Cyl heads for 1098

Side valve, 803, 948, 1098., 1275 and Vizard mods

Cyl heads for 1098

Postby ndevans » Thu Jan 16, 2014 8:50 pm

Evening all.

Been trawling through various threads on here & elsewhere on t'internet, looking for gen on heads for a 1098. As I understand it, both a 12G295 (1098 MG?) & 12G940 (1275 A-series?) are worthwile upgrades for a 1098. However, the more you read the more confused.com you become!

So firstly, is a 12G295 head just a bolt on mod for a 1098-no need to mod the block to avoid valves hitting it? Can the existing rocker shaft & pushrods be used?

On to the 12G940. Do you need to "pocket" the block to avoid having valves hitting it? I've seen it suggested that you need to pocket the block if you want to use a 12G940 (on a 1098), and I've also read that you "might not need to". Is there a definitive answer on this? And if not, how do you tell if you need to put pockets in the block? Apart from that, is a 12G940 a bolt on mod? Can you use the existing rocker shaft, pushrods etc?

cheers

Confused.com (aka Neil)

PS-I have the Vizard book, but it doesn't really go into whether you can re-use rocker shafts etc.
N D Evans

https://flic.kr/s/aHsjDY4xbd

MOG STATUS:- SUSPENSION RECTIFICATION
1969 Traveller
User avatar
ndevans
Man of Granite
 
Posts: 986
Joined: Fri Mar 14, 2008 3:19 pm
Location: Brizzle

European Union (EU) UK England (.g)

Re: Cyl heads for 1098

Postby tickman » Thu Jan 16, 2014 9:22 pm

No idea here.
I agree the more you read the more conflicting the information becomes.
The main problem is almost all of what you read is just opinion backed up with 'I did it this way'
Hopefully some decent information will come in and if it does one of our moderators might make it a sticky.
User avatar
tickman
.
 
Posts: 1421
Joined: Fri Mar 14, 2008 10:15 am
Location: Deepest Darkest Dundee.
Awards: 2
Contributions 2012 (1) Contributions 2013 (1)

Scotland (sf)

Re: Cyl heads for 1098

Postby MickEssex » Thu Jan 16, 2014 9:32 pm

What we need is for one of our members in the know to write up a definitive guide to fitting various cylinder heads and what is involved for each. We could then give it its own web page and add it to our guides section. :D
RagnarImage Previously owned Cassie Image Julie Image
User avatar
MickEssex
.
 
Posts: 5502
Joined: Sun Mar 23, 2008 2:23 pm
Location: South Benfleet, Essex
Awards: 8
Contributions 2011 (1) Contributions 2012 (1) Contributions 2013 (1) Contributions 2014 (1) Contributions 2015 (1)
Contributions 2016 (1) Contributions 2017 (1) MMO Annual Award Winner (1)

Great Britain (GB) UK Essex (.m)

Re: Cyl heads for 1098

Postby mogimad » Thu Jan 16, 2014 10:10 pm

MickEssex wrote:What we need is for one of our members in the know to write up a definitive guide to fitting various cylinder heads and what is involved for each. We could then give it its own web page and add it to our guides section. :D


ROY.............

THIS ONES FOR YOU.......

D.
C & C Trim Masters
Classic and Custom
Interior Specialists
User avatar
mogimad
.
 
Posts: 714
Joined: Sat Mar 06, 2010 12:03 pm
Location: North Lanarkshire
Awards: 4
Contributions 2011 (1) Contributions 2012 (1) Contributions 2013 (1) Contributions 2014 (1)

Scotland (sf) UK Scotland (.j)

Re: Cyl heads for 1098

Postby austin » Thu Jan 16, 2014 11:05 pm

12g295 is a good head for the 1098. Think I used that on at least a couple of 1098 engines (in the 70's and 80's). Also used a couple of 12g295's on 1275 engines (Sprite and Midget engines, though one was in a Ford!) But it doesn't make sense to put any head straight off a 1275 onto a 1098 as the compression ratio is likely to be drastically reduced.
austin
.
 
Posts: 295
Joined: Thu Oct 24, 2013 4:34 pm
Location: north yorkshire


Re: Cyl heads for 1098

Postby bmcecosse » Fri Jan 17, 2014 6:58 pm

Quite the opposite! The 12 G 940 from a 1275 RAISES the comp ratio very nicely. It is by far the better head - don't use a 'big valve' version - just the normal 33/29 valve size is fine. It's better (and easier) to 'sink the exhaust valves' in to the head - rather than spoil the block with pockets - which also expose the top ring.... You must have 320 thou (8mm) clearance from valve head face to exhaust valve head face - the inlets don't matter. If you don't have this - sink the exhaust valves down to get the clearance. We did this in 10 minutes (in lunch break) using a vertical drill and a large 45 degree countersink. Rotated slowly - it self centred on the seat and cut down the necessary 40 thou on my head. A light hand grind and I had perfect new seats! I then fitted ~ 40 thou washers under the ex valve springs to make the compression on the springs same as before. Rocker gear - you can reuse the original 1098 rockers - IF you re-arrange them on the shaft so they act directly on the valve tips. You will need a file - and some thin washers. It's a satisfying job when done right! Or - just use a set of 'sintered' rockers from a 998 or 1275 Mini engine. These have wide pads which hit the valve tips...BUT...they are 'off centre' on a 1275 head and perfectionists will not like it... MG Rover thought it was good enough - and indeed it does work well enough on a standard engine. The 12 G 295 (and almost identical earlier 12 G 206) is a poorer head - and it DROPS the comp ratio when fitted on a 1098 (or 948) with dish pistons. So - it needs 60/80 thou skimmed off the face before it can be used. If going this way - check the head before skimming - ALL heads start at 2.750" thick - any less then it has already been skimmed.... The head has smaller valves, and uses a normal 803/848/948/998/1098 head gasket - and frankly will do well on a 948 engine, but a 940 head is far better on the 1098. The 295 head uses the standard rocker gear - unmodified. The 940 head must always be used with a (copper faced ) 1275 head gasket - and usually the top of the water pump has to be filed down to make sure the head can seat nicely without fouling the pump. The top hose will be at an odd angle - I simply used a curved section cut from a bottom hose to make the connection, but there are other thermostat covers (MGB??) which can be fitted to allow a standard hose to be used. And standard push rods are used with both. There is little to be gained fitting either head unless you also fit a larger carb - on a good alloy inlet manifold. Avoid the twin SU trap! There is very little to be gained from twin carbs.... Standard exhaust can be used at this stage without any great penalty.
Just to add - a 12 G 295 on a 1275 engine is definitely NOT a good idea! It has smaller valves and ports than a standard 940 head... The obvious upgrade for a 1275 is the 'large valve' (35/29) version fitted to MG Metro and later S engines - and even better a 'genuine' Cooper S head which costs a fortune, but also has a slightly larger exhaust valve... They are however prone to cracking if the engine is ever allowed to overheat.....
 









Image
User avatar
bmcecosse
Deceased Member
Deceased Member
 
Posts: 4398
Joined: Sat Mar 15, 2008 6:53 pm
Location: ML9
Awards: 2
Contributions 2012 (1) Contributions 2014 (1)


Re: Cyl heads for 1098

Postby Linear.audio » Sat Jan 18, 2014 7:26 pm

Well said, Roy.
A couple of points: The last edition of the Bible was around '82. In those days the 12G295 head was still around in some numbers, but unless you could find some flat top pistons, you still needed to remove a fair chunk (like 80 thou) to get the compression up, and if you did the Vizard flowing of the chambers then it became nearer 120 thou, either of which ran into potential problems with the oil feed breaking through. Since those times, the 12g295 has become rare/ expensive in a useable condition.
If you compare the machining required to remove all that metal to the possible need to sink the exhaust seats on the 12g940 head, it can only make sense to go for the latter! Note that many people who have done the swap have found, like myself, that there is no valve clashing problem. It is just down to the particular tolerance stack-up.
The other objection that has been mooted is that the combustion chamber flow is compromised by fitting the 12g940 head (which in purely technical terms is a bodge!). However, this is as nothing compared with the huge overall increase in airflow. For the record, my moggy has slightly better fuel consumption with the 12g940 head than with the standard one, due to less pumping losses and the considerably higher compression ratio!
I am sure that we thrashed out some sort of "how to" a couple of years back- maybe Declan Burns could resurrect it so we could sticky it, as I remember him detailing the procedure in his typically thorough and expert manner!
It is very, very simple to determine whether the valves will need sinking, but like all modifications it does need a level of engineering understanding.
The business about the rockers is best overcome by, as Roy commented, using the sintered rocker shaft assembly from any a-series built after about 1980. This "one size fits all" approach was good enough for BL to the end, and they are still readily available.
Image
Err... Now where was I?
Linear.audio
.
 
Posts: 465
Joined: Tue Jul 06, 2010 2:15 pm
Location: Essex, nearly Suffolk


Re: Cyl heads for 1098

Postby bmcecosse » Sat Jan 18, 2014 11:07 pm

Just make this thread 'sticky' - pretty much covers it all! I will just add that it gains about 10 bhp extra from a 1098 (assuming a 1.5" carb fitted) and it is still perfectly driveable....indeed mine pulls like a 'train' (!) at lowish/medium revs and really hits a sweet spot at 60/70 mph in top gear - that with a 3.7 final drive ratio. If driven carefully - the mpg is 35/40. However, it rarely is 'driven carefully'.
 









Image
User avatar
bmcecosse
Deceased Member
Deceased Member
 
Posts: 4398
Joined: Sat Mar 15, 2008 6:53 pm
Location: ML9
Awards: 2
Contributions 2012 (1) Contributions 2014 (1)


Re: Cyl heads for 1098

Postby Big Al » Sat Jan 18, 2014 11:14 pm

Now a sticky... ;)
Image
User avatar
Big Al
Furry Feet
 
Posts: 8402
Joined: Sun Aug 29, 2010 10:20 pm
Location: Chelsfield, Kent, UK
Awards: 9
Contributions 2011 (1) Contributions 2012 (1) Contributions 2013 (1) Contributions 2014 (1) Contributions 2015 (1)
Contributions 2016 (1) Contributions 2017 (1) MMO Annual Award Winner (1) MMO Top Tester (1)

England (en) UK Hertfordshire (.h)

Re: Cyl heads for 1098

Postby ndevans » Sun Jan 19, 2014 12:40 am

Awesome thanks all. I am looking at a couple of 295's and 940's on Ebay. While I'm pretty much convinced of the superiority of the 940, the devil is in the detail as they say, and that's why I asked about rockers, valve rods etc. Obviously
I would fit a bigger carb, but I also need to weigh up whether I just put in a 1275.

Thanks again all. I hope others find this useful.

Cheers N
N D Evans

https://flic.kr/s/aHsjDY4xbd

MOG STATUS:- SUSPENSION RECTIFICATION
1969 Traveller
User avatar
ndevans
Man of Granite
 
Posts: 986
Joined: Fri Mar 14, 2008 3:19 pm
Location: Brizzle

European Union (EU) UK England (.g)

Re: Cyl heads for 1098

Postby austin » Sun Jan 19, 2014 12:31 pm

ndevans wrote: I also need to weigh up whether I just put in a 1275.


1098 or 1275? I feel it depends what is available. If you have the chance of a good Midget 1275 then I'd go for it. A Marina 1275 without a Midget camshaft would still be my choice over a 1098. But on the other hand there's not much wrong with a 1098. Twice when thrashing a 1098 I have known a little end to seize and one piston to break up, but twice doesn't mean it is a common problem.
austin
.
 
Posts: 295
Joined: Thu Oct 24, 2013 4:34 pm
Location: north yorkshire


Re: Cyl heads for 1098

Postby Linear.audio » Sun Jan 19, 2014 4:26 pm

The 12g295 head nowadays is more of an expensive antique, rather like Wolseley front brakes. Unless you are convinced it hasn't cracked across the valves, and you are happy that ploughing huge amounts off the head won't compromise the deck thickness and cause head gasket/warping problems(Vizard is quite clear about that detail!) then go for the 940 option.
If possible, hunt out Declan Burns thread on this from around 2 years back. He covered the whole job pretty well ,with photos!
I am still unsure about the modified 1098 versus 1275 question. While logic says that the 1275 should be superior, (and I have one waiting to drop in when the weather brightens), the one attraction of the 1098 is its very long stroke, which makes it handy for pulling a moggy traveller, especially if you tend to load it up a bit....
Working, as I have, on the principal that generally using what you already have is the cheapest option, there is a big satisfaction in "just" dumping a 940 head and decent carb/manifold on your engine and noticing the change :). The weak link will unfortunately always be the main bearings, unless you can happen upon a 1098 Sprite engine which will have the 2" mains(rolls on floor laughing)! I know where there is one, but even an optomistic fool like me won't touch it as it shows many signs of abuse (yep, the head is cracked on it!)
Bear in mind that if you later decide to drop a complete 1275 in, (which isn't at all a straight swap when you get to the flywheel end unless it is the spridget version), you will still have a 940 head that you can sell on, most likely at no loss!
Image
Err... Now where was I?
Linear.audio
.
 
Posts: 465
Joined: Tue Jul 06, 2010 2:15 pm
Location: Essex, nearly Suffolk


Re: Cyl heads for 1098

Postby bmcecosse » Sun Jan 19, 2014 6:01 pm

As above - it is a perfectly good modification, and easily done - if you have a serviceable 1098 but want a bit more GO. I have 2 X 1275 engines on standby for when my 1098 fails - but they have been there for 5 years now.... and the 1098 runs on just fine! Both engines will make the same power - since the air flow is limited by the 940 head on both engines - obviously the 1098 has to rev 12 % faster to get there - and with it's smaller bearings, it's not going to last the pace. But it is a good economical answer if you already have a decent 1098 in the car!
 









Image
User avatar
bmcecosse
Deceased Member
Deceased Member
 
Posts: 4398
Joined: Sat Mar 15, 2008 6:53 pm
Location: ML9
Awards: 2
Contributions 2012 (1) Contributions 2014 (1)


Re: Cyl heads for 1098

Postby ndevans » Mon Jan 20, 2014 10:28 am

Once again, thanks all. I think this has develop0ed into a useful thread which hopefully others will find helpful.

So, to sum up, as I understand it:-

1-Both a 12G295 & a 12G940 are useful improvements over a standard 12G202 1098 head, the 940 being slightly the better.

2-A 295 is a drop on replacement for a 202, rockers etc can be re-used, and a standard head gasket can be used. However it might need a skim to restore the CR.

3-A 940 is also a bolt-on swap for a 202, BUT depending on the thickness of the head (ie whether it has been skimmed), the engine block might need pockets into it to avoid the valves hitting it. Alternatively, the valves may be recessed into the valve seats if the seats are ok, depending on whether the head has been skimmed & by how much. The only reliable way to tell is measure the head thickness, and to do a test fitting with blu-tack on the valves. A 1275 copper head gasket needs to be used.

5-The rocker from the 1098 can be used on a 940 head, with some adjustment to make them align with the valves, or a rocker assembly off a 998/1275 Mini can be used.

6-None of the above is really worthwhile without a bigger carb & freer flowing inlet & exhaust manifold (presumably air filter too?).

7-A 1275 engine can be fitted instead, but it is not as straightforward as it sounds as it involves either changing the flywheel (& using a mating flange?) to fit to the existing Minor gearbox, or swapping for a Marina/Ford 5 speed box.

Is that a fair summary? Feel free to correct, I don't want to be giving false information out!

cheers N
N D Evans

https://flic.kr/s/aHsjDY4xbd

MOG STATUS:- SUSPENSION RECTIFICATION
1969 Traveller
User avatar
ndevans
Man of Granite
 
Posts: 986
Joined: Fri Mar 14, 2008 3:19 pm
Location: Brizzle

European Union (EU) UK England (.g)

Re: Cyl heads for 1098

Postby ndevans » Mon Jan 20, 2014 10:46 am

Linear.audio wrote:I am sure that we thrashed out some sort of "how to" a couple of years back- maybe Declan Burns could resurrect it so we could sticky it, as I remember him detailing the procedure in his typically thorough and expert manner!


Is this the one?
viewtopic.php?f=12&t=2106&hilit=Cylinder+head
N D Evans

https://flic.kr/s/aHsjDY4xbd

MOG STATUS:- SUSPENSION RECTIFICATION
1969 Traveller
User avatar
ndevans
Man of Granite
 
Posts: 986
Joined: Fri Mar 14, 2008 3:19 pm
Location: Brizzle

European Union (EU) UK England (.g)

Next

Return to Engine



Who is online

Users browsing this forum: No registered users and 1 guest