My new Lip showed up, all the way from Japan
Ok Everyone, random question of the day. It seems my car has a weird issue I haven't been able to diagnose. 91 miata, 99% track only. Stock motor and everything except suspension and safety mods. Also has a 4.1 torsen swapped in.
The car seems to be unable to rev at the top of 3rd gear (and possible 4th). 1st and 2nd are fine.
But when I get to around 6800 in 3rd, the car climbs in the revs verrryyyy slowly. The way this was discovered was by simply comparing my car to a friends similar car. There are parts of the track where he absolutely has to shift, but I can hold the gear way longer. It's difficult to hit the rev limiter in 3rd unless I really hold it in the gear.
My first instinct was possible crank keyway wear, but the car seems to be making good power everywhere else. I also thought maybe he has a 4.3 and doesn't know it, but we looked at the axles and it looks like a Torsen version 1. Also, that wouldn't change how the car revs at the top of the rev range.
Any thoughts or ideas? I'm going to take off the crank pulley and look at the nose anyway, and also replace the alternator belt since it seems to keep getting loose and squealing.
I checked the timing, and it does appear to be jumping around a tiny bit and the crank does have a bit of wobble. So that's why I thought could be keyway.
However the car does not really feel down on power, except at the top of 3rd (and possible 4th). On the street I revved 1st and 2nd and it revs very quickly, as expected.
On the track for example I was on the back straight of VIR and I could hold 3rd almost until past the crest of the hill and the flag station. The issue does seem to be exacerbated by going uphill.
I suspect you have SNC symptoms, at least the beginnings of them. That means, while your crank isn't totally fubar'd yet, the engine is on borrowed time.
For starters, it's a 1991 Miata, stock engine, unknown history (IIRC you bought it used a few years ago, right?) That's not a good start. Crank pulley wobble, while it doesn't impact timing directly, shows that the keyway isn't in the best of shape.
But the biggest red flag is that it's load dependent, usually indicative of a timing issue. Timing issues are usually exposed at high loads, since there's usually less tolerance for improper timing at higher loads. Checking static timing at idle is a great start, but it doesn't tell the whole story. That it "jumps around a bit" at idle is not a good sign. 1st and 2nd aren't great test of load on the engine, because the resistance on the engine isn't at great. This is why you don't test a clutch's holding capacity in 1st or 2nd gear, or downhill. Higher gears and/or speed and uphill grades are usually great load tests - as you're finding out.
So, short of actually pulling the crank pulley myself and giving a diagnosis, I'd say there's a good chance there's a timing issue going on. And on a 1991 Miata, that has a good chance of meaning that it's suffering from SNC issues, which means it might be time to shop for a new engine. It *can* be saved with the Loctite fix, but being that it's a track car, and knowing how much it sucks to show up to a trackdaybro and not have your car work, it would be wise to replace the engine with a later '91+ 1.6L or go with a 1.8 conversion.
(or Honda J-series, just sayin' )
Last edited by Stevo12; 04-10-2019 at 05:38 PM.
Tb done around 60k and currently 78k miles.
In any case that is my next step to diagnose so I'll go through with that. I've done a loctite fix before and that car was wayyyyy down on power but the keyway was savable. Given the power this car is still making, if that's the issue I'll loctite it and keep tracking it until it goes.
I forgot to mention, after vir I torqued the bolt to 120 ft lbs without checking anything or doing anything and it seems to have helped a bit. So it does seem to point to the keyway.
I'll update once I get it apart.
Speaking of trackdaybro
Signed up for my first Track Night in America which will be next Thursday at Dominion Raceway in Virginia. Taking my '90 which is pretty much as it came off the course in STS at the 2016 Solo Nationals. Added a roll bar and that's it. Changed the oil and flushed brake fluid. Pads have plenty of meat on them and three year old RE71Rs are about half worn.
Dominion, I think, isn't a big braking track. It has a looooooooooooooooong straight going into turn 1 (I'll bring a book) and not much else after that. I think I'll be OK with STS-spec Napa Gold pads up front and HPS in back.
Only thing that needs addressing is a halfshaft that's leaking from the outer boot. I have spares (thanks to 300munkeys) so that'll be addressed in the coming days.
There's half a chance that if I come out of TNIA all smiles, I'll give the time trial national tour at Pittrace a serious look. But that's probably too much too soon, especially since time trials are quite expensive to enter.
Now, I suppose it's possible I caught this issue REALLY early, and there's some .5mm wear I can't see yet, but that seems improbable to me because I noticed this issue a few weeks ago, and put 4 track days on the car. I think the keyway should have shown some wear after that abuse.
The 4 days had a lot of time, too - over 10 hours easily, maybe even 12 total track hours.
So any thoughts? Tonight I will get a very thin needle and try to put it between the key and the crank nose to see if there is some miniscule gap there. If there is, since I already have some loctice 660 I'll but a tiny smear in there and call it a day. The key is very tight in there so I'd rather not take it out unless I want to do a tb job which isn't necessary I don't think.
Any other reasons timing could be jumping around? It could just be a loose alternator belt and the crank was wobbling (no ac or ps so it's the only belt) and timing isn't actually moving.
But that doesn't explain the inability to rev in 3rd gear. Could it be a transmission issue?
Might not be a bad idea to throw some Loctite on it. That is a short nose crank engine - the key is not supported through the length of the crankshaft keyway.
Maybe before doing the Loctite, throw the pulley and bolt back in and check your timing marks again. How does the tensioner look?
If all checks out, throw some Loctite on the key for good measure, bolt everything back together and check timing again. Does it still jump around? If so, maybe look at the CAS on the back of the head - is it loose? Maybe itís a bad CAS throwing off the ignition timing?
Edit- forgot that you were re-torquing the bolt. Since you have an SNC engine, you should be torquing it to 80 ft-lbs not 120. It could be that the bolt is stretching (since they are known to be weak) which is why the load is reducing on the timing belt cog. Best to get a new bolt. Usually SNC guys recommend replacing the bolt during a timing belt job, but itís not often done
Last edited by Stevo12; 04-12-2019 at 02:01 PM.
edit: last 6 of VIN are 224889 so that should put me way into the BNC.
Last edited by 300_munkeys; 04-12-2019 at 03:52 PM.
So after taking everything apart, I've decided the crank nose looks too good to do a loctite fix at this time. I put everything back and torqued to 120 ft lbs. I'm putting a new alternator belt and tightening it properly since the old one was getting loose and squealing a lot. I'm not sure if that was due to a loosening crank bolt (thus leading to the pulley wobble) or something else but I figure a new belt can't hurt.
I've got some other plans to refresh the car, including new clutch master and slave and a shifter rebuild, and hopefully I will be caging the car soon. Worst case I will put a new engine in eventually. But for now the problem only appears in rare situations and I'm hoping that with the re-torque it will be alleviated. If not, I assume the crank will get worn out a bit in which case I'll do a loctite fix at that time and go with that until it wears out again.
The first three generations of Miatas are sitting at an interesting price point right now, really nice NAs, middle of the road NBs, and cheaper NCs are all hitting in the $4-6k range. I've had a couple NAs, but I'm getting curious about the NC now. My commute has become 60mi/day mostly highway at 70mph. I have a Frontier for when I need something to be a truck or the super reliable daily driver, so this is a fun car for me but I'd like to be able to use it all the time and only break out the truck as needed. I'm assuming 30s me wouldn't enjoy an NA as much as 20s me did back in the day and the newer platform might be the way to go for a more comfortable highway cruiser. Any comments? I'm looking at the low end of NC prices, so I'm sticking to an NC1. I'd like to have a limited slip, and I'm not sure about the differences between the 5spd and 6spd manuals. Any suggestions to help guide my purchase?
Random Google Image
Last edited by Nitroracer17; 04-15-2019 at 11:06 PM.
Losing is just a winning streak in the wrong direction -DD
Watch a headhunter find his own job - 9 month process
Biggest issues for me with the NC:
- stock suspension is pretty crappy. Needs an upgrade to become more fun
- engine has little character. There's a reason the 1.6 is the most fun engine even though it's the weakest. The 2.0 doesn't want to rev much
- seats aren't great especially on the early ones
- interior materials don't age very well
For the nc1, especially 06 I would avoid the 5speed. It had an issue with 4th gear I think.
If you can swing an nc2 the engines are more stout and have a higher redline. I believe the suspension and transmissions were also improved.
I'm considering one as my next track car. Let us know how it goes!
'14 F-150 FX4 (bread and butter)
'11 GTI (wifeys)
'13 MIATA (dumb modified weekend thrasher)
If you are not going to Auto-X or track, just get the nicest example you can find and don't worry about the LSD.
But if you are going to, then spring for one.
NC will be more comfortable and have more creature comforts for a semi-daily over the NA or NB.
I am quite happy with my stock NC2 which I use as a weekend and occasional Auto-X (5-6 events per year)
Nothing to see here move along.
Past: 1998 Accord V6 LX
2007 Mazdaspeed 3 (KIA 2-24-11)
2009 Mazdaspeed 3 (KIA 9-19-11)
2003 Jetta GLS 2.slow (good riddance)
2010 VW GTI
Here you go:
Gear Ratios (5-speed Manual) 1st - 3.136:1 2nd - 1.888:1 3rd - 1.330:1 4th - 1.000:1 5th - 0.814:1
Gear Ratios (6-speed Manual) 1st - 3.815:1 2nd - 2.260:1 3rd - 1.640:1 4th - 1.177:1 5th - 1.000:1 6th - 0.832
Last edited by Smigelski; 04-19-2019 at 03:12 PM.
NC's with their 170 hp are tempting...
Sell current Miata and buy this? Hilariously, it's the exact color, year and trim level as mine. Just looks significantly nicer, much fewer miles.
Last edited by 88c900t; 04-19-2019 at 03:20 PM.