I f***ed up my big bore and now my bike is garbage. - Page 6

ChopperCharles · 05-06-2021, 01:10 PM

Blue was on both wrist pin bosses, scraped off from the crank.

These are not air-cooled pushrod motors, this is an RX3, which has a 24 horsepower water cooled motor. A head gasket is far more critical on a water cooled motor.

I'm not willing to risk an unscheduled disassembly at 8000 rpm. A new motor is twice the price I paid for this bike. I'd like to get 30k out of this RX3 and then upgrade to whatever the new interesting lightweight adv bike is in a couple years.

Charles.

grumpyunk · 05-07-2021, 08:01 AM

I understand the critical nature for liquid cooled engines. My Super 9 is liquid cooled, and would get destroyed if coolant got to the bearings. If you were to get coolant into the cylinder, or to have gases pushed into the cooling system, that could be very destructive. Tis a different situation than the pushrod air-cooled tricycle / ATV motors in other bikes. Those are very forgiving of ill maintenance, and don't need nearly as much upper end lubrication as the OHC versions.
Hope you get some good parts soon. This is IMO an obvious manufacturer failure.
tom

ChopperCharles · 05-09-2021, 01:25 PM

Well it’s back together with the stock piston and cylinder. Started right up,
No noises or leaks. I’m about to go take it for a test ride.

Charles.

ChopperCharles · 05-09-2021, 03:13 PM

AAAaaand no problems so far! No big bore, but my bike isn't garbage! WOOOOO!!!

Charles.

pyoungbl · 05-09-2021, 06:27 PM

Glad you are back in the saddle again. Now just ride that sucker.

Jim Rogers · 05-09-2021, 09:29 PM

Been following this story both here and on advrider, but I think I've lost track of something:

You went back to the old piston and cylinder, but do you have a new head? Wasn't the original problem that started all this an exhaust valve seating problem that required a new head?

ChopperCharles · 05-09-2021, 10:47 PM

Yes I have the new head installed. That was the reason for taking it apart in the first place but I figured I’d do a big bore at the same time since it had to come apart the same amount anyways. Big bore failed but head successfully installed.

Charles.

SGCSCRX3 · 05-10-2021, 12:07 AM

Glad the bike is running. You have got me thinking about checking my valves early. Mine is at 3,000 miles still runs fine.

Jim Rogers · 05-10-2021, 06:57 AM

Quote:

Originally Posted by ChopperCharles

Yes I have the new head installed. That was the reason for taking it apart in the first place but I figured I’d do a big bore at the same time since it had to come apart the same amount anyways. Big bore failed but head successfully installed.

Charles.

Does the big bore head work with the stock cylinder, or do you also have a new stock head?

franque · 05-10-2021, 08:07 AM

It's the same head.

Skyd · 05-10-2021, 08:22 AM

I don't normally spend time in this part of the forum, I'm usually in the Dual Sport section but this caught my attention and I've been following along. I did a Big bore kit in a DRZ years ago which turned out great. Sorry you had issues but glad to see you have the bike running again.

Jim Rogers · 05-10-2021, 09:19 AM

Quote:

Originally Posted by franque

It's the same head.

Interesting. Doesn't a cylinder with an increased bore require a head with a combustion chamber bore that matches that larger cylinder bore?

I would have thought the big bore cylinder would have required a specific, matching head so the bores would match.

I also would have thought the head gasket would not work properly of the bore of the cylinder and the bore if the combustion chamber weren't the same.

franque · 05-10-2021, 09:26 AM

They use a different head gasket, but for many motorcycle motors, they just change the piston to suit the head. Sportsters are that way, too, and the CB/CG125-200 use the same heads, you just increase or decrease the dome of the piston to get appropriate squish.

It would kind of defeat the purpose of cheap displacement increases if you had to get a new head, too.

ChopperCharles · 05-10-2021, 09:49 AM

The big bore kit came with a larger diameter piston, larger cylinder, and a larger head gasket. Plus rings and wrist pin clips and other gaskets. It re-uses the stock head. There's not a huge difference, the piston is 82mm and the stock bore is 77mm. That basically means the head gasket seals 2.5mm back from where it would normally seal on the cylinder head.

Charles.

Jim Rogers · 05-10-2021, 10:39 AM

I see. Well, I'll be darned. I thought even a small mismatch in bores would have been a problem.

Learn something new every day, I guess!

Thanks for the info-- carry on and good luck with it!

05-07-2021, 08:01 AM	#77
grumpyunk Join Date: Jul 2018 Location: nw of atlanta Posts: 169	I understand the critical nature for liquid cooled engines. My Super 9 is liquid cooled, and would get destroyed if coolant got to the bearings. If you were to get coolant into the cylinder, or to have gases pushed into the cooling system, that could be very destructive. Tis a different situation than the pushrod air-cooled tricycle / ATV motors in other bikes. Those are very forgiving of ill maintenance, and don't need nearly as much upper end lubrication as the OHC versions. Hope you get some good parts soon. This is IMO an obvious manufacturer failure. tom __________________ vertical and above ground - my daily goal
	0

05-10-2021, 08:22 AM	#86
Skyd Join Date: Mar 2021 Location: New Hampshire Posts: 242	I don't normally spend time in this part of the forum, I'm usually in the Dual Sport section but this caught my attention and I've been following along. I did a Big bore kit in a DRZ years ago which turned out great. Sorry you had issues but glad to see you have the bike running again. __________________ 2020 RPS Hawk 250 - Build thread can be found here: http://www.chinariders.net/showthread.php?t=28374 "Do Wheelies and Forget your Feelies" "If vegetarians eat vegetables, what do humanitarians eat?" -unknown
	0

05-06-2021, 01:10 PM	#76
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 677	Blue was on both wrist pin bosses, scraped off from the crank. These are not air-cooled pushrod motors, this is an RX3, which has a 24 horsepower water cooled motor. A head gasket is far more critical on a water cooled motor. I'm not willing to risk an unscheduled disassembly at 8000 rpm. A new motor is twice the price I paid for this bike. I'd like to get 30k out of this RX3 and then upgrade to whatever the new interesting lightweight adv bike is in a couple years. Charles.
	0

05-09-2021, 01:25 PM	#78
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 677	Well it’s back together with the stock piston and cylinder. Started right up, No noises or leaks. I’m about to go take it for a test ride. Charles.
	2

05-09-2021, 03:13 PM	#79
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 677	AAAaaand no problems so far! No big bore, but my bike isn't garbage! WOOOOO!!! Charles.
	3

05-09-2021, 06:27 PM	#80
pyoungbl Join Date: Feb 2016 Location: Portsmouth, Virginia, USA Posts: 632	Glad you are back in the saddle again. Now just ride that sucker.
	0

05-09-2021, 09:29 PM	#81
Jim Rogers Join Date: Dec 2018 Posts: 38	Been following this story both here and on advrider, but I think I've lost track of something: You went back to the old piston and cylinder, but do you have a new head? Wasn't the original problem that started all this an exhaust valve seating problem that required a new head?
	0

05-09-2021, 10:47 PM	#82
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 677	Yes I have the new head installed. That was the reason for taking it apart in the first place but I figured I’d do a big bore at the same time since it had to come apart the same amount anyways. Big bore failed but head successfully installed. Charles.
	0

05-10-2021, 12:07 AM	#83
SGCSCRX3 Join Date: Nov 2020 Location: Wisconsin Posts: 47	Glad the bike is running. You have got me thinking about checking my valves early. Mine is at 3,000 miles still runs fine.
	0

05-10-2021, 08:07 AM	#85
franque Join Date: Nov 2017 Location: Marseille, France -> Conakry, Guinea Posts: 1,481	It's the same head.
	0

05-10-2021, 09:26 AM	#88
franque Join Date: Nov 2017 Location: Marseille, France -> Conakry, Guinea Posts: 1,481	They use a different head gasket, but for many motorcycle motors, they just change the piston to suit the head. Sportsters are that way, too, and the CB/CG125-200 use the same heads, you just increase or decrease the dome of the piston to get appropriate squish. It would kind of defeat the purpose of cheap displacement increases if you had to get a new head, too.
	0

05-10-2021, 09:49 AM	#89
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 677	The big bore kit came with a larger diameter piston, larger cylinder, and a larger head gasket. Plus rings and wrist pin clips and other gaskets. It re-uses the stock head. There's not a huge difference, the piston is 82mm and the stock bore is 77mm. That basically means the head gasket seals 2.5mm back from where it would normally seal on the cylinder head. Charles.
	0

05-10-2021, 10:39 AM	#90
Jim Rogers Join Date: Dec 2018 Posts: 38	I see. Well, I'll be darned. I thought even a small mismatch in bores would have been a problem. Learn something new every day, I guess! Thanks for the info-- carry on and good luck with it!
	0