Track NB compression test/leakdown - eating oil
 

Hey guys was wondering what you think is going on with my track car. Some background, car is basically track only at this point (engine mods listed below) and I noticed its been eating a bit of oil. Im feeding it about a .5 quart after every 30 min session out on track. Oil pressure is good and no smoke when out on track. The current engine is a junkyard VVT 1.8 that had 80k on it and since the swap I only put about 4 track days on it (about 8 hours or so). When I got the engine I changed all the seals, timing belt/water pump and oil pump before putting it in the car to freshen it up. So I pulled the spark plugs and noticed they were wet (oil) and smelled like oil. I looked into the plug holes and seen the tops of the pistons were also wet. I pulled out my endoscope to get a better look and sure enough all 4 pistons are pretty wet (see pics). I put the plugs back in, warmed the car up then did a compression test (results below). I figured the results were a bit skewed since it was so wet so I did a leakdown test (results below). I believe my piston rings are tired as the I could hear the air coming out of the oil fill cap on all 4 cylinders. Thoughts?

Edit: Wanted to add oil temp never exceeds 230*F on track, probe in the oil pan. Water temp never exceeds 190-195*F on track, probe in the heater hose hose at the back of the head.

99 NB with 1.8 VVT Swap
MS3
Boundary Engineering oil pump
Squaretop intake manifold
Custom carbon intake
Ebay headers
Spec miata exhaust
Castrol Edge Gold Bottle 5w30

Test
Cyl 1 - 180psi - 35% leakdown (sound coming from oil fill cap)
Cyl 2 - 175psi - 48% leakdown (sound coming from oil fill cap)
Cyl 3 - 173psi - 30% leakdown (sound coming from oil fill cap)
Cyl 4 - 178psi - 28% leakdown (sound coming from oil fill cap)


cyl 1
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cyl 2
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cyl 3
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cyl 4
https://cimg7.ibsrv.net/gimg/www.mia...54493e6b2e.jpg

Looks a lot like detonation damage on the pistons. When you pull the engine apart double check your timing belt.

The leakdown tells you what you really need to know though. The bottom end is done.

Yeah I see what your saying about the pitting on the pistons. Shame because I always run 50/50 93oct and 100oct mix at the track to ward off any potential detonation as cheap insurance. Of course this last event I just ran straight 93oct.. I thought I heard a slight tick under a high load, low speed, 2nd gear uphill section but I thought it was the valvetrain, very well could have been detonating. Ill post my tune a bit later if you wouldnt mind taking a look at it. To me, it was a little aggressive but nothing I would say omg at, then again im not the best at this tuning thing. My afr's were always in the mid 12s if that counts for anything lol so it was nice and rich "safe". I was thinking if it was possible that the VVT map was overly aggressive, I dk.. Im not upset though shit like this happens, especially in a racing environment, were not just doing a couple gear pulls on the street then shutting it down.. Glad everything is cheap on these cars lol.

Rings are toast. Pistons look like they're in rough shape. Would definitely check your tune and timing as well. The only reason your compression test is halfway decent is because there's oil everywhere which helps seal everything up when you're cranking it.

I don't think the pistons have detonation on them that's just carbon and rough casting looks normal to me besides the oil on them

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The only area where you'll see casting marks is on the valve reliefs. It's clearly rough on the machined surfaces

I agree that the pistons look like they have seen some detonation. I was looking at the pistons on my original BP4W motor that I smoked mishifting 3>2 instead of 3>4 and they have the smooth machined top besides the valve relief area. Attached is my tune if you guys wouldnt mind taking a look at it. Thanks

The later higher compression pistons are very different from the early low compression ones. There are casting marks all over the later ones.

ahh I didn’t know that, interesting 🤔

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Early BP


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BP4W


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BP6D

Sorry for the crappy pictures but you get the idea. None of these saw any detonation.

Thanks for the pics, yes looking at those they seem ok in that case. I was using the "compare tune" feature in tunerstudio comparing my tune against the MS basemap and it really isnt that aggressive at all. Actually compared to the basemap im running 1* less total timing in the high load cells (90-100kpa) and upto 3* less timing in the 80-90kpa areas. Besides rescaling to eliminate the boost areas since im NA, its a pretty "easy" tune. Im going to check my timing on the cams tomorrow. As a side note I did set the base timing per the MS instructions when I first installed the ecu.

Cam timing was good so that’s eliminated. Assuming there’s no detonation happening and me running a 50/50 mix of 93 and 100oct would you guys continue to track it and finish out the season? Reviewing my lap data the loss of power past the rings is costing me about 1-1.5 seconds per lap all else being equal. Oil pressure and all temps were fine with the motor in its current condition it just felt “lazy”. My fear is I don’t want to completely ruin the motor. If it will survive, just be down on power I’m fine with that. Either way it’s getting rebuilt at the end of the season wether I cut the season short now or finish it out.

I just tore my engine out and took it down to the bearings in 2 hours. Do yourself a favor, remove the engine, tear it down, order your parts, throw some pistons, ball hone, rings, and bearings at it, and enjoy the rest of your season.

Seconded. I've dingle berry honed my block 3 times now and it's still doing it's thing with rental car like usage.

When you say pistons, do you mean new ones in oem size?
I did all the above and since my pistons were damaged I just got a second pair used.

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You can get used non-damaged ones, or you can bore a block out for oversized pistons. A ball hone can be done at home, a bore requires a machine shop. Pour ATF over the ball hone, put it in your drill, and go at a medium constant speed up and down 3-4 times. You're just looking to scuff it up so the new rings can seat.

3-4 times? Wut
I used a 3(4?) Armed one I found unused at my work. But used engine oil and ran it for about 15 seconds up and down at rather slow pace.
The cylinders were glossy and they became more flat afterwards.

Yeah, that's 6-8 strokes, that's all I need ;)

Bumping my old thread in case this helps someone in the future. Engine is coming out this weekend and will be adding pics as it gets rebuilt. Ill be doing an inspection as I break it down to get hard answers on the problem. I ended up finishing out the season with that engine and it held up fine, smoking but fine lol.
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A little shock porn :burncash:

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Pulled the engine today. Ill be vapor blasting before reassembly for a fresh look.

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Got a chance to tear down the block this morning, was busy at Sebring last weekend for the 12hr. Overall looks good so far. Going to run everything through my parts washer tomorrow and start measuring. Bearings actually don’t look that bad, they look even better in person. Pistons didnt appear to have any detonation damage just the casting marks from the factory as mentioned earlier in the thread. In any case tomorrow I’ll be able to get a better idea with where the engine stands.


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Watching with interest! I'll be doing this myself soon to a spare VVT 1.8 motor. Nice to see your pistons and bearings are in good shape.

What's your plan for the rebuild?

Pistons and bearings look alright. The rings *and* valve stem seals are probably two likely candidates for the lower compression and consuming oil. Might want to do both!

Got everything cleaned and measured today. Well almost everything except the connecting rod big ends. My dial bore gauge wasnt small enough to fit so I’ll pick up some snap gauges to finish it up. Overall everything measured fine and I’ll be reusing mostly everything. Pistons did not have any concerning scoring on the skirts or damage on the head. Rods are fine. Crank journals and fine, no scratches and issues there. No concerns with the cylinder walls that a hone isn’t going to take care of, factory crosshatch marks still there but it’s glazed. Next on the list is the head which is mainly a cleaning.


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So far just planning on doing a hone and rings for the bottom end. Bearings are fine and measured out well under the “max” spec so I’m reusing them. I would prefer it on the looser end of the spectrum anyways.

Yeah new rings and a hone for the bottom end. Head will get new valve stem seals (they’re included in the Mazda overhaul kit anyways) and a general cleaning. Will probably lap the valves depending on how they look and measure out.

I slept on this last night and decided to change the main and rod bearings with ACL Race in STD size. Not due to wear, cost or any other reason but I did notice a couple bearings had a few tiny specs of foreign material embedded in them. You cant feel them with your finger nail but my thinking is as the bearing continues to wear these tiny pieces *could* become welded to the crank journal and possibly cause a spun bearing. So new plan on the bottom end is hone, rings, rod bearings and main bearings. If I was on a super tight budget or under really tight time constraints to get this motor back in the car I would have just reused the original ones. In all likelihood they would have been fine but whatever.

Honestly, bearings are cheap anyway. Once you have put in the labor to pull the engine apart and lay the bearings out on the table...might as well just spend ~$150 to slap some Kings XP or ACL Races in. What's the thrust bearings look like?

Edit: ah, yes. The thrust bearings in the picture you took. Derp.

I credit the lack of thrust bearing wear to my clutch bypass switch for starting.

That's not the first time I've heard of that either, enough to convince me seeing how they look.

Measured runout on the crank today, came in at .0008 which is fine. Sent the crank out to a local machine shop for a polish and hot tank. Getting a small case of "while im in there" syndrome lol.. Piston rings arriving tomorrow from Mazda Motorsports, pretty sure im on track to be final measuring and assembling the bottom end this weekend. This week ill be doing more cleaning and razoring the old rtv sealant off of the block, oil pan, thread chasing etc.

Something interesting I wanted to add to this thread before I forget. I measured my new ACL Race rod bearings compared to the *used* OEM Mazda rod bearings today and found something interesting. The ACLs were consistently .0004 smaller than the OEM bearings. So basically there is .0004 extra oil clearance with the ACLs.

If I’m not mistaken that number would be x2 because of there are 2 bearings per rod which equals .0008 extra oil clearance total per rod journal. I was sure the used OEMs would be smaller than the ACLs due to wear and less material left on the bearing from that wear. To be clear these are ACLs in Standard size too.

*pro tip* I also “part shelf balanced” the rotating assembly by matching the heaviest piston with the lightest rod etc. the heaviest piston/rod assembly will be placed closest to the flywheel. This is common in spec miata where everyone is looking for the slightest edge.

Pretty interesting regarding the extra clearance of std ACL race bearings!

Please share your notes about the rotating assembly weights of piston/rods. Curious how closely you could get them matched.

Did you have the machine shop hone cylinders or are you dingle ball'ing it yourself?

Got the block ready today since im still waiting on a few things to show up. I flex honed the cylinders, block sanded the deck with 120 then 240, cleaned the block 3 times with hot soapy water and lots of different sized tube brushes. I was debating on painting the block but said f**k it I need to get moving on this thing. So instead of painting the block I tore down the oil pump, got all the RTV off, parts washed it then repacked it with assembly lube. Cleaned the oil squirters and reinstalled them. Cleaned the RMS housing and got that ready. Thread chased and cleaned a bunch of various bolts. Tomorrow I will work on the head.

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Yeah im going to measure everything before reassembly with the new bearings etc to get hard numbers on the clearances. Yes just a ball hone on the cylinders.
So as far as the balancing goes, im not physically removing material from the components. Im just trying to match the weights as close as I can. While keeping in mind piston to wall clearances. I also keep the piston pin with the same piston as it wears together.

Piston 1 - 384g
Piston 2 - 384g
Piston 3 - 383g
Piston 4 - 381g
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Rod 1 - 542g
Rod 2 - 542g
Rod 3 - 544g
Rod 4 - 543g
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P1 + R1 = 926g (Going in Cyl 4 .0017 P to W)
P2 + R2 = 926g (Going in Cyl 3 .0020 P to W)
P3 + R4 = 926g (Going in Cyl 2 .0018 P to W)
P4 + R3 = 925g (Going in Cyl 1 .0017 P to W)

Did a half day in the garage today, you know Easter and junk.. checked the block for distortion with my new straight edge that is certified to .001 and I couldn’t even fit my .0015 feeler gauge under any area I checked. Got the head torn down, components cleaned and valve seals removed. Still need to clean the actual head itself though. Valves looked good but I’ll probably give them a light lapping for good measure.


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Did a preliminary clean on the head today, block sanded it with 120 then 240 and lapped the valves. The before/after pic shows the valve contact area (dull gray ring on the valve seat). There really wasn’t any pitting or any issues on the valves or seats so it was just a quickie. Tomorrow I’ll be doing a final clean and assembly of the head. To say this thing was filthy is an understatement.. I think the pics speak for themselves lol. I also checked the head for distortion with my straight edge and it’s about .002 out from cyl 1 to 4, 0 diagonally. Spec for distortion is .006

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I recommend buying a suction cleaning gun like the one I linked below. I hook it up to 100psi air and feed it with mineral spirits. This comes in really handy when you're blasting out the oil feed holes in the block for the mains and the galley that feeds the oil squirters. You would be very surprised at what gets blasted out after you think everything is clean. I would be willing to bet many new engine build failures are caused by inadequate cleaning. When you think your're good, clean it one more time.

https://www.harborfreight.com/engine...engine+cleaner

Made some progress this weekend. Got the head assembled and did a valve lash check. Painted the block gloss black using vht engine enamel, made it look alot fresher. Got the pistons and rods together while the paint dried then filed the rings. Becareful filing the second ring as it is a much softer material than the top ring, its easy to go overboard. I think I was sent oversized rings since I couldn't even fit them in the bores without them butting. There was also a 25 stamped onto the top of the ring, I figured .025 oversize. It worked out in the end because I could gap them to exactly how I wanted. Budget a few hours to do this correctly including hand filing the burs off the ends. Moved onto getting the crank in the block and checked endplay. Took all final measurements, ill post in a bit. Tomorrow ill be installing the pistons and rods in the block, getting the head mounted and hopefully the rms and oil pan on. My goal is to be seating the rings on a break in drive by this Saturday. *PSA* dont use permatex engine assembly lube, its wicked messy and stringy like honey which is annoying but ill deal with it. The problem is it doesnt stay put and sort of melts or thins out after a few minutes.

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Pistons/rods installed and put the head on. Also put on the oil pump on. Tomorrow I’ll get the engine off the stand and onto the hoist so I can install the rms. Tomorrow I should have the engine completed with all accessories installed and ready to go back in the car.


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So a bit of a hiccup this afternoon. Im my oem engine overhaul gasket kit Mazda decided to include 2 rear oil pan seals instead of 1 front and 1 rear.. :mad: called up my local dealer and they're overnighting one in for me so I can get this wrapped up tomorrow. In any case the RMS is on, water pump, timing pulleys, cam gears etc are all on. Only thing left pretty much at this point is installing the windage tray, oil pickup tube and oil pan once I get that front seal in then putting on the timing belt and crank pulley. Still on track to be ripping this b**ch on Saturday. Would like to get some first start and break in vids for you guys. Ill also be using my oil filter cutter to check for shavings after seating the rings.

All ready to go back in. Planning on getting it in and start hooking everything up tomorrow.


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In the car and ready to get hooked up. Fought me a little but with some persuasion she went in.

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Everything hooked up and running. Just need to fill the trans and hookup the cooling fans before a drive. Put the stock ecu and intake in as a control. No leaks, no odd noises, good oil pressure. Just ran it for a minute or two. First start video below, literally the first start. Also I’m running just straight 30wt conventional oil for now.

Took the car out to an industrial park this afternoon to seat the rings. Ran really well, no odd noises or leaks. Good oil pressure all the way through the rpms and at idle. Did the whole full throttle thing from 2500-5500/6000 engine braking back down to 2500 about 8-10 times. Came home and changed the oil and filter. Oil had that expected pearlescent effect going on which I wasn’t surprised to see. Cut open the oil filter and found just a few teeny tiny specs of metal in the filter material. I’m not concerned about it just yet since it was the break in oil change. First track event is in early May. It’s a 2 day event so I’ll take it a bit easy on the car the first day and change the oil/cut filter to inspect it before the second day. If something looks really wrong then I won’t run the second day.

My engine survived its maiden voyage this weekend but unfortunately my front right wheel bearing didnt. I did (4) 25min sessions on Saturday then (1.5) 25 min sessions today before I heard a loud growling coming from the front right which ended the day for me. The first 2 sessions on Saturday I took it a little easier on the car shifting around 5500-6000 but still WOT all over the place. Picked up the pace a bit on the 3rd session and sent it on the 4th session. No noises, smoke, ticks or anything like that. I changed the oil and cut open the filter at the end of the day on Saturday and have to admit I was a bit nervous of what I was going to find. Oil was a tiny bit sparkly but nowhere near as much that was in there after the first drive to seat the rings. The filter had absolutely nothing in it which I was pretty thrilled about. Im running straight 30wt conventional oil still but Ill likely change it out to a synthetic soon. When oil was at race temp 220*f or so towards the end of the sessions I was showing 40psi at 6500rpm. I was already expecting a bit lower oil pressure than before because my clearances are definitely larger than the OEM bearings. Ambient temps were pretty cool out (65*f) so im probably going to try 20w50 valvoline VR1 to help raise the oil pressure a bit especially when the summer rolls around and the oil could get even hotter/thinner. VR1 is cheap, high zinc and stocked at my local Advance Autoparts. Speaking with a spec miata engine builder he said he targets anything over 35psi+ WOT hot oil pressure and not to worry about it but I can play with the oil to get the pressure where I feel comfortable.

Glad to hear things went well on the first shakedown! Also glad to hear the wheel bearing was caught before something failed on that corner. I'm always paranoid of wheels flying off.

Even with summer rolling around, 20W-50 seems a little...thick, but let us know how much it bumps up the oil pressure, the clearances are larger so there's no real harm in stepping up the hot weight. I'd be inclined to just run VR1 straight SAE 40 if you don't expect the engine to be ice cold (is it available locally for cheap too?).

I run Mobil 1 15/50 in the summer and Rotella T6 in cooler weather YMMV.

Yeah ill report back at my next event which is mid June iirc. Just need to get my new hubs repacked with Amsoil Dominator grease and back on the car. Did the rear wheel bearings and refreshed all the control arms with POR15 and new bushings while I was under there.

The only thing I dont like about straight weights is the cold start psi. On straight 30 im showing around 75psi at idle until it gets some temp in it so anything thicker im concerned psi will be through the roof.

This car will most likely be turned into a arrive and drive customer racing car next season. Starting in champ car as my other nb will be raced in spec miata by me personally. Im building a spares package for this car now. Ill be starting another thread soon, economics of gentleman racing and the hidden costs.

OEM bearing clearances and an oil cooler?