Decided to replace the piston rings and at the same time strip down the bike for a good clean up.

First indication of that something was wrong i got at the end of last year. The engine didn't rew as easily as it should and it seemed a lot weaker at the top. Didn't have the time then for a inspection. First inspection this year showed that the RC-valve cables to the top cylinder were loose and that two screws to the RC-valve thingy on the cylinder was gone (later found on the engine covered in tar). Perhaps the vibrations made them unscrew themselves. Now, thinking I'd found the solution to the problem I continued with disassembling the bike and cleaning it.

Problem 1
Later, after removing the reed valves i could spot some little shiny metal objects at the bottom of the crank case housing. Intake to top cyl.. I picked up the objects with a magnet (so they are not from any aluminium part, but a bearing perhaps?). Metal objects What do you guys think the metal pieces come from? I am going to disassemble the engine later so we will know for sure later (if not the pieces came from outside the engine...)

Problem 2
Next step was to remove the cylinders, and what I saw then was not so nice. Top piston (without the piston ring on top). Obviously the piston have been exposed to extensive heat near the cylinder wall causing detonations. But why? Perhaps to little oil mixed with the gas? Bad jetting?
This is the bike set up:

Oil pump set to max.
165 main
Type B needle with the clip in the middle (i think)
42 slow jet
Two oval high flow air filters
HRC pipes
Parts from HRC wiring harness modified to stock harness, only changing ignition
Running on 98 octane unleaded gas
Running on Castrol TTS fully synthetic two stroke oil

Problem 3
There is also wear on both pistons at the exhaust side. Lower Piston & Upper Piston. The guy I bought this bike from was smart enough to fit the pistons with the piston ring opening towards the exhaust port, making the rings bend slightly in to the ports and making massive wear at the nicasil. The guy i later payed to replate the cylinders sent them to a company in England, which I think was Langcourt. Do they have a good reputation? I wounder since I think the replating of the nicasil was badly done Top Cylinder & Lower Cylinder

I have ridden the bike approx 4000 km since the replating, when I also installed new pistons with rings. And it was perhaps 1500-2000 km since I changed the setup of the bike with new pipes, air filter and jetting.
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MC21, GP-Replica (Daijiro Kato, Telefonica Movistar Team 2001)


Last edited by Bodoe on Sun Jun 10, 2007 9:47 am; edited 1 time in total

Langcourts, a good reputation? No!
Apart from being well known for hacking 1mm off the deck height (measure your cylinders, R spec cylinders are marked "H" and should be 86.3mm tall. The SE/SP cylinders are marked "L" and should be 86.5mm tall) their plating quality is a little questionable at times.

165's sounds very lean if you're not running the power jets.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

I have measured the inside of the cylinders with a piston ring and then measured the gap in the opening of the ring. Thought that the bore in the top cylinder was smaller than the other, but they were, as far as I could se the same (~0,55 mm). Will have a look at the height then! Will also have a look at my older pistons to see how they look, to bad I didn't mark them so I would know if the were mounted top or low.

My power jets are not plugged. Have been testing bigger main jets and with spark plug readings have come to the conclusion that 165 is OK, maybe a little rich.
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MC21, GP-Replica (Daijiro Kato, Telefonica Movistar Team 2001)

Are theese the "H"-marked cylinders you were talking about (in this case fitted on to a SP engine)?


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MC21, GP-Replica (Daijiro Kato, Telefonica Movistar Team 2001)

That doesn't look like detonation to me. That looks like the ring broke. Is that the same cylinder with the broken power valve?
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james
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The rings are intact. You have maybe looked at the picture where the ring was removed (used for measurement inside the cylinder).

None of the power valves is broken. But the surface, replated nicasil, around the valves, and especially the bridge, are damaged. Maybe because of a bad replating job.
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MC21, GP-Replica (Daijiro Kato, Telefonica Movistar Team 2001)

Or because the muppet previous owner fitted rings the wrong way and they broke, but he didn't fish the bits out of the crank case?

What size are those recovered pieces?
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Pieces are about 10-5 mm. They are soft in the edges so they seem to have been in the housing for a little while, but then it wont take much time for a sharp object to get round when rewing the engine.

Here's another pic.

I don't think they are from the previous ring. And also not from any bearing at the crank, since they go around pretty smooth. But to be sure I will of course take a closer look at the crank case.

Any one think the three problems are linked together? (metal object, detonation (?) and piston wear at exhaust side).

The metal object and the detonation was both on the top cylinder, and also the loose wires to the power valve was on this cylinder.
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MC21, GP-Replica (Daijiro Kato, Telefonica Movistar Team 2001)

Well, if they aren't from the inlect tract (reed cage) and not from the piston, bearings or any other part of the engine you currently can see, they MUST have come from outside.

Perhaps he was running open carbs and those bits got sucked in? Will they fit through the reeds?

Has it had a top end rebuild, and those bits dropped in whilst the piston wasn't fitted perhaps?
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

The pieces could have come through the reeds. When disassembling the engine it will become clear where they came from, outside or inside. If they come from outside the engine there is not much to do. Byt where they come from is not my main concern right now. Now I'm trying to figure out the other problems (2 and 3).

I've tried to measure the the cylinder height but having only a vernier caliper dosn't make the measurement as precise as I want to. They are somewhere around 86 mm.
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MC21, GP-Replica (Daijiro Kato, Telefonica Movistar Team 2001)

It looks like the reason the exhaust side of the piston has picked up is the exhaust bridge hasn't been a, relieved at all or b, hasnt been relieved enough.

From the photo I would say they havnt been relieved at all.

Plus circlips in pistons shouldn't be fitted like that.
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If I have to take the carbs off once more...

Problem two is just from running a little lean I think, so that'll be sorted by jetting correctly.

Problem two will be corrected by fitting the piston pin circlip the right way and installing the rings correctly, together with a little relieving as Stephen says.

I have use Langcourts twice, and had varied results. Firat time wa perfect, second time I had to return the barrel for replating and cleaning up. I won't use them again!

Once you're certain those bits come from outside the engine, get it back together with new parts, and sort the jetting.
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

What do you mean with "relieved"?

And what is wrong with the fitting of the circlips? And how can they affect the piston depending how they are fitted? Unless they don't fall out of place I don't see any problem.

Thanks for the help! Appreciate it a lot!
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MC21, GP-Replica (Daijiro Kato, Telefonica Movistar Team 2001)

The clips should be rotated round so the ends are opposite the slot, or you risk the ends springing out. Inlikely, but a risk you might as well do without.

Relieving is to make the edges rounded.
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

The exhaust bridge its self should be releived back (ground back) so the piston doesnt touch it (as much). This way when the bridge exspands it doesnt cause the piston to seize on it (like yours has).
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If I have to take the carbs off once more...