18 replies to this topic

[ibrooks]

The Micra gearing isn't badly enough affected to worry about - they came with 13" or 14" wheels as standard with not much higher profile tyres than the Mini so it's not like sticking a V-Tec in there from a car with 15"-17" wheels as standard.

 

You don't need to mess with the inner wings to fit a Micra lump. If you want to use the standard Micra intake then you need a bulge in the bulkhead crossmember but if you mdify the Micra's intake then that can be avoided. As I said in the other thread it would be perfectly possible to stick a Micra engine and box into a Mini and then convert back at a later date leaving no evidence that it had ever happened.

 

Iain

[ado15]

Skim the head, fit new studs & nuts and use a top quality head gasket. Fit it carefully, torque it accurately with a torque wrench which is properly calibrated and accurate and re-torque after 2 or 3 heat cycles. to re-torque, slacken each head nut half-a-turn in the correct sequence and re-torque. Then re-set the valve clearances accurately.

Make sure the timing and mixture are correct.

 

In addition, make sure all the nuts/studs are either dry or oiled. One or the other, not mixed, is what I mean! If some are dry and others are oily, it's amazing how much difference it can make when you torque them up. The friction of the dry threads clicks off the torque wrench rather sooner, leaving the dry studs with less clamping force than the oily ones.

 

We first came across this with my colleagues Cooper S many years ago. It would develop a misfire at higher revs. After much hunting without success, it went on the rolling road. We then saw at higher revs there was a thin film of water spraying from the head gasket. We hadn't noticed this before because it had dried once we stopped and popped the bonnet!

 

When all the studs/nuts were oiled before tightening them, the problem was solved. We have subsequently found this many times in cases of frequent HG failure.

[Rog46]

 

Skim the head, fit new studs & nuts and use a top quality head gasket. Fit it carefully, torque it accurately with a torque wrench which is properly calibrated and accurate and re-torque after 2 or 3 heat cycles. to re-torque, slacken each head nut half-a-turn in the correct sequence and re-torque. Then re-set the valve clearances accurately.

Make sure the timing and mixture are correct.

 

In addition, make sure all the nuts/studs are either dry or oiled. One or the other, not mixed, is what I mean! If some are dry and others are oily, it's amazing how much difference it can make when you torque them up. The friction of the dry threads clicks off the torque wrench rather sooner, leaving the dry studs with less clamping force than the oily ones.

 

We first came across this with my colleagues Cooper S many years ago. It would develop a misfire at higher revs. After much hunting without success, it went on the rolling road. We then saw at higher revs there was a thin film of water spraying from the head gasket. We hadn't noticed this before because it had dried once we stopped and popped the bonnet!

 

When all the studs/nuts were oiled before tightening them, the problem was solved. We have subsequently found this many times in cases of frequent HG failure.

 

Never heard of this before, but it makes absolute engineering sense. We live and learn!

[tiger99]

Yes, however I seem to recall that the Rover manual specifies the torques for clean, dry threads, so there is a fair chance of breaking the studs if you oil them, and use them more than once. Nevertheless, I do prefer to oil them, use a new hard steel washer, if available, and check that the nuts are free running on the full length of the threads, before I put the head on. That way, the tension in each stud, which is what matters, should be equal. Torque is actually a fairly poor way of setting the tension, due to the obvious variations in friction. You may not be surprised that the efficiency of a 3/8" UNF thread can vary from less than 8% to about 22%, and it is the 8% to 22% fraction of the torque that is tensioning the stud....

 

Next time I do an A series engine, I will probably pay the extra for a set of best-quality studs and nuts, as I have known the studs in a recon engine to break at their first re-torquing. It was impossible to tell how often they had been used, but it was only a 998, so only the lower torque figure of 40 lb ft was required, and they still broke.