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Gents,

 

I took the engine of my GS1000 apart because it had a bad vibration above 5000rpm..

 

When I took the head off I noticed marks in the bores. All 4 bores, on the front and the back of the cylinders. The rest of the bore look like it hasn't done any work at all..

From one piston the top ring is thight in the groove.

 

The piston to wall clearence is 0.14mm, that's within spec of what JE recomends.

The bike has no rattle when cold, but when I've done about 80km or so, the engine is getting some heat in it, I do notice that the engine starts to sound more quiet, les rattle, smoother, you get what I mean I hope.

 

I don't think this is acceptable, would a hone be ok?

I can't find marks on the pistons or rings, pretty sure ring gap is ok, probably on the big side, but will check.

Thing is, if iy's the rings, wouldn't the whole bore be damaged?

 

Thanks

Marks.jpg

Edited by Reinhoud
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I hate doing the imperial to metric conversions so maybe completely 'off the chart' with this . . . . .  1 inch = 25.4mm. 1/1000th inch = 0.0254mm. Most piston manufacturers 'rule of thumb' is 4 thou per inch of bore size, so assuming 78mm bore? = 3 inches give or take, so 4 x 3 = 12 thou clearance which equals 0.3048mm ?

So by my math your piston to bore @ 0.14mm is waaay to tight? - A knowledgeable adult may be along shortly to correct me LOL! 

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Looks pretty normal skirt scuffing to me. Oil film might be breaking down at operating temperatures. Oil brand/grade/service intervals should be assessed.

0.14mm (.0055") piston to bore is OK. Hone it and you will be fine.

Check crank is running true and indexed. Could be the vibration problem if it was not welded.

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15 hours ago, Gixer1460 said:

I hate doing the imperial to metric conversions so maybe completely 'off the chart' with this . . . . .  1 inch = 25.4mm. 1/1000th inch = 0.0254mm. Most piston manufacturers 'rule of thumb' is 4 thou per inch of bore size, so assuming 78mm bore? = 3 inches give or take, so 4 x 3 = 12 thou clearance which equals 0.3048mm ?

So by my math your piston to bore @ 0.14mm is waaay to tight? - A knowledgeable adult may be along shortly to correct me LOL! 

I thought that 0.14 already is a lot!!

I'll see if I can find the instructions, and do some measuring..

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3 hours ago, wombat258 said:

Looks pretty normal skirt scuffing to me. Oil film might be breaking down at operating temperatures. Oil brand/grade/service intervals should be assessed.

0.14mm (.0055") piston to bore is OK. Hone it and you will be fine.

Check crank is running true and indexed. Could be the vibration problem if it was not welded.

Cylinders and pistons have done only 3500km.

 

Crank is welded, it's true and indexed, spend a bit of time to get that right. I found the cause of the vibration I think, was a slight unbalance in the crank, about 25 grams

 

I'll give the pistons and the rings a proper inspection..

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6 hours ago, Reinhoud said:

I thought that 0.14 already is a lot!!

I'll see if I can find the instructions, and do some measuring..

0,14mm is a lot! On my supercharged EFE 0,11mm clearance made piston slap, but pistons were Busa pistons, not JE.

Now with JE pistons there are 0,05mm clearance. No piston slap and no scuffing marks on liners.

 

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Piston to bore clearance is governed by alloy, bore size and application. Check JE's recommendations, but if OP's engine was quiet at running temps the clearance will be fine. I regularly see these scuff marks andthey do not hurt performance or reliability. I would only be concerned if there was scoring or damage to the ring pack. Of course, if a slealership tore it down you would be up for new pistons and a rebore.

Revisiting the original post . . . top land crushing down on the ring is indicative of either excessive heat and temperature, or pistons contacting the head. Hopefully just a bit of excess carbon in the ring groove.

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8 hours ago, Reinhoud said:

I thought that 0.14 already is a lot!!

I'll see if I can find the instructions, and do some measuring..

Apologies - my 0.004 / inch bore related to ring gap - DOH!

The correct figure should have been 0.001" per inch bore, so revised calc is 0.0254 x 3 = 0.0762mm ! So, yes I guess your clearance is sufficient LOL!

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Did some measuring;

Bores are 78.31mm, pistons are 78.13mm = 0.18mm clearence. Max clearence according to JE is 0.17mm

The marks are causes by the pistons, just under the rings.

From 2 pistons the top ring is a bit stuck in the groove..

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19 hours ago, TonyGee said:

cylinder bore service limit is 79.080mm .  piston service limit is 78.880mm.   piston/cylinder service limit is  0.12mm.   from factory service manual.    

I don't understand..

Mine isn't stock..

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16 hours ago, Gixer1460 said:

That certainly won't help! Detonation likely cause?

You reckon?

It did have some detonation, but the grooves were narrow already..

 

I thought of something.. But I don't know if there's a name for it in English (I'm Dutch)..

Last summer I did a bit of a tour through the north east of Tasmania, was about 180km, but didn't ride like a retard, but in Launceston I had to wait for traffic lights, and slow traffic, so the engine probably got hotter then she should.

After that it was 50km back home on the highway, about 10km before I was home the bike sort of died, start running like crap, almost stalled.

Then she went back to normal, and it never happened again after that..

Now I'm starting to think the engine might have been to hot. In Dutch we call that a warmloper, hot runner ;). And that might have caused the the marks in the cylinders..

 

I never abused the bike for a long time..

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3 hours ago, Reinhoud said:

I don't understand..

Mine isn't stock..

Doh !!!!!  what a fecking plonker, i thought for some reason we where talking about a 1200 bandit ??????  just ignore me (its the drugs you know) i'll go away eventually :S 

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Posted (edited)
1 hour ago, TonyGee said:

Doh !!!!!  what a fecking plonker, i thought for some reason we where talking about a 1200 bandit ??????  just ignore me (its the drugs you know) i'll go away eventually :S 

Hahaha, it's a GS1000 with a 1245cc big bore ;)

A Bandit 1200 would have made my life a lot easier most likely ;)

Edited by Reinhoud
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10 hours ago, Reinhoud said:

You reckon?

It did have some detonation, but the grooves were narrow already..

I thought of something.. But I don't know if there's a name for it in English (I'm Dutch)..

Last summer I did a bit of a tour through the north east of Tasmania, was about 180km, but didn't ride like a retard, but in Launceston I had to wait for traffic lights, and slow traffic, so the engine probably got hotter then she should. After that it was 50km back home on the highway, about 10km before I was home the bike sort of died, start running like crap, almost stalled. Then she went back to normal, and it never happened again after that.. Now I'm starting to think the engine might have been to hot. In Dutch we call that a warmloper, hot runner ;). And that might have caused the the marks in the cylinders..

I never abused the bike for a long time..

No one can be absolutely sure as you have a mixture of non stock parts but turbo's and high CR engines tend to pinch top ring lands due to excessive boost creating localised overheating or through detonation. Detonation in a Nitrous engine is a different animal - squashes the ring lands to death then melts everything, usually in less than a second!

Running a hot engine is usually detrimental to the oil firstly, then power loss then if REALLY hot, seizure is a possibility but that would be so hot you wouldn't want to be sitting on the bike going slowly!       'Warmloper' - very descriptive the Dutch language LOL!

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  • 4 weeks later...
On 6/19/2021 at 12:17 AM, rodneya said:

I just looked at the sheet that came with my JE 1270 Kat pistons, and the recommended clearance is 0.0508mm or 0.0020 inch. That is for a 75mm bore.

Your clearance is 3 times more on a 78mm bore

I didn't notice you replied..

 

 

Installatie.jpg

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