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Old 02-23-2013, 10:18 AM   #74056
planemanx15
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Could I just get new rings and fix this?
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Old 02-23-2013, 10:19 AM   #74057
Adv Grifter
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Yes ... I remember from your build thread that you had trouble getting the piston into the bore and trouble compressing the rings. I remember you mentioned it was a "TIGHT FIT". To me that is a Red Flag. Either you were given incorrect rings or out of spec cylinder or incorrect piston. (???)

Did you measure each piece before assembly?

Perhaps the ring gaps were not positioned correctly? And of course measuring ring end gap is part of the process.

When you do this again ... try to organize your work area a little better.
Take your time, go step by step, check everything along the way.

New sleeve (or barrel), piston & rings?

Good luck, let us know what you find after measurements ... maybe you've got a refund due you?

Quote:
Originally Posted by planemanx15 View Post
Could I just get new rings and fix this?
No way. The Piston an cylinder are badly scuffed ... They look finished to me. Bummer.
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Old 02-23-2013, 10:37 AM   #74058
TinkerinWstuff
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Quote:
Originally Posted by planemanx15 View Post
The exhaust sounds fine, its just the valves, as if I adjusted then on the wrong TDC. But like you said the bike was fine right before and only started this under a highway load. Im 100% sure I did the valves on the correct TDC.
Obviously the scoring you found is a problem....

I'm suffering through a safety seminar today and unable to listen to your video at the moment; just wanted to share that my high compression piston upgrade also introduced nasty noises that progressively got worse. I replaced the spring loaded cam chain tensioner with the manual one I bought from Procycle and she's smooth as silk again.

I would recommend getting one on order to install once you've corrected the scoring problem.
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Old 02-23-2013, 10:42 AM   #74059
procycle
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Quote:
Originally Posted by planemanx15 View Post
As I said in my build thread, I did not measure the end gap. I assume had I done this, I could be riding today.
Quote:
Originally Posted by Adv Grifter View Post
of course measuring ring end gap is part of the process.
Quote:
Originally Posted by planemanx15 View Post
Could I just get new rings and fix this?
The first step would be to hone the damage out of the cylinder. This must be done with a rigid hone not a spring loaded or ball hone. Then measure to see if the bore will still be within spec. If you're lucky it may still be usable. It just depends on how deep the scores are in the cylinder wall.

You'll need at minimum a piston and rings. And of course check the ring gaps and file them as necessary to avoid a repeat.

The ring instructions call for .0045" of gap per inch of bore for the top ring. This works out to .020" Because DR650s do such good job of cooling the piston and have an air cooled cylinder I fudge this spec down to .018". The second ring should have a .004"-.008" larger gap. The oil control rings should have a minimum of .015" gap.
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Old 02-23-2013, 10:50 AM   #74060
planemanx15
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Quote:
Originally Posted by procycle View Post
The first step would be to hone the damage out of the cylinder. This must be done with a rigid hone not a spring loaded or ball hone. Then measure to see if the bore will still be within spec. If you're lucky it may still be usable. It just depends on how deep the scores are in the cylinder wall.

You'll need at minimum a piston and rings. And of course check the ring gaps and file them as necessary to avoid a repeat.

The ring instructions call for .0045" of gap per inch of bore for the top ring. This works out to .020" Because DR650s do such good job of cooling the piston and have an air cooled cylinder I fudge this spec down to .018". The second ring should have a .004"-.008" larger gap. The oil control rings should have a minimum of .015" gap.
Alright, sounds good, thank you for the weekend help .

Please PM\email me when you get a chance about the cost of a new piston and rings and a possible cylinder exchange.

I just went to look at it again, and the cylinder seems fine, it suffered very minimum damage compared to the piston. How can I tell for sure if its okay?

Top ring: .020"
2nd ring: .024-.028"
Oil ring: .015"
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Old 02-23-2013, 01:12 PM   #74061
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So sorry for the results, PM. The school of hard knocks has taught me to read instructions twice, go slow & follow the step by step. I still get caught occasionally being a guy....and then going back to do it right.

I'm sure with some measurements, PC will be able to tell you if it's recoverable with a hone, new piston & rings.

Best of luck with the fix.
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Old 02-23-2013, 02:04 PM   #74062
Carl Childers
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Quote:
Originally Posted by planemanx15 View Post

I just went to look at it again, and the cylinder seems fine, it suffered very minimum damage compared to the piston. How can I tell for sure if its okay?

By honing out all the visible scrape marks and then checking to see if the cylinder is still in spec. The shade tree way to do that is to push a piston ring into the bore squarely with an upside down piston and check it's gap at the top, the middle and the bottom of the cylinder with a feeler gauge. the gaps should be the same and consistent with the correct specified ring gap. A set of bore mic's are better but this method has worked well for more than a century.
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Old 02-23-2013, 05:30 PM   #74063
Harry94025
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Quote:
Originally Posted by planemanx15 View Post
Thanks for all the suggestions everybody, I opened everything thing up and found the issue:









The valves were completely fine.

As you can imagine I'm pretty disturbed. Everything ran fine, even on the highway going out to the twistys. On the ride back i assume the rings expanded too much and this happened. As I said in my build thread, I did not measure the end gap. I assume had I done this, I could be riding today.
That kind of scoring happens when the oil film fails. Not sure how much engine experience you have, but are the rings positioned correctly? The compression rings are usually directional; they have a top indicated with a dot or other mark. If they were upside down, the blow-by would cause the oil film to fail.

Regards,
Harry
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Old 02-23-2013, 05:45 PM   #74064
acesandeights
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Yep
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Old 02-23-2013, 05:58 PM   #74065
jessepitt
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Quote:
Originally Posted by planemanx15 View Post
Thanks for all the suggestions everybody, I opened everything thing up and found the issue:
The valves were completely fine.

As you can imagine I'm pretty disturbed. Everything ran fine, even on the highway going out to the twistys. On the ride back i assume the rings expanded too much and this happened. As I said in my build thread, I did not measure the end gap. I assume had I done this, I could be riding today.

Dang, I guess I was being optimistic thinking it was a valve. Sorry for your misfortune.
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Old 02-23-2013, 06:12 PM   #74066
Rob.G
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Quote:
Originally Posted by Harry94025 View Post
That kind of scoring happens when the oil film fails. Not sure how much engine experience you have, but are the rings positioned correctly? The compression rings are usually directional; they have a top indicated with a dot or other mark. If they were upside down, the blow-by would cause the oil film to fail.
I remember when I did my snowmobile top-end years ago that I posted about, they told me very specifically that the rings went on a certain way and the gap had to face a certain way. I wonder if this step might have been missed in addition to proper gapping?

I'd be tempted to send the cylinder back to Jeff... he's the master of the 790.. I honestly wouldn't want to trust anybody else but him when it comes to determining if the cylinder is still good. Maybe even see if you can pay him a little extra to install and gap the rings for you before shipping the replacement parts out -- assuming they will travel okay like that.

Rob
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Old 02-23-2013, 06:29 PM   #74067
planemanx15
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Quote:
Originally Posted by Rob.G View Post
I remember when I did my snowmobile top-end years ago that I posted about, they told me very specifically that the rings went on a certain way and the gap had to face a certain way. I wonder if this step might have been missed in addition to proper gapping?

I'd be tempted to send the cylinder back to Jeff... he's the master of the 790.. I honestly wouldn't want to trust anybody else but him when it comes to determining if the cylinder is still good. Maybe even see if you can pay him a little extra to install and gap the rings for you before shipping the replacement parts out -- assuming they will travel okay like that.

Rob
I did install the rings in the correct direction. They are marked and the directions tell you which way to install them.

Jeff emailed me and offered to hone the cylinder and to purchase a new piston.

I want to personally thank him publicly on here for his generous offer. There aren't many guys like him, thank you so much!
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Old 02-23-2013, 06:37 PM   #74068
Rob.G
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Quote:
Originally Posted by planemanx15 View Post
I did install the rings in the correct direction. They are marked and the directions tell you which way to install them.

Jeff emailed me and offered to hone the cylinder and to purchase a new piston.

I want to personally thank him publicly on here for his generous offer. There aren't many guys like him, thank you so much!
Awesome! Yep, Jeff's a great guy. It was great the day I got to meet him. He gave me a tour of the shop and everything. Every time I go down there, everybody there is just tops.

So... do we know yet what the problem was? If the rings were put on the right way, was it the gap that was the culprit?

Rob
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Old 02-23-2013, 06:52 PM   #74069
planemanx15
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Originally Posted by Rob.G View Post
Awesome! Yep, Jeff's a great guy. It was great the day I got to meet him. He gave me a tour of the shop and everything. Every time I go down there, everybody there is just tops.

So... do we know yet what the problem was? If the rings were put on the right way, was it the gap that was the culprit?

Rob
My theory is that since I didn't do the ring gaps, they expanded with the heat and pressure and scoured the cylinder and piston. This created some free play and the noise that was heard was the piston not seated properly.

Any other opinions would be appreciated.
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Old 02-23-2013, 07:32 PM   #74070
procycle
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Quote:
Originally Posted by planemanx15 View Post
My theory is that since I didn't do the ring gaps, they expanded with the heat and pressure and scoured the cylinder and piston. This created some free play and the noise that was heard was the piston not seated properly.

Any other opinions would be appreciated.
I'm certain the ring gap is the cause of the problem. I just put the top end on the DR900 Stroker Motor and the top ring had about .006" gap before filing.

Performance rings are normally sized to require filing or grinding to give the desired gap. There are lots of variables that prevent the rings from being sized precisely out of the box. The ring manufacturer relies on the engine builder to adjust the gap for his specific setup.
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DR900 Big Bore Stroker buildup
TurboDiesel Corvette - go to the end to start at the beginning
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