xr600 head on nx650 engine

[Bert Jan]

So.. been a while

Shop is going very well, mighty busy to keep everybody happy. ran into a problem i cant get my head around though and i hope you guys can shine a light on it.
I went for a ride on an nx650 when it suddenly stalled due to oil starvation to the head.

Piston, cilinder, cam, rockers... all went bad. As its really hard to find NX parts here i also searched for XR600r parts as they seems interchangable. Now..

Lower engine is still stock. Cilinder, piston, valve-unit is XR600r, valves/rockers XR600 - upper cover is NX650. problem is bike wont start. Not even a poofh. Nothing.

Triple checked timing of cam. "T" mark on flyhweel corresponds with the two lines on cam sprocket, altough theyre a liiiitle off. (assume from chain wear, as its waaaay less then a tooth)
Valves are .10/.12mm as per manual.
cam is XR600r, with no decomp unit. (also tried the old worn NX650 cam just to see if ot would run. Nothing)
10.5bar compression.
Great suction on intake, almost sucks your hand in.
Carb has not been altered or changed, and bike ran good before oil problem.
Timing is cdi and was not altered or changed. sparks like hell. Has wasted spark btw..
Checked the little metal thingy that holds the flywheel on the crankshaft (i figured it might have snapped, giving me a false "T" mark.) Still good.

Sprayed brake cleaner into intake, nothing. let some gas into the head via the sparkplug hole. Nothing.

Took the engine apart today. Valves are still good (i lapped them before mounting) and straight, leakdown with acetone in upside down head reveals no leaks, so valves have not touched piston. tells me timing is 'kinda' ok. Last thing i thought about is the cam chain guide. The XR600r and NX650 have other reference numbers and the pics dont look the same.

Is it possible that the NX650 guide (now sitting in the XR600 cilinder) is so much different than the XR600 guide, causing timing issues being so bad that valves are not closed at TDC?
I do not have an XR600 guide to check and they're 55,- bucks. Would like to know if its the problem before ordering a useless part.

Strangest thing i've had in my shop thus far. Can't figure it out and it pissed me off haha, so please shoot the most stupid shit you come up with as it might lead to the problem!

As we have compression, spark and fuel, i'm at loss here. Prolly something utterly stupid haha

 

[Bert Jan]

So.. Still struggeling here. I've buid her up again but she's doing absolutly nothing. It's driving me nuts.

I figured, since i removed the decomp unit that the battery wasn't strong enough to kick her over and fire. Mounted a automotive battery straight to the starter so the on board battery was only there for the spark.

Nothing. If you have any idea, please shoot!

 

[DohcBikes]

I have had this problem on a different cdi controlled engine.

I know you have spark.

Are you using the nx650 cdi or the 600 cdi?

Either way, try the other one.

Even if you are convinced that the cdi you are using is correct and shows spark, it can still be malfunctioning. The way I know is because I had the exact same thing happening. The spark looked the same with either cdi hooked up, but one of them just would not run the bike.

Hope this helps. If not, its mechanical. Be sure the exhaust is clear.

 

[Bert Jan]

Thanks for your message. Thing is that the bike rode fine with this CDI before the head took a shit. I can't imagine how the CDI would die from that. Besides, this CDI is only on the bike for 500km as the old one crapped.

Thing is, the chainwheel on the cam is not perfectly alligned when flywheel is on T mark. It's off by waay less than a tooth so i assume it's off due to chainwear. It is that minimal..

I've rebuild her again but even spraying lots-o brake cleaner into the intake rubber (with carb off) causes not even a poofh. Nothing at all. Good compression, good suction. You'd say it's spark then but i have no other CDI to check and like i said, it worked fine before the oil problem..

Using the NX CDI but it was listed as a FMX/NX/XR CDI and the bike ran fine on it.

 

[DohcBikes]

Well, it's not running fine now. And no, it didnt run fine, it blew up.

You might try a different cdi. Or you might not.

 

[Bert Jan]

Well, it's not running fine now. And no, it didnt run fine, it blew up.

You might try a different cdi. Or you might not.

You know.. I've been away from this forum quite some time now, but i've never met a guy on here or in real life more up in own ass than yourself. I hope it's an internet alter-ego because you won't get far in life with such a crappy attitude. I've read some other topics you started or commented on and they all end in rage and thunder.
So.. Thanks for your -completely useless again- comment i guess, just like 90% of all the crap you type.

Oh, and good luck with that 175 frame! Bye!

 

[DohcBikes]

I said nothing inflammatory at all. You are very sensitive, Bert.

I always find it so amusing when a small time mechanic tells me I wont get far in life.

Good luck to you as well.

Anybody else care to help this wonderful gentleman?