skillet

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  1. The con rods are the same...the problems with combining cylinders and heads from different models stems from different size head bolts. I tried tapping the XL cylinder to 9mm from 8mm, but the bolt length is considerably different. this is still not a big problem, but be very precise when machining the dowel pin holes to 12mm. If you don't get them exact, your head will not sit correctly on the cyclinder. See this thread: http://www.thumpertalk.com/forum/showthread.php?t=472106 It's very doable to combine top and bottem ends, but it's never as straight forward as it seems, even though all these RFVC engines are VERY similar. Crmc33 knows lots about this stuff. For more info on the differences between all the RFVC engines (GB, XR, XL, NX, XRL) do a search for GB500 FAQ on google and the first page that comes up explains it all.
  2. Back to working on project again. We all know that the xr600 and xr650L are VERY similar. So when I saw a 102mm xr600 sleeve on fleabay, I got it. Well, it's actually 100mm. Anyway, my machinist pressed out the L sleeve and went to put in the new sleeve and it's just a wee bit small. You can't see the difference, but it "drops" in the cylinder with no interference fit. Guess it makes sense now but they looked the same before. Anyway, if someone needs a NEW LA Sleeve sleeve 100mm (3mm over) for an XR600, let me know.
  3. Someone correct me if I'm wrong...It's a common misconception that advancing the ignition automatically gives more power. The GB500 timing allows the piston to actually travel further before igniting the fuel/air mixture - meaning the mixture is compressed more. In high revving engines, there is an advantage to advancing the ignition, i.e. firing the plug further away from TDC because it takes some time for complete combustion and the piston is traveling at high speeds. But in a slow moving thumper piston, it seems that there could be an advantage to this situation. The mixture is more compressed and the piston/crank is 10 degrees closer to TDC before ignition. Bigger bang? The downside is the consideration of detonation and all the damage that can do. If you're already using a high compression piston, there could be a problem without high octane gas. The GB500 ran a stock ratio of 8.9:1 I believe. When I used to race 650 Hawks, power was better if you could retard the ignition some. Iginition Advance is not always and automatically better.
  4. Has anyone tried a GB500 CDI in the XR650l? It's basically the same engine and electrical system. The full advance on the 600r and 650L are about the same from what I can find 29-33 BTDC, just a difference in curve. But that GB500 is 10 degrees retarded, has a higher rev limit I think and likely a different curve:excuseme: Could the answer be so simple? From GB500 FAQ Honda RFVC CDI boxes CDI part # idle advance full advance MG3-003 6 BTDC below 1200 31 BTDC at 4000 - XR500R MK6-671 8 BTDC below 1200 21 BTDC at 4000 - GB500 MG2-871 11 BTDC below 1200 31 BTDC at 4000 - XL600 MG2-891 11 BTDC below 1200 31 BTDC at 4000 MG2-892 11 BTDC below 1200 31 BTDC at 4000 Model bore stroke XR600 98mm 80mm (long stroke motor) GB500 92mm 75mm (short stroke engine) XL600 100mm 75mm (NZ, Australian model) XR650L (NX650) 100mm 82mm (longer stroke again) (NX650 also called Dominator)
  5. Anyone know of an aftermarket manufacturer for the valve adjustment caps for the XR600/650? I've seen some that are taller and are finned to provide better head cooling:confused: , but have had no luck finding even just the stock ones except OEM.
  6. A little diggin' revealed the head bolt problem. The XL600 used 8mm head bolts and the XR650L and NX650 used 9mm head bolts. It seems the dowell pins are different too - 10mm vs 12mm, which of course makes sense. Guess I'll just tap the cylinder for the 9mm head bolts. Hope this helps anyone trying to use the 100mm XL600 cylinder to Big Bore their XR600 or GB500.
  7. UPDATE - Not sure if Honda used different size head bolts on the XL600 or if the previous owner of this XL cylinder heli-coiled it. Long story short. I got the XL cylinder bored for the 102mm JE Piston, slapped on the cylinder and piston. Went to stick my new Eric Gorr head on top and the darn Head bolts will not thread into the cylinder! Different size dowell pins and everything! Guess I'll resleeve the original cylinder.
  8. Hmmm...I can see putting the XL head on, but not the XR cam in the XL. I only say that because I had a Megacycle XL Race cam that came with an NX650/XR650L engine that was in parts. I could not figure out how that cam was supposed to work with the XR head. Finally I realized that it was an XL cam (stamped 148-x12). The guy had just thrown it in with some of the other stuff because he did not have a use for it. I'm sure it's possible, but it seems like it would be more cost effective to just buy the proper head/cam configuration. Out of curiosity, why the XL head on the XRL?
  9. Nummie - I let you know how the swap goes. As far as the cams, they are not interchangeable. The XL cam is longer and the journals are spaced differently. They will not come close to fitting. Are use going to use one of those RS600 pistons? For 17.00 it's hard to go wrong.
  10. Thanks, I'll be more clear. The motor is a XR650L. I'm not trying to shrink the displacement at all. Both the XL600 and the XR650L are 100mm bores stock. The XL has a shorter stroke at 75mm vs. the XRL of 82mm. I am aware of the inability to swap pistons between the XL, XR, and XRL, but interestingly, I can find no measurable difference in the sleeves of the XRL and XL. The only reason I'm considering using the XL cylinder instead of the XRL one is that ithe XL is in better shape - no chipped or bent fins. Plus the fact that it is a full pound lighter is always nice when you're building a custom bike. I'll check with the guys at XRsonly to be sure. Thanks, and I'll post the result for anyone interested - sometimes XL cylinders are easier and cheaper to find than XRL or NX650 ones.
  11. Trying to decide if the XL600 and XR650L cylinders are interchangeable. I'm going to be boring for oversize piston. The sleeve lengths are the same, as well as the length from the bottom of the sleeve to the bottom of the cylinder. The only difference I can see is the smog ports and the XL600 cylinder is 1 lb lighter on my high tech trusty bathroom scale. Any thoughts?
  12. If that piston is indeed for the 600, you'll have problems. As the stroke increased on the RFVC motors, Honda "hid" the extra length in the wrist pin to piston top distance because the rods are all the same length. It's easier to do this than make a bunch of new cylinders and rods, etc. So if you use a 100mm piston for an XR600 on an XR650L, you'll definitely have issues with compression to say the least. More like kiss your head goodbye.
  13. If it came from XRs Only, then I would assume it would be right. You can tell by unscrewing the little bugger just like you would a main jet (only much smaller). It has tiny (hard to read) numbers stamped on it like you see on any other jet. But if it came from them, it should be fine. This is just a common issue for carbs bought on eBay and such.
  14. Is that a Mikuni flatslide set up for XR's or is it one that came off a Harley? The air screws are very different. That's the little one on the air filter side carb near the outisde of the "cone". If you don't have the right air screw, you'll never get it dialed in right.
  15. I would double check that they are interchangeable. I think that the journals are spaced differently. Doesn't the XL cam have those "worm gear" threads in the middle? I have what I understand to be an XL600 cam and it will not fit in my XR head. By the way, it's a Megacycle Full Race cam ( high lift, etc.) and is available on eBay. Maybe I'm wrong, but I'm almost positive they are not interchangeable. I wish they were, it's an awesome cam for my use.