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Post by biggelmo on Oct 9, 2011 16:07:59 GMT
Here goes.....
The next of our project will be a rebuild of a MG Metro Turbo engine and gearbox that we brought from Dean.
The engine was fairly complete but without the turbo and manifolds,this isn't a problem as it will be a normaly aspirated engine.
There are many myths regarding Metro Turbo engine specs so I several hours scanning through the Turbo Minis website to try to work out what we had.
The engine number is 12H959AA which makes it an early engine and this has proved to be true with some casting marked February 84 and a CAM6581 crankshaft (more on this later).
The engine is standard in every respect,the bores a standard but will be rebored to some oversize which is yet to be decided.The gearbox will be reconed and will retain its 3.2:1 final drive.
Tha CAM6581 crankshaft was an early turbo only fitment and was Tuftrided as standard from the factory and as the main and big end journals appear to be in great condition it would be nice to leave them standard size.
The same cannot be said for the flywheel/crankshaft taper which has seen better days but hopefully can be reground smooth.
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Post by Miniböttcher on Oct 9, 2011 18:03:18 GMT
You never hang around. Glad the hear that everything is in good condition. I never removed the flywheel so never had a good look at the tail of the crank. But your right it could be cleaned up.
It answered alot of the questions you had about the crank. And that Harding on the mains and big ends is the reason why they are still good.
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Post by biggelmo on Oct 9, 2011 18:25:12 GMT
:)Yes Dean all is good inside apart from the crank nose and the cam bearings which will replaced when the block is bored.
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Post by Miniböttcher on Oct 9, 2011 20:08:18 GMT
cam bearing are always change when you do a cam shaft change, as i know you already know, i think i have a new set in the shed, you can have,
i bought them for my 1275,and when it came round to sending off to the machine shop months later, i could find them, and though i did not buy any, so bought a new set,
untill one of those days when you go digging through the shed looking in boxes that have been there for a while and you find things that you have forgot about. and guess what i found ages after the engine was built.
yeap cam bearings. just done the same thing today with my rear subframe bushes, i found the original ones i bought, after i have now bought some new ones,
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Post by Stephen on Oct 13, 2011 11:44:36 GMT
Are you changing the cam then? I have an MG Metro cam going cheap if you want something slightly uprated. Been checked over by AC Dodd and wrapped up ever since.
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Post by biggelmo on Oct 14, 2011 16:45:24 GMT
Thanks for the offer Stephen but I've got a Kent MD266 to go in,unfortunately its a spider/star drive cam so I need to get an adapter to suit the later slot drive A+ oil pump.
Minimania in the USA are the only people I can find that make one unless anyone knows different .
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Post by biggelmo on Oct 15, 2011 16:43:05 GMT
I'm going to have a good look at the head tomorrow and see if its usable,at first look it looks like a home ported non turbo A+ 12G940 head of unknown spec but it has had bronze guides fitted at some time so it needs a closer inspection.
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Post by biggelmo on Oct 16, 2011 15:11:21 GMT
OK here's what I've found today..... First off I'm following this book,I prefer it to Vizards bible as I find it easier to read because it doesn't baffle me with graphs and charts. Attachments:
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Post by biggelmo on Oct 16, 2011 15:57:59 GMT
I removed the valves and measured the heads Inlet 35.6mm Exhaust 29.4mm The valve spring free length varies between 50.2mm and 51.3mm. So going on this info the head could be a MG Metro item. A standard 1275 A+/MG Metro measures 69.9mm from head gasket face to rocker cover face,this one measures 67.8mm so has been skimmed 2.1mm at some time. After all this measuring it was time to inspect what had been done to ports. The inlet valve guide bosses have been ground back and blended in as has the bridges between the inlets. The exhaust valve bosses have been left intact but bronze valve guides have been fitted to all valves. I placed a head gasket on the head and scribed around the fire rings and the carefully ground back the head to unshroud the valves. Attachments:
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Post by biggelmo on Oct 16, 2011 16:12:13 GMT
Then I turned my attention to the valves, I placed each valve in a power drill held in a vice and then when it was running carefully ground off the sharp edge above valve seats with a small mounted grind Stone spinning in a cordless drill. The I polished the valve head with 80grit paper and t-cut on a rag. I've done this to the valves in the current engine without any problems so far. Modified valve on left. Standard valve on right. Attachments:
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Post by biggelmo on Oct 16, 2011 16:26:14 GMT
Then I opened up the inlet and exhaust ports. Attachments:
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Post by Miniböttcher on Oct 16, 2011 16:41:12 GMT
when i checked the CC of that head it came out at 18.60
bore 70.61mm
stroke 81.28mm
engine cc 1273 (1275)
pistons 12cc
ring land 0.78cc
gasket. 4.00cc
piston deck cc 0.99
total volume=17.77
chamber volume 18.60cc
unswept volume 36.37 cc
swept volume 318.25 cc
compression ratio= 9.75:1
so that head has been skimmed to allow for the 12cc pistion and with out a turbo, so its back to a standard 1275. proberly done as it was cheaper than changing the pistons,
standard 12g heads are 21.40cc , so you need to get back 2.8cc in each chamber . not sure how far to go it will be a case of keep checking it
i also did notice it had had the next size up valves on the inlets, i checked the number on the stem of the valve with mini spares website
i have had the same problem with my 998 engine, the head had been skimmed so much that i would of had around 11.3:1 cr, which is way to high,
i have had to run 2 payen gaskets, and a 3cc head shim
you could do the same, they do 3cc , 6cc, 9cc, head shims bu you also have to allow for 2 head gaskets, its what they do on the supercharger kits
or just use another head and sell that one
soo many opitions.
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Post by biggelmo on Oct 16, 2011 16:42:10 GMT
Then I tried to sort the crank nose taper.
I held the crank in the workmate and placed the flywheel on the taper,there was a slight but unwanted rock.
I them placed coarse grinding paste on the taper and carefully lapped the flywheel on to the crank to try restore a snug fit between the two.It worked to a point but now the crank nose pokes through the flywheel so I cannot bolt it up at all......Bugger.
As a last resort I'll try another undamaged flywheel and see how it fits.
If this doesn't work then I'll have to find another crank.
Has anyone got a flywheel with an undamaged taper I can borrow,I won't bolt it on I just want to see how it sits.
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Post by Miniböttcher on Oct 16, 2011 16:45:35 GMT
i have a spare flywheel
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Post by biggelmo on Oct 16, 2011 16:54:14 GMT
Hi Dean,I'm hoping my bit of deshrouding will increase the chamber cc enough to to allow me to runs 9.75:1 pistons and up somewhere near a 10.5:1 Cr.
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