14 replies to this topic

[sootyco]

Today I identified my engine by removing the head, but it's badly corroded in two cylinders.

I would be very grateful if anyone can tell me -

a) can it be rebored and what is the maximum bore for a 998
b) can the pistons and head be done as well
c) how much will it cost(approx) fo a rebore, skim the block/head and rework the piston and new rings, basically undo the corrosion? Is it practical and is it worth it, or should I just buy a new engine
c) has anyone got any experience of this and can you recommend anyone to do it?

Again, thanks for all the advice it's greatly appreciated.

[Carlos W]

If you rebore the engine you will need new pistons and rings.

An accurate build will be better than a second hand engine.

How bad is the corrosion? Were the pistons seized?

[Stiggytoo]

Was yours the cooper engine?

[sootyco]

Yes. Seized. Corrosion is bad in two chambers, surface corrosion, but hard to know how deep it goes. I can pick it at it with my fingernail. Lots of rust dust. I'd much rather rebuild the engine I have than take a punt on a second hand unit but obviously cost is a factor, plus originality. Are new pistons needed with any rebore, even a shallow one? Are there any other areas that are likely to need machining too? I would prefer to keep the D shaped pistons and keep it as close to original as possible. I can post a pic tomorrow but not sure it will illustrate it properly. What are my options? So grateful for any help. I am learning as I go and this forum is priceless.

[sootyco]

Yes, Cooper 998cc.

[sootyco]

Why don't people just block off the ports and fill with oil or even WD40 before leaving a piece of history to the elements? Very frustrating. A little bit of prep would have avoided this. Now I just want to bring the thing back to life. I know I will be so much more chuffed if I can bring this block back than simply opting for a new/second hand unit.

[Cooperman]

You can bore a 998 out by 0.080" and fit new flat top pistons. This gives a capacity of 1060 cc.

Whenever the engine is re-bored it obviously needs all new pistons and the bores are done by the machine shop to suit the pistons provided.

D-top pistons are no longer available in any oversize and with flat tops you will need to measure and calculate for the required compression ratio.

There is no point in buying a 2nd hand unit as you already have a complete engine.

It will probably need a crank re-grind with new big-end & main bearings, new cam bearings, new camshaft and followers, new oil pump, new water pump, new crank thrust bearings, new timing chain, new valves & valve guides and all new gaskets.

 

Then there is the clutch & transmission to consider.

[sootyco]

If I rebore and fit flat top pistons, is it even a mini cooper anymore? With so much change doesn't it just become a generic refurb, I mean without the 'hallmarks' what is to say it's a cooper at all? Or is this common place? Seems a trait of the 998 is the D top piston. Is there any room for machining that will still allow the same old D tops to be used? Do the rings allow some leeway? Originality is key for me. I don't want to end up with a 'stateless' engine, I want a Cooper. If it's a rebore and flat tops then am I just better off with an original replacement in terms of cost and originality?

Thanks so much for replies. Very much appreciated.

[Carlos W]

If the cylinder is scored or badly pitted you need a rebore.

No-one is going to know what's inside without taking the head off, and without the engine work the car isn't going anywhere.

If you accurately measure and build everything, get the compression ratio right, have the head ported, polished and skimmed you will make improvements to how the car performs

[coopdog]

Can you sleeve a 998?

That could be an option if you don't want to scrap the block?

[Vipernoir]

998s will go out as far as 68mm ( about +.135") though that is right on the limit - the equivilent of a 74mm bore on a big block.

 

+.080 and +.100 are sensibly as big as you need to go, though you almost certainly won't get hold of D-crown pistons any more unless you are lucky, rich or probably both.

 

You could get the block sleeved back to standard and just re-use your existing pistons with new rings, and while that would very rather expensive you would at least keep the original block and not have to ruin the head by excessively skimming it.

[Cooperman]

998s will go out as far as 68mm ( about +.135") though that is right on the limit - the equivilent of a 74mm bore on a big block.

 

+.080 and +.100 are sensibly as big as you need to go, though you almost certainly won't get hold of D-crown pistons any more unless you are lucky, rich or probably both.

 

You could get the block sleeved back to standard and just re-use your existing pistons with new rings, and while that would very rather expensive you would at least keep the original block and not have to ruin the head by excessively skimming it.

Would it be wise to use pistons which have been sitting in a seized engine, even with new rings and sleeved bores?

It's a typical classic car issue where parts are NLA and have been for many years. We all just have to use what is available.

In the 60's the 998 Cooper was used in competition with different pistons from the D-tops and still were Coopers.

[ACDodd]

Easy enough to make raised D pistons from flat top. Just need a lathe and mill. It will add about £100 to the cost of the pistons.

[Cooperman]

Easy enough to make raised D pistons from flat top. Just need a lathe and mill. It will add about £100 to the cost of the pistons.

But it's not really worth is as the raised D-top was to increase the CR and with a piston with the top milled down to create the D-top, the CR will be too low unless the block is decked by a further amount, or the head machine down to reduce combustion chamber size.

You might as well just use a flat-top piston and skim the head to get the CR correct.

No-one worries about originality to the extent of considering piston part numbers.

In my 1964 Cooper 'S' I run Karl Schmidt pistons, because they are so strong. it is still a Cooper 'S'.

[ACDodd]

Of course the block needs to be skimmed. It is more reliable to skim the block rather than the head as th deck thickness is much greater on the block. Doing it this way eliminates the chance if gasket weeping. With flat top pistons, the block deck has to be skimmed any ways they fall short, so its negligible extra cost.
Any extra CC you can gain from a raised crown maintains head deck thick ness. That's a plus in my book.

Ac

Edited by ACDodd, 17 May 2014 - 08:57 AM.