I am looking for any info on a head modification that will help take away the "2 stroke ping".I was told that you had to remove some material in a certain location on the head to resolve the execessive ping these 490's have.An old motorcycle guru told me about this and now hes dead,so i cant get the details on how to do this.Any info would be great.Books,websites,people,places,something to help me find this out.Thanks
83' YZ490 Head modification(no ping mod)
- Thread starter rideblue0
- Start date
smokeyhaze
Member
- May 2, 2001
- 28
- 0
http:///www.2strokeheads.com/ can hook you up.
David Trustrum
~SPONSOR~
- Jan 25, 2001
- 1,396
- 0
Some tuners can put in anti detonation insert rings. Or you could twin sparkplug the head which would help & is easier on a aircooled bike. Machining the squish band so it is closer to the piston than std (ie in it’s effective band) will help cool the piston staving off detonation a bit. About 1mm clearance should be ok for a big sloppy single. Hmm maybe more.
But this will increase compression ratio which is going the wrong way so about a similar amount removed from the inside of the head in the same machining operation will cancel the increase. Putting a bit more angle on the squish band will reduce the MSV which should also help.
But this will increase compression ratio which is going the wrong way so about a similar amount removed from the inside of the head in the same machining operation will cancel the increase. Putting a bit more angle on the squish band will reduce the MSV which should also help.
mxbundy
Sponsoring Member
Woho,
Dont i feel smart.
Yes Al Holley is still modifing thes old bikes.In fact I meet him at last years big YROC and World vintage nationals at Glenn Helen. I have a 465 that i vintage race and he is going to do the full race mods on it. Head mods, porting and if you really want it to rip, stuff the crank.
he said he can do it all and I believe him. he did all his sons mods when he raced the 465`s and 490`s.
Holley Racing 818-349-7541
bundy
Dont i feel smart.
Yes Al Holley is still modifing thes old bikes.In fact I meet him at last years big YROC and World vintage nationals at Glenn Helen. I have a 465 that i vintage race and he is going to do the full race mods on it. Head mods, porting and if you really want it to rip, stuff the crank.
he said he can do it all and I believe him. he did all his sons mods when he raced the 465`s and 490`s.
Holley Racing 818-349-7541
bundy
EricGorr
Super Power AssClown
- Aug 24, 2000
- 708
- 1
SFO, I still do work for DGY! Back in the 80s we did tons of work on 465/490s. At the amateur nationals we consistently spanked the factory prepped Yamahas. Assuming rideblue is looking for a low cost solution, and considering its a teenage year old motorcycle, the pinging may have more to do with maintenance and wear.
Cylinder head: The head is prone to warpage. Look for black gas trails across the copper gasket. You can lapp the top of the cylinder and head to remove the warpage. I like to countersink the stud holes to prevent "mushrooming" of the stud hole that can cause a leak. Regarding the head dimensions, if you have access to a lathe with a 3-jaw chuck, you can use a spark plug mandrel available for $25 from Goodson, a large aftermarket automotive tool supplier. Then narrow the width of the squishban by adding a blend angle to the combustion chamber. The bland angle should be 30 degrees and start 8mm from the edge of the squishband.
Car jetting: That carb was a mess. We used these baseline settings for super-unleaded premium (no ehtanhol!) at 80 degrees Fahrenheit, and 40:1 with Spectro. 40 pilet, 3.5 slide, R-0 needle jet, needle in the middle clip, and a 440 main. The pilet jet, slide, and main jet are leaner than stock but the needle jet is much richer. Use stock reeds because Boyesen dual stage make the bike surge at low rpm and mimic a lean condition. Make sure that the hole in the slide is uncovered by the cable retainer and that the rubber seal in the top of the cap is in good shape. Replace the needle if it has any ridges down the length, those are wear marks caused by vibration. The slide can be filed to a 3.5mm cutaway height so you'll need to buy the R-0 needle jet, pilet and main. That will cost you under $25. DGY probably has the parts in stock Tel. (630) 971-2602
Air leaks: All the fancy head mods in the world won't help it if the engine has air leaks. Check the intake manifold for dry rotting, the left crank seal for leaks (pump gas with ethanhol causes swelling of the seal and leaks), cylinder base gasket leaks, and seal the front of the exhaust pipe with RTV high temp silicone.
Good luck
Cylinder head: The head is prone to warpage. Look for black gas trails across the copper gasket. You can lapp the top of the cylinder and head to remove the warpage. I like to countersink the stud holes to prevent "mushrooming" of the stud hole that can cause a leak. Regarding the head dimensions, if you have access to a lathe with a 3-jaw chuck, you can use a spark plug mandrel available for $25 from Goodson, a large aftermarket automotive tool supplier. Then narrow the width of the squishban by adding a blend angle to the combustion chamber. The bland angle should be 30 degrees and start 8mm from the edge of the squishband.
Car jetting: That carb was a mess. We used these baseline settings for super-unleaded premium (no ehtanhol!) at 80 degrees Fahrenheit, and 40:1 with Spectro. 40 pilet, 3.5 slide, R-0 needle jet, needle in the middle clip, and a 440 main. The pilet jet, slide, and main jet are leaner than stock but the needle jet is much richer. Use stock reeds because Boyesen dual stage make the bike surge at low rpm and mimic a lean condition. Make sure that the hole in the slide is uncovered by the cable retainer and that the rubber seal in the top of the cap is in good shape. Replace the needle if it has any ridges down the length, those are wear marks caused by vibration. The slide can be filed to a 3.5mm cutaway height so you'll need to buy the R-0 needle jet, pilet and main. That will cost you under $25. DGY probably has the parts in stock Tel. (630) 971-2602
Air leaks: All the fancy head mods in the world won't help it if the engine has air leaks. Check the intake manifold for dry rotting, the left crank seal for leaks (pump gas with ethanhol causes swelling of the seal and leaks), cylinder base gasket leaks, and seal the front of the exhaust pipe with RTV high temp silicone.
Good luck
I am going to Al's shop this afternoon--He did my wr500 . We found that the sealent in the cases was leaking and resealed with yamabond 5 i beleave it was. did the head mod, lined the transfer ports up, one was 1mm higher than the rest. We trued up the crank , one side was out 3ths the other 1.5ths. Then spot welded the crank pin so that when it kicked back would not get out again. The phone number above is right 818-349-7541--address is Holley Racing 18557 Napa Street Northridge Calif 91342--If I can help let me know. LOVE MY WR 500--Ed
