| Author | Message | ||
     Dueller |
Can't find answer in either. I'm having to remove the front head to repair a broken mount casting. While I've got it off, I might as well pull the rear and freshen them both. Couple of questions I need answered: 1. Easier to drop the whole engine first or leave it in per the manual? 2. The manual says if you're removing the front head, bring to TDC before removing the head. Do you to have to move the rear to its TDC stroke? Never worked on a 45 deg twin before so pardon me if that's a stupid question. I'm assuming this precaution is relieve pressure on the pushrods, yes? 3. While I have the thing torn down, I might as well remove cam cover and see what's going on in there and do a cut down on the cover. I've heard of problems with cam bushings getting out of line when reassembling...precautions? 4. What other maintenance/replacements do I need to consider in this routine while I have it torn down this far? Oil pump? Tensioners? Oh yeah. It's my 97 M2 beater if that helps. Thanks in advance. jim | ||
| Aaron |
1) Leave it in. Support it with a jack under the front of the shock mount. If you need to move the bike around, use a tie-down wrapped around the underside of the motor and hook it to the frame. 2) The piston position is irrelevant, and in fact, there are two TDC's and only one of them is suitable. The idea is as you stated, to relieve the pressure from the pushrods (i.e. close the valves), and you actually have to do this before you remove the rocker box, not the head. Yes, that applies to both cylinders. Pull the top off the box. Rotate the motor forward (it really helps to have a swingarm stand, then you can just put the bike in gear and bump the rear wheel around to turn over the motor) and watch the intake valve. When it closes fully, the rocker box can be removed safely. If you go too far, the exhaust valve will start to open. Do not try to position the motor between the exhaust close and the intake open ... that's overlap and there is no position there where both valves are closed. 3) When you cut down the cover, preserve the lower left alignment dowel, that'll help keep everything aligned right. Some people cut it off, but I'd leave it on. I'm working right now on a CNC program to do the cam cover cut down, if you're interested. 4) Definitely look at your oil pump drive gear, as well as the cam wear. Consider a hone & ring job, maybe even a re-bore and oversize pistons (or better yet, a 1250 kit), you're basically there. Stock base gaskets love to develop leaks, if yours hasn't already you might consider changing them out to a high quality steel gasket as a preventative measure. Ditto the head gaskets, if I were you I'd just buy a set of Cometics. Update your primary chain tensioner if you haven't already, and upgrade your rotor arrangement to the new style that has 8 bolts connecting it to the hub instead of 4, sometimes those old ones break. Consider a set of XB heads instead of trying to fix your fractured head mount. They'll work with your stock flat tops and they'll also make a bunch more power and the they're not prone to fracturing that mount like the old heads, and you'd have a squish band, which you don't have right now (your heads have a 10 degree shelf but there's no matching dome). Consider a better set of cams, stock M2's are terribly undercammed and it holds the motor back. The new SE grind (same as what the XB uses, called the "E" grind) is tailor made for XB heads, very gentle on the valvetrain, and works great. edited by aaron on May 07, 2004 | ||
| Bomber |
Aaron -- you write The new SE grind (same as what the XB uses, called the "E" grind) is tailor made for XB heads, very gentle on the valvetrain, and works great. new for XB series motor? | ||
| Dueller |
Aaron...thank you so much for yopur input. I'm truly flattered someone of your stature in the engine building world is willing to help a do it yourselfer. I hate to trouble you or sound totally stupid but...."The piston position is irrelevant, and in fact, there are two TDC's and only one of them is suitable". How do I know which one is suitable? It's my understanding from the manual you can detremine TDC on the front cylinder by virtue of viewing the mark on the timing observation hole (don't know the exact terminology). Do I place the front on its TDC, remove rocker box and head and then move to the rear and place it at TDC before removing the rocker box? Also...you say: "that's overlap and there is no position there where both valves are closed." HUH? Don't both have to be closed at some point to get compression? The head upgrades sound great, but I'm preserving my performance budget for my S1.  My apologies for being such a neophyte...thanks again for your input. After I make a mess of it, I'll just ship it to you. Thanks so much again. | ||
| Josh_ |
>How do I know which one is suitable? >Don't both have to be closed at some point to get compression You want it just after the intake closes and before the exhaust opens. This is where compression builds. Aaron was refering to the other end of the cycle when the exhaust is almost closed when the intake opens (overlap). | ||
| Dueller |
Thanks Josh...sometimes I don't see the forrest for the trees.  | ||
| Aaron |
Dueller, thanks for the kind words, but lately I feel like quite the idiot. Long story. Oh, and what Josh said (thanks Josh). Bomber ... yes, the "E" grind was introduced on the XB's, both the 9 and the 12 use it. And now it's available for XL's as well, as the new 2004 SE grind. It's the same grind, but the XB version has the keyway for the timing cup in a different place, so if you're buying a set for an XL or a Blast you want to buy the SE version. These cams have a small base circle and as such, when putting them in a pre-2004 XL you have to make sure the tappet roller follows it around the base circle. The stanchion for the tappet axle may try to hang up on the cam bushing, preventing it from coming all the way down and following the lobe when the valve is closed. Easy to clearance though. The E grind has too much lift for the stock pre-04 heads at .551, you need some springs and also to check retainer to guide clearance to use them on the older heads. But the tdc lifts are modest so valve to valve and valve to piston aren't big issues. | ||
| Bomber |
Aaron -- thanks for the data . . .. I'm assuming that a tuber (M2) would use the same physical cam as an XL, yes? | ||
| Aaron |
A domestic M2, yes ... "D" cams which came in most all 5-speed XLH1200's (except the 1200S) as well as XL883's. International M2's got the Lightning cams instead (SE bolt-in). They say "15-1", "15-2", etc on them instead of 1D, 2D ... | ||
| Bomber |
thanks, sir! |
