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General MG 1972 Midget cylinder pitting

Maraldo

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Hi. New to the forum. Picked up a ‘72 midget, 1275cc rebuild a while back. Engine started dragging and recently died. Turns out two of the cylinders have excessive pitting and I am no longer getting compression. First option is a machine shop...curious if others have experience or advice in this space. Many thanks in advance.
 

JPSmit

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Hey there, welcome! can you post pics? I may make to sense to take it to a machine shop - but I wonder if that is what provided the symptoms you describe. Pitting might lower combustion and and increase oil consumption but, did it outright doe and refuse to start?

Also, perhaps a moderator can repost to the Spridget forum (Sprite + Midget) While the MG crowd here are accustomed to dealing with hulking pieces of metal, it is the Spridget crowd that truly comprehend the genius of a beautifully engineered brilliantly executed smaller piece of precision machinery :grin:

seriously, come on over and we will sort it out.
 
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Maraldo

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Hey there, welcome! can you post pics? I may make to sense to take it to a machine shop - but I wonder if that is what provided the symptoms you describe. Pitting might lower combustion and and increase oil consumption but, did it outright doe and refuse to start?

Also, perhaps a moderator can repost to the Spridget forum (Sprite + Midget) While the MG crowd here are accustomed to dealing with hulking pieces of metal, it is the Spridget crowd that truly comprehend the genius of a beautifully engineered brilliantly executed smaller piece of precision machinery :grin:

seriously, come on over and we will sort it out.

Thank you very much!!! Have to stop into the shop to snap a few pics. Will also submit over to the Spridget forum :encouragement:. Picked it up ~2500 miles ago...ran beautifully...about a month ago, the fuel pump went...no issues replacing. The following week it started to ‘choke’ as i was driving...would bog down and then catch and run even again. Finally it died. Rebuilt the carbs...pulled the shafts (felt like it was taking on air). Finally brought it into the shop...he pulled the plugs/gaskets and looked down the Cylinders...said two had no finish with significant pitting. His recommendation was finding someone to do the honing...sounded like bottle brushing or the like was off the table. Now we are trying to find a shop that would be willing to do it. Anything to look out for if we were to move forward with machining the two cylinders? Thanks again
 

DrEntropy

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Welcome to the forum Maraldo!

Just my tuppence worth, but: do all four to the same size, not just two. That "beautifully engineered brilliantly executed smaller piece of precision machinery" will be more sensitive to displacement variation than one of our hulking pieces of metal. :wink:

I suspect you'll get a similar opinion from the cute, dainty little engine crowd. :devilgrin:



 

Grantura_MKI

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Yes, I agree...doing two cylinders is like doing brakes one one axle end.
Was the coolant at low levels, or maybe the water damage was done before you purchased?
 

DrEntropy

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"Two bangin', two draggin'! " :smirk:
 

Bob Claffie

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If it ran fine before the latest fiasco I doubt if the condition of those cylinders have anything to do woth the current problem. A LITTLE loss of power , maybe a LITTLE more oil consumption. I think you're looking in the wrong place for a solution.
 

NutmegCT

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JPSmit

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Thank you very much!!! Have to stop into the shop to snap a few pics. Will also submit over to the Spridget forum :encouragement:. Picked it up ~2500 miles ago...ran beautifully...about a month ago, the fuel pump went...no issues replacing. The following week it started to ‘choke’ as i was driving...would bog down and then catch and run even again. Finally it died.

that sounds a lot more like a fuel issue - either something is clogged/ sucking crud/ or a bad filter, or you are getting air into the system - had the car been sitting? how old are the fuel hoses?

edit: could even be a duff pump.
 

Grantura_MKI

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OP said there is NO compression in two cylinders. This needs sorting before looking at a fuel issue....
Would remove the rocker cover and crank the motor over sans plugs and watch the valves, etc.
Just my 2p.
 
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Maraldo

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Thank you all very much for the input. Mech indicated low compression in two. When it started to drop rpm’s i could give it fuel and nothing would happen...then all of a sudden it would catch and it would take off. This cycled about two or three times then it died. All new fuel lines, filter, pump, etc. Thought was around air...full rebuild (including carb shaft) and cleaning of fuel system which led us to pull the cover and see the pitting.
 
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Maraldo

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Thank you all very much for the input. Mech indicated low compression in two. When it started to drop rpm’s i could give it fuel and nothing would happen...then all of a sudden it would catch and it would take off. This cycled about two or three times then it died. All new fuel lines, filter, pump, etc. Thought was around air...full rebuild (including carb shaft) and cleaning of fuel system which led us to pull the cover and see the pitting.

One other naive question...if i do find out that honing is required, assuming one of two things, pitting is surface and will still have a fit with the existing rings or will need to take off quite a bit...if that’s the case, anyone ever use a liner in the rebuild? Thanks
 

Bob Claffie

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By your own description " start to drop rpms and suddenly take off" is NOT a description of two bad cylinders ! Ignition or fuel related or possibly stuck valves, but NOT pitting. I think you are going to send a lot of money down a rabbit hole and not solve the problem except possibly by accident.
 
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Maraldo

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By your own description " start to drop rpms and suddenly take off" is NOT a description of two bad cylinders ! Ignition or fuel related or possibly stuck valves, but NOT pitting. I think you are going to send a lot of money down a rabbit hole and not solve the problem except possibly by accident.
Thanks Bob. Will take a look when I jump into the shop tomorrow. Appreciate the feedback!
 

DrEntropy

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The symptoms described sound like a fuel delivery issue. New pump with "no joy". Tank is suspect, as are the soft lines from tank to the pump.

I'd not jump into an engine rebuild, but rather hunt for fuel delivery problems first.

BTW: How low is "low compression" in the two suspect cylinders? Numbers?
 
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Maraldo

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So i spent the day with this...checked fuel delivery, checked ignition, checked wiring. All good. Scoped the cylinders...rings are passing...estimated 80% blow-by...swapped the rings...still passing badly...help!
 

Bob Claffie

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I currently have an MGB engine apart and upside, when I took one rod cap off the piston and rod assembly fell out of the cylinder absolutely no tension between the rings and the cylinder wall BUT it didn't happen overnight, it took a long time to get to that point.

In your case I would look at the diameter of the valve stems vs the inside diameter of the valve guides. It's possible when the engine gets up to temp the valve clearance goes to zero and when the valve opens it stays there and when it cools a bit it closes. Possible marginal (weak) valve springs too.

You mentioned previous engine work, can you describe what was done and how long ago ? We would like to help you out with this problem for the least $$$ possible. I would get a second opinion from another shop if possible, this guy doesn't give me a warm fuzzy feeling.
 

Joe Schlosser

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Please repost in the Spridget section. Although the A series is not that much different from the B series there a lot of people there who have a lot of expertise in the A series.
Also, the pitting issue seems like something that is not related to your "it ran fine then just stopped" condition. Power loss and maybe oil consumption but it should still run.
 
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Maraldo

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I currently have an MGB engine apart and upside, when I took one rod cap off the piston and rod assembly fell out of the cylinder absolutely no tension between the rings and the cylinder wall BUT it didn't happen overnight, it took a long time to get to that point.

In your case I would look at the diameter of the valve stems vs the inside diameter of the valve guides. It's possible when the engine gets up to temp the valve clearance goes to zero and when the valve opens it stays there and when it cools a bit it closes. Possible marginal (weak) valve springs too.

You mentioned previous engine work, can you describe what was done and how long ago ? We would like to help you out with this problem for the least $$$ possible. I would get a second opinion from another shop if possible, this guy doesn't give me a warm fuzzy feeling.

Thanks Bob...will give the stems, heads, and springs a look. The paperwork from the prior owner on the engine rebuild is vague at best...i reached out to the prior mechanic to see if i can get more detail. I do trust my mechanic...has not done me wrong in 3 decades...just out of my depth on this one...thanks!
 
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