Miata Turbo Forum - Boost cars, acquire cats. - Rebuilt motor .. now dreading that rings didn't seal .. am I right ?

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Rebuilt motor .. now dreading that rings didn't seal .. am I right ?

So I recently wrapped up a rebuild of a junk yard 95 block and a VVT head. Bored it out to 84mm and ran ST 8.6 pistons with XXX rings and Manley rods.

The break in

Engine back in the car about 2 weeks ago and it started pretty much on first try ( after priming oil ). First start was done with LUCAS break in oil. Took about 5 minutes checking timing / leaks / warming car up / ect before I took it on a test drive as an NA ( I/C piping disconnected ). Motor was idling during this 5 min. First drive was about 5 minutes around the block ( 2-3 miles ). I followed the FM method of going to 5k RPM and snapping foot off throttle to let it engine brake down to 2k RPM .. then rinse and repeat. Car ran pretty well, no major issue noticed. VEAL helped smooth out the fuel map.

When I got home, I drained the oil and cut the filter open to look for issues. Some glitter, no 'chunks'. Nothing too major to speak of.

New filter and a second round of LUCAS break in oil went into the car. Second break in drive was longer using the same FM method. About 10-15 min and maybe 5+ miles. Third break in drive same day was about 30 min and 15-20 miles up / down a hill trying to do as much of the FM method as I can with the traffic around me. No issue noticed and VEAL was working the entire time.

Same thing when I got home. Drained the oil and cut the filter again. Same glitter as first time but again no chunks.

Filled the car up with Redline 5w30 and new filter. Connected the IC piping to finally run boost. Test drove about 20 miles around town to let VEAL dial it in. Still no problem!

Cool, its ready to race! Did one autox last weekend. Ran both days so about 15 total runs on the big course ( 50-60s course ) .. and about 10 run on a 30s test track. No issues!

The problem ..

Got home that night, saved the current tune and loaded in another one with higher boost and 8100 rpm vs 7100 and went for another test drive. Immediate I felt the car sputtering and making weird exhaust noises around 4k RPM. I tried 2-3 times again but always got that sputter so I limped it home. About 2-3 miles this drive.

Next morning test drove again, exact same issue. I figure okay lets put the old tune back on before I f' something up. Then .. uh oh .. the old tune is back .. but the car is still running like shit. I noticed that it was going lean when it was sputtering so I tried to 'fix' by adding a bunch of fuel ( +5 ) to the map. Didn't help. If anything it got worse.

Crap crap crap.

Limp back to the house. Triple checked that the tune I'm using is the one that worked well all weekend. It was. Then talked to some folks and changed spark plugs. Old plugs BKR5E-11 was not gapped out of the box and was .04x gap. New spark plug ( BKR7E-11 ) gapped to .030 went in. Fingers crossed. Test drove the 2-3 mile route again.

Same issue. Crap!

Went home and disconnected the IC to test it NA.

Compression test.

Immediately I did hot compression test and it was 157-160-160-155. Then wet compression test was 215 for cylinder 1 ( prev 157 ) and 210 for cyl 4 ( prev 155 ). Urg.

Conclusion and many questions ?

Based on the wet test, I have to think that the issue is my rings never worn into the cylinder wall .. but that doesn't explain why I was able to do all my test drive and the autox weekend without any major issue! In fact I went faster than ever ( based on finishing results compared to others ). I was just patting myself on the back for the motor 'making it' through the weekend before this happened.

Is there any other possible causes that would explain what happen aside from rings never seating ?

Or maybe the new tune messed up the rings ? I wasn't driving hard on the new tune and was keeping an eye on AFR and never went past 5k. I feel like that's unl likely but not ruling it out either.

Would it be pointless waste of money if I bought more break in oil and tried the break in drives again ?

Really would hate to pull the motor apart again at this point.

If you listen to the exhaust, you can hear the sputtering .. the car lurches as well when it sputters.

https://www.youtube.com/watch?v=M_POfd-2uZc

I'll add the tune and logs soon.

i definitely would have run non synthetic much longer. you need to do a leak down test

Worrying about your rings is the last thing to worry about. First, your tune. Sounds pig rich with all the sputtering and spitting. Do I detect a rumble and sputter at idle or decel? Again, rich. Let's see your logs and tune.

You can't look at your plugs for evidence of rich/lean until you have more miles on it.

sixshooter: It is possible that my fuel pump is the problem since it is an old one from my 93 donor car .. though would it it be that sudden from running great all weekend to sputtering hell ? I'll look into swapping it out to test though.

ryansmoneypit: Good idea! I'll rent a kit to do that tonight.

mudflap: I don't have a video of it but I assure you that the car was running great this entire weekend on this tune. That's why I saved it thinking I could revert to it if the new tune didn't work out. Will have tune / log uploaded in the next 15-20.

Fuel pumps work great. Until they don't.

Hmm .. okay, fuel pump seems like an easy-ish thing to cross off the list. I've been meaning to upgrade mine anyways to push for higher boost. Guess it just moved to the front of the priority list.

In the mean time ..

Here's the map:
https://drive.google.com/open?id=1oB...AUaJA1kG9SMtyT

This is one of the log from autox this weekend:
https://drive.google.com/open?id=1i6...tVTV0YvhJglReL

Here's the log when running with IC piping in:
https://drive.google.com/open?id=1vX...Hk51HYlW5f98IO

Here's the log when running NA style:
https://drive.google.com/open?id=1Kw...DDOzt32i8gx7oE

Also . . . fuel filter.

Rings won't cause this. What you are describing is a misfire, either from lack of fuel or spark.

BTW, when you misfire, the AFR reading goes "lean" because you haven't burned the oxygen. Don't mistake that for actually being lean.

Hornetball, thanks for the explanation! I think that explain why me ( and VEAL ) trying to add fuel in response to a 'lean' condition made it run worse!

Out of curiosity, what coils are you running?

Currently running stock VVT coils.

Your compression numbers look perfectly fine to me.

after i rebuilt my 94 block with stock 94 pistons, but new rings, bearings and ebay rods and a hone, my compression was also about 160psi +/- 5psi or so.

my motor been running perfectly fine for 2 years now, no oil smell from exhaust and no burning.

Whats wierd, is i compression tested another 94 Miata with almost 200k miles, and that car had 180-190 compression across the board. wierd that an old ass motor has more compression than a freshly rebuilt one.

but like others have said, it doesnt sound like you have a motor problem. likely fuel or ignition issues.

btw, im running stock nb2 coils with ngk copper plugs and pushing 17psi (309whp) on a efr 6258 with zero ignition issues.

I bought the whole LS truck coils kit, thinking i will need it, but so far stock nb2 ignition is working perfectly fine.

Quote:

Originally Posted by ryansmoneypit (Post 1528285)

i definitely would have run non synthetic much longer. you need to do a leak down test

Same, on my break in I ran Rotella Dino oil for 1000 miles before I switched to synthetic. It was my understanding that running synthetic early in the engines life is adverse to ring seal. OP, I dont think you put enough miles on the engine before the switch to synthetic oil. Also, I dont wait long to get into boost. I was boosting my engine ( not full boost but up to 10psi ) after the first 25 miles. I also did a lot of engine braking as well on deceleration.

I'm no expert for tuning but I've ballsed mine up plenty doing autotune on my Emerald then had to rework it.
You are running rich as a start point.

I would recommend attaching a log for the MS folks too.

Quote:

Originally Posted by andyfloyd (Post 1528348)

yep, on my most recent engine, i ran regular 5-30 for 1k miles and was autocrossing with 17psi within the first 50 miles.

Automotive engines do not have standard rebuild instructions from the engine manufacturers but aircraft engines do and we could maybe learn a little something from their years of experience. This is from Lycoming website:

Quote:

A new, rebuilt or overhauled engine should receive the same start, warm-up and preflight checks as any other engine. There are some aircraft owners and pilots who would prefer to use low power settings for cruise during the break-in period. This is not recommended. A good break-in requires that the piston rings expand sufficiently to seat with the cylinder walls. This seating of the ring with the cylinder wall will only occur when pressures inside the cylinder are great enough to cause expansion of the piston rings. Pressures in the cylinder only become great enough for a good break-in when power settings above 65% are used.

Full power for takeoff and climb during the break-in period is not harmful; it is beneficial, although engine temperatures should be monitored closely to ensure that overheating does not occur. Cruise power settings above 65%, and preferably in the 70% to 75% of rated power range, should be used to achieve a good engine break-in.

Remember that if the new or rebuilt engine is normally aspirated (non-turbocharged), it will be necessary to cruise at lower altitudes to obtain the required cruise power levels. Density altitudes in excess of 8000 feet (5000 feet is recommended) will not allow the engine to develop sufficient cruise power for a good break-in.

For those who still think that running the engine hard during break-in falls into the category of cruel and unusual punishment, there is one more argument for high power settings during engine break-in. The use of low power settings does not expand the piston rings enough, and a film of oil is left on the cylinder walls. The high temperatures in the combustion chamber will oxidize this oil film so that it creates a condition commonly known as glazing of the cylinder walls. When this happens, the ring break-in process stops, and excessive oil consumption frequently occurs. The bad news is that extensive glazing can only be corrected by removing the cylinders and rehoning the walls. This is expensive, and it is an expense that can be avoided by proper break-in procedures.

IMO your engine is fine. How is the idle? Can you pull each plug wire off the plug one at a time while it is idling? See if it wants to die or if continues running the same. I had a dead cylinder last week after rebuild, new plugs, ls2 coils, ngk wires. Turns out #4 cyl had a brand new ngk plug go bad after beating on the car for an hour. Not saying it is a plug but it could be a bad coil or wire.

Quote:

Originally Posted by sixshooter (Post 1528410)

To summarize with a paraphrased adage from the muscle car guys “break em in fast and they’ll always be fast”