cg250 rocker arm failure

joeb · 06-09-2024, 10:48 PM

Rocker arm fixture failed on the intake side at about 50 miles after assembly. Ali cam similar to 290 (stock lift with longer duration), Ebay roller lifters, Ali 70MM cylinder with .025" inch shaved off, Motocult thin head gasket (-.030"-ish), Motocult rocker arm spacer plate. It ran noisy from the start after initial run, I rechecked the valve lash which was still at .004". It ran great until it failed all at once while in slow speed cruse. I'm not finding any signs of valve clearance problems. Thinking that possibly the roller lifters are a different ratio causing the springs to bind or possible they are just a different geometry, anyone have any ideas.

Megadan · 06-10-2024, 12:52 AM

the rocker didn't fail, the casting of the rocker box probably just had a flaw/crack in it. The rocker is still whole and on it's shaft.

I've been running a WGK 292 duration cam for a few years now without any issues.

joeb · 06-10-2024, 10:11 AM

Quote:

Originally Posted by Megadan

the rocker didn't fail, the casting of the rocker box probably just had a flaw/crack in it. The rocker is still whole and on it's shaft.

I've been running a WGK 292 duration cam for a few years now without any issues.

Yes, no damage to the rocker itself, just the mounting. I have considered it could have been a defective part but feel like I should explore all the possibilities while I wait on parts. I dropped a push rod down into the abyss while disassembling, if I can't retrieve it with a magnet, I'm sure I will get a closer look at everything.

red2003 · 06-10-2024, 11:41 AM

You noted the engine was noisy upon starting it up (and not valve lash related). This suggests SOMETHING is making contact that shouldn't be. Could well be coil bind, and you can easily check that once you get it back together. If not, it's gotta be related to the followers. There isn't really anything else in there to make noise (unless you are mysteriously missing a bolt or socket).

Mudflap · 06-10-2024, 01:22 PM

I would have thought that the push rod would be the weakest link and would bend before the casting would break. Megadan is probably correct that it is a flawed casting. Some rocker supports are made of stamped steel instead of cast. Maybe they're stronger.

J4Fun · 06-10-2024, 02:20 PM

Just wondering after rereading post #1, is there a chance that the valves and piston made contact? Could that have been the noise from the get go and short life after changes? I’m interested too in all these changes. Just thinking out loud…

joeb · 06-10-2024, 11:27 PM

I've seen a few post about noisy roller followers ending with changing back to stock. I haven't really seen an answer as to why they were noisy.

I agree that if binding, the push rod would usually be the first to go.

I had checked valve clearance by installing light test springs on the valves, set the lash to zero, then pushed down on the valve until it touched the piston in a variety of places between 15 btc and 15 atc. the smallest was around .200", factoring the angle of the valve to the piston I'd guess that is about .140" perpendicular to the piston. If they were going to hit, I don't think they would do it until revved up high. I plan on taking a look with a bore scope anyway.

I'm taking comfort that Megadan is Megadan and I am likely looking for a problem that does not exist.

I'm having a good time experimenting with insanely cheap Chinese parts, then measuring, machining, calculating, assembling and repeating. If your concern is more the finish product than the experimenting experience, I'd say the Moto-cult kits seem to be the best deal out there.

06-10-2024, 12:52 AM	#2
Megadan Join Date: Apr 2017 Location: Omaha, NE Posts: 8,045	the rocker didn't fail, the casting of the rocker box probably just had a flaw/crack in it. The rocker is still whole and on it's shaft. I've been running a WGK 292 duration cam for a few years now without any issues. __________________ Hawk Information and Resource guide: http://www.chinariders.net/showthread.php?t=20331 2018 Hawk 250 - Full Mod list here. http://www.chinariders.net/showpost....62&postcount=1 2024 Royal Enfield Shotgun 650 https://chinariders.net/showthread.php?t=34124
	0

06-10-2024, 11:41 AM	#4
red2003 Join Date: Jan 2007 Location: Northern Vermont, USA Posts: 1,245	You noted the engine was noisy upon starting it up (and not valve lash related). This suggests SOMETHING is making contact that shouldn't be. Could well be coil bind, and you can easily check that once you get it back together. If not, it's gotta be related to the followers. There isn't really anything else in there to make noise (unless you are mysteriously missing a bolt or socket). __________________ First Chinabike: 2006 Roketa RSX200E Current Chinabikes: 2023 Titan DLX & 2022 Lifan KP Mini w/ 210cc BRT kit, 22 RWHP! Last edited by red2003; 06-10-2024 at 01:52 PM.
	0

06-09-2024, 10:48 PM	#1
joeb Join Date: Jun 2024 Posts: 3	cg250 rocker arm failure Rocker arm fixture failed on the intake side at about 50 miles after assembly. Ali cam similar to 290 (stock lift with longer duration), Ebay roller lifters, Ali 70MM cylinder with .025" inch shaved off, Motocult thin head gasket (-.030"-ish), Motocult rocker arm spacer plate. It ran noisy from the start after initial run, I rechecked the valve lash which was still at .004". It ran great until it failed all at once while in slow speed cruse. I'm not finding any signs of valve clearance problems. Thinking that possibly the roller lifters are a different ratio causing the springs to bind or possible they are just a different geometry, anyone have any ideas. Attached Thumbnails
	0

06-10-2024, 01:22 PM	#5
Mudflap Join Date: Sep 2014 Posts: 1,892	I would have thought that the push rod would be the weakest link and would bend before the casting would break. Megadan is probably correct that it is a flawed casting. Some rocker supports are made of stamped steel instead of cast. Maybe they're stronger.
	0

06-10-2024, 02:20 PM	#6
J4Fun Join Date: May 2021 Posts: 312	Just wondering after rereading post #1, is there a chance that the valves and piston made contact? Could that have been the noise from the get go and short life after changes? I’m interested too in all these changes. Just thinking out loud…
	0

06-10-2024, 11:27 PM	#7
joeb Join Date: Jun 2024 Posts: 3	I've seen a few post about noisy roller followers ending with changing back to stock. I haven't really seen an answer as to why they were noisy. I agree that if binding, the push rod would usually be the first to go. I had checked valve clearance by installing light test springs on the valves, set the lash to zero, then pushed down on the valve until it touched the piston in a variety of places between 15 btc and 15 atc. the smallest was around .200", factoring the angle of the valve to the piston I'd guess that is about .140" perpendicular to the piston. If they were going to hit, I don't think they would do it until revved up high. I plan on taking a look with a bore scope anyway. I'm taking comfort that Megadan is Megadan and I am likely looking for a problem that does not exist. I'm having a good time experimenting with insanely cheap Chinese parts, then measuring, machining, calculating, assembling and repeating. If your concern is more the finish product than the experimenting experience, I'd say the Moto-cult kits seem to be the best deal out there.
	0