MG Midget engine rebuild

[Chris152]

I'm not sure if this should be in Projects, of even if UKW is the best place at all, but I know some of you are knowledgable about such things, so thought I'd try here.

A couple of years ago we removed this from a Midget in poor condition, but the engine seemed fine. But, as it was bought as a learning project, we took just about everything apart. Lots of distractions along the way have slowed the process but we're ready to start the rebuild. I've been tasked with the engine, so here goes.

We'll be using this as our general guide
https://mossmotoring.com/restoring-british-engine/
and MG sources for specifics. We're going for hardened exhaust seat inserts but keeping most of it standard (maybe a little head skim), and the cylinders are very good.

First question: How should we clean the block before reassembly? I've looked at various videos etc, but wonder specifically about washing. Brush out passages and chase threads, then soak in parts cleaner for a day or two, then soapy water followed by air/ heat and WD40 in the cylinders - does that seem to be a reasonable way? Or should we be paying someone to do that bit?

Plenty more questions to come as we go...

Thanks for any thoughts, Chris.

 

[deema]

Waiting with anticipation for the next update. Brilliant

 

[Terry - Somerset]

I suspect the key issue is not the obviously visible surfaces, but oil ways, and cooling system to ensure all crud easily displaced by the cleaning process is removed. A high pressure air line would no doubt be useful.

 

[Spectric]

How should we clean the block before reassembly?

A chemical dip is easiest but you can lightly sandblast providing you have a bare block and throughly wash it afterwards. To do a through job you could remove and replace all the core plugs as it is much easier on the bench.

Being Iron you should have no issues with the block face but get the bores checked and if ok then a light hone before using new rings.

 

[johnnyb]

Sizer and a scrubbing brush with a long and intensive (pref hot) pressure wash, blasting all ways especially if it's been machined at all.

 

[Cozzer]

Ah...
I had a '74 Midget once, in an ugly "Tundra" colour. Didn't like it at all until I went to one of the Nationals at Donnington, and saw how comparatively rare a colour it was, so decided I liked it after all.
Not having a garage, the engine and gearbox sat on a cradle in our kitchen for a while : I'd had the cylinder head skimmed by Sheffield's Beckett & Garner, and they'd seen to the bores and crankshaft as well...it was going to be an over-sized shell bearing job if memory serves me.
Anyway I'd decided to use some recommended cleaner for the lump - apply, scrub, re-apply, leave, rinse....
Worked very well, until I noticed that it had managed to change our vinyl (?) floor tiles into sponges....

It won't surprise you that Mrs.C was singularly unimpressed....

 

[Amplidyne]

Know more about Minis than Midgets. Change the oil pump, and the timing chain and sprockets for sure.

 

[Cabinetman]

I may be wrong as it’s many years ago but I think the gold colour of the block shows it is a reconditioned engine? Which might be good as it will have done a lot less miles than the car says.

 

[Amplidyne]

I may be wrong as it’s many years ago but I think the gold colour of the block shows it is a reconditioned engine? Which might be good as it will have done a lot less miles than the car says.

The factory recon units were named "Gold Seal" IIRC, and painted gold.

 

[Chris152]

Thanks all. It is a Gold Seal engine, came from a Dolomite before reconditioning, apparently. It still has clear honing marks so all good in the cylinders. We'll be buying some brushes for cleaning the oil/ coolant channels, and definitely replacing the core plugs allowing better access. (I had a Midget back in the day, the coolant froze one night and a plug popped out, very lucky that was all!)
Somewhere we have a list of the components to replace, and I think we bought some when one of the parts firms closed down last year (iirc).
@johnnyb - what's sizer?
@Spectric - if we can, we'll do the clean-up ourselves, which precludes chemical dip/ media blasting, we'll see how the parts cleaner works.

The original plan was to prepare the engine for hill climb, but for now we're going with a basic rebuild and can upgrade later if we still want to. I'm keen to get it back on the road!


ps Is there any reason not to use a pressure washer on the channels?

 

[Mickjay]

Know more about Minis than Midgets. Change the oil pump, and the timing chain and sprockets for sure.

Weren't they both same basic 'A series' engine? Annoyingly the engine had to come out to change the clutch on our 73 midget.

 

[Chris152]

Weren't they both same basic 'A series' engine? Annoyingly the engine had to come out to change the clutch on our 73 midget.

Ours is a later rubber bumper model, so has the 1500 Triumph engine, but previously they had the same engine 1275 as the mini. I understand that's the better engine for tuning.

 

[johnnyb]

Jizer is like water rinsable white spirit. Hot pressure wash then blow out with an airline with brake pipe extension. Rinse and repeat until bored. Most home engine rebuilds fail due to poor cleanliness. Why mechanics prefer to transplant is because an engine is mostly a sealed unit. Dirt has very limited ways to enter. To also reassure you it's a relatively rough process on those old engines. Many have been rebuilt in garden sheds. If its clean then it should work. There very sensitive to swarf in the wrong place.

 

[Diver Fred]

Deleted as crossed with ribber bumper comment.

 

[Amplidyne]

Weren't they both same basic 'A series' engine? Annoyingly the engine had to come out to change the clutch on our 73 midget.

Pig of a job. I helped a mate do one in my garage. As said the later Midgets were a Triumph lump.

Ours is a later rubber bumper model, so has the 1500 Triumph engine, but previously they had the same engine 1275 as the mini. I understand that's the better engine for tuning.

Ah yes I'd forgotten that. I thought I didn't recognise the layout with the head off. Been a while since I had an A series engine apart though. Same sort of thing though. Change all the bits and pieces that can be changed, at least anything that's awkward to get at without pulling and stripping the lump again.

 

[Torx]

If you can find a local engine reconditioning place they might be willing to put it through their ultrasonic tank for a small fee.