50 replies to this topic

[Gr4h4m]

Are the pistons installed the correct way around? I know my 998 ones are handed.

[Pigeonto]

The pistons aren't directional,I looked into that at the time and measured to check;- the pin is in the centre.Cooperman,I confess I didnt try that,I suppose a manometer check in the crankcase would have been adviseable too but I think I just reckoned that with the degree of oil usage and smoke( it sometimes overtakes me when I stop!! , there was no option but to rebuild it.This bore wash thing is whats troubling me,no experience of it before,specially as I have AAA needles which I have since been told are the very likely culprits so I just wanted to see if people recognised it here.A proper chack of the bore sizes may reveal something though

[Cooperman]

It is unlikely that bore wash would cause an amount of wear so great that it would cause smoking to that extent after such a short distance. The mixture would have to be so over-rich that neat fuel was going into the cylinders and then the engine would not be running properly. Indeed it would be worse than continually running with full choke on when fully warm.
The main suspicion must be over-size boring for the pistons fitted.
Until you have measured and checked you really won't know for sure.
What a bugger!

[Ethel]

Are all bores the same? That'd suggest a machining/sizing error to me.

[ACDodd]

It is possible to remove 0.002" of bore in less than 100miles, due to bore wash. The ONLY way this is going to be determined, is to accurately measure the components. Sometimes I have to hone cylinders to determine if it was bore wash that caused the issue.

Sorry this cannot be determined by pictures,

AC

[KernowCooper]

We still dont know yet what the needle was in the carb to rule out excess fuel causing bore wash, I doubt very much it was running that rich, I suspect the needle may have been a BDP MG Metro ?? be interesting to know

[ACDodd]

It can just be the idle setting so needle unimportant in this respect. Also if the float needle valve was leaking this can also cause it.
As a matter of insurance, new engine should also mean new/rebuilt carb.

AC

[KernowCooper]

Standard MG Metro needle is a BDL.......

oops So it is, see what happens when you try and do two jobs at once

[Pigeonto]

Back again.Blimey you have all been busy.Ok, the 3rd post on this page says I have AAA needles. Bores measured today, exactly 2.840" .Absolutely no step at the top Well there couldnt be as this is the size it should be at +060". OH, and carbs were rebuilt with new viton tipped shut off needles, float heights set correctly. Am slightly concerned that there was pressure in the fuel tank(I had to loosen the filler cap to stop fuel rushing out when the pipe to the carbs was removed) The car has the vent pipe from the tank running to the charcoal canister in the wing so I'd better check theres no blockage in that line

Edited by Pigeonto, 11 February 2013 - 09:41 PM.

[monster_mini]

What measuring tool (and where to buy) do you guys recommend for accurately measuring the cylinder bore diameter at different depths, and what other tools are needed for accurately measuring the different components:)?

Thanks

Nick

[Pigeonto]

This is what I used but its fiddly and slow if you are to be accurate.Theres some much better ones

Attached Files

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[monster_mini]

Okay cool:) thanks:) it'll be interesting to see what engine builders that do it all day every day use:)

[Cooperman]

A long shot, but is there any chance the middle scraper ring(s) is/are upside down?
With that amount of oil blow it really has to be bore/ring related.
It's a pity the head is off as a 'leakdown test' and compression test would give an answer. Maybe worth putting the head back on and running it up again. It's that or just take it out and strip it.

[Pigeonto]

I suppose anything's possible Peter.I have had that before and it is pretty effective at sending oil up the top!! I believe the pistons came with rings fitted but cant be sure.They'd have come off to check gaps but gone back on same way if so. I'd have looked for any marking 'top'..The reason I took the head off was partly to look at the bores but also I have produced a max-sized valve head and wanted to get it on to see if there are any isues such as poor low down torque etc so I thought I'd get it on and then if full rebuild necessary I'll know if I want to use it.I roughed up the cylinder walls and have fitted the head,went and borrowed my mate's leakage tester only yesterday! so will test it after a run with very weak carb setting and needles (AC).Probably bolting the stable door after the (Cow??!!) has bolted but had to do something.Will report back.

[ACDodd]

Firstly 2.840 is too tight. 2.841 is more like the finished size? What pistons are fitted? Secondly, are all the rings showing full face contact?

Ac