17 replies to this topic

[minivanman8]

Looked in through my spark plug holes today at the bores. What does this look like to you? Seems quite worn looking. Could it be bore wash?

 

 

[KernowCooper]

AC will shed some light on that vertical scoring

[Icey]

Looks like light piston scuffing. I would suspect either oil issues (lack of or low pressure) or possible worn rings and/or bore.

But! I would hang on for the likes of AC as Kernow says, I'm not 100% in my comment.

[Dusky]

Is it a fresh rebuild?

[Carlos W]

If it's a fresh build it may be that the pistons are too tight in the bores

[carbon]

As above, is this a freshly rebuilt engine?

 

Another recent post on this forum had issue with new rebuild using replacement pistons. The ring grooves were not deep enough for the rings fitted, which came with the replacement pistons.

 

In this case I think the engine would not even turn over, which alerted them to this problem.

[minivanman8]

Fresh build. 0.005" bore to skirt clearance (mid bore 90 degrees to pin line) bored by Vmax.

New Omega Pistons supplied by MED with rings.

Got oil pressure before starting do the first time. It's always had good oil pressure since then.

Been on running in oil for first 200. Changed oil filter after 130 ish miles. Just dumped that at the weekend to switch to millers classic 20/50 and another filter change. (Not run it yet with that oil)

[whistler]

Just rebuilt my 1293 after only 1200 miles 'because of tensioner snapped and wanted it balanced. Strip down revealed same as yours on all 4 bores. All pistons showed scuffing on both sides. Machinist checked measurements and rehoned bores another half thou. No definitive answer, suggestions were overheating, dirty oil, lack of oil, bores too tight, pistons too large and on and on. Measured bores, ring gap, ring depth, piston diameter. Couldn't find an answer so as I said, rehoned, wet'n dry the scuff marks on pistons and reassembled.

Pistons were County 21253 +20.

Love to hear if anyone has an answer for yours.

[carbon]

Fresh build. 0.005" bore to skirt clearance (mid bore 90 degrees to pin line) bored by Vmax.

New Omega Pistons supplied by MED with rings.

Got oil pressure before starting do the first time. It's always had good oil pressure since then.

Been on running in oil for first 200. Changed oil filter after 130 ish miles. Just dumped that at the weekend to switch to millers classic 20/50 and another filter change. (Not run it yet with that oil)

5 thou clearance on the skirt sounds quite large, are they forged pistons or is it a turbo engine?

[minivanman8]

Forged and supercharged

[minivanman8]

Fingers crossed there's an answer in it for us both whistler!

Vmax were adamant that 0.005" was correct. There was a slightly contrast story from MED. they thought nearer to 0.003"

[Spider]

Mate, awesome photo - how did you manage to take that?

 

In regards to what it shows, It doesn't look worn, but as others have said, scuffed.

 

Could be a variety of reasons, being what appears to be more towards the mid stroke of the bore, I'd say the honing wasn't done right and was left in an hourglass shape, ie, it is undersized mid-stoke. Can't really say much more without stripping it down.

 

How's it been driven to his point?

[Magneto]

Are you running an air cleaner?

[ACDodd]

Usually in my experience pistons can be a bit tight with a wear pattern like that. Can also be thrashing from cold. Measurement is key here. No good asking opinions really, it needs checking if there are problems. Is it burning oil? Are there any problems with it? Or is it fine and producing  good power. If it is it will cause no harm.

 

AC

Edited by ACDodd, 17 May 2016 - 11:01 PM.

[minivanman8]

Just iPhone with a pen torch shining down the bore.

Driven carefully. Gentle loads. Not grandad driving but not with a heavy foot.

Mostly around town so plenty of engine speed changes.

No oil burn as yet. No untoward noises. 0.005" skirt clearance mid bore.