MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - air injection ports

On a 12cj engine these can get clogged with carbon deposits (especially if they were plugged with some bolts/set screws for a long time). The ports have double flared fittings placed in the head with what look like short lengths of steel brake line. Now this may sound nuts or irrelevant to some, but my warmed over midget still has the smog gear on it and whne they redid the head they discovered that the air injection ports were all clogged. Now I was wondering if anyone might have any suggestions for clearing these out to make them functional again. Would a drill bit do it without damaging the tubing?
S.A. Jones

My understanding is the little golf tees inside the head were used to clog the holes and held by the bolts that screws into the side of the side of the head...

If Im wrong, you could just pull the little golf tees and screw the smog manifold into place...if the holes get clogged agian with carbon, you can just drill them out with a small bit.

My plan is to use the 4 smog ports on the head to screw in 4 EGT sensor probes...Im not sure they will fit dricty to the head, if they cant then Ill canablise a smog port manifold to make it fit...I already drilled the holes larger...the holes are 2 tiered..the 1st part is 5/16 x 24(?) (freaken hard to find thread size)the 2nd part is liike 1/8th inch in diameter.


Prop
Prop

SA,

I don't claim to fully understand the emission system, but I have seen some of the parts.

I don't think the little flared tube is critical in the way a carburetor jet is. It is just feeding air from the pump to further complete the combustion process to reduce hydrocarbon emissions, and a tiny bit more or less air is not an issue.

So, I think any reasonable care in cleaning them out should be sufficient. Just take care that the drill bit you choose is not larger than the inside diameter of the tube, and I expect you will be okay. As a precaution, you might start with a small bit and work your way up.

Charley
C R Huff

When "they" redid the head, why didn't they clean them out? The tubes come out easily using a pin punch from inside the port, or you can usually pull them out with a suitable sheetmetal screw from outside. No problem cleaning them with a drill bit, but if the ex is open, carbon falls down the cylinder.

FRM
FR Millmore

What would happen if a little carbon falls down into the combustion chamber?
S.A. Jones

I really dont want to appear questioning FRM, But how does the carbon fall into the cly. I would think it would just get blown out the exhaust port.

Im wrong somewhere, just not sure how.

Prop
Prop

Think about it Prop, if you are cleaning out the head ports and the exhaust valve is open on that cylinder the carbon that you dislodge can fall down the port, past the valve and into the cylinder. It wouldn't be blown out unless you were trying to clean out the ports with the engine running. If the exhaust manifold is off the engine then S.A. could make sure the engine is turned over so that the exhaust valve is closed on the cylinder he's working on and then use a vacuum to get the crud out of the port before moving on to the next cylinder.
Bill Young

Little bits of carbon probably wouldn't do anything evil. It is very bad practice and evil mindset to ever allow anything to fall down or in an engine though, so I pointed it out.

The deposits can be somewhat abrasive, larger pieces can get trapped on a valve seat and stick there, leading eventually to burned valves. What if the tube breaks off, or somebody sealed it with epoxy, or you break the drill, or loose your grip and the drill falls down hole?

And if you think that it will just blow out the exhaust first time you start it, you have surprises coming! Once in the engine, things travel in very odd and unexpected directions, with evil intent. I've many times taken bits of debris that originated in one cylinder out of one or more other cylinders - like pieces of piston rings. Here's sequence for your consideration:
Jaguar V12 has the distributor buried between the V, under the intake. It's really hot there, so the dizzy cooks; and it's very difficult to service, so people don't. The grease on the mechanical advance dries up and the advance gets sticky. While it's stuck in some random position, the timing gets reset, so now the timing is off a lot in unknown directions, which may or may not change if or when the advance decides to move. This engine has a lot of advance motion, and depending on how things stack up, it can wind up very much advanced, very retarded, or both at random intervals. Too advanced gives detonation and melts/blows the piston tops out. Retarded gets the head and valves very hot (which can also give detonation, but it stays hot after load is removed). On shutdown, if the right valve is open, seat inserts fall out of the head. The insert then breaks up as the piston beats on the held open valve. Pieces of insert, maybe also valve and piston and rings, are then found distributed all over the engine by way of the inlet manifolds. I forget the pattern, but commonly the broken bits from one cylinder will end up in several, including the diagonally opposite one on the other bank of the engine! It is very difficult to notice one or two dead cylinders on a well silenced many cylinder engine, so the grand finale comes when the combination of random timing and unburned fuel in the cats sets Kitty on fire, and that pretty well destroys the evidence.

Loose crap of any form doesn't belong inside an engine, and we all know that the worst "loose nut" is the operator. Like the old song says "the leg bone connects to the hip bone", and it all starts and ends up at the head bone.

FRM
FR Millmore

what if I did it with the engine running? What happens if I start getting exhaust gasses puffing out those ports? Is there a risk of burning myself that way?
S.A. Jones

S.A. I really never thought about it, but you should be able to do it with the engine idling and that way anything knocked loose would most likely be blown out the exhaust. Wear some good mechanics gloves and eye protection and with the correct size drill chosen before hand you should be able to ream out the ports in very short order.
Bill Young

Sure. The process is self limiting, in that when exhaust comes out, the port is clear; and, unless you have leprosy or other neurological disorder, you'll move when it gets hot! Glasses! And don't jerk the drill sideways as you jump. I use a drill bit in a disattached chuck and do things like this by hand.

FRM
FR Millmore

But if you go in too far, you will hit the moving valve with the drill, and break it off!
I really suggest the sheetmetal screw to pull the tube, or forget the whole non problem.

FRM
FR Millmore

Sheetmetal screw? Now there's an idea. What size should I be looking at? Would a drywall screw be better? I am assuming the whole point is to grip the tube and remove it.
S.A. Jones

That'd be the sheetmetal screw I mentioned in my first post, above. It will be something small, like #6, but needs to be pretty long, I prefer a real self tapping or sheetmetal type, since they are tough. There are some nice ones somewhere in the interior of Spridget, but I can't recall exactly where! Drywall sacrews can be brittle, and you do not want a busted piece of one in there.

FRM
FR Millmore

Duh!!!

I got ya now, That does make sence if the engine is sitting still that the carbon would fall into the cly.

I got to agree with the drywall screw and the self tappers....the drywall screw will also shead little particals off its screw threads...granted something that small wont by a bomb detenation but you dont want somethng like that floating around....Id certianly try magnitising the screw 1st, to hold any little bits and shavings


Still SA, If your anything like me...And Yes you are! 8 ^ ) your going to have the head off at least once every 3 years for one reason or another...Id clean it out then.

Prop...No longer headless...Prop
Prop

Alright S.A. here's a plan where you could safely remove the inserts or clean out the blockage without having the engine running. First you'd need to make yourself an air pressure connection from an old spark plug and a suitable quick disconnect air fitting. (I think it'd install a ball valve so I could regulate the flow) Then crank the engine over by hand until the exhaust valve on the cylinder you plan on working on is open and apply some air flow through the spark plug hole. It will exit out the exhaust valve and purge any crud out of the port. You can then use a screw or drill or what ever you want to clean out the insert without any worry about getting crud in the cylinder. Just repeat the process with each cylinder and you're done.


Bill Young

I have always found it easy enough to work a drill bit into the restrictor tubes and to extract them. Then it is easy to clean them out with the bit or with bailing wire. Be sure to clear the injection manifold tubes as well. The #4 tube with the elbow is particularly prone to clogging. Blow compressed air through each pipe after cleaning with a wire.

Bits of carbon that fall into the head should be blown into the exhaust with no harm as the air is injected beyond the exhaust valve, not into the cylinder itself.
Glenn Mallory

Ok, so I finally got around to doing this. Here is what I did.

http://www.spridgetguru.com/Air_Injection_Ports.html

Any thoughts? Reactions?
S.A. Jones

This thread was discussed between 21/10/2009 and 30/11/2009

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.