. She has no blow by issues at all (lets all knock on wood).
 
Thank you all for your feedback. That makes sense.
It is just weird that 2 out of 4 cylinders are lower than expected, that makes me think there is an issue in those cylinders. I suppose I could borescope the cylinder and look for excessive vertical scoring.
I will try to post a photo. Maybe you guys with engine building experience can review the photos and let me know what you think?

Thank you
 
It took my 420a 3000 miles to be fully broken in. The compression readings kept getting higher and higher all the way to that 3000 mile mark. And I could feel a difference in how the engine ran as I ran it more, I also noticed my vacuum readings were getting slightly higher. Obviously the 420a is a different monster than the 4g, but the concept is still the same.

500 miles is just that point when you need to change the oil & filter to get out all the metal shavings.

Some rings will take longer to seat based on their shape and material, and also how well you crosshatched the cylinder. One good way to get an engine broken in quick is high vacuum situations. Like letting off the throttle while going down hill with it in gear. And letting off while on the highway in gear.
Just curious what was your vacuum reading at an idle 750 RPM? i ask because I have HKS 272 EH and 264 IN so i am at -11hg hot idle.
 
Just curious what was your vacuum reading at an idle 750 RPM? i ask because I have HKS 272 EH and 264 IN so i am at -11hg hot idle.
I've got Crane 242/242. First startup I was at 11 in hg, now it's at 13 in hg idle.
 
here are the photos from the borescope. they are all from Cyl#2 as that was the cylinder with the lowest compression.

It does look like vertical scoring, i just hope a hone will clean this up.

What do you think?
I appreciate all the help

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Lack of lubrication on the piston skirts it looks like plus the vertical scratches. No fault of yours one bit, It was just sitting a while. A Flex hone will clean it up fine and clean the bores out until a white paper towel comes out with no grey on it at all. New rings and lube the ring lands for free floating rings. Coat the skirts with assembly lube.
 
Lack of lubrication on the piston skirts it looks like plus the vertical scratches. No fault of yours one bit, It was just sitting a while. A Flex hone will clean it up fine and clean the bores out until a white paper towel comes out with no grey on it at all. New rings and lube the ring lands for free floating rings. Coat the skirts with assembly lube.
thanks I appreciate the tips! i will repost once the motor is out and if the honing is successful.
 
Update,
honed block, replaced rings, everything’s good now.

what can we learn…. Well don’t assemble and engine and not prime it then wait 17 years to finish it and start it.
Thanks to everyone for the suggestions
 
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