1976 MG Midget

[Loren]

Spent some time off and on out in the hot garage today trying to troubleshoot this no-start condition.

Checked the ignition system first, it all seemed in order. Nothing worn, coil checks out.

Can't get this thing to fire AT ALL.

Pulled the plugs to check them. They weren't that bad. Kind of dark tan, darker on #2, and a little oily/smelly (fuel) on #3. Nothing terrible.

After cleaning the plugs, I got the car to at least fire a couple times.

It's really starting to feel like a timing problem. Checked the diaphragm on the vacuum advance, it's not blown out. And good vacuum hose to the carb.

Started messing with ignition timing (because I had to move the distributor to access #3 spark plug) and was able to get it to "start". It would do that fairly reliably. But, it seemed like it was running on 2 cylinders.



Weirdness ensued when I noticed that plug wires 3 and 4 were reversed. I swear I didn't do that today! When I pulled the plugs, I only removed one wire at a time. It was set up with a firing order of 1-4-3-2... and I'm not sure it's even possible for the car to run normally with that. So, maybe I switched them around somewhere in the heat of battle? Must have.

But, that "almost starting" condition was at 1-4-3-2. You'd think that simply switching 3 and 4 back to where they should be would get this thing running like a top, right??? But, no, it doesn't even attempt to fire with them at 1-3-4-2.

Better still, I just set them back to 1-4-3-2, got the weak 2-cyl start. Then did nothing more than unplug 3 an 4 at the cap... crank it up, no firing at all!

After taking a break and skimming the interwebs for ideas... I decided to do a compression test.

14 months ago, it was:
136-128-122-139

Now it is:
134-115-95-138

What are the odds that I've got a head gasket leak between 2 and 3 that's getting progressively worse?

Also... I pulled all 4 plugs to do the compression test. All freshly cleaned a few hours ago. 1, 2 and 3 (especially 2 and 3) were very wet with fuel. 4 was dry and very carboned. Clearly, the little bit of running that I accomplished was ONLY firing on #4. And now that makes sense that switching 3 and 4... or unplugging 4... would cause it to no longer run. 4 was the only active cylinder.

I'm telling you, this happened suddenly. That's why head gasket make sense. (nothing weird in the oil or coolant, though) Was running pretty normally, and has been for many months. Just recently, it's gotten a little wimpier with its idle characteristics. (stalled on me leaving a Wal-mart the other day, and maybe once more somewhere else recently) And then when it stalled at the light yesterday... that's when something changed. Something got that #3 cylinder down to 95. No bueno!

Well, crap. I knew I was going to have to come up with an engine sooner or later. I just thought I'd have more time!

[Loren]

Someone pointed out that if there was a head gasket leak between 2 & 3, they would read exactly the same. Good point. I was thinking "partial leak", but still... they'd probably be the same.

I'm going to do a quick wet compression test on #3 and see what it does. If there's a big difference there, then it's clearly a ring problem. If not, then maybe a valve problem.

Either way, the head has to come off. I may just do that tomorrow, as I have the day off.

[Loren]

I had a few minutes before heading to work. Put on some rubber gloves (gawd, I hate rubber gloves... but, it kept crud from getting under my fingernails!) and did that wet compression test on #3.

Used some 80w90 gear oil (just because I had an open bottle) to give it the best possible chance of sealing. And it did.

Dry Compression on #3 was 95. Wet shot up to 220 instantly!

So, clearly a ring problem.

Now, I need to pull the head and have a look to see just how bad it is. Is it possible to just give it a hone and slap some new rings in without pulling the block? That's not the "correct" way to do things, I know. But, I also wasn't planning on doing my engine "under pressure". The plan was to just keep driving the car. Do up my spare head, put it on the car, then source a spare block and work that up... THEN swap in a good bottom end. So, I'd like to just "band-aid" this bottom end problem. I know the bearings are good (great oil pressure) and the thrust washer is good (no fore-aft crankshaft movement). If the cylinder walls aren't so mangled that they can't take a hone, I'd like to just slap some fresh rings in and get the compression back. That buys me some time to get another block and do things right.

It is physically possible to drop the oil pan, pull the pistons out the top and do a ridge ream, hone and re-ring job in the car. Just a question of is it feasible for the bores in this block?

[Loren]

Was going to check wet compression on the other 3 cylinders today. But, even with a fresh battery, all I got was a click when I tried. This happened exactly once a couple weeks ago. Took a few attempts to get past it. Not sure if it's the starter being sticky, or the starter solenoid. It doesn't feel like the starter is getting power at all, so it's probably the solenoid. It's really old, no surprise. A problem for future me.

So, I didn't do that. Got right to taking things apart. Pretty uneventful. But, I do have to say that putting a V-band at the collector of the header was BRILLIANT! I was able to remove the intake and exhaust manifolds without jacking the car or getting under it at all!

Got the manifolds off, the water pump, all of the hoses, the radiator. Disconnected the alternator and set it aside. All the usual stuff. Really not that far from just being able to yank the engine out. I probably should. Then I could do the transmission mounts. But, that opens me up to feeling like I should do a lot of other things, like oil seals and clutch and stuff. This project is already growing too much!

Removed the valve cover and pulled the rocker shaft. Labeled the lifters so they can go back in the proper places. (probably won't matter as I might replace them due to wear, and I might shave the head... which might require them to be shorter, anyway)

The head came off pretty easily. Only one stud fought me. Some penetrating oil and a little heat loosened it up. And while I was fighting with that, the head rotated sideways on me. Good! Means it's not stuck! I put another stud back in to hold things while I finished removing the stuck one.

I still haven't found a "smoking gun". Cylinder #3 has a bore that's a little rough, but not THAT bad. I'm not sure how much it takes to affect compression. And it could be a broken ring, haven't gotten that far yet.

The rest of the bores look better, none of them are terrible. And there's no ridge at the top. Apparently, these engines very rarely do that. Something about lots of nickel in the cast iron. Quality cast iron from England. Who knew?

The head looks good. No problems with the head gasket. The rest of the cylinders look better than #3, though #2 is similar. They all have some vertical scoring.

The pistons are NOT the flat tops that I thought they were, and the head is a low-compression head. So, it's probably pushing 7.5:1 compression. Likely about 54 HP when new. Should be a rocket ship with increased compression!

Did some research, the block SN is FP28444UCE. That decodes as MG Midget, a serial number, US market, CA emissions. I found anecdotal evidence that the serial number should put it likely manufactured in early 1975. Means that either it's from an earlier car, or it just sat at the plant for a while before being put in a car. Who knows? They didn't use VIN back then. So, the car has a Commission Number, and the block has a serial number, but they are not correlated (unless you buy a "heritage report" from some outfit in UK that has access to old records).

The head part number TKC1410 most places list as being from 78-79. But, those same places also don't make it clear what head a 1976 CA spec car should have. I'm betting they just didn't do the high coveted '76 high-compression version for CA spec.

None of that really matters. All the blocks are the same, and all the heads are interchangeable. Only difference in heads (whether they're from a Spitfire, Midget or other application) is their height. They mill them from the bottom, so it affects combustion chamber height, which affects compression ratio. This one is really tall at a measured 3.106 (which is correct for this head). All of this is really well documented. So, "the formula" for me is the flat top pistons and shaving the head to a height of 2.98". That should put the compression ratio at 9.6-9.8:1. Which will be nice for a street car. I don't mind running premium.

Looked at parts a little bit. Rings are cheap. Around $80 for a full set. But, also found that you can get a quality set of pistons WITH rings for $180-300. Seems like a no-brainer. Worth $200 just to not have to clean the old pistons, nevermind wondering how much life they have left in them! Even if they weren't dished pistons, I'd already decided I was probably going to replace them.

Fun Fact: "MaxSpeedingRods" is actually a reputable brand for forged connecting rods! They're pricey, but not as much as you'd expect. $400 per set. They are well-made and very light. About .4 pounds less per rod. That's HUGE on this engine. It's got that long stroke and tries to pull itself apart if you rev it over 6k. So, these rods would raise the safe rev limit by reducing some of that stress AND putting it onto a sturdier rod. Plus the benefit of less rotational inertia that would feel a lot like a lightened flywheel. Good stuff. But, they're not quite "plug & play". As with a lot of performance parts, some modification is required. In this case, the bearing caps can contact the side of the block and the oil pump. Not a huge deal, but some clearancing would be required. Not sure I want to do that, OR spend the money. Not a race car.

Photo time!

Here's the bottom of the head. #3 looks cleaner because it had all that oil from the wet comp test, had to wipe it out.



If you look closer, you'll see some scarring on the flat part of the #3 combustion chamber. Something got bounced around in there at some point.



Head Gasket, top and bottom. The block has .030" deep recesses around each bore. The head gasket has to fill that gap. They do that for better sealing/reliability. I'm not sure it really does anything. The earlier 1300's didn't have it, and they never had a problem.





Here's the top of the #3 piston. Shares the same pock marks as the head. I wonder if maybe a tip broke off of a plug or something?


These 4 photos are all of cylinder #3. Interesting that, at some angles, you can still see some cross-hatching. The vertical scoring is evident. And you can see the rust scar in the middle of the bore in a couple places.

Looking rearward:


Looking forward:


Looking left:


Looking right:



Before I take it apart any further, I want to measure the bores. I've ordered a digital bore gauge that should be here tomorrow. With that, I check to see how round the bores are, as well as consistency from top to bottom.

If that all checks out, I've got some decisions to make. I'm leaning towards using a 3-stone hone to do a serious hone down to .020". That should be plenty to really smooth things out. Then I can do 20 over pistons and rings.

I'm going to try really hard to leave the bottom end alone. This engine has always had good oil pressure, that means the bearings should be decent. I'll probably change the thrust washers, but leave the bearings alone.

[Loren]

My bore gauge showed up, and I figured out how to work it.

I'm VERY pleased with the measurements! They were so consistent that I didn't even bother writing them down. Score one for quality British iron! (plus, if it's the original engine, it's only got about 55k miles on it)

I zero'd the gauge at 2.9000. The gauge reads three digits plus a "half" overflow. So, it can read as little as .0005".

Every cylinder was within .001" of round and straight. (mostly within .0005"winking smiley Measured at centerline and 90 degrees, and 3 points top, middle and bottom (bottom without removing the piston).

#4 actually read .0005 small (2.8995"winking smiley in exactly one dimension.

#3 is about .001" larger than the others, but still very consistent, round and straight within .001"

Every other measurement was between .000 and .0015"

Now, I have no good means of measuring the depth of the scoring in the bores. But, I'm willing to chance that. (still expecting to find a broken ring in there somewhere... or to find that there was some other cause for the engine stalling and not restarting... like maybe a broken chain tensioner or something)

I like these measurements. My current plan (again, pending further disassembly and re-measuring everything after more thorough cleaning) is to do a minimal hone just to clean things up (not looking for perfection, accepting that I may not get rid of ALL of the imperfections). Put a set of standard size County flat-top pistons and rings in there (after ample cleaning). Put the original head back on it with some cleaning. And SEND IT. (in as much as I "send" anything these days)

I may jack up the car, pull the oil pan and try to get the pistons out tomorrow. Then I'll know the status of those old rings. (and a few other things that nobody has laid eyes on in many years).