I f***ed up my big bore and now my bike is garbage. - Page 4

grumpyunk · 05-01-2021, 11:44 AM

Maybe the big hammer and chisel used to fit things together at the factory made those marks... ... joking.
Most times when you pull the restraints, whatever they may be, off a cam that has a chain and tensioner, the 'far' end of the cam will want to lift from its position in the bearing support. Picture shows the cam resting without apparent chain tension trying to pull down on the sprocket and lift the other end(pivoting on close in ball bearing). I don't think that is normal. My experience, limited as it is, has been that the cam has to be pushed down on the distal end due to tensioner pushing on the chain.
All that makes me consider the tensioner not pushing on the chain or ???(something...)
The video is informative, but difficult for me at least to pause on the actual spot I want to look at closely. IOW, still images for visual inspection are a lot more handy to view, can be 'blown up' as needed, and allow easier study. Have you thought about posting a few? I know when I posted the site limited images to ~200k(if I remember) but I have seen images that are significantly larger with increased resolution. Don't know how to post them, but they are helpful when inspecting for 'things'.
Have you pulled the head off yet? Is that planned? One thing you can do with the followers removed is pull the plug and crank the engine over, listening for 'the sound' you get when running. You KNOW the valves are closed, so won't have any interference there, so any noise would be from something else. Maybe do that, and post on y'tube.

tom

ChopperCharles · 05-01-2021, 12:32 PM

The engine doesn't spin fast enough on the starter to make the sound, either with the rockers installed or without.

Charles.

ChopperCharles · 05-01-2021, 02:48 PM

While what you say is true for some cams, it's not true for this one. Cams that exhibit that rocking will have both bearings on the inside of the sprocket, and the sprocket itself will be cantilevered. Therefore, without the cam covers those cams will pop up on one side from the tensioner's pressure. The RX3's cam however has a bearing supporting the outside of the camshaft, and the sprocket is therefore not cantilevered. This means the cam chain tensioner pulls the entire cam straight down, and there is no way for either end to pop up unless the tensioner is released.

I do plan to pull the head if indeed there is nothing wrong here. Which sucks because I only have the one (installed) head gasket for the big bore kit.

Charles.

grumpyunk · 05-02-2021, 10:15 AM

You are surely correct. I blame old age.

Given you cannot reproduce the sound at lower rpms, there must be an explanation. What changes with rpms? Only thing that comes to mind, offhand, is the CR. It could be moving around, though it should not. The heavy end of the arm on the side of the sprocket should keep it firmly in place, extended if you will, with the spring-load trying to move the mechanism in the other direction fully overcome.
Other things that come to mind are the sprocket on the crankshaft and the tensioner mechanism. The sprocket is likely a press fit on the crankshaft, not held on by the flywheel, but surely prevented from wiggling around by the flywheel being bolted firmly in place. The spring load on the tensioner should press the guide against the chain. It could allow the guide to wiggle if the tensioner spring load was not enough or the guide was out of place. I assume one end of the guide is held in a 'pocket' that allows deflection, but does not allow more movement than that. It can rock back and forth to move and apply pressure to the chain, but one end is a pivot, the other end free to move in a slight arc.
What else is there? I figure you didn't mess with the oil pump and other 'bottom end' stuff. Only things fiddled with would be the chain, guides, tensioner, and the cylinder head 'stuff'.
Is it possible the spring on the CR is not tensioned enough? Some could require more than one 'wrap' of the spring in the tension setup. IOW, one wrap of the spring will apply X force. Go around another turn, and the force is higher, thus tending to keep the CR from moving as the rpms increase. Was it taken apart when doing the installation?
tom

ChopperCharles · 05-02-2021, 06:57 PM

No I didn’t take the compression release apart at all, nor did I do any other unnecessary disassembly. I took the left side cover off to make sure the front cam guide was in place and the crankshaft sprocket was firmly attached AFTER the noise occurred. And it’s all properly in place. Tensioner has a nice bit of tension too, and releasing it and reinstalling had no effect.

Charles.

grumpyunk · 05-03-2021, 10:23 AM

Went back and listened to the first vid. Knowing what's inside, and all you have reported, the sound became an oscillation of something that was quiet until you revv'd the engine. Past a certain rpm, you get the sound.
My internal video imagination system came up with a CR that is flopping back and forth due to a weak spring. It is fine to xxx rpm, but can't restrain past that point.
I realize centrifugal force should keep the CR pinned in place, but I still think it is oscillating, perhaps due to pulsations in the rpm that a human cannot discern.
I can think of nothing else internal that has been pictured.
What parts were replaced when doing the BB install? Still using the same set of cam followers? I don't know what they look like.
I will try to think of what else could be rpm-dependent.... that could have been replaced or adjusted...
tom

TxTaoRider · 05-03-2021, 11:51 AM

That auto decompresser looks like the ones used on the ktm rfs motors, and it's true that they'll knock like crazy if the idle drops below about 1400rpm on those, but it goes away by just idling up a little. On those the spring has hardly any tension on the arm. I doubt that's the problem with this engine.

ChopperCharles · 05-04-2021, 12:05 AM

Well, I believe I have definitively found the problem.

I took the head off, and inspected the valves. I didn't see any evidence of contact at all.

So I rotated the crank and looked at the cylinder. No evidence of wear or any markings whatsoever.

Then I took the cylinder out, and noticed two bright shiny areas on the crank. So on a whim I rotated the crank while holding the piston centered. Once it got to the bottom of the stroke... it BOUND UP ON THE CRANK.

I removed the piston and there is wear on the piston too. I measured the distance from the wrist pin hole to the bottom of the piston, and it's 0.104" larger on the big bore piston.

Charles.

ChopperCharles · 05-04-2021, 12:06 AM

So now my question is: Is that rod supposed to be discolored like that? I don't remember what it looked like when I took it apart the first time. I don't feel play in the rod bearing, but I'm concerned by the coloring.

Charles.

SGCSCRX3 · 05-04-2021, 04:21 AM

Glad you found the problem. I'm not expert just been following this and actually learning some things about this engine. I hope you can just clean up the bottoms of those pistons and put it back together and give it a go.

Emerikol · 05-04-2021, 08:27 AM

The rod is likely tension stressed from getting stretched out when the bottom of the piston contacted the counterbalancer. With the rod at the opposite end of the crank throw, and the counterbalancer all the way up, there would have been incredible mechanical advantage trying to pull that rod apart. It probably got pretty toasty with those types of stresses on it. I would start by carefully filing down some clearance in the counterbalancer, and then use a set of jewelers files to clearance the bottom of the piston. Not sure about the rod, though. It's a cast unit, which means it will take a generous helping of abuse, but at the same time, all those casting imperfections could be where a failure starts and propagates through the rod, leaving you with a very high speed, high energy, unscheduled engine disassembly, if you know what I mean. If you can get a new rod, I would think replacing it would be the best way to go. If you can't, maybe try to find a machine shop that can inspect it and reheat/temper/anneal it for you. If you can't find any of that, I would clean it up, put it back together, and be very careful with the first couple of heat cycles when you start riding it again. There's my two cents' worth, hope it helps!

ChopperCharles · 05-04-2021, 10:08 AM

Well, I’m actually going to from the seller instead. I did buy it from a US-based seller, so hopefully he will stand by it. Also hopefully he has a good one. I will need all new gaskets and you can’t buy the big bore head gasket separately, which is why I dragged my feet about taking it apart until I was sure it wasn’t a top end thing.

Charles.

pyoungbl · 05-04-2021, 10:52 AM

Remember that the NC250 has a pressed crank. That's why CSC does not sell rods, only a crank/rod assembly. Given the stress indicated on this rod I'd be hesitant to use it. If in stock the crank/rod assembly is $165 from CSC.

ChopperCharles · 05-04-2021, 11:05 AM

Damn. No individual rods. Well that sucks.

HOWEVER, looking on aliexpress, I'm seeing that new crank/rod assemblies are discolored just like mine.

https://www.aliexpress.com/item/32825891307.html

If I can get a piston and gasket I'll just put it back together and hope for the best.

Charles.

Working_ZS · 05-04-2021, 11:16 AM

Quote:

Originally Posted by ChopperCharles

So now my question is: Is that rod supposed to be discolored like that? I don't remember what it looked like when I took it apart the first time. I don't feel play in the rod bearing, but I'm concerned by the coloring.

Charles.

The rod is fine, check out AliExpress for a picture of a new crank and rod assembly - it's identical to yours, with the same discoloration down around the big end, signifying heat treatment:

https://www.aliexpress.com/item/4000...archweb201603_

What was most likely happening was the skirt on the piston flexing and giving way each time it contacted the engine case. This makes it highly suspect to me. Either thoroughly inspect the existing piston for cracks, or junk it and start again, with either a new kit or the stock piston and cylinder. If it were me, I would go the latter route and put it back to stock. This big bore kit does not impress me one bit, and I would not waste any more time or money on it. My two cents, take it for what it's worth.

05-01-2021, 11:44 AM	#46
grumpyunk Join Date: Jul 2018 Location: nw of atlanta Posts: 169	Maybe the big hammer and chisel used to fit things together at the factory made those marks... ... joking. Most times when you pull the restraints, whatever they may be, off a cam that has a chain and tensioner, the 'far' end of the cam will want to lift from its position in the bearing support. Picture shows the cam resting without apparent chain tension trying to pull down on the sprocket and lift the other end(pivoting on close in ball bearing). I don't think that is normal. My experience, limited as it is, has been that the cam has to be pushed down on the distal end due to tensioner pushing on the chain. All that makes me consider the tensioner not pushing on the chain or ???(something...) The video is informative, but difficult for me at least to pause on the actual spot I want to look at closely. IOW, still images for visual inspection are a lot more handy to view, can be 'blown up' as needed, and allow easier study. Have you thought about posting a few? I know when I posted the site limited images to ~200k(if I remember) but I have seen images that are significantly larger with increased resolution. Don't know how to post them, but they are helpful when inspecting for 'things'. Have you pulled the head off yet? Is that planned? One thing you can do with the followers removed is pull the plug and crank the engine over, listening for 'the sound' you get when running. You KNOW the valves are closed, so won't have any interference there, so any noise would be from something else. Maybe do that, and post on y'tube. tom __________________ vertical and above ground - my daily goal
	0

05-02-2021, 10:15 AM	#49
grumpyunk Join Date: Jul 2018 Location: nw of atlanta Posts: 169	You are surely correct. I blame old age. Given you cannot reproduce the sound at lower rpms, there must be an explanation. What changes with rpms? Only thing that comes to mind, offhand, is the CR. It could be moving around, though it should not. The heavy end of the arm on the side of the sprocket should keep it firmly in place, extended if you will, with the spring-load trying to move the mechanism in the other direction fully overcome. Other things that come to mind are the sprocket on the crankshaft and the tensioner mechanism. The sprocket is likely a press fit on the crankshaft, not held on by the flywheel, but surely prevented from wiggling around by the flywheel being bolted firmly in place. The spring load on the tensioner should press the guide against the chain. It could allow the guide to wiggle if the tensioner spring load was not enough or the guide was out of place. I assume one end of the guide is held in a 'pocket' that allows deflection, but does not allow more movement than that. It can rock back and forth to move and apply pressure to the chain, but one end is a pivot, the other end free to move in a slight arc. What else is there? I figure you didn't mess with the oil pump and other 'bottom end' stuff. Only things fiddled with would be the chain, guides, tensioner, and the cylinder head 'stuff'. Is it possible the spring on the CR is not tensioned enough? Some could require more than one 'wrap' of the spring in the tension setup. IOW, one wrap of the spring will apply X force. Go around another turn, and the force is higher, thus tending to keep the CR from moving as the rpms increase. Was it taken apart when doing the installation? tom __________________ vertical and above ground - my daily goal
	0

05-03-2021, 10:23 AM	#51
grumpyunk Join Date: Jul 2018 Location: nw of atlanta Posts: 169	Went back and listened to the first vid. Knowing what's inside, and all you have reported, the sound became an oscillation of something that was quiet until you revv'd the engine. Past a certain rpm, you get the sound. My internal video imagination system came up with a CR that is flopping back and forth due to a weak spring. It is fine to xxx rpm, but can't restrain past that point. I realize centrifugal force should keep the CR pinned in place, but I still think it is oscillating, perhaps due to pulsations in the rpm that a human cannot discern. I can think of nothing else internal that has been pictured. What parts were replaced when doing the BB install? Still using the same set of cam followers? I don't know what they look like. I will try to think of what else could be rpm-dependent.... that could have been replaced or adjusted... tom __________________ vertical and above ground - my daily goal
	0

05-03-2021, 11:51 AM	#52
TxTaoRider Join Date: Oct 2020 Location: Flower Mound Texas Posts: 904	That auto decompresser looks like the ones used on the ktm rfs motors, and it's true that they'll knock like crazy if the idle drops below about 1400rpm on those, but it goes away by just idling up a little. On those the spring has hardly any tension on the arm. I doubt that's the problem with this engine. __________________ 2021 Tao Tbr7 - "Lucille" Mods so far- Brozz swingarm, 21" front rim (Bridgestone Tw302 rear/Dunlop D606 front tires), Digital gauge cluster, pz30b pumper carb, after market hand guards, aftermarket brake and clutch levers, round fold away mirrors, Fly handlebars shortened slightly, 13t front sprocket 2009 Q-link Legacy 250 1982 Suzuki GS1100ES - "Jolene"
	0

05-04-2021, 08:27 AM	#56
Emerikol Join Date: Oct 2016 Location: Carrollton, GA Posts: 1,467	The rod is likely tension stressed from getting stretched out when the bottom of the piston contacted the counterbalancer. With the rod at the opposite end of the crank throw, and the counterbalancer all the way up, there would have been incredible mechanical advantage trying to pull that rod apart. It probably got pretty toasty with those types of stresses on it. I would start by carefully filing down some clearance in the counterbalancer, and then use a set of jewelers files to clearance the bottom of the piston. Not sure about the rod, though. It's a cast unit, which means it will take a generous helping of abuse, but at the same time, all those casting imperfections could be where a failure starts and propagates through the rod, leaving you with a very high speed, high energy, unscheduled engine disassembly, if you know what I mean. If you can get a new rod, I would think replacing it would be the best way to go. If you can't, maybe try to find a machine shop that can inspect it and reheat/temper/anneal it for you. If you can't find any of that, I would clean it up, put it back together, and be very careful with the first couple of heat cycles when you start riding it again. There's my two cents' worth, hope it helps! __________________ First Rule of Aviation: -Never Pass Up The Opportunity to Pee I was struggling to get my wife's attention; I sat down on the couch and looked comfortable. That did the trick! My wife says I only have two faults. I don't listen and something else... If at first you don't succeed, try doing it the way I told you to... The Stable: 2005 Yamaha V-Star 650 - SOLD 2015 Suzuki DR 650 2015 RPS Hawk 250 - SOLD 2016 Ural Gear Up
	1

05-01-2021, 12:32 PM	#47
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 683	The engine doesn't spin fast enough on the starter to make the sound, either with the rockers installed or without. Charles.
	0

05-01-2021, 02:48 PM	#48
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 683	While what you say is true for some cams, it's not true for this one. Cams that exhibit that rocking will have both bearings on the inside of the sprocket, and the sprocket itself will be cantilevered. Therefore, without the cam covers those cams will pop up on one side from the tensioner's pressure. The RX3's cam however has a bearing supporting the outside of the camshaft, and the sprocket is therefore not cantilevered. This means the cam chain tensioner pulls the entire cam straight down, and there is no way for either end to pop up unless the tensioner is released. I do plan to pull the head if indeed there is nothing wrong here. Which sucks because I only have the one (installed) head gasket for the big bore kit. Charles.
	0

05-02-2021, 06:57 PM	#50
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 683	No I didn’t take the compression release apart at all, nor did I do any other unnecessary disassembly. I took the left side cover off to make sure the front cam guide was in place and the crankshaft sprocket was firmly attached AFTER the noise occurred. And it’s all properly in place. Tensioner has a nice bit of tension too, and releasing it and reinstalling had no effect. Charles.
	0

05-04-2021, 12:05 AM	#53
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 683	Well, I believe I have definitively found the problem. I took the head off, and inspected the valves. I didn't see any evidence of contact at all. So I rotated the crank and looked at the cylinder. No evidence of wear or any markings whatsoever. Then I took the cylinder out, and noticed two bright shiny areas on the crank. So on a whim I rotated the crank while holding the piston centered. Once it got to the bottom of the stroke... it BOUND UP ON THE CRANK. I removed the piston and there is wear on the piston too. I measured the distance from the wrist pin hole to the bottom of the piston, and it's 0.104" larger on the big bore piston. Charles.
	1

05-04-2021, 12:06 AM	#54
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 683	So now my question is: Is that rod supposed to be discolored like that? I don't remember what it looked like when I took it apart the first time. I don't feel play in the rod bearing, but I'm concerned by the coloring. Charles.
	1

05-04-2021, 04:21 AM	#55
SGCSCRX3 Join Date: Nov 2020 Location: Wisconsin Posts: 47	Glad you found the problem. I'm not expert just been following this and actually learning some things about this engine. I hope you can just clean up the bottoms of those pistons and put it back together and give it a go.
	0

05-04-2021, 10:08 AM	#57
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 683	Well, I’m actually going to from the seller instead. I did buy it from a US-based seller, so hopefully he will stand by it. Also hopefully he has a good one. I will need all new gaskets and you can’t buy the big bore head gasket separately, which is why I dragged my feet about taking it apart until I was sure it wasn’t a top end thing. Charles.
	0

05-04-2021, 10:52 AM	#58
pyoungbl Join Date: Feb 2016 Location: Portsmouth, Virginia, USA Posts: 632	Remember that the NC250 has a pressed crank. That's why CSC does not sell rods, only a crank/rod assembly. Given the stress indicated on this rod I'd be hesitant to use it. If in stock the crank/rod assembly is $165 from CSC.
	0

05-04-2021, 11:05 AM	#59
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 683	Damn. No individual rods. Well that sucks. HOWEVER, looking on aliexpress, I'm seeing that new crank/rod assemblies are discolored just like mine. https://www.aliexpress.com/item/32825891307.html If I can get a piston and gasket I'll just put it back together and hope for the best. Charles.
	1