7 replies to this topic

[rasputin22]

Hey guys

I have an mg metro head in standard condition. It is the one with the larger intake valves. The exhaust valve seat has a small crack in it on number 3 cylinder but it does not go through to the inlet valve. The crack leads to the manifold or spark plug side of the head if you will, across the head.

I'm also getting alot of other recession on this valve seat and one other. Is it a possiblilty that this cylinder head is not unleaded??

What are my options here, would getting valve inserts be an option or should the head now be discarded??

[dklawson]

An unleaded head will have inserts that should easily be visible once you've removed the valves and cleaned the combustion chambers. If you are seeing a crack in the head (in the chamber itself) and it is radiating from the valve seat and is IN the valve seat proper, this is a good indication that the head is not unleaded (that it does not have the hardened seats).

A machine shop will be able to look at the problem and determine if installing seats is viable. However, from your description I would say it is not. Once the head itself is cracked I would not feel good about using it even if welded. I'm sure you don't want to invest in a new head but buying a used one and having it reworked would seem to be money better spent than trying to revive this one.

[rasputin22]

That's what my reckoning was to be fair. I can get hold of another but not straight away.

What would be the implications of using a 998 head, apart from the obvious power loss, in the mean time and would running a hif 44 be too big for the head??

[MRA]

It would certainly be interesting ........ try going for a run with breathing apparatus, you get out of breath very quickly and overheat with the extra exertion................. your engine won't be much different, although if you choose this route then use the gasket for the head... ie 998 head, use a 998 gasket.

[rasputin22]

Thats was my next question about the gasket, thanks.

Surely having smaller ports would just be like having a restriction so you wouldn't get the full potential of the engine. Would there be a risk of overheating??

[Deathrow]

It's not just the ports and valve sizes that are different, the design of the combustion chamber is quite different also.

998 heads have a closed chamber design whereas 1275 heads have an open chamber design, I would imagine that fitting a 998 head would also mess with your compression ratio quite alot because of the smaller chamber size.

[Cooperman]

In fact the combustion chamber in a 998 head is much greater than on a 1275 head. The reason for this is because the 1275 will almost always have deep-dish pistons with about 8+ cc of dish volume.A 998 has either flat-top or shallow-dish, so the combustion chamber needs to be larger. A 998 head on a 1275 will really lower the compression ratio and, combined with its small valves and poor tract and chamber shapes you'll find it so down on power it would hardly pull the skin off a rice pudding!

[MRA]

It may not overheat, however it would run hotter, how much hotter I am unsure, possibly not enough to worry about....