Unleaded cylinder head replacement

Hi Folks.
Im thinking of exchangeing the cylinder head on the hornet for a unleaded replacement, my querys are

1. Do the casting numbers need to match
2. Are A series heads interchangeable ie mini for wolseley
3, Do you think a uprated head would be beneficial ie 1275 etc

Thanks
John

Short answer is.
No
Yes
And yes definitely
:-)

THanks for that,
One more question if anybody can help:- will a AA+ 1275 head fit ? and is there a way around it not having the water pump bypass connection ?

Cheers
John

If you are contemplating using a 1275 cylinder head, you will need to consider several things. The valves as you would expect are larger and unless you modify the engine block, will hit the surface of the block. You will need to measure the combustion chamber volume as if this is too large, the compression ratio will be too low and any benefits gained with better breathing will be lost. Unless you are looking to completely rebuild the engine with performance in mind, I would just get your existing head modified. Typical costs for fitting hardened valve inserts, between £50 and £100. If you are looking to improve performance, try installing a stage one kit and if your budget allows, look out for a 295 Cooper head (eBay, Mini shows etc) but as mentioned earlier, you will need to ensure the combustion chamber volume is no larger than your existing set up.

Fantastic advice elf service, thankyou very much
cheers John

Full part no. for Cooper Head is

12G295

...but is nearly always referred to as a "295"

It should fit on your 998 engine with no modifications required......but...

the inlet bores are "counterbored" slightly to accept tubular rings which are used to align the appropriate twin carb inlet manifold as per ...

http://www.minispares.com/Product.aspx?ty=pb&pid=35895&title=

If you are staying with your original inlet/exhaust manifold, it shouldn't present a problem.

Cheers

Must have said this hundreds of times a 12g940 head will fit and may not require any modification to the block or head. Keith Calver has a good article on the minispares website you may want to look up. For the doubters I run a 940 head on my 998 elf motor and she runs great. Only thing I had done was the exhaust valves sunk in the head a little at the cost of a tenner a valve.

Many thanks for all your valued advice guys,
John

With normal rockers and factory camshaft the valves of a stock (not skimmed) 1275 head wont hit the block. But the compression will be lower just as Elf Service told. You can compensate this by skimming the head, although in this case, You should measure how close the valves get to the block (a minimum of 0.8mms is required).
Most importantly, You wont have any gain if You dont mach the carb to the new setup on a dyno. You may expect 5-7hps with a 295 small cooper head, and slightly more with a 1275 with normal valves. A bigvalve 1275 head wont do any good, especialy with stock exhaust/carb.

If Your engine needs to be reconditioned, The best way would be to get cooper D top or at least flattop pistons and fit a 295 head. That would bring the CR to a desireable point. I have this setup in my Elf, and even with the stock exhaust and carb it offers nice improvement.

CamelotR has summed it up perfectly. It really depends on your goals and what you wish to achieve. If you fit a modified or improved head to a standard 998cc Elf/Hornet engine and use the existing exhaust and carburetter then don't expect any significant improvements and even with this simple modification a session on a dynomometer is a good idea. Again as mentioned in my earlier message what is you budget and what do you hope to achieve. You can start with a simple upgrade and before you know it, the cooling system needs improvement, the brakes may need upgrading and the transmission and the rest of the engine start showing their age. I and I'm sure other register members have been down this path and before you know it, you have spent hundreds of pounds. If your goal is to have a car with modern day performance then personally go for it, as an old car with a decent top end and acceleration is serious fun.

Andrew

I had a 12G940 head on a 998 block. This block had been pocketed, and the compression was really high - it needed a big battery to turn it over and was prone to running-on. But boy did it go!

My daughter eventually killed it by forgetting to top up the oil - by the time we found out we were recovering the car! The big end bearings were a strange shape and the crank is scrap.

I'm now looking into fitting that head to a spare block. I have an estate that I want to keep with a 998 for now, but would like a bit of extra oomph!

Hi folks.
Finally gettin around to changeing my cylinder head to a unleaded one. i need advice on the bypass hose setup.
1- Does the screw/blanking plug in the replacement head (red one) come out to enable fitment of the bypass tube from the old head (green one) ?
2- my temp sender switch is located in the thermostat alloy housing (old head) and on the replacement head it is located directly in the head, whats your views on useing which one ?



Cheers John

If it were me I'd leave the bypass blanked off; blank off the one in the block as well. Drill a few small holes in the thermostat plate to provide an alternative bypass. Your heater will tend to get hotter too which is a bonus.

As regards the temp sender, use the one in the head and fit the later thermostat housing.

the bypass connects to the water pump.

You're right, must have been that bash on the head with a hockey ball yesterday! You can blank the water pump outlet or, if you're replacing the pump, get the later type with no bypass outlet.

Thanks Asahartz John