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Bore Ridges

geodoc

geodoc

Cruisin' Guzzisti
Joined
Oct 27, 2008
Messages
205
OK, this is not from a Guzzi, but I'm perplexed.

This is a cylinder liner from a Triumph T150 Trident used for vintage racing. After an oil pressure loss caused by stripped drive gears at Ridge Motorsports Park this past weekend, this was found on the center cylinder. The other two cylinders looked fine. The rod big-ends & bearings were torched, crank cracked at one of the big end journals ..................... and this found on the center cylinder.

The pistons looked OK - no stick rings or evidence of blow-by.

It was raced a few weekends before with an incorrectly calibrated tach that had it probably reving to over 10,000 RPM - 1000 past it's normal red-line.

So what would cause wear like this? Ring flutter during over-reving?

Stumped ..........................

George

ridges.jpg
 
Being the middle cylinder and the oil pressure loss you'd think it would be seizing due to heat but I have never seen a pattern like that before - kind of interesting.
 
2 things come to mind: Worn ring land on the piston allowing the ring to flutter (as you said) & possibly an incorrect (not enough) end gap on the ring.

With the rings on the pistons use a feeler gauge to measure & compare how much ring float there is on each ring. You can also take the rings off the piston and put them in the cylinder and measure the end gaps for comparison. Keep the rings matched to the cylinders. To make sure the ring is square in the bore you can slide a piston in the cylinder and then push the ring down on top of the piston. Slide the piston out and measure the end gap. Repeat this at different heights in the bore and you can see if you have an out of round cylinder.

Trout
 
Yep, ring-to-piston-groove clearance checked on assembly and were end gaps. Std. stuff. The stumper is that this was only on the 1 cylinder. Seems like it would be on all 3 if it was ring flutter from over reving. Then again, perhaps there is a harmonic component to this and the center cylinder is where that shows up 1st. ?????????????

The bore diameters (taper) has not been measured since the bore is shot and rathar than bore all 3 cyl. to the next oversize, just the center bore is getting a new sleeve & bored to the same as the 2 outboard cylinders.

Will be measuring the piston and ring lands today on the effected piston. It all looks unaffected, but we'll see.


Trout said:
2 things come to mind: Worn ring land on the piston allowing the ring to flutter (as you said) & possibly an incorrect (not enough) end gap on the ring.

With the rings on the pistons use a feeler gauge to measure & compare how much ring float there is on each ring. You can also take the rings off the piston and put them in the cylinder and measure the end gaps for comparison. Keep the rings matched to the cylinders. To make sure the ring is square in the bore you can slide a piston in the cylinder and then push the ring down on top of the piston. Slide the piston out and measure the end gap. Repeat this at different heights in the bore and you can see if you have an out of round cylinder.

Trout
Click to expand...
 
Why just one cylinder ?

Sorry I don't know the english for "calage" : the pattern (angular distribution & order) of the explosions seems to assymetrically distribute the load on the cylinders/pistons/rods/etc. Not sure this is relevant here, but as an example : on Harleys, the front cylinder well seems to be the hottest one.
 
ChopSauce said:
Why just one cylinder ?

Sorry I don't know the english for "calage" : the pattern (angular distribution & order) of the explosions seems to assymetrically distribute the load on the cylinders/pistons/rods/etc. Not sure this is relevant here, but as an example : on Harleys, the front cylinder well seems to be the hottest one.
Click to expand...

Rear cylinder on a Harley as it has restricted air flow. To solve this some model Harleys will now cut spark & fuel to the rear cylinder when idling.
 
The reason that the rear has the ignition killed at idle is that when in a run condition it heats the riders legs uncomfortably.
Nothing to do with airflow because there is none at idle.
 
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