Head Gasket Woes Fixed

[panky]

Earlier this week Ted developed all the symptoms of a blown head gasket that had failed between cylinders.
As it turned out it was between three and four
Could this be the culprit?



The head was cleaned, valves lapped in, checked for flatness, new head and rocker pedestal stud fitted and an OEM Payern gasket fitted.

12G940 head





Making sure it's the correct way round



I recon I should have opened up that oilway a bit



All back together now after making sure the new gasket was 'conditioned' and the car is running as well as it ever has if not better

[svenedin]

Glad it's all sorted. Pardon my ignorance of such things but in your last photo there seems to be a hole in the gasket that does not line up and seems to be partly obstructing a hole. Or is that just the angle of the photo?

[panky]

Yep that's the one I wished I'd opened the port up a bit. It's the feed to the rocker shaft but every gasket I've used has the same issue - there should be enough oil through the port but there's no harm in opening up the port with a small burr to aid oil circulation to the top end. Maybe next time (hopefully in a long time)

[svenedin]

Yep that's the one I wished I'd opened the port up a bit. It's the feed to the rocker shaft but every gasket I've used has the same issue - there should be enough oil through the port but there's no harm in opening up the port with a small burr to aid oil circulation to the top end. Maybe next time (hopefully in a long time)

Thanks for explaining. I will try to remember this and not panic when I have to do a head gasket!

[panky]

After removing the rocker cover to re-torque the head studs I can confirm there is plenty of oil getting to the rockers.

[philthehill]

The part shrouded hole is for the transfer of coolant not oil.
The outer unshrouded hole is for the transfer of oil from the block to the head and then onwards the rocker pillar and rocker shaft.

[panky]

Thanks Phil, I should have known by the position of the port.

[Grumpy21]

Am I missing something here?

I don't remember my gasket being over sized and off centre like yours looks. It looks like the gasket is for a much larger diameter bore.

Clearly you know why but I'm interested to know too ?

Thanks

[philthehill]

The head being used appears to be a version of a 940 head .
If it is a 940 head the 1275cc head gasket must be used when fitting a 940 head to a small bore block.
If you do not use the 1275cc head gasket there will be too much head gasket exposed to the combustion chamber and the head gasket will burn away which may cause damage to the block and/or head.

[Grumpy21]

Thanks, as always.

mines a 1098 and the gasket was a much better fit.

cheers

[panky]

Yep it's a 12G940 head from a '91 Mini Cooper

[Grumpy21]

Again pardon my ignorance but why put that head on a mis-matched block? I’m sure there’s a good reason but I don’t know it.

I’ve been looking at your posts from 2015, précis:- 1275 head hence bigger gasket. Valves would hit block so you reduced the thickness of the valve head.

I don’t understand why you just didn’t fit a 1275 engine, the in-cylinder turbulence must be limiting? No?

This isn’t a criticism, more an attempt to understand.

[philthehill]

Panky may come back with his own ideas but here is a brief overview.
The reasons for fitting a 940 head on a small block engine is to do with the breathing. That is getting the air/petrol mixture into the cylinder and the exhaust gasses out. The larger the inlet valves the more air/petrol mixture you can get into the cylinder means a bigger bang which gives more power.
Unfortunately the small bore heads do not have sufficient inlet and exhaust tract size, the exceptions being the 12G295 and the 12G185 heads which these days are hard to come by and are expensive. The easiest and most cost effective way to get additional power is to use the 940 head from the 1275cc engine. The problem with using the 940 head on a small bore block is that the exhaust valves will foul the top of the block when opened which means that either the block has to have cut outs, the valves sunk into the head or the thickness of the head of the valve reduced.
Fitting the 940 head is a good move but it is not just a straight swop.
Below is a photo of a 1098cc block with the cut outs in place to allow fitment of the 940 head.

1100cc block with 940 cut outs.jpg (77.18 KiB) Viewed 1153 times

[panky]

No problem and I'm very happy to give an bit of insight to the modifications I've done over the last few years.
I'm a natural fiddler I just can't help myself. When I first got Ted I absorbed all the modification information I could from the forum gurus like Phil and BMC Ecosse. I couldn't afford a 1275 engine but fitting the head off one was reported to give a decent increase in power and I just happened to have one under the bench. One of the problems doing this was the possibility of the exhaust valves hitting the top of the block so the valves were modified by shaving about .020" off the faces. An alloy inlet manifold with a HS4 SU (I also had these under the bench) and an MG Midget exhaust manifold into an 1 1/2" exhaust system gives a pretty decent performing engine. I also fitted a Riley 3.7:1 diff, which dulled the extra acceleration I'd gained but gave nice long gearing and the engine is well capable of pulling through the gears, also Wolseley brakes were fitted up front.
If I do happen to find a reasonably priced 1275 then I might go for it but right now I'm very happy with how the car performs

[panky]

Panky may come back with his own ideas but here is a brief overview.
The reasons for fitting a 940 head on a small block engine is to do with the breathing. That is getting the air/petrol mixture into the cylinder and the exhaust gasses out. The larger the inlet valves the more air/petrol mixture you can get into the cylinder means a bigger bang which gives more power.
Unfortunately the small bore heads do not have sufficient inlet and exhaust tract size, the exceptions being the 12G295 and the 12G185 heads which these days are hard to come by and are expensive. The easiest and most cost effective way to get additional power is to use the 940 head from the 1275cc engine. The problem with using the 940 head on a small bore block is that the exhaust valves will foul the top of the block when opened which means that either the block has to have cut outs, the valves sunk into the head or the thickness of the head of the valve reduced.
Fitting the 940 head is a good move but it is not just a straight swop.
Below is a photo of a 1098cc block with the cut outs in place to allow fitment of the 940 head.
1100cc block with 940 cut outs.jpg

Thank Phil that explains it all As I wrote in my previous post I only needed to shave the exhaust valves but any future cam change might need the block pocketing.

[Grumpy21]

Thanks for the explanation. I wondered how the valves would be prevented from hitting the block face. I’ve come across ‘pocketing’ but couldn’t see any evidence in the photos. Interesting that the valves were skimmed to achieve the same effect.

Thanks for thanking the time to enlighten me