27 replies to this topic

[JonnyAlpha]

Push rods should also be replaced in same order ...

 

It's all in the planning and preparation - so i'll replace these then with a standard set - I have no idea which order they were in

[JonnyAlpha]

At the start of this thread I said that this was a 12G940, but that was based on the fact the it had come out of a Metro A+ 1275. I can't find 12G940 on the head though! Just what looks like 17H4 behind the thermostat area.

[nicklouse]

between the middle rocker posts raised cast text. and if it is 1275 then is is most likely be 12G940

[JonnyAlpha]

Mmm interesting, I had a quick look at the head before popping out for dinner and unlike many I have seen there does not appear to be an text on the casting apart from 17H4 located behind the top hose mounting.

 

 

 

There looks like there possibly may have been some text between the two middle rocker posts which looks like it could have been 12G940, but it's been machined off? The metal in this area is machined to the same level where the rockers bolt on and the rocker cover gasket sits:

 

 

I also measured the head thickness and it is around 70mm.

 

I measured the exhaust and inlet ports and found.

Exhaust ports is around 25mm and the Inlet port is around 30mm.

 

So what is this head?

Has it been modified?

And should I keep working on it?

Edited by JonnyAlpha, 14 October 2018 - 07:17 PM.

[Turbo Phil]

Unless somebody's installed the larger inlet valve, it's an early MG Metro head & a 940 casting, though as you can see the numbers aren't clear. Those ex seats are knackered, you could get them recut, but ideally you'd be better off with inserts fitted.

Phil.

 

[JonnyAlpha]

Unless somebody's installed the larger inlet valve, it's an early MG Metro head & a 940 casting, though as you can see the numbers aren't clear. Those ex seats are knackered, you could get them recut, but ideally you'd be better off with inserts fitted.

Phil.

 

 

New seats then, valve guides, push rods, reface the valves, new springs, oil seals and re-face the head.

So machine shop then not a DIY job, about £175 + parts.

[Cooperman]

The actual valve sizes are 35.6 mm inlet and 29.5 mm exhausts. That is the standard sizes for an MG Metro head and the most popular sizes for good heads for the 1275 engine.

When you look at the surface finish and the 'step' adjacent to the edges of the valves it is no wonder that a small amount of work on those chambers can give such good results.

Valve seat inserts will be the way to go, but it would be worth cleaning up the chamber surfaces and removing those steps as well. That in itself would give an improvement in gas flow for little effort. Then, if the valve guide bosses were cut back a bit before the new guides were fitted that too would be a further improvement.

Have a look at photos of fully flowed heads to give you some idea, but you needn't go too far with the work, just smooth the surfaces out. Then skim a bit from the head face, about 0.020" would be good, which will increase the CR just a bit, but not too much and will ensure the face is good.

[gazza82]

When you look at the surface finish and the 'step' adjacent to the edges of the valves it is no wonder that a small amount of work on those chambers can give such good results.

Valve seat inserts will be the way to go, but it would be worth cleaning up the chamber surfaces and removing those steps as well. That in itself would give an improvement in gas flow for little effort. Then, if the valve guide bosses were cut back a bit before the new guides were fitted that too would be a further improvement.

 

 

Cooperman,

 

Do you mean these "steps"?

 

 12G940_CombustionChamber.jpg   42.87K   9 downloads

[cal844]

Here is a rough price from Turbo Phil on here, the work is very good



INLET VALVE(7.20X4) £28.80
EX. VALVE(8.40X4) £33.60
SPRINGS. (1.96X4) £15.68
GUIDES. (1.46X8) £11.68

Mpi Stem seals ( do you recommend 4 or 8?)
1.82 x4 £7.28
1.82 x8 £14.56

TOTAL (MINUS POST) (8 MPI stem seals) £285

[JonnyAlpha]

Here is a rough price from Turbo Phil on here, the work is very good



INLET VALVE(7.20X4) £28.80
EX. VALVE(8.40X4) £33.60
SPRINGS. (1.96X4) £15.68
GUIDES. (1.46X8) £11.68

Mpi Stem seals ( do you recommend 4 or 8?)
1.82 x4 £7.28
1.82 x8 £14.56

TOTAL (MINUS POST) (8 MPI stem seals) £285

 

Are you touting work for Turbo Phil

 

Is that £285 including all the parts mentioned and machining (Skim off of the surface) What about acid dipping and re-painting inside and out? 

[Cooperman]

 

When you look at the surface finish and the 'step' adjacent to the edges of the valves it is no wonder that a small amount of work on those chambers can give such good results.

Valve seat inserts will be the way to go, but it would be worth cleaning up the chamber surfaces and removing those steps as well. That in itself would give an improvement in gas flow for little effort. Then, if the valve guide bosses were cut back a bit before the new guides were fitted that too would be a further improvement.

 

 

Cooperman,

 

Do you mean these "steps"?

 

12G940_CombustionChamber.jpg

 

 

 

Yes, those are the steps which really are poor for performance/gas flow.

 

Your best option would be to ask TurboPhil to do a head for you. Then you know that will be the ideal basis for more performance from your engine. remember: 'Quality and performance are remembered long after price is forgotten'.

[gazza82]

I know someone who can help ... although I need to check my 12G940 first as I think it may already be 'modded'

[johnv]

did yours have a collar for the spring to sit on? The one I have just taken apart had the springs sitting directly on the head