Polished head! | MG Midget and Sprite Technical

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MG Midget and Sprite Technical - Polished head!

Hi All,

Yes I have little hair but I'm not losing it all... Yet!

I'm hoping someone can help me with a few pictures...

I'm in the middle of a 1500 rebuild for a friend (major bodywork done 3 years ago, bumpers removed last year, engine this winter!). We picked up a spare engine to rebuild and its turned out to be quite good! It's +40 and I've put in a -.010 crank. I've used the standard tips for the centre oilway, external head feed, uprated bottom end bolts etc but now I'm rambling....

Back to the point..

Because we have a spare head to play with and the tools required. We (I) have decided to do a little work on the spare head just for the fun of it! I've read extensively (including PB's SpeedPro book) and I'm happy with the work needed on the ports but I'm a little confused with the level of work needed in the combustion chamber.

Hopefully PB or Deb's will pop in soon and keep me striaght but until then, has anyone got a few good quality pic's of a modified 1500 head to use as a refernce?

The chamber seems quite deep and the walls quite straight (compared to my 1275 a-series 1300, but that's another story!). I'll do the maths on the CR before deciding on how much to skim to get a CR close to 9.5 but what I really need to know is how do I deal with the "wedge" on the spark plug side and do I need to slope the chamber walls a bit?

Many thanks in advance for any help and I'll give you all an update when it's up and running (soon!)

MGmike

M McAndrew

Hi Mike

I suggest you lay the wedge back by joining the combustion chamber roof to the head face in one angle rather than the standard two angles.

More important is the shape of the back of the valve, valve throat and three angle seats. Without the three angle blended seats you will be wasting your time. People tend to jump in and grind away the port and chamber (easy bits) and forget the bits that really make the head work.

Peter

P Burgess

Lol when choosing experts to read, it helps when they agree .... Or do the best of both worlds and buy a Peter head and have it machined out by Debs' machinist :)

Heads aren't something to try and save money on - so spend as much as you can - it's worth it as the shampoo ad says

rachmacb

I wouldn't have anyone mess around with one of Peter's heads :)

Bill 1

Call me Zaphod Beeblebrox :)

Peter

P Burgess

Hi Mike. Whereabouts in Lothian are you? I'm in Broxburn, currently restoring my 1275 midget. always pleased to meet fellow MG enthusiasts.

Graeme

p.s I was going to offer you a loan of Vizard's 'A' series book until i read the post properly.

graeme jackson

Peter,

Thanks for the quick response. I am planning three cut seats once the inserts are fitted and will blend these in to the throat as suggested. I'll take on board the valve back cut as well.

However, I'm still confused on the "wedge"! I just can't visualize the changes or translate the words to an image. hence my request for pic's (take me back to the 70's and a Telly Sav song!) I think it's the one and two angle thing that's confusing me.

Are you saying to remove the wedge and have one 90 deg angle from the chamber roof to the wall of the chamber similar to the other side? Or gently radius the wedge from the roof to the face ending with an angle eg 90 deg to the face?

Graeme, SQF just up the road! Always good to increase the local contacts. PM me with your details and I'll get in touch. Shell looks good BTW.

rachmcb, Bill. I know it's probably better to just buy a head from Peter but it'll cut down of the fun and challenge! If all goes paer shaped that can alwasy be the backstop....

Michael aka. MGmike

M McAndrew

Mike

this is usually my angle too

I love chance to muck about

(specially when there is always a back up available, like god old Zaphod up in Alfreton)

[that MGmike @ PH?]

Bill 1

Mike - I got one and I'm still going to fiddle - despite what Bill says, since a) it's a 1500 head, and Mr Burgess is brilliant with A-series, or MGB ones and b) it's my head and I'll do what I want with it ....!!!!

That aside, it's a darn sight better than the standard head even as it is!

People tend to forget that the basic principles of engines are the same - no matter WHAT the engine is - and Vizards book is very interesting and has many things that are really useful anyway, so, if you can borrow one - do

rachmacb

rachmacb, Mr Burgess is on the shopping list for my B series, might re read Viz and play with the A-series for the 1380 with kent 276 and belt drive. I'm not sure what I'll do with the V8 and God knows when I'll get time to transplant a 1950 into the 58 ZB which is screaming for attention ;-)

Would you be so kind as to send a couple of pic's to my personal email of the 1500 chamber, pleeeeease..... if Mr B doesn't mind.

Bill, wot you mean there's someone else out there using my nickname! Where's that copyright form. lol

M McAndrew

Hi Rach, we aint so bad with the 1500 heads either,I was paid to flow develop the casting many years back in Performance Tuning mag in the 80s when I used to be given a task of developing whatever head the Editor fancied. We also won a few championships with the work so it must be on the right lines :)

Mike, the next head we do I will send you a pic, I meant take the join away where the two angles meet so without changing where the side touches the face or the chamber roof, remove the two angles to leave one.

Peter

P Burgess

Hi Mike,

If you go to my website & scroll down to the PDF technical documents, there is a copy of the David Vizard manual on tuning Triumph engines.

Really meant for the larger 6 pot engines in the TR cars but the same principles apply as the chambers are very similar in shape and size.

http://www.tooke.org.uk/

Hope this helps.

Bob

Bob T

Hi Mike

The Soeedpro book has pictures of the chamber mods in the section re modding Spitfire/Midget heads.

Peter

P Burgess

Hi Peter,
I'm just curious whether the Vizard stuff agrees with what you would recommend?
I would assume you've had much more knowledge and practical experience since that book was written!

Bob T

Lol did I miss the bit where I said to buy one of your heads ...?

As even the MGA forum has discussed at length - racing rules are just that and the other areas are different!

rachmacb

Hi Rach what racing regs are we talking about?

Hi Bob

I have pursued slightly different paths to David. I try and keep shapes simple which seems to work well and lends itself to repeatability. My heads go out and work for their living whether for road or race. Sometimes it can be tempting when writing articles to look too hard for improvements that don't always replicate. Sometimes bhp graphs of engines jump about as more than one item is changed and trends can be difficult to see. My current philosophy tends to high CR compact chambers being more important than any flow gained by unshrouding, it has to be a compromise.

Peter

P Burgess

Peter, the pic in my copy of speedpro isn't the greatest but after further read (thanks Bob) I've got the jist of where I'm going.

Thanks to all for your inputs and when it's bedded in I'll get it set up on a RR and let you know the output (might be a while)..

till the next challenge....

MGmike

M McAndrew

Hi Mike

I will post some chamber pics later today. In the valve throat (bowl) do not undercut the long side of the throat to make a venturi as shown in some of the TR mod diagrams I have seen.

Peter

P Burgess

Standard chamber

Peter