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MG Midget and Sprite Technical - Engine banging

Yikes, another problem. I haven't posted here in a while. 1970 midget. I had a bad pinging problem, determined the timing was too far advanced. Got the timing right, re-adjusted the carbs, and it ran great. After maybe 50-100 miles of great driving, I stopped for gas. 2 miles later, the car started driving like a it was on 3 cylinders.

Bad gas? Here's what I've done with resulting in a little, but not much, improvement.
-replaced the gas
-checked and rechecked timing
-checked and rechecked carb adjustments
-checked gap on points
-replaced condenser and rotor
-checked plugs
-thinking maybe a head gasket,checked the oil for gas and the antifreeze for gas or air bubbles. negative for each.

more info:
-with the car idling, if I pull the first or second plug wire, NOTHING HAPPENS! I'm getting spark to the plugs, switched plug wires and dist cap with a known good set.
-with the air filters off, when I rev the engine, it seems like the front carb is shooting out vapor... the back carb does not do this.
-I have not done a compression test- don't have a tester.

sorry for the long story. any ideas would be appreciated!!!

-Don
don g

wow Don ... you have had that problem with the knocking for awhile havent you... I was thinking we talked about it here some time back and people where thinking it was exhauste... Or am I cofusing you with someone else.

can you pin point where the banging is coming from... try a long piece of thin dia steel rod pressed agianst your forhead and put the other end of the steel rod agiant what your testing. you will know when you find it

make sure you are video tapeing this if you touch the steel rod to anything electrical while pressed agianst your forhead... I want to see that!

If Im correct in my memory of what we talked about... Id say its time to drop the oil pan and have a look at the bearing shells... I certialy wouldnt drive it far
Prop

okay so just re-reading...the vapor mist got my atten.

Are both carbs working? which cly or clyinders is not firing

what does it do if the choke is pulled out ... does it run better on all cly.

is it flowing fuel out the brass vent on the float chamber

Im just wondering if tha little tube that runs from the botttom of the float to the Jet is clogged on one of the carbs... making it run off of one carb... if one of those tubes gets fully blocked it will certianly act like a broncing bull

you will need to remove the float chamber lid with the platic float bowl pined to it then remove the jet from the bottom of the carb body and run the little red flex straw from the carb cleaner can into the jet hole of the tube and spray it out thur the jet tube and into the float chamber to clear the junk out

becareful, those tubes if old can be vary brittle

check also that the dash pot spring isnt in bad shape exp. corroision or broken or binding up

doulbtfull here becuase your cars are always clean... but look at the air vent hole isnt clogged the one that equalises the pressure of the carb piston... its the one that people always cover up inadvertiantly when putting on differant air filters ... the hole is at 2 oclock on the rear carb and 10 oclock on the front

Do the carb pistons slide up and down okay ... no hang ups


let us know what happens
Prop

just one last thought.... its an embarrening one. so dont feel that you need to tell us the truth

>>>>>I stopped for gas. 2 miles later, the car started driving like a it was on 3 cylinders<<<<<


Gas or diesel?

Are you sure? I tried for 2 weeks to get my engine started swearing the plug wires where installed correctly, they werent ... DUH
Prop

>>>>>>>>>thinking maybe a head gasket,checked the oil for gas and the antifreeze for gas or air bubbles. negative for each.<<<<<<

Im sure you mean oil in the radiator and water in the oil a nice greenish brown slimy mess... and that white snot inside the oil cap and white foam in the radiator, and white smoke blowing out the exhaust

Prop
Prop

The bad pinging problem you endured could have been the key. This could have caused a problem in one of the cylinders and now that seems to have manifested itself into the problem you now have. Could be a blown piston , burnt valve, etc etc. I think removing the cylinder head would show you the problem Doug. You can either do this or if you want piece of mind then get a comp tester which I am sure will demonstrate the need to remove the cylinder head.
Bob Turbo Midget England


Don. I'd say head gasket between 1 and 2. It happened to me the other week between 3 and 4. The banging noise was really scary, but it was just the noise of the semi compressed mixture from 3 blowing through the hole in the gasket and out through the carb via 4. No oil or water contmination either. When I took the head off, the hole in the gasket was about an inch accross.
Your front carb blowing out vapour and the back carb not seems to confirm this.
I renewed the gasket, warmed it, up allowed it to cool then re-torqued it. All is now fine.

Bernie.
b higginson

yeah but don jusst replaced the head gasket like 2 1/2 years ago with a payen black composit and had the head resurfaced... So id be hard pressed to say its a blown head gasket...It might be but whats the odds

Prop
Prop

Thanks, guys. Prop, dont know how you remember this stuff- yes, head gasket about 2-3 years ago, had the head redone, etc. I visually inspected the carbs, checked floats etc- might be good to check the tube before pulling the head.
i guess if it's the head gasket a compression check will verify it?

don
don g

Ouch... yeah, do a compression check and let us know what you see.

-:G:-
Gryf Ketcherside

I guess I'll get to harbor freight and buy a tester. hopefully i can do it tomorrow.
headgaskets arent that bad- i've done a few, last one only took 3 hours or so.
don g

If it is a blown head gasket between 1 and 2, take the plugs out, put the car into top gear and get a freind to slowly push the car forward while you hold your thumb hard on the plug holes one by one. You'll be able to feel the compression, or lack of it as the engine turns over.

Bernie.
b higginson

ok, looks like i have compression! i'm now thinking the carbs need rebuilding. i did discover another question- what's the tube between the carbs that runs to the canister behind the fan blade? i ran out of time, but it appears it might be messing things up.
i now cant get the car to idle at one speed... it's at 600 rpm, then when i give it gas it revs and idles at 2500-3000! when i disconnect the hose between the carbs, it seems like maybe it evens out better.

ideas appreciated, as always!

Don
don g

Hey Don

Thats the evac system... the little canister attached to the timing chain cover is an oil seperator

The carbs create a vacume thur the hose and to the engine block, thus sucking Positive air pressure out of the crank case, and "Throretically" LOL HAHA keeps the oil from pissing out thur the rear engine scroll seal


what does that mean with the engine running better with the evac disconnected? ... I wish I knew

Is there any chance you can bribe "lee fox" to stop by one evening and have a looksy, Im sure he would have a working therory

Tomarrrow is monday night, maybe stop by Johns shop and talk some tech with the club... Just bring a new Girly mag... LOL


Prop... Don you semblises and define what cool is for guys over 75 years old (LOL... HAHAHA) Id never want to forget you...(friend)
Prop

Hey Don,

I was only approching the carb angle solely on the basis that one of the carbs may have have compelely failed and the engine is running on only one carb, or vary little of the 2nd... even though the car isnt funning well, both carbs do appear to be running so its probably not buocning like a wild bull. So Im leaning away from a carb issue as the source of your bangng

a little more discussion... how did you set the timing when you figured your to far advanced... I dont question your ability... just getting some clarity

when you adjust the timing by turning the dissy.... turning the dissy clockwise is "advance", turning the dissy counter clock wise is "retard" (the dissy operates/runs counter clockwise NOT like alot of other engies

you have to disconnect the hose from the vacume advance on the disyy and plug it so you dont loose vacume on the carbs and intake manifold the spec is around 10 degrees BTDC at 1000 rpm

are you using a timing light and crawling under the car looking at the little teeth on the bottom of the timing chain cover then crawling back out and moving the dissy on top and back under agian .., ect.

Im just wondering if you moved the dissy to more advance instead of retard... that would deffintaly give some banging

If this is the case... its far better to be retard then overly advanced for a short interm time frame

over advanced makes the ignition fire Before the piston has reahed the top of the clyinder Vary hard on bearings if your to retarded the ignition is firing after the piston has reahed the top so a lack of power and heavy fuel consumption

Now that said... if its really retarded, you can ignite unburnt fuel in the exhaust pipe... making sorta of a banging noise..(shot gun LOL)


Can you elaborate a little more on how you retimed the ignition? step by step

Id be curious how the engine got over advanced,,, Just fiddling on a nice boring saterday afternoon,(vary common, If not the #1 reason for out of adjustment dissys)

or did it happen just out of the blue with no advanced warning...

If the later Id be looking at the springs and wieghts for rust and improper funtion, also look to see if the vac advance is working properly.

Prop
Prop

when you timed the engine to correct for being over advanced and used the timing light on the crank shaft pulley

there is a small notch on the outside edge of the pully to match to the teeth on the bottom of the timing cover

dont use the little "indention" half drilled hole on the front on the pulley ... vary common mistake


the little notch on the outside edge of the pulley can be a real bear to find,, and certianly not easily seen with the eye,,, might try a few drops of oil on your finger tips to help soften the skin and make them more sensitive and run your fingers around the edge of the pulley... once you find it then mark with a dab of white paint
Prop

Prop, thanks for the info. You are 'da man.

being mother's day, i ran out of time to thoroughly check the canister thing.

timing- i got it close with the timing light, and it made a noise unlike a timing issue. banging, not chattering. i retarded the timing a little. not it. i know if i'm withing a couple degrees of timing i can hone in by advancing until pinging, then retarding until it stops. Not in this scenario.

i wonder if the canister could cause this type of problem... however i the banging could be done. i took both carbs apart, blew thought the jet hole to be sure it was clear, checked what i could and put them back together.

i need more time in my day for this crap. might be time to tow it to the MG doc for an official fix. i'll try a little more before i resort to paying a professional!

Don
don g

Don if you figure out how to turn 24 hours to 30... LET ME KNOW... LOL I hear ya


Any chance the banging is comming from the front timeing cover... perhaps a worn out timing chain and sprockets.. if the chain was hitting the cover it may be pushing/ vibrating the noise thur the hose ... once you disconneted the hose, you cant hear the banging.... Boy thats a guess and a half, Im sure someone will slap me for that one...

but just based on recent experiance... I had a banging noise and turned out to be the valve cover... a valve was just touching the side (meagerly non noticeable) but it did make some noise untill I reground the inside out agian

So maybe the vavle cover is loose... try running the engine and easily remove the valve cover and see what that does.... it could be loose or just a jar... just becare full lifting the cover off with the engine running cause there all kinds of stuff moving inside


Prop
Prop

Id certianly try to bribe Lee fox, or one of the others to stop by for a look later in the week... they are all great guys and would be more then willing to pop in for a look

In the mean time if the club is still doing the informal meet on monday nights at johns shop, Id certianly get a cold 6 pack and offer one to anyone that will talk tech for a few minutes

certianly be cheaper then a tow... not to mention the lack of stress watching a tow driver back the car into johns lot... even in my truck just backing out of johns lot makes me go "wee wee tinkle tinkle" really fast at the QT across the road...

certianly an area a blind man can driver better and safer then someone with 20/20 vision


BTW... Can you better discribe the banging, how loud, its pitch tone (high or low), where it might be coming from, how constinant, does it have a rythem ... part time vs full time...Im a little vague and just graphsing at tid bits of info

Prop... for some reason I just cant here the banging in your engine on the south side of Jeff city, most likely the wind is in the way...LOL
Prop

as long as im throwing stuff up agianst the wall and just guessing, I had another thought based on all the stuff thats happening

what about a sticking valve... it would be an exhaust valve... that would make a bangng sound due to the valve slapping the piston top, and make it run on 3 cly. and be hard to idle.

Id start with the engine cold and pull the valve cover and start and look for the exhaust valve to not be moving ... if all are moving (most likly they will) run the engine to temp and wait for the banging and misfire then pull the valve cover with the engine running and look for a valve NOT moving or moving vary little, or even out of rthym with the other valves...dont look at just the rocker arm look at the springs for compression ad if one is staying down .... also remeber the valves dont go in leap frog order of (ex in ex in) ... the seq is (ex in in ex ex in in ex)

if it is, pull the head and get some new valve guilds and take to machine shop...if you need any valves (incase one is to damaged)... Let me know I got a good set of standard size your welcome to

Prop
Prop

The sound is like this- "bang". lol
so what's with the canister?

"Thats the evac system... the little canister attached to the timing chain cover is an oil seperator
The carbs create a vacume thur the hose and to the engine block, thus sucking Positive air pressure out of the crank case, and "Throretically" keeps the oil from pissing out thur the rear engine scroll seal"

can i bypass this? i dont see a replacement in vic/brit...

don g

Sorry don ... Not really, its what keeps the positive air pressure out of the engine, and makes the air pressure Negitive pressure which keeps the oil from leaking out the rear seal when speeding down the road... its okay at idle... but if you take it off and go for a 10 minute drive at around 50 miles an hour then stop and look under the car at the rear of the engine it will be like a faucet is turned on and the oil will be just shooting out.

any chance you can make video of the banging and post it on youtube, or record it and see if you can email me a copy of the file , perhaps if I could hear it over the phone, Im just having a hard time imagining a bang and wraping my mind around what it can be


is the banging constant, does it have a rythem , does it do more banging as the engine speeds up,Does it sound like someone is beating on a piece of steel pipe with a hammer. can you detect a genral area where the banging is comming from Just any additional info you can provide about the banging, I still need to go to the G. store but should be home for the evening at around 7:00 Pm tonight (monday may 10th)

Just email me and with your Phone Number If you want to talk a bit

Propaper (at) Mchsi (dot) com

Prop

Prop

Prop, the sound is as if you are running on 3 cylinders.
don g

Hey Don,

The more I think about it, Im thinking a sticky exhaust valve As I mentioned and outlined above.... thats the one thing that would share and encompase all the issues your having


sticky exhaust valve arnt uncommon, probably more evident in todays world with the trash we call gasoline..

But thats where Id spend my next day off looking at.

Did you get by Johns shop last night?

Prop

Prop

meeting night last night.
so, if sticking valves.... what do i do about it?
don g

Hey Don,

If its a valve sticking (most likly an exhauste valve)...

you will need to pull the head and get some new valve guilds and take to a machine shop to have them replaced... for no more then valve guilds cosst and the cost to have them replaced,,, Id have them all done ... if one is going bad then most likely another in the future...have them check the valve for straightness and damge also.

Id also move the piston to the top and clean off the carbon and have a look at the piston top for any damage caused from piston slap of the valve face, if there is take some photos and show john or the board...to figure out what to do from there.

others may suggest having the valve guild re-reamed, that will work, But its one of those things you have to decide if the $50-100 in savings is worth the risk of it repeating... to me Id just have the new valve guilds installled and be done with it for another 20 years

Ive found british parts north west is a great place to find the parts you need for this at a great price

you might even consider having the shop do a no lead head conversion if not already done so... check with them to see if they have the inserts... if they do (Im sure they will) it will be considerable less expensive thur the machine shop then the no lead head kit thur moss or VB.

Prop
Prop

ah... had this work done when i replaced the headgasket a couple years ago, so hopefully its still ok. havent looked at the car since sunday, i'll see if i get time this weekend.
don g

Update!
Did a compression test-
163
163
.
.
.
.
.
.
.
25
25

so.... I guess this means headgasket time??
don g

ouch!!!!


that would be my 1st guess also... make sure you have the head vac tested and magnafluxed for any cracks


prop
Prop

Don -

Wow, two of those readings are really high.

;-)

Good luck,

-:G:-
Gryf Ketcherside

back to the top may 30th 2010

Prop
Prop

This thread was discussed between 08/05/2010 and 30/05/2010

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