Valve job on 12G295

[David W.]

What engine does the 12G295 head come from? It's not from the 948 I have in the car. I'll need to order parts accordingly.

[IslipMinor]

Mini Cooper 998 and Sprite/Midget 1098. The best 'small valve' A Series head there is, BUT the combustion chambers are very large as the pistons that go with it as standard have a raised 'D' section, whereas normally there is a dish in the piston.

What is the spec of the engine you have? What pistons etc.?

[bmcecosse]

And also the MG 1100. However - I'm not aware (it's possible - I'm just not aware..) of any 'raised D' pistons for the 1098 engines - do you know otherwise Richard?? The exhaust valves are same as the 948 head - the inlet valves are larger (1.25" head) - and very hard to get now as standard parts. Some specialists may be able to supply - but possibly they will need different caps and cotters to match a different groove in the valve stem. And best to fit guides with the location groove for the 'top hat' oil seals. And yes - the 28.4 cc combustion chamber means heavy skimming required to use on a standard engine. However if you bore out (+65 thou on std) and use std Mini 998 flat top pistons (and matching rods) - you will have a 998 engine and the skimming for the head will be a lot less. Always worth checking if the head has already been skimmed - many have...... The standard thickness is 2.750". Any less means it has been skimmed.

[David W.]

There's a lot of info there.
I have .020 over dished pistons. I bought the car from a "Bug-Eye" guy who says he put an Austin engine in it.
I still have the 2.750 in thickness, and have not decided if and how much to skim. The power is adequate, it's not a racer.

[bmcecosse]

Without skimming - the comp ratio will be miserable. I would take 80 thou off it.......

[IslipMinor]

any 'raised D' pistons for the 1098 engines

Not as far as I am aware - should have made it clear that the comment was about the 998 Mini Cooper only.

[bmcecosse]

Which is why I have sometimes wondered how they got the comp ratio on the Spridget/MG (and Riley) 1100 engines. Perhaps very shallow dish pistons? Not flat top as far as I know. Or did they skim the head? I don't think so.....but??

[daveyl]

As you surmise BMC. Riley/MG/Wolseley have a smaller dish, 2.46cc and less. Well, according to the 'Morris minor modification manual, pg45'.

[bmcecosse]

Ahh thanks - I'm not aware of the Modification Manual you mention........is it available to read online?

[Declan_Burns]

PM sent
Regards
Declan

[IslipMinor]

Declan,

Is that a link to the 'Modification Manual'? If so can you send it to me too please?

[Declan_Burns]

Richard,
No it's not a link-send me your email address.
Regards
Declan

[KalKat]

I know that with Minis, if you have flat top pistons in a 998 engine, the theoretical skim is 52 thou

[bmcecosse]

Such precision! It depends on the work done within the combustion chamber, and if the exhaust valves have been sunk (either intentionally or be recession) - and the desired final compression ratio.

[David W.]

Here’s the place I find myself now.
Not knowing what I had (12G295) I ordered valves for the 948. They dropped right through the seats of the 295 head. Oh well, the original valves didn’t look so bad, I’ll use them.
My machine shop called and asked if I can find wider intake valves. If he grinds the seats, there’s little left on the valve to mate.
I got 1.313 wide face valves from Moss USA. I guess they are for the 1275 engine. I had to turn around and get different keepers and seals also.
After all the valves are installed, the intakes stand a bit taller (.150) than the exhaust. And, I don’t have enough adjustment on the rockers to compensate.
Can I get shorter pushrods? Mine measure 8+7/16 inch.
Can I grind a bit from the valve stem? And/or can I grind a bit from the face of the tappet?
How much can be ground from either without going through the hard part?

[bmcecosse]

I wouldn't do ANY of these things. The valves are too long for a 295 head and that is too much to grind off the stems. Anything you do there will seriously alter the rocker geometry. You should ask on here before making changes !! You will also need different valve caps if you do go ahead with these valves - the 'keepers' (we call them cotters) are very different and require matching caps..... you may seriously risk dropping a valve if you use the old caps. What was so wrong with the original inlet valves (1.25" diameter) ? Ideally you only want a very thin seat - so why were they worrying about cutting seats?? I suppose if you are desperate you could put spacers under the rocker pillars to lift the whole assembly enough to get the adjustments - but then you will compromise the exhaust valve rockers. Maybe you could get away with 50 thou spacers?? But make SURE you allow for the oil flow into the rocker shaft - so make sure the spacers (if you go that route) have an oil hole to match the delivery port in the head. Good luck! A 940 head (ex 1275 engine) would be SO much less trouble, and SO much better for power too!

[David W.]

We have a phrase over here in Florida...When you're up to your a** in alligators, it's hard to remember that you came to drain the swamp.
I’m having trouble remembering why I took the head off in the first place.
Here are some pix of the original valves in the newly ground seats. If there seems to be enough contact, I’ll reinstall them while I try to sort things out.
Can I have new seats installed and start over again?
[frame][/frame]
Original valve in newly ground seat.
[frame][/frame]
Large valve and original valve showing contact area.
[frame][/frame]
Newly ground seat showing contact area.
[frame][/frame]
New wide face valve
[frame][/frame]
Height difference

[bmcecosse]

Look perfect to me - although for best power ideally the surface around the outer edge of the seats could be flattened out with a mounted point in a drill......but frankly it will only be 1 bhp or so - and risk of the stone bouncing across a seat and ruining it... I wouldn't hesitate to fit the old valves. Oh and don't bother about the little clips on the cotters!

[David W.]

OK, it goes back together today! It's morning here, I'm sure I would have slept better if I had read that last night.
Thanks.

[bmcecosse]

And now you have a spare set of inlet valves for a 940 head - so start looking!!