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I would actually say yes it could be the reason for the compression issues as the upper limit is there to limit the gap between rings and bores, if the bore is bigger than the upper limit with a hot engine this could be enough to drop some compression 

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3 hours ago, Mickly said:

That’s the conundrum - is 0.05mm above the tolerance enough to make the difference?

I would be tending towards new rings but I dread to think what they will cost for a Triumph ,  and a light hone to allow them to bed in . By the way , were all the rings completely free to expand when freed from the bores ? 

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.005mm is roughly 2thousands of an inch ...may not seem a lot but in engine engineering that is a lot

And remember that the rings are there to create a seal and if they can't expand and maintain that seal ... Not doing their job

Plus consider the extra wear placed on the liners caused by the slop in the pistons travel where the rings are not cushioning so to speak will mean that tolerance is even more critical .

 

 

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10 hours ago, TimR said:

.005mm is roughly 2thousands of an inch ...may not seem a lot but in engine engineering that is a lot

And remember that the rings are there to create a seal and if they can't expand and maintain that seal ... Not doing their job

Plus consider the extra wear placed on the liners caused by the slop in the pistons travel where the rings are not cushioning so to speak will mean that tolerance is even more critical .

 

 

He's talking end gap, not side gap.

@Mickly - how square were the rings when you measured the gap? A little bit on the wonk and you'll get a false reading.

Also, you should take a number of readings down the bore to give you an idea of whether it's the rings or bore that's worn.

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15 hours ago, fastbob said:

I would be tending towards new rings but I dread to think what they will cost for a Triumph ,  and a light hone to allow them to bed in . By the way , were all the rings completely free to expand when freed from the bores ? 

New rings are £45 per piston !!

yeah, all the rings were free when the liners came off.

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4 hours ago, Mr Fro said:

He's talking end gap, not side gap.

@Mickly - how square were the rings when you measured the gap? A little bit on the wonk and you'll get a false reading.

Also, you should take a number of readings down the bore to give you an idea of whether it's the rings or bore that's worn.

Good point, I did try to ensure they were square, I’ll measure the distance from the end of the bore to make sure it’s square.

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44 minutes ago, Mickly said:

Good point, I did try to ensure they were square, I’ll measure the distance from the end of the bore to make sure it’s square.

Get the ring in and poke the piston up after it - presto, nice and square.:classic_cool:

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Beyond the upper tolerance . Well it's set for a reason I suppose . I couldn't actually tell you whether that is enough to cause a drop in compression or not . Generally , by the time an engine gets to me it's usually obvious what's wrong with it from the smoke or the telltale stink of petrol in the oil . 

1 hour ago, Mickly said:

New rings are £45 per piston !!

yeah, all the rings were free when the liners came off.

While we're on the subject of pistons , remember my ER5 ones ? Now look at them . There's still some bad scoring on on side of both the skirts but what I thought to be severe scoring around the rings has all scrubbed off with a Scotch Pad . So what was going on here ? I think all the carbon in the combustion chambers came loose when I initially fired it up and revved it . The lower portion of the bores is also quite badly scored so I would have replaced them anyway . Coming as it did from a training school , I wonder whether  this scoring is a result of the bike lying on the ground while still revving it's tits off ? 

Polish_20201121_154157814.jpg

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1 hour ago, fastbob said:

Beyond the upper tolerance . Well it's set for a reason I suppose . I couldn't actually tell you whether that is enough to cause a drop in compression or not . Generally , by the time an engine gets to me it's usually obvious what's wrong with it from the smoke or the telltale stink of petrol in the oil . 

While we're on the subject of pistons , remember my ER5 ones ? Now look at them . There's still some bad scoring on on side of both the skirts but what I thought to be severe scoring around the rings has all scrubbed off with a Scotch Pad . So what was going on here ? I think all the carbon in the combustion chambers came loose when I initially fired it up and revved it . The lower portion of the bores is also quite badly scored so I would have replaced them anyway . Coming as it did from a training school , I wonder whether  this scoring is a result of the bike lying on the ground while still revving it's tits off ? 

Polish_20201121_154157814.jpg

My pistons don’t look anything as bad as that. The bikes only done 30k so I’m scratching my head about how the compression has dropped, these engines are renowned as being robust, the early Hinckley Triumphs were over engineered to break the link to the bad reputation that the Meridan bikes had developed.

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On 21/11/2020 at 15:10, Mr Fro said:

Get the ring in and poke the piston up after it - presto, nice and square.:classic_cool:

Right, taking @Mr Fro ‘advice I’ve measured all the gaps - I checked that the top ring gap was the same, top middle & bottom down each liner, which they were although they differed across the liners.

024BE6A3-19D2-4E74-A6C3-D85512DDF1D3.thumb.png.0f7cc5580c45999636d973b5466d860e.png
so it seems that all gaps are within tolerance although towards the top end .... The head scratching continues !!

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1 minute ago, Mickly said:

Right, taking @Mr Fro ‘advice I’ve measured all the gaps - I checked that the top ring gap was the same, top middle & bottom down each liner, which they were although they differed across the liners.

024BE6A3-19D2-4E74-A6C3-D85512DDF1D3.thumb.png.0f7cc5580c45999636d973b5466d860e.png
so it seems that all gaps are within tolerance although towards the top end .... The head scratching continues !!

Looks alright. Did you check the ring gap at a few points down the bores?

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3 minutes ago, Mr Fro said:

Looks alright. Did you check the ring gap at a few points down the bores?

Yep

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Right, I’ve found a place that will skim the head, hone the barrels (& properly clock them) & reseat the valves.

I decided to remove the valves myself to have a look at the condition of the seats.

obtained a cheap valve spring compressor & oh bugger, because it’s a shim & bucket arrangement it can’t act on the spring76480527-FEB9-4901-BBF9-1618E19E22D8.thumb.jpeg.f5968738a0205c9083d0373f2608e77c.jpeg

coz it’s hidden. So a bit of head scratching & with the help of a modified old spark plug socket ..



64F9AD7B-DFE0-4EC3-A67C-96C65D23455B.thumb.jpeg.c911d5dee426a1968a00fa5987055572.jpeg

all 16 out - it got easier as I got the knack, still took 3 hours !!

C2E32A68-BC68-4061-B7B4-D577D330954F.thumb.jpeg.a212b1f2fca615638b4e037d8ff41fd6.jpeg
All out, Tagged & bagged.

The inlet valve seats look ok, the exhaust seats look a bit crusty, but passed the diesel test?

5E5B2D60-A419-4A56-B28B-CC9713F6C018.thumb.jpeg.658fd221496eafbae1c8aa4634517a27.jpeg

866BD31A-DAAC-43F4-85E4-057F9C67B6B7.thumb.jpeg.a0f359937e86900979d3cb08ff5010fc.jpeg
exhaust valve.

Edited by Mickly
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Even though my Z500 valves passed the liquid leak test they looked like yours. I filled the port up with water and blasted my airline around the valve seat in the combustion chamber and saw bubbles at certain points. a light grind in sorted it. worth a try just keep them press in with the spring compressor no need to refit the collets to test, see photos

Regards

Rob

 

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