Cylinder Head

Post by **aaroncollett** » Mon Jun 19, 2006 9:55 am

Hello All,

After covering quite a few miles in my Minor now, I have noticed that the tickover has become a little lumpy, so I am going to give it a service at the weekend, and check the valve clearance as well.

I was wondering about this unleaded issue. The car had a recon engine about 8-9 years ago, but I have no documentation to indicate whether it was prepared for unleaded or not. The previous owner asked his local Morris garage and they advised him it would be fine. But I think that this advise may have been because he used the car very rarely. Since I plan to make a little more use of the car, I think I should probably look into the issue a little more.

What is the difference between a Head which can run on Unleaded, and one which cannot? Is it just the hardened exhaust valves, or is there more to it? Is it going to be more economical for me to change the parts of the Head affected by the unleaded fuel myself, or just get a recon unleaded-ready Head and fit it?

I may pull the engine at somepoint (perhaps at the same time as I work on the Head - assuming that I need to) because I want to clean my engine bay (I saw an absolute minter at a classic car show yeaterday and it has me motivated). While it is out, are there any other mods, performance or not, that I should look at making to the engine (I was thinking along the lines of a Cam, and one of those things that allows a spin on oil filter etc)?

Lastly, before I actually do anything to the engine, I am going to compression test it to make sure that I don't throw good money at the top while the bottom is on its way out. Is there a good target result I should hope to get?

Thanks, Aaron.

Post by **bmcecosse** » Mon Jun 19, 2006 10:21 am

160 psi would be good - more important all very similar than actual reading although anything below 140 is trubble. Engine hot, battery fully charged, all plugs out and throttle wedged open before taking readings.
U/L head has hard valve seats - so if lots of miles, this what you need. Don't change cam unless doing other mods to the engine - and you can clean around the engine ok without taking it out!!

Post by **aaroncollett** » Mon Jun 19, 2006 10:48 am

Ok, I will get the compression tester out!

So if you are going to fit the hardened valves, do you have to regrind the seats?

What other mods should I do to the engine along with a cam?

I want to remove the engine because the engine bay is grubby and needs a respray - I am not sure if I could do a good job of that without pulling the engine, though I suppose if I pulled the head and cleared out the other ancilleries, I might get close if I masked the block...

Post by **Stig** » Mon Jun 19, 2006 11:55 am

As bmc says, it's the seats that need replacing, not the valves. Not a DIY job I'm afraid so keep an eye on the valve clearances until you can afford a recon head. Or a recon engine if you get bad news from the compression test!

Post by **bmcecosse** » Mon Jun 19, 2006 1:16 pm

There is no end to the engine conversion list. Start with a better head, then inlet manifold and bigger carb. Then decent exhaust manifold and system - finally worry about the cam. Although - if the engine is out for overhaul - that's when to change cam. MG MEtro cam is cheap and works very well - needs matching oil pump (it's a much better pump anyway) and new followers with cam change.

Post by **aaroncollett** » Mon Jun 19, 2006 1:38 pm

Well, the cost of a recon head ready for unleaded is not that much, so it may be worth doing sooner rather than later.

Can you expand on 'better head'? Does that just mean one that has been reconditioned, or one that has bigger valves, polished ports etc?

Rather than buying a reconditioned head, I suppose I could buy a used one and take it to an engine shop and have them recondition it if any of the above is applicable. Will a stock MG Metro cam just fit in to a 1098 engine?

As a general rule, are most A Series engine upgrades compatible across the board (with the exceptions being those related to the FWD cars)?

Are there any sites or suppliers that you can recommend.

Are upgrades like twin SU's overkill on a 1098?

Thanks, Aaron

Post by **chrisd87** » Mon Jun 19, 2006 3:16 pm

Can you expand on 'better head'?

He means one with bigger valves and a better flow rate - like the 12G295 head from a 1098 midget or 998 mini cooper.

Are upgrades like twin SU's overkill on a 1098?

Better to go for a single, larger carb such as a 1 1/2 inch HIF38, as fitted to the 998 metro. Twin carbs have the disadvantage of needing to be balanced.

Post by **aaroncollett** » Mon Jun 19, 2006 4:01 pm

So with these engines, does it not make much difference what CC the head came from? I have located a few of 12G295, but depending on the source, it has been used on a 998, 1098 or 1275...

Will this operate OK with the standard cam, or is changing that at the same time going to make more of a difference? If so, should I go for an MG Metro cam as mentioned above? I have found that you can get Kent and similar fast road MG Metro cams, would these also be suitable or is a tuned Metro cam going to be too much for the 1098 engine?

Post by **Stig** » Mon Jun 19, 2006 4:41 pm

aaroncollett wrote:So with these engines, does it not make much difference what CC the head came from? I have located a few of 12G295, but depending on the source, it has been used on a 998, 1098 or 1275...

Careful with that, the 1275 head apparently needs some machining to the block to clear the larger valves and whatever the head you need to know its combustion chamber volume as it'll affect the compression ratio. Not having done a head swap I can't give specifics but there's an excellent book by David Vizard that you really should get - you'll learn loads from it.

Post by **aaroncollett** » Mon Jun 19, 2006 5:28 pm

If you mean this one: http://www.amazon.co.uk/exec/obidos/ASI ... 13-5992612 then I have it on order, I have heard it is good!

Post by **chrisd87** » Mon Jun 19, 2006 6:47 pm

That's the one - fantastic book.

Post by **bmcecosse** » Mon Jun 19, 2006 10:48 pm

12G 295 head was used on 998 Cooper and 1098 MG 1100 - and 1098 Spridgets. It's a good head - if you can find one, then have it converted to U/L - and skimmed about 60 thou to raise the compression ratio. This works well with single 38 HIF SU on MG Metro inlet manifold - you can still use the original ex manifold - just cut the old inlet off! The standard cam will be fine - but MG Metro cam is good upgrade - but needs a different oil pump. This is as far (cam-wise) as is sensible with a 1098 engine - they don't like to be revved too hard. I have recently removed 12g295 head (not for sale!) and fitted 12g940 head from 1275 engine. This works very much better - yes you need to 'pocket' the block, or as I have done - sink the exhaust valves in to the head by 40 thou. This was much easier to do - the head was very cheap (£5 I think) because ex valve seats were damaged anyway! I still need to sort it out properly - the carb has benn'Vizardised', so it will need some needle fiddling - it pulls like a train - but I can't put an air filter on it or I get chronic stumbling on full throttle !!

Post by **aaroncollett** » Sun Jun 25, 2006 11:46 am

Is the 12G940 an 11 stud head? I am assuming (without checking) that the 1098 block is a 9 stud? Are they otherwise compatible? Do you have to tap a thread into the block?

Post by **bmcecosse** » Sun Jun 25, 2006 5:43 pm

Some have 11 stud holes- simply don't use them ! Even the MG Turbo had only 9 studs clamping the head down.

Post by **les** » Sun Jun 25, 2006 9:52 pm

The trouble with sinking the valve seats is it spoils the gas flow,and the seat becomes rather wide.

Post by **aaroncollett** » Sun Jun 25, 2006 11:11 pm

So is the 12G295 a better option than the 12G940?

Post by **Kevin** » Mon Jun 26, 2006 11:42 am

It can be a simpler solution as you dont have to pocket the block, but having said that it does depend on the block as they have been fitted without pocketing it just depends on the block.

Post by **bmcecosse** » Mon Jun 26, 2006 1:18 pm

For the sunken exhaust valve seats - I opened up around the seat, unmasking them - effectively bringing them back to the surface - just 40 thou down. My car goes very much better on this head than it did on my quite extensively modified 295 head. The part throttle operation is particularly impressive - roars up hills, and cruises at 70/80 mph. I still have some problems at full throttle - which I am sure is down to the standard exhaust which is hoplessly restrictive.