trent04shee Posted February 25, 2009 Report Share Posted February 25, 2009 what are the advantages/disadvantages of a milled head? im about to do a rebuild on my bike and just wondering if its worth doing since i dont have a cool head and its already apart. thanks Quote Link to comment Share on other sites More sharing options...
donkeypuncher Posted February 25, 2009 Report Share Posted February 25, 2009 milling your head increases compression, which increases bottom end power. if your not wanting to spring for a cool head, then you might as well mill your stock one. but keep in mind, the more compression you have the higher octane fuel you will have to run after a certain point. Quote Link to comment Share on other sites More sharing options...
Bill Posted February 25, 2009 Report Share Posted February 25, 2009 Shaving the head will give you more compression which will give you more torque. The only disatvatige is the higher you go in compression, the higher the octane you must use. Quote Link to comment Share on other sites More sharing options...
trent04shee Posted February 25, 2009 Author Report Share Posted February 25, 2009 alright thanks guys, im going to buy a cool head but the funds are tight right now, so i figure ill just get the head milled until i have the coin to purchase a cool head. thanks again Quote Link to comment Share on other sites More sharing options...
donkeypuncher Posted February 25, 2009 Report Share Posted February 25, 2009 alright thanks guys, im going to buy a cool head but the funds are tight right now, so i figure ill just get the head milled until i have the coin to purchase a cool head. thanks again no prob, thats what we're here for. :beer: Quote Link to comment Share on other sites More sharing options...
pinned247 Posted February 25, 2009 Report Share Posted February 25, 2009 (edited) So if I took my head into a shop how would I know what size (not sure what the proper term is) to get it milled? Is milling your head similar to resizing your domes in a cool head? Edited February 25, 2009 by pinned247 Quote Link to comment Share on other sites More sharing options...
spurdy Posted February 25, 2009 Report Share Posted February 25, 2009 So if I took my head into a shop how would I know what size (not sure what the proper term is) to get it milled? Is milling your head similar to resizing your domes in a cool head? No it is not the same. When you mill the head you change your squish clearance. The distance between the crown of the piston and the squish band of the dome. When you change domes in a cool head this distance is adjusted in the new dome. With the stock head you haven't changed the dome just the the volume by removing material from the original surface. You can have the dome re-chambered but now your getting into more more and should just by a cool head at this point unless you want the stock head (sleeper) look. I would measure the squish clearance before milling and take that into consideration for how much to mill off. I wouldn't run the squish any tighter the 0.40-0.45mm. SP Quote Link to comment Share on other sites More sharing options...
klemet banshee Posted February 25, 2009 Report Share Posted February 25, 2009 For 60 ft above sea level how much should i take off mine? Quote Link to comment Share on other sites More sharing options...
Rodneya Posted February 25, 2009 Report Share Posted February 25, 2009 Not all stock heads are the same. You need to measure the stock domes first. No point changing a 21cc stock head for 21cc coolhead domes. Rub some grease around the combustion chamber and place a piece of glass or clear perspex with a small hole through the center over the combustion chamber. The grease will seal the glass to the head. Use a pipette to fill the chamber up through the hole in the glass and the amount of water that it takes to fill the head will be the cc's of the combustion chamber. 1ml = 1cc Dont quote me on my calculations, but 30 thou mill will be about 0.25cc Quote Link to comment Share on other sites More sharing options...
RIPPEN Posted February 25, 2009 Report Share Posted February 25, 2009 Also when bumping up the compression very much its good to have/get the crank trued and welded.. RIPPEN Quote Link to comment Share on other sites More sharing options...
Rodneya Posted February 25, 2009 Report Share Posted February 25, 2009 Not all stock heads are the same. You need to measure the stock domes first. No point changing a 21cc stock head for 21cc coolhead domes. Rub some grease around the combustion chamber and place a piece of glass or clear perspex with a small hole through the center over the combustion chamber. The grease will seal the glass to the head. Use a pipette to fill the chamber up through the hole in the glass and the amount of water that it takes to fill the head will be the cc's of the combustion chamber. 1ml = 1cc Dont quote me on my calculations, but 30 thou mill will be about 0.25cc My bad. 30 thou is 0.76mm. With a 65mm bore diameter 30 thou milled off = 2.5cc Quote Link to comment Share on other sites More sharing options...
deckheight Posted February 26, 2009 Report Share Posted February 26, 2009 Yeah, that looks much better :cool: Like has already been said... Good idea to check the "before" dome volume and an especially good idea to check the "after". Then all the geometry for squish velocities has to be addressed... IMHO, you probably want to send it to someone competent who knows about these things or just get aftermarket... My bad. 30 thou is 0.76mm. With a 65mm bore diameter 30 thou milled off = 2.5cc Quote Link to comment Share on other sites More sharing options...
klemet banshee Posted February 26, 2009 Report Share Posted February 26, 2009 soo i should take .30 off for sea level and wanna stay on pump? Quote Link to comment Share on other sites More sharing options...
deckheight Posted February 26, 2009 Report Share Posted February 26, 2009 I personally wouldn't. Facing .030" without re-chambering will, in all probability, leave you w/a squish velocity that is through the roof and a compression ratio that, in all probability, is too high for pump gas. I have no idea what your starting with so I do not know what you should do, exactly. Quote Link to comment Share on other sites More sharing options...
klemet banshee Posted February 27, 2009 Report Share Posted February 27, 2009 im 147 in both cylinders at sea level and i trail ride with long straights so any recommendations? Quote Link to comment Share on other sites More sharing options...
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