KR-1S.co.uk Forum

today I openned my engine after I lost a cylinder during a ride .(more than six months ago ). it was only the second ride after an engine rebuild. everything was new : cranck with new seals/bearrings, 2 new pistons (Wöesner), left cylinder was newly plated, right one was still ok.

took off the right exhaust first (it was the right one that didn't work any more) and I only saw some minor damage on the rear transfer port. So I thought I was lucky ...

... untill I took the cylinder off ...



the metal between the rear transfer port and and the port below it (these are tuned KR1 cylinders) is gone first time ever I see this kind off damage.

engine was doing ok before it happened. when exciting a corner I thought I heart a slight change in the noise from the exhausts so I pulled over. at no monet it felt like a seizure or made it mechanical noise.
don't know what happened, but looking at the cylinderhead, I guess there was a problem from the beginning, since the right one has almost no colouring :



and this is what the piston looks like at the back, at the front it still looks like new :



hopefully I'm lucky with the cranck , it's still in the engine, but when turning it round I can't feel anything abnormal. fingers crossed [-o< I just wonder where all the metal has gone then . Or dit it go on top off the piston , desintegrate and "metal-blast" the dome off the head ?

HOLY CRAP!!!
Looks like a ring has on snagged the boost port during the up-stroke, but I'd think there must have been some fatigue from a previous failure or something to cause it to brake off like that.
I'd be seriously concerned about that crank though. That's a lot of debris floating around in there if it didn't brake up an exit through the exhaust.
I guess your pretty damn lucky that it didn't go staight into the combustion chamber in one piece causeing a mechanical siezure as you were exiting that corner.

It is caused from the port window not being dressed/radiused correctly

.

Agree with Scotta - judging by the fracture angle on the port bridge it happened after BDC - on the up stroke.
But that doesnt tell you what was going on, only the end result.
mmmm not the first failure on here running Woesits
where is the ring gap position on Wossners - others have run with a ring gap in the port but probably not on B series barrels (boost port bridge)?

I know of a KR ridden for 20 miles on one cylinder after lunching itself - you CAN get away with JUST flushing the case out carefully with methylated spirits and bits of rag if youre not going to split the cases (so long as it didnt happen because of cooked bearings) - see if you can find the debris in the exhaust pipe.

Theres Not much damage to the head from what I can make out, so probably bits made it out early. Pull the piston maybe the little end/pin shows signs of a lubrication problem (piston is flopping forward under its own weight though). From direction of engine rotation laymans guess would be if the piston was to seize on the rod it would jamming into the main exhaust port not the back side of the bore.
running premix? otherwise check for airlock in your injector pipe.

What breed on conrod is that ProX? (isnt standard) - or is that what you have to run with on those pistons?
Those conrod faces look polished to an edge? I'd be wondering if there should be a radius along the stressed edge (at least from a design perspective). (Might cause an I-beam to twist or buckle with temperature or load)

[There is looks some minor pitting/melting on the crown - detonation? (squish, deck height, rod length)? One barrel was reconditioned - were they identical heights afterwards? the tops of the barrels get ground/milled after replating - but THEN youd expect the problem to be on the left cylinder (shorter) not the right]

The back half of the piston and bore seem to show lots of pick up - questioning roundness or tolerance/size. [The water galleries look rusty]
You reused a head gasket (or is it o-ringed? cant tell). (Is that base gasket still on - looks moist, came off in one piece?) The right chamber is probably so clean because has been Steam cleaned by coolant? this might account for uneven lubrication on the bore.

the inner powervalve (right cylinder) looks a bit cleaner than the others - maybe head water has leaked back down the spool and pushed into cylinder on a returning exhaust wave

the Jury is hung Im afraid - let me know if you find Kennedy's bullet somewhere in there.

[apology for any perceived critisms]
.

try a bit of petrol pipe attached to a vacuum cleaner nozzle to suck out
any bits of metal that might still be loose in the case

what other vacuum attachments has Bruno lent you... GARRY?

Borat gets in touch with his feminine side...
http://www.meinspace.com/bruno

off course I'm going to split the cases, would be very stupid not to.

.

you did the right thing JAN, pulling over - a less mechanically sympathetic person would have pinned it and hope it cleared itself out...
was the best outcome, since continuing might have been personal injury and far more expensive repair.

the final reward of riding a stroker is making it home in one piece.

.

Probably a good idea to pull the crank apart dude. Even if the majory of big bits have made it out the exhaust, you can bet your balls there are little bits hiding in the bearings that wont come out...
Also maybe measure the conrod for straightness and twist from eye to eye now that its had a hit. Or you may wind up lunching another cylinder as soon as you put it back together.

But from the point of view of someone who doesnt have to pay for it, it was a pretty cool effort! =D>

found out what the problem was last week, when I wanted to reinstall the other cylinder .

apparently, the woesner piston's have the pin's that secure the rings not on the original position, but "somewhere nearer " to the centre off the bore. by "somewhere" I really mean somewhere : had already a new piston, and that one was closest to the original position : the outer end would run on the cilinder, but the inner was going in the port. the damaged one was the worst : pins were 0.5cm closer to each other than original. The "good" piston that was still in the cylinder untill last week, wasn't that good after all : one ring-end (to the centre) was missing, on the other ring it was already bent. on the top off the piston, there are about 4 very little punchmarks from the missing piece, and it's hammered in the piston upon another mark

took everything to the importer, including a cylinder and an original piton, and he is gonna send them everything, with a "nice request" to get me 2 piston's with the pins in the correct position. I can't run other piston's since one cylinder has an oversize, and woesnner are the only ones who make them. Will take a while though ...

I know some people run rings with the pin in the centre port. Going up won't be a problem, but going down definitly is. Maybe it the pins is in the centre, the rings won't come out too far, but if the are close to the bridge between the ports, the inner side definitly comes out too far . Knowing this now, I'de never do it, and from now on, I always will check the pins .

Hi Jan,

have you heard anything from Woessner since your last posting?

Charles

Whenever I have a KR-1 cylinder to replate I get the plater to weld up that silly second boost port.

Charles wrote:Hi Jan,

have you heard anything from Woessner since your last posting?

Charles

I saw the importer last week and still no news. He told me though it could take some time. They are not just gonna make 2 piston's for me, I'll have to wait untill a production-lot is planned

TwoStroke Institute wrote:Whenever I have a KR-1 cylinder to replate I get the plater to weld up that silly second boost port.

I just cleaned it up nicly so now I have one big port

only downside I see is that the ring has less surface to give away it's heat to the cylindre.

JanBros wrote:

TwoStroke Institute wrote:Whenever I have a KR-1 cylinder to replate I get the plater to weld up that silly second boost port.

I just cleaned it up nicly so now I have one big port

only downside I see is that the ring has less surface to give away it's heat to the cylindre.

It's been some time now since the piston problem. Did you ever get a reply /explanation from Woessner?