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MG Midget and Sprite Technical - Head Job
|Some advice please! I'm no engineer but trying to learn|
I've finally got round to cleaning up my MG Metro (big inlet valve) head that I acquired a good few months ago with the aim of achieving some cheap, easy bolt-on power, along with a hif44 to my otherwise fairly standard engine. The existing block is a gold seal unit and according to the engine numbers I think it may have a +20 overbore but I've not taken the head off to check and don't really want to until I'm reasonably ready with the new one on the basis that I'd probably bugger it up!
The Metro head was very coked up and the water galleries are pretty rusty. The face looks pretty clean and flat but I presume I need to get this machined to raise the compression ratio a little. On stripping the valves out last night I also discovered that no 3 exhaust is bent like a banana, presumably why this head is no longer with its original block! The valve guide was cracked and extracting the bent valve has now broken it.
All the remaining valves were pretty coked up and I've managed to clean these fairly successfully and they appear straight. The chambers however are still black and cruddy. Any tips for cleaning these out and also shifting the corrosion in the water galleries?
So, as I see it, I need a new exhaust valve, some outside machining to reface the head and remove and press in the valve guide, the valves lapping at best, new seats cut at worst and a good clean up and paint. Anything I've overlooked?
I don't want to spend hundreds on this!
Is it worth it?
|it's always worth it. You need the basic data about your current block (bore) & pistons, and decide what CR you are aiming for, then you'll be able to work out how much to have the head skimmed by. A hot caustic tank treatment will clear the waterways; spec up the work and get a quote from somewhere like Classic & Modern in Bracknell. Do you know any other good machine shops in your neck of the woods?|
|Some new valve guides and valves aren't that expensive? (IMHO) Try minispares.|
|Alex G Matla|
|you have already gone to the effort of finding a better head, and better carb and sound more competent than you suggest (have faith its not an f1 engine). . . if it were mine i would replace all the guides, just to ensure that all is well, Alex is correct the guides are not expensive, and whilst i dont have a casual disregard to money and understand everything has a price i would get the lot done. Skimming is essential, and the advice to work back from your desired CR is sound as is the hot caustic treatment. . .|
|It's a dilemma faced by anyone on a tight budget and one I've often been, and sometimes still am, familiar with. |
Doing the bare minimum will be ok but the alternatives are to save up (or sell something) and buy a brand new head with the same or bigger valves or spend more money on the Metro head you have.
If you can find a machine shop or chum that will assist with your project as a 'tea break' job it will be worth it.
|Worse case.... Deliver pizza for a month or so, or rake leaves and clean gutters with fall just Round the corner, if your going to do this then go all in, otherwise i find just doing a partial just a waste...just my opunion|
|Prop and the Blackhole Midget|
|As said guides are not that expensive and prevent a smokey engine. |
Take a look at Keith Calver's page about what can easly be achieved with head work.
Iirc the biggest single gain was a simple backcut on the valves and 3 angel valve seats.
Having this done on your head with a slight increase in CR should have a nice effect.
As for cleaning it.
Stick it in the dishwasher
|dishwasher it as Onno says. It works really rather well, especially if cleaned with gunk or similar first.|
Valve guides are easy with the right diameter drift, and checking the head for flatness is also not hard if you have a metal edge and feeler gauges. Skimming is not a necessity if the head's flat and in OK condition.
Get some grinding bits and spend a week or so of evenings sorting out the combustion chambers & ports. I did and it made a huge difference to the engine (same big-valve MG metro head), which I didn't skim.
a pic lives here:
|If you are going to dishwasher it make sure the wife/710/g/f is well out of the way first....don't ask me how i know to do that..|
Do you have an LCB? I know adding bits is a threat to the budget, but the potential of the head improvements & HIF44 is limited by the standard exhaust manifold.
Many thanks for all your words of encouragement and advice.
It sounds like the first job is to bung it in the dishwasher! (does washing oily engine bits leave a nasty residue in the machine likely to be noticed by those who care?)
I have a copy of Vizard but don't pretend to understand half of what he says and I'm not entirely convinced he's the guru some would have us believe. I feel on balance that I won't go as far as trying to modify the head myself as I could turn into another Prop and one of those is enough!
I just need to find a local machinist to quote for pressing a new valve guide in and possibly skimming the head and I should be OK from there assuming the seats are OK. If I can get all that lined up, the plan would be to whip the existing head off one weekend this winter when the weather's horrible so I can have a look at the bores and get my calculator out and a lot of headscratching to work out the CR and how much if anything needs to come off. Alternatively like a lot of my projects it will probably get so far and then sit gathering dust......
Rob, I noticed on your website that you said your MG Metro head came with double springs and rimflow valves. Mine has neither. Are either or both a good thing?
Paul, Thanks for the comments. Fortunately I do have a LCB and decent exhaust already on the car.
Prop, I've already got a well paid job that occupies too much of my time without having to seek extra work. The problem is I have three high maintenance women (and a cat) at home who all seem to be of the belief that they come higher up the pecking order than the Midget and indeed me when it comes to the allocation of precious resources. If I earned more by getting another job it would just go on more cushions, candles, staircarpets, food, washing powder and other inessentials! You have no such excuse. Get your car fixed!
The dishwasher could use a spin with some cleaner afterwards.
Vizard is good, do try to understand it fully.
He is no guru just some one with a lot of knowledge about internal combustion engine's who has put in the time to systematically check and write down a lot about our little engine.
His latest book is not the most up to date but the laws of physics have not changed so most is perfectly usable.
And as Paul mentioned the inlet and exhaust trace should be able to cope with any improvements
|double springs reduce valve bounce at higher rpm. Not sure of the benefit on a road engine if I'm honest. But it has them so I fitted them. Cooper 'S' engine had them too.|
The rimflow anti reversal valve (think it's in Vizard) was designed to try and stop flow reversal in the ports, and worked pretty well. K series valves are built the same shape underneath. Supposed to be worth a few horsies maybe.
My A went from 64 to 75 bhp with ported head, twin 1 1/2 carbs off a 1979 MGB (needles correct!) and an LCB with RC40. 88 torques as well (done on Minimania rolling road in Penrith, ages ago) Made a much more enjoyable engine, it's in dad's midget now, currently chewing it's way through it's 3rd gearbox.
|Best part of Vizard is that if you pay attention, you can get an awful lot for very little. Years ago (1976 dollars), I did, and with my $150 worth of junkyard Austin America bits was able to trounce a Mini with a $3500 engine, a Saab V4 that cost $6500 to build, a Volvo B18 and a 510 Datsun both over 2L and running Webers, alcohol, etc - in a class that was supposed to be "as stock".|
No offence was ever intended on the income front...you wouldnt belive the crazy stuff ive done for extra cash... Sadly ive found a universial normal... Yiu spend what you make wheather its 250xxx a year or minimum wage... 3 women, ouch, good news is i bet you smell better then everyone else here on the forum...hahaha
As to vizard... He covers a wide range... I certianly would never attempt to do the chamber reshape, even with his technical design measurements.. for that id talk to peter burguss
BUT... Id highly recommend dia grinding the metal blob that holds the valve guild... Just remember you want an arching swipe not an 90 degree angle... And sanding all the sand casting crap off the port walls... Dont enlarge them... Just clean them up and polish the exhaust port and keep the intake port like sand paper
Thats stuff you can do by your self that is huge performance
Yeah im still procrastinating on my project as i keep poping head gaskets...with this next attempt... Ive got a feeling ill be transfering the problem further into the engine and start popping pistons... Instead of head gaskets
So will see... But yeah... I do need to get back on it soon enough... Thank you for the encouragement....esp now that the weather is more tolerable
But yeah... Give the work i mentioned above some thought, id certianly encourage anyone to give it a try..it just sounds harder then it appears
|Prop and the Blackhole Midget|
|Thanks for the encouragement one and all. I was just teasing you Prop!|
Maybe I should have a go with a grinder just for fun. Is a Dremel powerful enough to cope?
|Dremel a bit slow, but how is your patience quota?|
My wife did a 948 head with a copy of a Speedwell catalogue and files and sandpaper.
|did mine with a cheap electric drill with some grinding stones. Slow, but it worked.|
Here is what i use....its china made so you should be able to get one at your machine mart
Before you do this with your head ... Get an old 4 banger trash gead from the salvage yard to practice on first...that way you get a feel for how to work it....also i got a screen door spring and tied it to the back of the grinder and attach it up high so the grinder is about 2 inches over the cly head... That way it makes it more easy to manuver... I use duck take on the head surface to protect it from the grinder getting loosei
|Prop and the Blackhole Midget|
|Sorry ... Thats duck tape....and no the dremil is to small and not powerful enough|
|Prop and the Blackhole Midget|
This thread was discussed between 29/08/2012 and 08/09/2012
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.