Morris Minor Owners Club

I've managed to acquire a 940 head. I know the exhaust valves need to be sunk by 40 thou. I presume this assumes the head has not been skimmed in the past. Just in case it has been, what are the actual measurements I'm looking for. ie measuring from the face how far should the valves be and if it has been skimmed can anything else be done to offset this?

Also can I use the head with my existing manifold and carb until I acquire an Hif38?

I have the sintered rockers to go with it. This will probably be a medium term project as I want the car back on the road in the next week or two so the engine is going back in with the original head for now.

you can use the old manifolds etc.. if you choose to.

The valves need to be recessed from the gasket face by however much the valve lift is (plus 20 thou if you want to be careful)
Can't remember the standard lift of the top of my head but I'm sure it won't take more than 5 mins to find it on google.

Not all heads need the valves sinking. Trial fit yours first and check for impact with blue tac. You might save yourself the expense. Someone on here went into great detail re measurements etc. I think it may have been georgehurst. Do a search of his posts as it may help you out....

Look at my original post. Rule of thumb-if you have 8mm from the exhaust valve to the base of the cylinder head, it should be fine.
http://www.mmoc.org.uk/viewtopic.php?f= ... on#p245225

Regards

Yes -in Imperial terms - you need 320 thou from top face of exhaust valve to surface of head. To check if the head has been skimmed, measure it's thickness - ALL heads start life at 2.750" thick, so any less is the amount that has been skimmed off. For use on a 948 or 1098 engine you want a head that has NOT been skimmed!

OK, I can do that. So just to check, fit a new gasket, put a thin blob of blue tack in the relevant areas on the engine block, fit the head and torque it down, adjust the rocker gaps then crank it over several times. Remove head and inspect blue tack.

EDIT - just been speaking to a machine shop about possibly having the valves recessed if they need to be and there was a lot of sucking of teeth. He thought 40 thou was a lot and was worried it would reduce the compression ratio too much. I told him the combustion chamber on the 940 head is smaller 21.4cc versus 26.1cc on the 202 head and that recessing the valves would still leave me with a better compression ratio than before. Do I have my facts right?

Drat. Received the head today and it has been skimmed. It measures 0.026" less than it should. Can I still use it? Clearly the valves will need sinking now.

As I am ever the optimist I would still do the checks as above..... I've never had one clash yet but in "theory" they all should.

26 thou is not a 'standard' skim - maybe it was warped by over heating and has been 'cleaned up' . This machine shop knows all about it do they ???? 40 thou will be fine - it take sless than 10 minutes - so don't let them rip you off. Just needs a 45 degree countersink, let it self-centre on each seat, then cut down 40 thou. However - if your head really HAS been skimmed 26 thou - you 'may' need to sink by 66 thou - which is a 'lot', but still do-able. And no - don't mess with bluetak - just measure with a digital gauge - or even a good steel rule.

OK, thanks. 26 thou is my conversion from metric using the calipers I use for woodwork with the head on a granite block. I need to get some accurate measuring kit. I did measure the caliper displacement with a steel rule too but that was only to the nearest half mm.

A steel rule will tell you 2.75" - surely! But in any case - it's the size from valve top to head top that matters - you need 320 thou = 8mm. If you have that - then you still have the 30 thou gasket thickness for 'safety'.

I'll have to get something I can use to measure the gap from valve to face. Yes the steel rule tells me the head thickness is less than 2.75". I can't measure direct face to face with a steel rule because there are no directly opposed surfaces but I used the calliper and measured the calliper gap with the rule.

Just measured the distance from face to valves and I get .299" .307" .307" and .314" near as I can tell. I must get an accurate calliper. Most likely they will need sinking to be on the safe side but if I'm looking for a total of .320" plus gasket then they are not going to need sinking as much as 40 thou.

Even though this head has been skimmed I presume I'm going to end up with a better compression ratio than with the original 202 head?

Well - the camshaft (assuming standard AEA 630 cam) has lift of 0.250", and the rocker ratio is 1.27 , so that gives an actual lift at the valve of 0.3175" BUT then less the valve gap you set, so take away 15 thou, gives 0.3025". The gasket has 30 thou thickness (at worst) and so even your worst case of 0.299 still has ~ 25 thou clearance - which is fine! Just don't run it without a gasket!! I would just give that valve an extra good grinding in, and it will be fine. You could of course remove a small amount of metal from the top of the valve too - to get a little extra clearance, but frankly - it looks fine as is!