brcpaige

The other day I was running my Miata through town setting up my new fuel injectors. I wasn’t romping on it and was cruising in light boost when my motor randomly died on the road and spontaneously kicked back on, only now it was pinging/knocking very loudly at all rpms.
I have no idea what caused it to die and restart so suddenly other than possibly a bad connection with megasquirt, but now I have the issue of determining where this knock is coming from.
I replaced the timing belt and associated pulleys in hopes that my timing skipped and caused the noise, but that didn’t change anything. The one odd thing I did notice was that my motor was easy to crank until I got to TDC, at this point the motor became incredibly difficult to turn over. This made me think it could be a stuck/bent valve. But I though that the 1.8 being a non-interference motor meant that the pistons couldn’t come in contact with the valves even if they were still fully open.
I’ve also replaced the HLAs, but that didn’t solve my issue either.
At this point I’m thinking it’s a valve, any advice would be greatly appreciated! I’m new to this and I’m entirely learning as I go.

borka

iTrader: (1)

the hard turning of the motor at TDC is the pistons compression fighting you.
as you turn the motor, the pistons raise, and you start compressing air until you reach TDC and the exhaust valves open to release said compressed air.

as for the noise, that is not a healthy noise, something is up mechanically.

hks_kansei

1: stop starting the car, if it's pinging, it's causing damage.

2: pull plugs and borrow a borescope to see if there's damage to the piston crowns+bore, and also to see if there's any foreign material.


Being new injectors, the hard to crank at TDC could have been hydrolock, ie: the cylinder was full of liquid fuel.


Basically, look inside the engine and check it's all ok before running it.


edit: as above, it's normal for it to get hard to crank at TDC because of compression.
I'm assuming you meant it got REALLY hard to turn over rather than the normal firm feeling.

sonofthehill

iTrader: (1)

Sounds like you bent a rod enough to make contact with something in the block. That's exactly how it was with my old motor, ran perfect except that is sounded like my boost solenoid was in my helmet all of a sudden. Tack tack tack, then when I cranked it manually it got stuck, but I could push it past with a bit of force.

brcpaige

Thanks for all of the advice everyone! I took off my engine's head last night and didn't seen anything out of place. The only thing I noticed was a small divit/groove on one of my cam bearings. I'm assuming there is no way this could be the source of such a loud noise, now I'm assuming ill have to do a whole engine build to solve this. I attached the picture below. Unfortunately my car decided to blow up right before I moved back for college so I'm currently only able to work on it occasionally, any advice on what the next best step would be? Should I just pull the whole motor before continuing? Or should I just rebuild the head to be safe? My car had close to 200k miles on it so I'm not particularly surprised it blew up, I just don't know what to do now without knowing what the culprit is.

SpartanSV

Do you still have a tight spot when turning the engine over by hand with the head off?

sonofthehill

iTrader: (1)

^^^
This.

brcpaige

I’ll test that out after work tomorrow, should’ve been obvious to crank the motor over last night but I got fixated on finding a flaw on my head after pulling it.