DAS Forum für Yamaha XT600 und XT600Z

Hello to all XT enthusiasts,

I'm having a bit of issue with my '84 43F XT600L. When i rev beyond 3500RPM it makes a stuttering noise for some reason that i can't figure out. I only have been revving it up to 3500RPM just in case i don't damage anything before i'm able to solve it. It's always been the only issue with the bike ever since i purchased it. I had rebuilt the entire engine with top quality Koyo bearings, Wiseco top end kit, Cylinder head fully serviced by a local motorcycle shop, carburetor overhaul and all were double checked and adjusted prior to assembly however it's still happening for whatever reason. Any of you guys experienced this before? Is there anything critical i have missed?

Jacky.

Hi to down-under!
Did you proceede the pre-oiling-procedure? How long did it take, until Oil escaped throug the vent-screw on top of the oilfilter-cover?
Did you check piston-head-deck-clearance, (squish) and is ist not less than the necessary 1,2mm?
Did you adjust valve clearance in the compression-DTC, not in the overlap-DTC?
A soundfile could be helpful.
Cheers,
Hans

G'day

Nice to meet you Hans
Yes, i have loosened the inspection screw during the initial running after the rebuild. From what i can remember it was less than one minute before the oil sprays out.

Valve clearance adjusted at compression TDC and set at 0.10mm for the intake and 0.15mm for the exhaust.

Squish was checked prior to the head assembly and it was around 1-2 mm

One minute would have been a lot, and is often enough to let piston-rearside scuff. 10 seconds would have been better...
But there are different things that can cause noise.
The original piston has a piston-pin offset, which AFAIK Wisecos don't have. Thats noisy.
Forged pistons, as Wiseco's are, need more piston-cylinder-clearance than the original cast one.
Do you trust your cylinder-workshop?
No more ideas in the moment ...
Hans

Hello Hans,

Yes i do trust them. I worked there during my high school life and their quality of work is simply irreplaceable within my town. Oh wow i didn't know that the OEM has a piston pin offset and why it's noisier for not having the piston offset?
It does get a bit scary when starting it in a cold morning for the forged piston however it goes away quite quickly. All i can do is to use the top quality oil in the right grade. 20W-50 is what i use throughout the year.