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MG Midget and Sprite Technical - MG Metro head
| Been musing on this a while and thinking of fitting such a head to the old nail. Providing I have the proper head, what else should I consider...initial thoughts include.... Replace valve guides - do these drift out easy enough, and is it a case of carefully tapping the new ones back in with a soft mallet? Replace valve seals - easy job I would have thought. Valve springs - use the current ones - standard AFIK - any recommendations? Mention is made in various missifs on this subject re the cooling bypass. What/where is this on the head? Porting - on inlet manifold - is this necessary. I note on some of these heads it has a recessed step. Porting in combustion chamber - some have been done - sort of, some not. Vizard may assist I guess...is it necessary and does a very basic guide for the newbie exist? Manifold gasket - does this need opening up a tad? Anything else? Cheers Mark |
| Mark O |
| Ive been there and done alot of that 1st... DO NOT RESHAPE THE COMBUSTION CHAMBER unless you have a good machine shop in your garage, if this needs done let a pro do this....vizard does have a illistration for what to remove ...but its beyound the amature and you would really want a flow bench to do this correct As to porting the head as an amature...ive done it, its risky and you have to be willing to end up with a large chunk of iron as lawn art in the flower bed What you want to do, is grind down that lump metal that holds the valve guild...dont grind it like an L shape or squared off or worse a J shape, you want a nice gentle slope curve to it I dont know about the metro but on the 1319 heads there is a casting ridge a step that needs smoothing out you can feel it with your fingers by feeling around, next lightly clean the port walls floor and roof, theres alot of gritty sand casting crap in there In my personal opinion... thats it, dont go any further onless you have the training, experiance and tooling... if you need something more extreme then you need a pro A special note... before you do any grinding on this head, find an old junker 1275 head and go to town on it, learn what you need then go nuts on it and enlarge the ports, enlarge the combustion chamber pockets everything you can imagine do it, get it all out of your system that way you will have an idea of what to expect and will not have the temptation to over do it on your prized head The guilds can not be drifted out, at least not any way I know of a pro will need to do this as well as install them as this is a job of microscopic inches A crucial note because the metro has over size valves ... you MUST protect the valve seats from damage those little port grinders can get away in a flash and turn your haed into lawn decor without warning The best valve springs in my opinion are issky My best advise having done this... drop this on peter burguss door step, DHL shipping and a phone call isnt that expensive for your side of the pond The reason I say this, its time consuming and your still going to need a machine shop to finish this project, and it will be just as expensive to DIY as it will be to have peter do it, unless your on somekind of wacked out spiritial journey or live in the wilderness absent of machine shops that have never seen a 1275 engine then seriously drop a dime and call peter burguss for at least a phone converstion... the bottom line to do this DIY, you have to be perfectly fine with investing alot of time to devolop the skill, and then you have to be willing to screw up a big chunk of expensive iron that will be used a flower pot, or boat anchor, or a door stop Prop |
| Prop and the Blackhole Midget |
| Replace valve guides - do these drift out easy enough, and is it a case of carefully tapping the new ones back in with a soft mallet? only replace them if they're worn - I didn't cos mine weren't. I also didn't mod them at all either. Replace valve seals - easy job I would have thought. Yep, new ones as standard. Valve springs - use the current ones - standard AFIK - any recommendations? Std midget 1275 had double (?) springs - refit those to the 'new' head Mention is made in various missifs on this subject re the cooling bypass. What/where is this on the head? it doesn't have one - or at least, mine didn't. Get a water pump with a blanked bypass and a stat with a hole in it. Porting - on inlet manifold - is this necessary. I note on some of these heads it has a recessed step. not necessary but nice. Less impact if you're on the 1 1/4 carbs, but no harm to be done by following the Vizard book, or just a clean up rather than huge port enlargement. What's the engine spec on the rest of it? Porting in combustion chamber - some have been done - sort of, some not. Vizard may assist I guess...is it necessary and does a very basic guide for the newbie exist? smooth things, but not shiny, I took the step out at the inlet face and matched the inlets to the manifold. In the combustion chamber, take out the little step that lives round the valve seats (don't hit the seats) and smooth it back into the wall of the chamber, don't change the outer shape of it too much. Manifold gasket - does this need opening up a tad? nope should be fine Anything else? Go for it, if you're careful and take your time you'll be OK. Buy the Vizard book. Don't get one to practice on, just do it right the first time, as after you've done one, the inclination to do more is somewhat lessened.. |
| Rob Armstrong |
| >>Mention is made in various missifs on this subject re the cooling bypass. What/where is this on the head?<< a 1/2" rubber hose about 2.5" long, sometimes a concertina type, goes from bottom of cylinder head to water pump do bear in mind that what's good for track use isn't always good for road use |
| Nigel Atkins |
| Valves guides are not a simple job. Yes, drifting the old ones isn't too difficult, but fitting new ones, reaming them and re-cutting the valve seats is beyond most amateurs. |
| Dave O'Neill 2 |
| The Metro head has no bypass facility. Hence the Metro water pump has no outlet for it either. You'll need GWP154 or GWP187 / QH QCP3710. The step in the inlet tract on some heads is for the manifold locating rings, all Spridgets have them, I don't know about Metros. Valve guides should be done with a stepped drift and a press. If you open up the inlet ports you also need to match and open up the manifold, and then you will probably need the competition manifold gasket (Minispares CAHT381). |
| David Smith |
| There is no by-pass stub/hose on the MG Metro head, as already noted by Rob. A-series water pumps without the by-pass stub are easy to find on eBay, MiniSpares etc. I didn't bother drilling holes in the 'stat - no cooling issues whatsoever over 12k miles. Just (not) visible top right of the pic.  |
| Steve Clark |
| Beaten to it by Smiffy. |
| Steve Clark |
| I've replaced valve guides on a number of occasions and found it an easy job but I had access to a press which is better than hammering them in, also a lathe is useful to make the push piece so you don't press directly on the guide and a spacer so the guide height is correct. When the OE iron guides were available, maybe they still are, I never found the need to ream them after fitting but maybe things have changed. With regards re-cutting the valve seats, if you have access to a lathe, angle grinder, files, and a suitable torch then making a 3 angle valve seat cutter set is not a difficult job. I made various sizes some years back and they have been used to recut the seats in a number of A series heads and a FIAT twin cam. As regards porting a head, I've done it according to Vizard and got good results but would warn against using the usual stubby die grinder as they can run away and damage things too easily, an extended length die grinder is a much better choice as you have the extra leverage to keep it under control. |
| David Billington |
| Rob said.... Go for it, if you're careful and take your time you'll be OK. Buy the Vizard book. (((Don't get one to practice on, just do it right the first time,))) as after you've done one, the inclination to do more is somewhat lessened.. Sure... what can go wrong... its just like doing heart surgery on your dog, or dismantling an ISIS terrorist bomb at your childs school Hahaha ... sorry rob, I got to disagree, but I see the classic match up here like tyson and holyfield, tyson just goes for it and beats his opponent into submission, holyfield is thinking and stratagieing all the time and looking for the perfect punch to throw. Sadly, tyson for got to eat supper and just had a nibble of holyfields ear as a snack...haha For me... I might think about my next 5 sec grind for 5 hours before I ever turned on the die grinder, and I always tested the grind on an old junker head, the real benifit, there was no on the fly mods, everything was thought out well before hand, all possiable problem areas planned for and compensated for. But thats how I self tought myself how to port heads Anyway...im not making fun of you, i just find it interesting how 2 opposites get to the same place I do have to admite... I love the deepth and focus of precision needed to do cly head work...its hypnotic and you can really get into a trance state ... i just love that zone of being, its spiritial and intoxicating at the same time... in yoga I guess thats what the call zen Machining to perfection, is just spiritual for some reason, Prop |
| Prop and the Blackhole Midget |
| different strokes for different folks Prop ;) I did mine in my student room at uni over about 8 weeks. Then popped it on the car and all was fine. Not unplanned, but just done right first time :p car eventually was rolling roaded with 75bhp and 88lbft of torque. So I must have done something right.. |
| Rob Armstrong |
| Gents My thanks for this, especially to Rob - very useful stuff. The head I purchased - for a tad more than I wanted to pay from Fleabay - is what looks like a Metro head from a 1380 Mini - Blue painted. Appears to be in good nick and has been worked on somewhat. Cannot see the water bypass, so I assume it does not have one - I thus assume, no cooling mods necessary and plumb in as per old head - which for me is just refit the thermostat housing and the brass heater take off valve. As an aside, if it did have the bypass, can it not simply be blanked off? Look forward to doing the minor porting mods as per Rob/Vizard, and a satisfying upwards lift of the mouth after fitting it. Mark |
| Mark O |
| mark., Rob mentions 1 1/4 carbs. I'm going to stick my neck out and recommend going to a single 1 3/4 Hif44. Since fitting one to mine, I couldn't contemplate going back to the twin HS2s. Setting up is so much easier and the car feels a lot swifter - there's no low revs stuttering despite running a piper 270 cam and high lift rockers - and the engine now revs very freely up to max power. I've gone with a maniflow manifold which is quite an improvement over the standard mini / metro one. |
| graeme jackson |
| Graeme HIF 44 already fitted for the resons you state - good improvement especially from low down. Yes, I am tempted by the Maniflow exhaust manifold mated to an RC40 single exhaust - as per Magic Midget web site. All of which will be mated up with my new shiny blue head! Cheers Mark |
| Mark O |
| something also to consider is your compression ratio With the head blue printed then you will have the stat math for it .... you might be able to run one of your cly to TDC and brunnel measure it to find the total cc volume to comput the compression ratio If the compression ratio is to far in the extremes you can get a custom made head gasket from ( cometic ) in any thickiness you need Prop |
| Prop and the Blackhole Midget |
| If this head was already riding on top of a 1380, id say there is a good high chance that the mods have already been carried out, id definatly make a play for the carb and intake to go with it...this could be a plug and play modification I would also go with arp hardware...no pount getting cheap now Prop |
| Prop and the Blackhole Midget |
This thread was discussed between 22/09/2014 and 23/09/2014
MG Midget and Sprite Technical index
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.