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MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - 12G295 head

I have decided to sort out my 5 spare cylinder heads. Well 4 in reality, as one is cracked. Of the remaining 4, 3 are ordinary 948 heads and one is a 12G295 from a long defunct 1098 engine. I have been trying to follow Vizard's recipe for a road 998, which uses this head, with 1 1/4" inlet valves and 1 1/16" exhausts. The problem is, where to get the valves? Admittedly Vizard was writing nearly 40 years ago and the choice is likely to be a lot less now. I haven't been able to track them down.

So I am wondering whether to use standard inlet valves, which are less than 1mm smaller. 1275 valves are too big for the chamber, or has anyone tried that? Standard small bore exhaust valves are 1" (25.4mm), but I see that CAEG587 are quoted by Somerford Mini at 26.5mm which is a small increase. These are competition valves and very expensive at 23 each! The next size up for 1275 heads is 29mm which is too big.

I could use Rimflo valves but I'm not convinced they are worth the small increase in power. Any thoughts?

Les
L B Rose

You could try Paul Ivey/G&S Valves

http://www.gsvalves.co.uk/race-engine-components.html

Which pistons are you using? The 998 Cooper used a domed piston with the 295 head. Even with flat-top pistons, you'll still need to take some off the head.

The chambers are very large.
Dave O'Neill 2

I get a bit of stuff from Englishparts.com in the US

Had a look and found these, there are probably other sizes if you search through their listings
If you go to order off them ,give them an email and they'll get better postage for you
I usually just get them to do a small parcel through US postal,and just take the punt on insurance, cheap as chips --If you pay with Paypal it's insured through there anyway


VALVE, Exhaust, 1.156″ head.
Part Number: CAM4601
Price
$7.16

INTAKE VALVE,
Part Number: 432-190.
1.313"
$6.26

Cheers
willy
William Revit

The 12g 295 head has a 28.2cc capacity compared with the standard 948 one of 24.5cc. if the head is not skimmed flat top pistons will give a CR around the same as a standard 1275 engine of about 8.8.
Bob Beaumont

Thanks Dave, I would normally use flat tops and certainly do expect to take a fair bit off the head. I prefer flat tops so I can flush the pistons to the deck. The engine has a Metro head on it at present, with 10.5:1 CR.

Thanks Willy, very useful. Not the first time I have had to go to USA for British parts. These valves are a bit bigger than what I want. Do you have experience of using them in this head? Or does anyone else?

Les
L B Rose

Hi Les, we run the standard valve sizes on 295 heads.
The ex valve is 82% of inlet valve. In theory one only needs 68% of in valve to achieve full ex flow, this would be a 21mm ex valve! our full race 1950 B runs 72% ex to in ratio and still works fine. We tested this by introducing a longer duration and lift ex cam profile , even though we had increased the valve time area of the ex we gained no bhp, in fact we lost some lower rpm torque.
The inlet throat is crap on the 295, it has a 1mm 45 degree seat straight into the throat. To gain a bottom cut to increase flow we fit inlet inserts with a smaller ID than the original throat so we can reshape and improve the valve throats.

On full race engines we have run 1275 valves, work well but beware ex valves hitting block :)
Peter Burgess Tuning

Thanks Peter, that's the advice I need. A pity you are a long way from Salisbury or I would drop the head in for some work.

Les
L B Rose

Send it by courier. It's not so big and heavy that it can't be done. When I had my V8 heads worked by Peter he sent them back to me as I'm over 300 miles from Alfreton. You are actually much nearer to PB than I am - just a day trip.
Mike Howlett

LB.Rose. Be careful how much you take off the 12G295 head. The oil gallery runs quite close to the head face.

Bernie.
b higginson

I sent my full head (just under 15kg including packaging) up to Peter this week. It was delivered 12 hours after collection. On Peter's recommendation I used DHL via Parcel2go.com.
G Lazarus

Bernie makes a good point.

It's not uncommon to break into the rocker feed oilway when skimming the head.

Vizard does cover this.

I had a couple of heads on my A35 which had the oilway brazed up and rerouted up the stud hole.

This one's a 12A185


Dave O'Neill 2

We always check how much we can skim off before we start work, that avoids disappointment and costly mods to feed via head stud hole, usually only done on full race heads. As was mentioned, the 295s are more awkward as they are large cc heads to start with and the first mill off the head only gets rid of approx 3cc!
Peter Burgess Tuning

Les / Peter
The valves from Englishparts I put up earlier were just a sample of what's available from them, they have Rimflow etc as well
They were the closest size I could see with a quick look to match what Les asked for
I've had another look and found those listed below which might be more suitable
There's always the choice of getting slightly larger than what you need and spinning them down to the required size if what you want isn't available
Anyway, it's not much use me crapping on from the other side of the world, I expect there are valves to suit what you need in the UK,and Peter to advise you-
It's just that I've always found these guys can come up with the goods
Cheers
willy
--------------

Intake Valve, 1.215 inch diameter, AE brand
Part Number: V34167
Supersession(s): RV34167; CV34167
1/4″ Groove in shaft.


INTAKE VALVE 1.156 IN HEAD DIAMETER, STEM A
CV3568
Part Number: CV3568
Supersession(s): 423-175; RV3568
VALVE, Intake, 1.156″ (29.4mm) head, 1/4″ Groove in shaft.
$5.30


VALVE, EXHAUST VALVE, 1.00 IN HEAD DIAMETER, STEM A
Part Number: V3569X
Supersession(s): 423-320; AHU1049; V3569; AEA400
1/4″ Groove in shaft.
$5.84

STAINLESS EXHAUST

Valve Exhaust 25.4mm 948 1098
Part Number: V3569
This is a 214N Stainless exhaust valve for a 948 and 1098 A-Series
$6.80














William Revit

Yes I'm well aware of the oilway issue.

Thanks Willy - I think I might settle for ordinary 1098 valves as Peter suggests.

On a related matter, I will want to use unleaded fuel. I am getting eye-watering quotes for fitting 4 hardened valve seats - from one engineer £175 + VAT and from another £300! Are these typical costs?

Les
L B Rose

Les
When I was rebuilding a 1275 to put in the Frogeye (not on the road yet...) I spoke to a long establshed local engine rebuilder, who did some of the work, and he insisted it didn't matter about hardened exhaust seats so I didn't bother. He'd been rebuilding A series engines since Adam was a lad and I trusted him. Was he wrong?
Bill Bretherton

I recall some testing group tested a number of heads for the effects of running unleaded fuel and the A series was found to suffer the worst valve seat recession.
David Billington

Hi Les
It is difficult to say how much the work should cost. A cheapy job with only fitting 4 ex seats and cutting ex seats and in seats is 80, you then have to think, should you have new guides, new valves new springs, chemically clean and grit blast the head, skim the head, thoroughly clean and repaint/assemble? We charge 235 plus vat for a fully reconditioned head.

Bill, sounds like a bad move, but you can put in inserts at a later date. We have seen A series and TR4s destroy ex seats rapidly running on cast iron seats. David is spot on about A series suffering if not converted to lead free. If you have an old head that has had a good life running on leaded fuel, as long as you do not lap the valve seats ever again, you should be ok running leadfree as the seat has been protected by all the years on leaded fuel...known colloquially as a 'lead memory'
Peter Burgess Tuning

David, Peter
Oh dear, I seem to have taken the wrong advice then! I've read about the "lead memory" so maybe that will help a bit plus I won't be doing a big mileage so maybe it will see me out!
Bill Bretherton

I forgot to mention earlier that apparently it is RPM related, if you potter about you may be OK whereas if you thrash the engine hard you'll more likely suffer valve seat recession. Likely down to the higher impact of the valve hitting the seat harder due to higher acceleration/deceleration at higher RPM leading to more micro welding of the valve and seat. IIRC below 3k - 4k RPM it may be small but above that it increases significantly, likely varies with such things as cam choice, more details likely in the archives.
David Billington

Bill,
You can always use an additive such as Castrol Valvemaster especially with low mileage.
Thats what my cousin has done with his 'B' - he does a low mileage and when ? the head is next off we will have inserts fitted then.

R.
richard b

David, I've trawled the archives and, to an extent, the jury was still out! Standard cam as is rest of engine.
Richard, thanks, I've thought to use an additive now and then.
Les, I didn't mean to hijack your thread but maybe the information is useful for you too.
Bill Bretherton

Bill,
if low mileage is in short journeys then this will have some effect on the rest of your engine too, so appropriate oil protection too (whatever is consider or believe that to be required, another debated subject).

As an alternative to MGOC owned (look it up) Castol Valvemaster and more specifically Valvemaster Plus you could also look at Millers VSPe Power Plus (multishot) which covers -
"An ALL IN ONE petrol fuel treatment providing ethanol protection, lead replacement and an octane improver dependent on selected fuel quality."

As I worked out for a MGB poster that the Millers cost 6p per litre to use and my wife told me I pay 12p a litre more for my Tesco 99 I thought I'd give the Millers a go, bought a bottle but not been able to start using yet. It's available at my local "car bits" shop so I'm able to get it there and support them.

Millers VSPe Plus - http://www.millersoils.co.uk/products/0/624

Valvemaster - https://classicvalvemaster.co.uk/products
Nigel Atkins

I always went with the idea that even though valve seat recession would eventually occur there wasn't much logic in having new seats fitted until the old ones had become eroded. On that basis I continued to run my 1275 without getting them replaced, and without bothering with any of the " snake oil" additives.

The plan was to monitor, and get new seats fitted when they were needed. But after around 35,000 miles I replaced the head with an MG metro one (with hardened seats) 'though there was still little evidence of deterioration of the seats or valves on the old head.
GuyW

Nigel, thanks for the information. Maybe I'll use additive from time to time.

Guy,interesting, your experience seems similar to some people in the archives. It must depend, partly, on how much lead has been retained.
Bill Bretherton

I remember the general view being as David has put, that if you're going to be taking it reasonably steady (in a Spridget?) then the 'lead memory' would probably see you through until you need to do other engine or head work.

I think 'snake oil' is a bit harsh on these products, both of which now cover the lucrative ethanol fears and bear in mind the gentle old folk of FBHVC endorse both products, mind they'd probably be a group most fearful of the likes of ethanol. - https://www.fbhvc.co.uk/fuels

There are 'snake oil' products for vehicles (many more so for heath and "beauty") but without the benefit of real world long term useage or testing that only the likes of the oil companies could afford then to a certain extent as with many things in life it's a matter of your belief or the extent of your belief, as long as it does no harm and makes you happy why not go with your belief, or question or change your belief if you want to or can be bothered.

Nigel Atkins

b*gger missed the edit again (forgot her name)

As Joan Armatrading sang, .... I'm open to persuasion.
Nigel Atkins

So I dont like to contradict PB because he is a very knowledgable and professional guy but...

Did 10000km+ per year in the midget for several years when she was my daily without hardened seats and never noticed any valve seat wear, never used any lead replacement and did re lap the seats early in my ownership.
Have just bought an MG Metro from 1989 with 130000km on the clock (verified) that according to the paperwork has always used either unleaded or lead replacement, you guessed it worst valve seat recession Ive ever seen

So I might have been (un)lucky but I generally believe as long as the seats are fine you are better off with no hardend seats for the limited milage most midgets do.
With castings becoming limited you can only remove metal from a casting once.



O K

Nigel 'snake oil' was intended as bait.

But the point remains, I have never found a need to spend extra money on any additives, tested, endorsed or othrrwise. It's not a question of being closed to the idea, it's simply that I haven't found it necessary.
GuyW

😲
Good grief Onno, I've never seen it like that. What else is wrecked? Rockers? Camshaft? Followers?
Greybeard

I've had several Ford Courier utes just like that with around 80-90000klm on them
You just don't know until they start missfiring
The Couriers have hydraulic lash adjusters which just follow the wear and it's not until the lifter runs out of travel that the engine starts to misfire
There is probably a slow decline in performance that creeps in as the head sinks into the seat but really they go quite well until it gets bad enough for the travel of the lifter to be bottomed out causing the missfire
The valve seats you get now are a whole lot better material than what they had then
William Revit

Onno
I cannot explain why you did not have a problem, have you inspected the seats lately?
The picture you posted is typical of what we see on a very regular basis.
Peter Burgess Tuning

Just had a thought Onno, could it be you already have leadfree inserts in your cylinder head?
We have been producing leadfree head since 1987 as have many other machine shops so there are quite a few about.
Peter Burgess Tuning

Had the head of recently and still looked good guess I am just lucky.
As for the metro head afaik that SHOULD have inserts being late 80s yet that was wrecked.

Ive never had good luck with putting in hardend seats for the 2nd time, any trick to it?
O K

I have not seen high quality ex seats wear out. In the event of physical damage we take them out and if the counterbore is good we fit a new insert. We make a larger OD insert if needed or recut the hole a few thou and make larger OD inserts.
Not all Metro heads were leadfree even when they were meant to be. Also folk swap heads from engine to engine so it may be an early one. Some of the leadfree ones shed inserts as they were rather shallow in depth, that may also depend on engine problems allowing the head to overheat.
How do you know your original head does not have inserts in?
I once had to take an ex insert out of a modified B head to prove we had fitted inserts, talk about a Doubting Thomas! The customer could not see the very slight difference in colour of the cast iron to the insert. When we have finished the heads, before they are washed we can see fine dust collect on the interface between the insert and head in the chamber.
Peter Burgess Tuning

Just catching up with all this, and very happy for my thread to be hijacked! Yes Peter the head will have new valves and guides, and anything else required. I was quoted 300 + VAT for just 4 exhaust seats, not including anything else. I was expecting more like the 80 you suggested. I am quite concerned that the job is done well because years ago I bought an A Plus head from a well known (at the time) A series tuner and one of the inserts rotated when recut. Why it had to be recut is another story, involving a broken valve etc.

So I think the decision is, if I can't get hardened inserts done for under 100 I will go with an additive.

Les
L B Rose

the head in my midget is a very early 12G940 with the flat machined top.
Never found any trace of inserts in that one and the valves are to close together to fit seats imo

The metro one seemed to be the original one (rather stuck) and the paperwork shows no evidence of headwork.
Lets be clear here the wear in the metro head seems totaly expected after 130000km.

Point is I would expect a head without inserts to survive 40000km without hardend seats as that is what they seem to do for me easily
But I could just be lucky
O K

I would go to the very lucky end of the spectrum Onno :)
The factory fitted Metro and A series exhaust seats will not wear in use. They might fall out or get batter damage of some kind but I have never seen them wear.
Another point is it is not a matter of 'hardened' seats. The material just has to be leadfree compatible ie does not allow the valve to microweld to the valve seat material in operation.
Peter Burgess Tuning

Well in a few weeks Ill pull the head of my 1932 MG D type midget after the race season and see what those valves have done.
It only gets thrashed with no hardend seats and unleaded fuel.
See how lucky I am ;)
O K

How many miles/hours has that done Onno and what sort of bhp/litre? We can see interesting effects after 30 minutes flat out in the endurance race FIA Bs with the higher % ethanols we are now using in the UK
Peter Burgess Tuning

850cc with 60bhp supercharged about 6h of race conditions.
6500-7000rpm max. Non crossflow head with to big chambers (or to small blower ;) ) giving just 7pounds of boost
Am running fuel with max 5% renewables.
O K

Onno, I have run unleaded seats in my B for 30+years despite the valves nearly touching each other (1.75" inlet, 1.44" exhaust). Originally done from necesssity to reclaim pocketed inlet seats, how we did it was to overlap the inserts: fit the inlet seat first, then cut the exhaust seat into it (about 20 thou I think). Just having the one valve inserted risked cracking it at the thin point. This way, there is nothing to crack and therefore no risk of the crack extending downwards into the valve throats. It has been 100% successful for 30+ years of agressive competition use.

A couple of other observations about unleaded heads:

Engineering workshops that are not specifically set up for the work will need to price as a one-off, and such jobs always gobble up time. Someone like Peter B who does it more frequently will always be more efficient.
This would probably explain the cost differences, unless they just quoted high because they didn't want the job ... which also happens.

I have found seat inserts a real plus for protecting the head in the event of a burnt valve. Without an insert, if a valave burns badly (leaving that classic big Vee notch) it's odds-on the head will be cracked under it. With an unleaded seat in there, the valve seat is hardly affected,let alone cracked.
Paul Walbran

Sounds like a good un, shame you aren't nearer so we could dyno it with you.
To add to what you say Paul, we do not have many heads at all that come in that would not sink the ex seats if we recut them, they all benefit from restoring the seat height with ex inserts.
Peter Burgess Tuning

Interesting to hear Paul.
Have not had luck with seats close let alone through each other but it seems I might have not used the right machine shop.

Peter It goes quite well ;)
Most of my racing is in the UK so who knows when I have something interesting to test I might be able to drop in.
Though this winter is suspension optimisation and just a quick check of the engine.
O K

Is the SU carb one of those brass bodied ones?
Peter Burgess Tuning

Peter,

As someone that does a fair bit of machining what is the process for fitting valve seat inserts, what sort of tolerances are required for the seat bore and are they shrunk(cooled) before fitting. I think this may vary between CI and aluminium heads as years ago the late Terry Sanger told me about the trick process of fitting the seat inserts into the Jack Knight twin cam head which IIRC relied on the ductility of aluminium to retain the inserts which may not work with CI.
David Billington

Hi David

My understanding has always been about 5 thou on an ally head and 4 thou on a CI head, in practice the seats are cut the same as most cutters are fixed. If I use my adjustable seat cutter for one off or odd sizes I do use 4 for CI and 5 for ally. On ally we use an adhesive which is intended to lubricate the fit, glue it in and aid heat removal.
https://www.cylinderheadsupply.com/kl1378.html
We use a drift and pilot to fit the inserts. We did try heating a head and using liquid nitrogen once as an experiment but not happy with the instant icing on the CI head around and in the valve seat counterbore.
Our seat inserting centre is made by IDL and the drift system is what it came with. It has been ok for 30 years. I must say I do not like ally ones being any tighter as I get the horrible feeling that with heat the inserts may be 'squeezed' out
Peter Burgess Tuning

Peter,

Quite a heavy interference fit then from those numbers. Good to know that with that adhesive the seats will still be held in place when the head around them is a molten puddle ;) .
David Billington

Some webpages seem to say up to 11 thou fit for ally which seems terrible to me.
Can't accuse me of being old fashioned when I use space age ( Sputnik 1957!) gluey things :)
Peter Burgess Tuning

Shh Peter
Ive sneaked through the rules using a single MGA H4 carb.
The original brass one I had was to small (1) and the price of a proper HV5 was prohibitive.
Now dont start asking about the ignition as that is a Bosch beetle unit because it was cheaper than rebuilding the lucas without advance mechanics ;)
O K

Just wondering, many years ago we got a generous increase by radiusing the entrance to the brass carb. It looked good too being brass. That was on methanol
Peter Burgess Tuning

Saving the switch to methanol to when I can afford a blower that goes up to 18psi.
The carb has a nice big radius sub stack from MED made a little thinner to account for the proximity of the chassis rails
O K

This thread was discussed between 22/11/2019 and 05/12/2019

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.