9 replies to this topic

[Minigman]

Having recently cracked the refurbished 12G295 head on my 998 I’m looking for recommendations for a replacement.

The spec is 998 with standard bottom end,
Kent 266 cam
Twin HS2s with K&N filters.
Cooper freeflow manifold
Somerford works replica rally exhaust

Is a 12G940 too big even in smaller valve version?
And would the block require pocketing with a 266 cam?

[cal844]

266 cam is similar to the MG Metro cam so shouldn't need pocketed.

If I was In your position I'd use a CAM4810 head(factory fitted with unleaded valve seats), or smaller valves on the same head code that cracked.

Just my opinion, I'm in no way an engine builder but have been learning as I go these past few years.

Someone will definitely be along soon with solid(better?!) Advice

[Minigman]

Be good to find out from someone who knows for sure.

[Retroman]

The only way to know for sure re fitting a 940 head on a small bore ;

 

Try it with no head gasket and some blutac on an exhaust valve, turn it over by hand.

 

Assuming it does not 'stop' solid...the blue tack left with the imprint of the exhaust valve should be at least 0.020" then you are OK.

 

You will loose some lowdown with a 940 but still be perfectly drivable and from 2500 they make a big difference

 

A 12G295 head would be my choice unless you really want a 940, and the block does not need to be pocketed. They are cheaper and readily available with unleaded seats

 

Its an engine out full strip and rebuild job to pocket the block.

[Minigman]

Thanks for the info Retroman.

I just considered it as an alternative to the 295 as I’ve cracked two 295s in the past so don’t hold a lot of trust for them.

Maybe need to try again....

[absx2]

How about sticking on a standard head with slightly cleaned up valve seat areas as per Vizard and see what you think.

Yes it has to be said the 12G295 is the ultimate off the shelf small bore head but your cam timing and distributor advance will probably have more of a noticeable impact on road performance than the head. Who knows, you may gain a bit of grunt down low and an extra couple of mpg.

 

I had a well put together 998 A+ 3.44;1 diff with a Piper 270 with a 12G295 and a HIF38 with butterfly mods on a Howley inlet, MG Metro air box and maniflow full system that would rum rings around standard 1275`s until a split radiator cracked the head. Stuck on a cleaned up standard head with the same chamber volume and couldn`t really tell the difference.

 

Beware that not all CAM4810 heads are unleaded as its just a late casting number. I have over a dozen CAM4810 heads and only three have unleaded seats.

There is also the 12G202 1100 and 997 Cooper head for a slightly bigger inlet valve, good enough for 55 bhp on the 997 Cooper and usually cheap to buy. 

[Minigman]

I did think about a 202. My biggest worry is cracking another 295. Cost a few hundred quid each time to buy them have one reconditioned and then they crack. Not normally at high revs either. Might just buy a Calver ST head. I’ve got a few small heads knocking about which could be worked.

[Cooperman]

Looking at it logically, you are never going to make a road-going 998 into a quick car and it still be nice to drive. It is an old classic car, but some sensible modifications can make it more easy to drive in modern traffic. 

The first thing is to get the gases flowing into and out of the head. That is the key to unlocking a bit more power/torque. A standard 998 head can be made to work well with some sensible port relieving and de-shrouding of the valves. Vizards book shows how to do this. Larger inlet valves help together with getting the CR up to a higher level like 9.75:1 or slightly higher, but be aware of the maximum you can skim from a 998 head. You need to 'deck' the block to get the pistons to come right to the top at TDC, or even a few thou out of the deck level.

But in the end, you'll still have a not-quite-so-slow classic Mini which will be fun to drive and reliable (or as reliable as an old classic can be).

You could spend a fortune on engine mods, but it still won't be 'quick' in modern terms. Enjoy it for the 1960's icon it truly is.

[carbon]

Minigman - out of interest where did your 295 heads crack?

 

Also had they been skimmed much, and were they fitted with valve seat inserts?

[Minigman]

Both cracked between the inlet and exhaust valves. And both on no3 if I recall correctly.

I’ve now bought another 295 head. Hopefully his time it will do the job.