Rings? Need Help with Diagnosis

5.0L Miata · Nov 16, 2007

Hey All,

I just purchased a used long block from 1991 Mustang with the intention that of using the short block for the basis of my buildup. Of course my assuption was the short block was in good condition, but the engine was already out of the car so I was not able to hear it run or do a compression test on it.

I've started tearing the engine down and I filled the cylinders with carb cleaner before pulling the heads to clean up the pistons. Last night I pulled the heads and found that #7 was dry, although you could tell that carb cleaner had been there. All the other cylinders still had carb cleaner in them.

I then re-filled the cylinder with cleaner and left it for the night. This morning it is pretty much empty again. I'm thinking this means I have a bad ring on #7...sound right?

Thanks.

5spd GT · Nov 16, 2007

Interesting...

How many miles?

The only obscure thing I can thing of, is that rings do rotate, and possible the ring gap rotated to the outside (where the liquid will settle because of the angle of the block), and it seaped down.

But then again, it is just one cylinder...Hmm...

Someone else should be able to help you better, good luck.

Blandnuts · Nov 16, 2007

It's possible that when they indexed the rings they aligned them inorder (not suppose to). If the car is running, you might want to consider doing a rebuild with the spare engine.

Fred

Wallzy · Nov 16, 2007

The engine is out, so no big deal. If the pan's not off, drop it. Pull the Rod and pison and check it out. Look to see if the ring grooves were inline or the second ring is broken. If they look good, take them off and check the gap on them. Also check out the cyl wall. This is a good place to start.

Walz

stykthyn · Nov 16, 2007

if your re-building the motor arent you getting new rings? If it's really bothering you new pistons arent that expensive and IMHO are a must in any re-build. No sense in skimping at this stage of the game.

ninety15.0 · Nov 16, 2007

I agree you are already down to the shortblock. It will only take another hour to take it apart and give it a through inspection. If all looks good then just button it up. but if it were me i would re-ring it and put new bearings in. Fairly cheap and good piece of mind! Good luck man.

5.0L Miata · Nov 16, 2007

Thanks guys for the advice. This is what I thought, so I appreciate the confirmation. I do not have experience working on the bottom end of an engine and I purchased this particular engine (around 100,000 miles on it) with the assumption that the shortblock was good so that all I'd have to do is bolt the top end back on and go.

That said, I had little to no experience working on cars at all before I started the 5.0L Miata project, so I guess there is only one way to learn. Really though at this point I was really hoping to simplify my life and not have to get into new bearings, rings, pistons, bla, bla, because it all adds up to more time and more money and the possibility (with my luck lately more like probability) that I'll screw something up and have the engine let go just as the summer diving season starts up next year.

I wish I had more $$$, then I'd just take my shortblock to a local engine builder and have them make me a nice new fresh 306. Maybe I need to have a chat with Santa.

stykthyn · Nov 16, 2007

it's actually not that hard. take the oil pan off, flip the motor over. then you remove the main caps and the rods and pistons are right there. once the rods and pistons are out the crank will lift right out. like ninety15.0 said it should only take about an hour. If you still need peace of mind about that cylinder take the block to a machine shop. for about 100-150 dollars they will chemically clean the block and re-hone the cylinders which at 100k miles will really need the attention.
They will then put in new freeze plugs and new cam bearings.
then your cam, and crank can go back in. Once you get new rod and main bearings from your parts store they can go back together. slap the oil pan back on and your short block will be ready for its new top end.
this is the difference between a motor that will last 50k miles and one that will last over 150k miles.
taking short cuts here could seriously cost you more money and time in the long run.

5spd GT · Nov 16, 2007

Or taking shortcuts during the rebuild could hurt you as well.

You may very well be okay.

You need to realize that it could cost several hundred dollars at a machine shop, for cleaning, honing, prepping, polishing the crank, plugs, oil pump, and assembly.

Piston rings rotate in the bore, so they could have just gotten rotated making them inline for that moment or close to it.

Rebuilding it may not even be necessary, but of course it is better than a higher mileage engine

PUNISHER RACING · Nov 16, 2007

Deglaze and re-ring, even if the rings were phased correctly do you not think liquid can find its way down one ring gap around the cylinder and through another ring end gap. The cylinder is a tad bigger and allowed the end gap to open up that is why you are losing your cleaner in that cylinder. Take to a machine shop get bores checked, get it honed and a set of file fit rings to suit the bore.

irish · Nov 16, 2007

shortblock

Def do rings/all bearings, I'd do freeze plugs as well and for sure an oil pump, and an hd oil pump drive shaft. It would be a pain to finish your monster and find out you need to redo the motor. If you are going the t-5 route, now is an excellent time to have it checked out and drop a good clutch in it.....all the above is totally standard if you want to save some cash in the long run. Optional and not super expensive is upgrading the rod/main bolts, they are mandatory if you plan on any kind of racing. Better head bolts when you do a head upgrade, etc.....
If you are using Martins kit don't you need to send him an oil pan so it can be altered to fit? Can't remember offhand.
Matt

5spd GT · Nov 16, 2007

The pistons are angled in the 90* block. So if the gaps where on the lifter valley side, it would obviously take a little longer. So at a certain level, the leak will slow down significantly, if the gap is on the inner side of the block, because the fluid will puddle on the outside of the block.

5.0L Miata · Nov 17, 2007

Thanks everyone for the suggestions and support. I've actually had the car together for about 3 years now and had an 88 5.0L in up until this past summer when my lovely local e-test center put an end to that engine.

I have already purchased all my new top end pieces (Eddy RPM's, Explorer Intake, ARP head bolts, felpro head gaskets, plugs, wires, cap, rotor, etc.) and when I put together my 88 engine before I had installed a new water pump, oil pump, balancer, PCV, IAC, etc. So I'll be pulling all the new pieces from my 88 and putting them onto this 91.

Of course I would love to have this new engine completely redone, but my plan was to throw this engine together for cheap and run it for a couple of years. Then I can take my 88 short block and have it done right when I can afford it and without and time pressure. This was my plan anyway.

I think I will definetly pull #7 though and see what I've got. If nothing else it will be good for me to learn about tearing appart the bottom end of a 5.0L.

Rings? Need Help with Diagnosis

5.0L Miata

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5spd GT

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Blandnuts

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Wallzy

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stykthyn

I want to measure mine. It doesn't look that tall.

ninety15.0

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5.0L Miata

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stykthyn

I want to measure mine. It doesn't look that tall.

5spd GT

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PUNISHER RACING

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irish

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5spd GT

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