Condition opinion:

[Saint aka ML]

Please check photos if pistons/bore and comment:

http://sdrv.ms/1kfJof4

[Capo]

For sure I would not reuse those pistons. The bores are also questionable

[Saint aka ML]

For sure I would not reuse those pistons. The bores are also questionable

Why?

I was looking odd at those pistons as well but bores do not have the same marks as pistons, also bores look identical to my stock 900ss ie bores. As in those lines are symmetrical and from the same pattern so they look to me like machining marks.

[Dookbob]

the black specks on the last photo of the bore are a bit ominous. It looks like pitting, if it is, then it needs reboring at least, if it,s pitted quite deep then it,s a resleeve or a new barrel.
If the marks are not pitting then I would mike up the bores and if there is any sign of ovality, then once more it,s a rebore. If the engine has done 40 or 50 K miles, then dont even bother with the mike, just rebore.

[Saint aka ML]

I had a look at those photos now and they actually look worse then how those parts look in real life.

I know some of the lines are dirt, nothing more.

[Saint aka ML]

the black specks on the last photo of the bore are a bit ominous. It looks like pitting, if it is, then it needs reboring at least, if it,s pitted quite deep then it,s a resleeve or a new barrel.
If the marks are not pitting then I would mike up the bores and if there is any sign of ovality, then once more it,s a rebore. If the engine has done 40 or 50 K miles, then dont even bother with the mike, just rebore.

Black specs is oil.

Engine done about 10k since it was re-bored to 944.

What is mike up to check for ovality?

[Dirty]

Yes they are definitely pistons :)

[Cobra88]

If your gonna reuse those pistons are you also reusing the rings ?

Bores look like a hone might be useful at least.

Hard to tell with so much dirt on for pics ;)

Personally i would not reuse the pistons as one of them has a lot of pickup on its skirt.
But im a fussy bugger :)

Regards
Rick

[crust]

Pistons - I'd replace the rings and polish the marks out of the skirts.

Barrels - The only 'machining' marks you should be able to see are diagonal criss cross lines around the bore - honing marks. The lines running up and down the bore are score marks - you can see evidence of them on the piston skirts. I'd take them to a reboring specialist and ask them to check the ovality of the bores and if they can hone the scores out without going too big.

What air filter have you been using? How often was it cleaned?

[pompone]

If those are scoring marks the nikasil is probably at very best worn out in strips. JE pistons right? A set of rings is not that expensive

[Saint aka ML]

Photos are of my m944. It has JE pistons and big bore. No Nikasil as it is steel sleeve so I can get that replaced.

I have asked as my stock 900ss engine, with 37k on it, (stripped today to use bottom end) has exactly same marks in same place and I was under impression there should be no marks.

I will have pistons polished, bores as well if possible.

Saying that 96mm pistons will also fit yes :)

[Dookbob]

Mike up to check for ovality.
Bores don't wear at the same rate all the way round, they wear more at the front and back of the bore as compared to side to side. Take a micrometer reading about 10mm from the top of the cylinder front to back and then side to side, the difference in the measurements is the amount of ovality. Then take a measurement at the bottom of the bore below the area that is swept by the piston, ie. the bit at the bottom where the piston doesn,t reach. This will be the original size of the bore, subtract that from the front to back reading at the top of the cylinder and that will give you the amount of wear overall.

[utopia]

There are many different types of micrometer (usually abbreviated as mic but pronounced as "mike") but the one that you need is not the common type which measures outside diameters.
You need an internal micrometer/bore gauge and furthermore, it has to be in the correct range to be able to measure your bores. These are basically a T-shaped device where the leg is a handle and the cross-piece is a graduated measuring screw, as in a normal (external) micrometer.
I'm guessing that you won't have one of these, and even if you did their use requires a bit of a technique for accurate results. The best bet would probably be to get these measurements done by a professional.
There is possibly a cheaper way to measure the bores though, and that would be to use a pair of inside calipers. These are extremely simple devices which should be cheap enough to buy for just a few quid.
They will not give you an actual measurement reading (ie a number) .... they are comparative devices only able to compare one measurement with another.
But by first setting them to the dia of the unworn lower section of the bore, you should then be able to detect a difference when you try them in the worn areas.
If you're really good, you could possibly then measure this difference with feeler gauges.
Its a tricky process though, involving a fair degree of mechanical "feel" which may elude someone doing it for the first time. ....but the same goes for using an internal mic too.

But there are many types of wear, and a component with a scored surface may still appear to be more or less dimensionally correct, but might be unusable simply due to the damaged surface finish.

Another way to check for wear in the bores might be to feel with your finger or fingernail for a lip or ridge very close to the top of the bores where the piston leaves a short section untouched as it goes over TDC.

As Crust implies, the type of scoring in your pics could well be due to the engine being run without adequate air filtration.
But its hard to judge accurately from photos.

Internal calipers look like this.....
http://www.ebay.co.uk/itm/Silverline-656583-Internal-Spring-Caliper-150mm-/130785009386?pt=UK_Measuring_Tools_Levels&hash=item1e7364deea

Or like this...
http://www.ebay.co.uk/itm/2pcs-140mm-Length-Machinist-Metal-Friction-Joint-External-Internal-Calipers-/121166471502?pt=UK_Measuring_Tools_Levels&hash=item1c3615a14e

Internal micrometers look like this.....
http://www.ebay.co.uk/itm/Internal-Bore-Gauges-/251276596377?pt=UK_Measuring_Tools_Levels&hash=item3a81409499

[Dookbob]

That internal " micrometer" is actually a bore gauge, they will help you get the measurement you are looking for from the cylinder bore, but you would still need an outside micrometer to measure the bore gauge.
If you don't have access to the required measuring devices I would keep it simple and use what Utopia refers to as " the finger nail test". Feel for the ridge at the top of the bore, if there is no ridge , or if there is only a very small ridge then build it and run it. If there is a pronounced ridge then new pistons and rebore.
If you are happy to check the bore and piston wear with a set of feeler gauges then remove the rings from the piston, taking note how they come off, ie. they need to go back exactly the same way up and in the same groove. Hold the piston at the bottom of the cylinder and check the gap between piston skirt and cylinder bore, measure at a point 90 degrees from the gudgeon pin, that will tell you how much the piston has worn. Then turn the piston round and put it back in the cylinder upside down and do the same again at the top of the bore just below the wear ridge, this will tell you how much the bore has worn.
Bear in mind that the normal clearance on new parts is usually one thousandth of an inch per inch of bore diameter.

[Saint aka ML]

Ok by finger there is no ridge at all anywhere on bore or piston. It feels smooth as baby's bum where piston rings work. Where rings never get to it is still smooth with no ridge or bump in transition but feel of bore is slightly different.

Frankly those pictures were not good as after I removed oil and cleaned cylinder plus bore with smooth cloth but firm pressure few of the vertical lines went away, some mostly away.

[Rockhopper]

At 10,000 miles I'd have expected to still be able to see the original honing marks on the bores. The pistons are certainly scrap though.

[Saint aka ML]

Thx for all teh replies.

Now I want to know why pistons are scrap?

I mean there are always rocking marks on pistons as pistons rock at top/bottom of movement living slight marks. They are however smooth to touch with no groves and look the same as other sets of pistons I have from stock, healthy engines (they also have rocking marks).

[Dookbob]

Ok, here we go with the final analysis, screw it all together and thrash it up the road. If it don't drink oil or smoke, then it's ok.

[Saint aka ML]

Ok, here we go with the final analysis, screw it all together and thrash it up the road. If it don't drink oil or smoke, then it's ok.

It was not drinking oil or smoking before I put it apart, it was spitting oil back to airbox but looking at crank return valve well it was blocked.

[utopia]

That internal " micrometer" is actually a bore gauge, they will help you get the measurement you are looking for from the cylinder bore, but you would still need an outside micrometer to measure the bore gauge.


Ah yes, correct. Its been decades since I used them.
Though I guess you could still use them comparatively in conjunction with the feeler gauges.
A true internal mic would give an actual measurement and, for the record, would look more like this.

http://www.ebay.co.uk/itm/SHARDLOW-2-8-INTERNAL-MICROMETER-COMPLETE-WOODEN-BOXED-/310806865563?pt=UK_Measuring_Tools_Levels&hash=item485d88669b

[Dookbob]

Great, Unblock the valve and put it all back together.

[Capo]

Blocked with what?

[Dookbob]

I did wonder about that too, but didn,t want to make a fool of myself by asking, but now I,m not the only one I will. Blocked, with what?

[pompone]

I may be wrong but isn't the valve a regulated way up, not return? (Hence the reed system?)

[Capo]

I may be wrong but isn't the valve a regulated way up, not return? (Hence the reed system?)

Indeed this is true, however there is a small hole about 2mm dia that allows oil to return by gravity to the engine from the separator.

[pompone]

Indeed this is true, however there is a small hole about 2mm dia that allows oil to return by gravity to the engine from the separator.

So how much oil are we talking here? Has to be a sizeable amount to fill the pipe work, the separator and end up in the airbox. I'll be surprised if a blocked 2mm hole would do that. Further investigation is needed I think.

[Saint aka ML]

Well it was spitting it inside only at sustained high revs so for example town riding up and down rev range all good. Constant 90 or more meant up to about 20ml of oil in 1 hour.

Saying that if I oil level dropped to about 3/4 below high oil level mark (still within markings) it was not spitting it out at all or maybe a occasional puff to airbox. Box was moist with oil only.