my new big valve head

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superchargedfool
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my new big valve head

Post by superchargedfool »

Well I have just removed the big valve head from my new 1275gt and replaced it with an mg metro one that was laying about.

The head has indeed been opened up nicely and the rockers look brand new. Double valve springs and all new collets and caps.

The valves are 37mm and 29.5mm so for a freebie I am well chuffed. All it has cost me is a few hours and a few spares that were laying about the workshop.

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Post by toginthemog »

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Kevin
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Post by Kevin »

So what size valves are on your big valve head then as my stage 11 uses 35.7mm and 29.4mm.
Cheers

Kevin
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bmcecosse
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Post by bmcecosse »

These sintered rockers are not the best ! If you have a set of the 'pressed steel' rockers they are far stronger. However - you will likely need to re-align them on the shaft so they operate directly on the tip of the exhaust valves. 37 mm inlets are Cooper S size inlets - should go well provided the throats/bend/ports have been modified to suit. Hope there is still sufficient metal between the throats to prevent cracking - or have the inlet valve guides been moved to increase the distance between centres ?
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Kevin
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Post by Kevin »

These sintered rockers are not the best ! If you have a set of the 'pressed steel' rockers they are far stronger.
Why's that as I would have thought that the solid type were the stronger.
Cheers

Kevin
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eastona
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Post by eastona »

don't know, but vizard recommends the pressed ones as stronger than sintered.

IIRC for belt and braces he recommends a bead of weld between the two halves.

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bmcecosse
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Post by bmcecosse »

The sintered rockers are not 'solid' ! They are pressed metal powder - then sintered of course. Fine in standard use - not at all fine with strong springs and/or high lift cam. They are also heavy. Their design is 'crude' - wide tips which spread across the valve tips without the rocker needing to be aligned with the valve tip. Far far better to use pressed steel rockers - and take the few minutes to align them carefully over the valve tips. This prevents then tilting/twisting on the rocker shaft - and puts less strain on the valve stems as they slide up and down the guide - because they are being pushed in perfect alignment. I've never needed to weld them - but then again - I don't use stupidly heavy valve springs!
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Kevin
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Post by Kevin »

Thanks for that, so basically they are fine up to MG Metro standards but no more.
Cheers

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bmcecosse
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Post by bmcecosse »

Well - MG Rover fitted them - but not unknown for them to break - and the ends 'pit' quite badly. And as above - they are not properly aligned, and so there is an element of twisting and sideways force on the valve stems. Pressed steel (or v early forged) rockers are much better.
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rayofleamington
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Post by rayofleamington »

Why's that as I would have thought that the solid type were the stronger.
I'll second the unreliability comment - it's not unheard of for them to break. Sintered steel is nowhere near as good as a forging.
However on a standard 1275 they are not a big problem and as already mentioned they align with any valve position.
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Declan_Burns
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12G940

Post by Declan_Burns »

I managed to get a nice 12g940 head from ebay. While on the issue of lining up the rockers, can anybody describe how to do this? I think there are spacer kits available-
http://www.minispares.com/Product.aspx? ... 0with%20sp...
Is this the way to go?
I noticed that some people are not happy with these rockers.
Please take a look at the photos below which shows the alignment at present.
Can I file grind or file down rocker 2 and 3 as they are too wide?
Can I reverse the spring on valve no. 1?
I think a spacer behind no. 4 would be OK.
What is the brass bit that looks like it has been cut off in the thrid photo? I don't like to mention the infamous bypass but is it easy to remove for replacement?-I'm a bit afraid to touch it.
The fourth photo shows the MGB thermostat housing that was recommended on here just for reference. A slight dress with a file and it fits nicely.
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Thanks-would appreciate any tips
(DEC 1964H / formerly HMP 960B)
Declan


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bmcecosse
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Post by bmcecosse »

The inlets are not too bad - their position never changed - but the exhaust valves were all moved to allow the larger vlaves to be fitted - so yes - it's mostly the exhaust rockers you need to move, although the inlets can be improved too. But far better to get pressed steel ones and do the 'fitting' on them. You will need to file the sides of the rockers and perhaps also the pillars - and add washers as necessary till they all line up nicely. The 'springs are sometimes changed for steel or copper tube spacers - but I have never bothered - just stick with the springs. It's quite a satisfying job when you get it right!
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Declan_Burns
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Post by Declan_Burns »

Thanks BMC,
Anybody got an idea where I could get the pressed steel rockers?
Are they still available as new parts?
(DEC 1964H / formerly HMP 960B)
Declan


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Declan
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bmcecosse
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Post by bmcecosse »

Well they are extremely plentiful as second hand parts ! I'm sure someone on here will have a spare set. Dunno about new supplies though.
Minspares certainly have the necessary washers for re-spacing - but don't seem to have the pressed steel rockers. They do have a forged rocker - which they describe as 'high lift' although I doubt it!
MOSS have a forged rocker 12G1221 which is ~£10 each - but actually that is much less than they ask for the sintered rockers at £18 each !!!!!!! You would need to check with them if the forged rockers have bushes fitted - or do you need to bush them (and ream the bush) before fitting.
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bmcecosse
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Post by bmcecosse »

PM sent!
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Declan_Burns
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12G940

Post by Declan_Burns »

Thanks BMC, I'll look into that in the morning.
Declan


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Declan
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Declan_Burns
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12G940

Post by Declan_Burns »

Could I ask this question again. What is the brass bit that looks like it has been cut off in the third photo above? I don't like to mention the infamous bypass but is it easy to remove for replacement?-I'm a bit afraid to touch it and it does look a bit corroded.
Another question:
On fitting the 12g940, will I have to modify the take-off for the heater tap? I think I read somewhere on here that it can collide with the battery box. Any suggestions as I would like to keep the original late type heater tap as it is new?
Thanks
Declan
(DEC 1964 / formerly HMP 960B)


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Declan
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bmcecosse
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Post by bmcecosse »

The brass plug - plugs an oil way cross drilling. I wouldn't touch the bypass unless you absolutely NEED to - it can be a nightmare to remove. Heater tap - yes it may foul the battery - just need to find a way round it when you do the job.
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Declan_Burns
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12g940

Post by Declan_Burns »

Thanks Roy.
Declan
(DEC 1964H / formerly HMP 960B)


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Declan
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