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MG Midget and Sprite Technical - Engineering problems and cranks...

So ive finally (after 6 months) got my midget engine back from the engineering shop. However I think theyve f*cked up.

I droppped off a marina block, crank, pistons and rods and a midget block, crank, pistons and rods.

I asked them to check over both engines and components, choose the best one to go with and then rebore block, regrind crank, fit new pistons to rods.

It was decided to use the midget block, and I thought (I did tell them) to use midget crank and rods.

What I think ive got back is the midget block, midget crank and marina rods fitted to new pistons...

Just to check, EN16t 12AG1321 is a midget crank yes?

But the rods theyve balanced and fitted to pistons are definetly marina and have a much bigger journal size. So they need to go back and be swopped that possible, or does pushing the pin out wreck the pistons?

Also, if you regrind the EN16T crank 020' does it need a hardening process again on the journals?

So questions:

1./ Is EN16t 12AG1321 a midget crank - pretty sure it is
2./ Does it require hardening if youve had it reground
3./ Does pushing the pin out of the pistons damage the pistons?

C Mason

My understanding is they heat the pistons rods and pins then press the pins in and out, so no damage should be done to pistons and rods...but thats only true if the shop is competant and experianced

As to hardening the crank I think it depends on what your going to do ...if your going to drive it to church and the Grocery Store on sunday, then no, no hardening, but if this is a race engine that will see 8k rpm more then it idles then somewhere in the middle... not an answer, but the question is diffearnt for each person...I probably would just to add reliability,alot of people dont, but they only race stop sign to stop sign and the occassional parking lot orange cone race (gymkanias??)

One thing id more conserned over is if they line bored the crank to the block...thats a biggy

Prop and the Blackhole Midget

Why not just take it back to them and get them to put right their error. If they have fitted pistons to a set of con-rods which have journals that don't match the crank they have ground, then they have obviously made a mistake and mis-matched the parts supplied. Get them to put it right.
Guy W

"1./ Is EN16t 12AG1321 a midget crank - pretty sure it is"

Dave O'Neill 2


After reading guys post

I didnt realise you were trading the pistons and and rods

NO, I WOULD not do this, id say the odds of damaging a piston or 2 are fairly good...take it to a pro
Prop and the Blackhole Midget

You don't need to do anything to the crank after a regrind, mine has been thrashed for 10 years after a 0.030 grind and is still OK.

I'm guessing a decent machine shop should be able to remove the pistons without damaging them, especially if they use a tool like the original BMC one as shown in the manual.
I removed a load of scrap pistons on the press at work and even doing it that way I think I could have salvaged good pistons.
I had to reset the gudgeon pin position on one of mine using a press with everything cold and didn't damage it

It's their cock up so no matter what they should be sorting it out for you.
john payne

Prop is talking gibberish again by the way, no need to line bore the block when swapping cranks!!
john payne

Prop is talking gibberish again by the way, no need to line bore the block when swapping cranks!!


You can also use sanding cylinders on a hand drill to bore out your block .20 + and you dont need a torque wrench tighten your cly head nuts, nor do you need a timing gun to set the dissy timming

But... people that do the above, are just a little gibberish in the head

Or have a bad drinking problem

Prop and the Blackhole Midget

I got my block line bored, but that was because l was using different main bearing caps. Using the original caps, the right way round, its hard to see what benefit there is in line boring.
What exactly goes out of alignment on a block, and why?
Guy W

What happened to the parts that didn't get used?

Do you any photos of anything?

If the Marina rods have a bigger journal size than Midget rods (you say they have a bigger journal size) how could they be fitted to a Midget crank?

Are you certain your Marina engine is a Marina engine and not an Ital engine?
Daniel Stapleton

So its not necessary to harden the crank, and the crank is definitely midget origin. Good.

The marina engine as far as I am aware uses mini sized conrod journals and a lesser spec of steel in the crank. The block is non a+ but has the oil filter on the side and revised oil and water ways. Only the ital got the a+ block.

The rods have bigger journals and a large balancing pad on the end cap... But I will get a pic tonight because I want people's opnions on how they've balanced the rods as well.

I spoke to engineers today and they hope to be able to swop the pistons over to the midget rods without damage.... Let me put it another way, they better had swop them over without damage,!!
C Mason

And yes all my surplus a series stuff needs to be sold. Express an interest if that's your intention as it'll be on eBay soon otherwise. :-) I'm confident its marina based
C Mason

Yes can really only be Marina if it's got the oil filter housing cast into the side.

So basically if you've ended up with your new Pistons on your Marina rods you are going to have to either get them swapped back onto the Midget ones or you will have to use the Marina crank. Daniel will know more about this but I'm pretty sure you can use the Marina crank but then you will have to have your flywheel (or the crank?) modified as they aren't compatible. (There are books with this stuff in - discounted on eBay at the moment I noticed!)

Really the best outcome is to end up with the Midget rods and crank in the Marina block so if your engineers are happy they can swap them back then you should be fine.

I balanced my own rods before fitting the Pistons but I didn't really know what I was doing so I can't really comment! I tried to get them so they were balanced end to end but it was so difficult I just plumbed for overall weight being the same. One was miles heavier than the rest so it now resembles a fully polished rod while the others just look standard!
john payne

I haven't changed A-series piston pins in a while but I seem to remember the pins press or drift out fairly easily and little ends only require a little bit of heat to expand them to fit; a few seconds with oxy or a few more with a regular blow torch so you should be able to change them yourself.
Nick Nakorn

I plunged my pistons into boiling water to expand them. Used the wifes biggest saucepan. Best make sure she is out when doing this.
Also as been stated on here there are quite a few differences between Marina and Ital engines but most people refer to them as Marina engines. Ital in my view is better but harder to find.
R Mcknight

This thread was discussed between 17/09/2015 and 21/09/2015

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