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[Pigeonto]

 DSCF4121.JPG   39.8K   89 downloads  DSCF4128.JPG   38.15K   94 downloadsI decided to bite the bullet and investigate the horrendous oil consumption on my recently built 1000 mile engine.The honing marks are mostly still there except for this area which is the same on all cylinders,just on the front and back,in line with the throw of the crank.I'm resigned to having to at the very least re-hone and new rings,I'll get the bores measured but I need to prevent it from happening again and would value opinions.If its bore wash then I think I'll tow it up and down the road with no fuel in the carb for 50 miles before running it after I rebuild it!!!

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[Fast Ivan]

it looks like it could be piston slap, is it noisy when you first start it?
Was this a re-bore and hone or just a hone and new rings?

[KernowCooper]

The correct termination of bore wash is when excesive amounts of fuel enters the combustion chamber and the excess fuel washes down the covering oil film on the cylinder walls causing excessive amounts of wear to the pistons and rings

No reason to get bore wash if the carburation is setup correctly and the block is rebored and new pistons are used with correct ring gaps, get the bores measured if its outside tolerence then its time for a rebore.

Have you got a different carburettor on then what was used before or altered the fuelling after the rebuild?

Edited by KernowCooper, 10 February 2013 - 09:14 PM.

[Pigeonto]

No it was the complete job,bored/honed.As I recall he kept the piston fit to the lower of the recommended tolerance so I'd be surprised if it was slap. Not noisy on start up no.Ring gaps...I can see your point but why just front and back of the cylinders. I seem to remember aiming for 11 thou ring gaps and I will see if they are right when I get it apart.Its +60 now so I'm very glad I didnt go to 1380 if it needs reboring

[Fast Ivan]

It looks like uneven wear so something is out of tolerance. It has to be the bore to piston tolerances. Did the machine shop bore and hone to the supplied pistons/rings?

[Pigeonto]

Yes he had the pistons and rings to measure

[Cooperman]

It doess ound like the bores are oversize for the pistons.
You need to measure very accurately and check for ovality as well. That will tell you whether the boring was oversize, thus allowing piston slap and excessive wera on the thrust faces of the cylinders.
It's unlikely to be ring gaps, unless the bores are oversize for the pistons, in which case the gaps would be bigger and thus not as efficient for compression and oil control.
It might be that the machine shop has to bore and sleeve your engine and supply a new set of pistons.
A 1380 was brought to me as re-built by a local engine builder. The bores were, on average, 0.004" oversize. It was not surprising it smoked like a Boeing 707. At 1380 it needed a new block, especially as it had not been offset bored. Very expensive to resolve.

[mk3 Cooper S]

What oil did you run it in with?

[Pigeonto]

Duckhams 20/50

[Cooperman]

How much oil is it using?Running-in after a full re-build it could be as low as 200 miles/pint without it being an issue.
Do you have valve guide stem seals on all 8 valves?

[mk3 Cooper S]

Compression test results?

[Pigeonto]

Inlets only. It just reeks of oil from the exhaust and several people have commented.Wafts up when sitting at traffic lights,very embarrassing.Pretty sure its got worse and the marking on cylinder walls does look quite bad

[Pigeonto]

Compression test results?

not done one recently but when we did a leakage test they were 20%ish and at that time compressions were around 200 (10:1 cr)

[Cooperman]

When you take the oil filler cap off when running, does it 'chuff' smoke out of the filler hole?

[minidaves]

chuck some oil on top of the pistons as see how quick it disappears it should stay overnite, if its disapears instant then apart it comes if not then look at other things before u strip down