What's happened to my engine?

[Inksta]

I seem to have hit a snag changing my timing belt, and I am at a loss what to do next. I am hoping against hope that someone can tell me why I can no longer turn my engine over.

The story is that some months ago I went about changing my timing belt (in this thread). This involved a bit of mucking around with a blowtorch in order to get the crankshaft bolt out, with some great help from the forum. At one point I even resorted to the starter motor bump method.

Everything seemed to go back together smoothly, but I could tell something was wrong as soon as I started the motor - it was shuddering weirdly and didn't start after a few of cranks. I figured the timing was slightly out, but as I was re-adjusting the timing, it seemed like something was snagging as I was turning the engine over (by hand). I removed all of the belts etc, and it was still snagging. There is slight resistance at TDC of cylinders 1 and 4, and major resistance at TDC of cylinders 2 and 3. The slight resistance I can overcome easily by hand, but the major resistance I can only push past by using a length of pipe (see video, below).

I'm now at the point where I am guessing something has gone wrong internally. I considered corrosion inside the cylinder/s, but that doesn't sound right because it was turning over okay when I was setting the timing (shortly before trying to start her up). If it's not that, could it be something more serious, like a bent rod?

I've asked my friends and they are stumped. I'm concerned that I might have royally mucked something up. I am really hoping that I've missed something obvious, as it seems like the next step could be an engine rebuild or replacement

Here is a video of the issue in action. The white things are zip ties sticking out of the cylinders to show where they're at.

If anyone has experienced this before or has ideas of what it might be, I would be incredibly grateful.


(Note that a few months has passed since I ran into the problem, as I didn't have time to keep working on it and have left it sitting in the garage until now.)

[JBT]

Hydraulic lock in 2 or 3? If you forced it past it could now have a bent rod.

[RS2000]

Is this an interference or non interference engine?? I personally wouldn't even rotate a non interference engine without the timing belt attached.
You might have piston/valve contact.

[JBT]

Standard engine is non-interference.

[Inksta]

Thanks JBT. Would that be from oil or fuel etc gathering in the cylinder? I had the spark plugs out for most of the job and one of the last things I did was put new ones in. I would have peered down the holes at the time, and didn't notice anything odd (but I guess it's fair to say I wasn't actively looking for big puddles).

RS2000, this is a stock NA 1.6, so it is non interference.

[JBT]

You won't get hydraulic lock while the plugs are out. There may have been an issue when you first started it up.
Can be caused by pooled oil, fuel, coolant, water ingestion.

[Inksta]

Okay fair enough, thanks.

Seems like it's probably time to get a crane and take the engine out, in order to find out what's gone wrong. Will be a good learning experience!

[JBT]

Sadly, I don't think you have any other option.

A bit late now, however, it's always best to turn the engine over by hand (with a small lever/spanner) at least two complete cycles after a cam belt change to make sure there is no obstruction or interference.

[Inksta]

Yep fair call. I did turn it over a few times in the process of getting the belt tension correct, and everything seemed fine then.

Thanks for the help. Will post back with findings once it's out.

[93_Clubman]

slight resistance at TDC of cylinders 1 and 4, and major resistance at TDC of cylinders 2 and 3. The slight resistance I can overcome easily by hand, but the major resistance I can only push past by using a length of pipe

Referred back to your old thread & had a look at your video - agree video appears to show what you say above, & your old thread of course mentions using a small blow torch to heat the old Loctite used to overcome worn crankshaft keyway, & then replacing weeping front crank oil seal as well as timing belt & water pump.

could tell something was wrong as soon as I started the motor - it was shuddering weirdly and didn't start after a few of cranks. I figured the timing was slightly out, but as I was re-adjusting the timing, it seemed like something was snagging as I was turning the engine over (by hand).

Sounds like something occurred when you started the motor & it shuddered weirdly. Agree that you're going to need to strip it further to ID issue.

[Inksta]

Here's what I found after removing the head. I have never taken an engine apart before, so I'm not sure what is considered normal - but this seems like excessive carbon build up, right? #2 piston is especially nasty. I'm not sure what has happened, but maybe the carbon dried out in the few weeks it took me to do the timing belt, and on first crank it dislodged and started fouling?

As soon as I took off the head, it started turning over freely. I'm not sure what the best course of action will be now - maybe it's worth doing the rings? And maybe taking out the valves to check if anything got bent? Take the head to a professional? This is all new to me so advice definitely appreciated.

Piston 1:
https://www.dropbox.com/s/vkduoptjp5jgs9y/piston%201.JPG?dl=0

Piston 2:
https://www.dropbox.com/s/8sqiq23twzaz6sj/piston%202.JPG?dl=0

Piston 3:
https://www.dropbox.com/s/ekln7nsbocbxdxh/piston%203.JPG?dl=0

Piston 4:
https://www.dropbox.com/s/yl0yhbqjv857fx6/piston%204.JPG?dl=0

Valves 1:
https://www.dropbox.com/s/n5wha5s9m9ikciz/valves%20a.JPG?dl=0

Valves 2:
https://www.dropbox.com/s/xi9qncbfce4gcwe/valves%20b.JPG?dl=0

[Inksta]

Researching my question about what to do next, I found this thread on Miata.net, which I might use as a guide to do rings, valves, and have head and block cleaned and skimmed:

https://forum.miata.net/vb/showthread.php?t=487926

[1600Dave]

Looks a little, ummm, "ordinary".......

Basic things I'd check before I did much else :

Bore - will you get away with rings only (if you do, plan on getting the block honed as well), or will you need a rebore and new pistons (bores worn / scratches in bore) ? New pistons aren't very exxy in the overall scheme of things, perhaps this may be a better route anyway ? If you're pulling the block out for machining, I'd also get the crank checked over by a machininst, and chuck new bearings in it. Get his opinion / measurements on bore state as well.

Head - I'd particularly look at valve stem oil seals, did the engine blow any smoke at startup previously ? This may explain the amount of carbon on top of the pistons. Do the valves seal - ie are valves worn / pitted, is valve seat worn ? Hard to tell over the interweb, but I'd be looking into getting a professional rebuild of the head

[Inksta]

Thanks 1600Dave, appreciate the tips.

I'll take a closer look at the cylinder bore tonight.

Also spoke to Gary from Adelaide Cylinder Heads this morning, who was quite helpful. Lots of good reviews on Google so might be where I end up taking the head.

[project.r.racing]

The cylinder walls look fine. I'd be researching as to why you have such excessive carbon buildup in some pistons. And some values surface flaking off.
Every had previous fuel pressure issues?