Anyone out there have experience running a CA77 crank with a CL72 top end?
Building a spare for my flat tracker to run vintage 250 on a local short track. I'm a bit worried about balance running the lighter 250 top end on a 305cc 360 degree bottom. I don't think we will ever push it above 7500 rpm in the arena at the fairgrounds.
Thanks,
Mark
TwingleThanks G-Man. I'm gonna index CL cams and run 26MM carbs. My concern is whether or not the crank and top end are enough out of balance not to be to be ridable and/or self destruct at moderate RPM. I would like to use a CA72 crank, but I've got the 305 and I'm kinda throwing this thing together on a shoestring (out of hard-headedness not cheapedness) and this is not our #1 engine but rather a "spare" to drop in for the arena races. If it proves sucessful we'll probably build up a chassis for the #2 bike and dedicate it to the short tracks.
Thanks, Mark It evidently has been done before:
http://www.honda305.com/forums/viewtopi ... ht=twingle 66 dream, 78 cb750k, 02fz1, 09 wing
Great choice for a flat track bike. Type II motors make less top end and more moid range with the same cams etc.
I don't know enough about the CA crank, but with a CB, the 77 cranks is slightly heavier than a 72 cranks on the webs which should also be a benefit. The only issues should be balance factor and there are two ways to work that out. One is to work it out from the theory or a quicker way is the empirical method. try it and see. If vibration turns out to be really bad (which I doubt), then strip it and adjust the balance factor. Try to get the compression as high as practical to aid bottom end punch off those turns. Got the 250 twingle engine assembled and bolted in the chassis last night.
I thought I’d pass along my experience with an installing the endless cam chain while it’s still fresh on my mind. I ordered an endless Tsubaki chain and master link from Z1 with intentions to just cut and splice as usual with the head fully assembled. While I was waiting for the chain to arrive I went ahead and assembled the bottom end, less the oil pump, so that I could feed the chain around the crank after cutting. The chain arrived, I cut it as I normally do, fed it around the crank, and buttoned up the oil pump. I then went to put the master link in temporarily. That’s when I discovered that the links they supply are the rivet type, not the clip type. So I figure, no big deal, I can rivet it back together before I put the cylinder on. I rolled the engine over on its side and using a 3/8” extension as an anvil and a center punch as a staking tool, riveted this thing back together. FYI the Tsubaki chain from Z1 is a super heavy-duty chain of excellent quality with flat-sided links for around 30 bucks. I installed a set of NOS standard bore, early high compression, pistons into a re-sleeved cylinder. I cut the valve seats, lapped, and installed the valves only in the head. Brought the pistons up to TDC, placed the cam sprocket at the proper position in the chain and marked the chain with a paint marker at the timing mark. I tied the chain up so that it couldn’t jump a tooth at the crank and loose timing. Dropped the head over the studs while holding the chain up with a wire. I washered up the studs on two opposite corners and put nuts on finger tight so that I could double check the timing by turning the crank and not risk lifting the cylinder on the up stoke. Then the fun began. The cam sprocket assembly is about .030 “ too wide to slide down beside the already installed chain, but it can be made to go. Wiggle, twist, wiggle, twist, all one handed while holding pressure on the chain with the other hand so not to loose the timing. After about 5 minutes I got it in there and lined up the marks. Next thing is the cams. I had ground a tooth off of the spline on the left cam to index it 90 degrees and had checked it earlier by inserting it into the sprocket assembly. It was a little tight but did go all the way down. I started by inserting a 3/8” extension thru the right side of the head to hold the sprocket up while I tapped the left cam into the head. Got it just about to the sprocket and realized that I didn’t have the tightening bolt in the cam. Drove it back out, put the bolt in, and re-inserted it back into the head. Then I noticed that the chain was so tight that the splines were not going to line up without the sprocket being perfectly centered in the head. So I hold up the sprocket with one hand and attempt to tap in the right cam with the other hand. After about 30 minutes success, but I can’t see the splines so I can’t verify if I’m indexed correctly. I took a blind shot and was lucky. The right cam lined up and I was able to tap it into the sprocket and feel the point cam insert into the advance unit as it went home. The left cam slid right into place. I put the end covers on and torqued them down to check the side-to-side clearance. Feeling good at this point. Removed the end covers to install the rockers. What a dumb ass. Cylinder studs in the way. So then I removed all the studs, two at a time, and install the rockers. I rolled the crank over a time or two with an indicator in the right cylinder to double-check the timing. Everything spot on. Buttoned it all down, set the valves, and dropped it in the frame. As far as the endless chain goes, it can be done but it probably took me 2 hours longer than normal to assemble the top end vs. using a master link. I really like the look of these Tsubaki chains, but I don’t think I’m going to assemble another one endless. If there isn’t a clip type link available, I’m going to come up with a way to rivet it together over the sprocket. It’s a real PIA to assemble the head while trying to hold the sprocket in place with the chain and I don’t think I could have gotten the cams in with the rockers in place. Now on to bending up a set of right side exit pipes. Mark It's Alive!!!
Fired up the twingle this afternoon after a trip to the salvage yard for a 12V dual output coil. I had a terrible time trying to get the chineese CDI to fire on the bike with the KS. I could get a good spark at the bench but not trying to kick this thing so I opted for a total loss system. I also made a mistake by thinking I could use two coils with the stock dual condenser. It would produce a good spark at both plugs with a kick thru and would start the bike but only run about 10 or 12 revs and die. I didn't realize that I was putting about 10 Ohms in the system with the coils in parrallel so I guess it just couldn't keep up. The bike started first kick with the CB750 coil and would take throttle well until the slide in the right carb stuck after warming up. I always seem to have to fiddle with these carbs no matter how much I cleaning, flange surfacing, and slide fitting I do so I guess thats expected. Anyway the concerns that I had earlier with the balance issue using a CA77 crank in a CL72 engine seem to have been unwarrented. There is a bit of vibration but not anything near what I expected. I've not ridden it yet but I don't think that it's gonna self destruct from a balance issue. BTW anyone out there got experience using the 26MM carbs on a 250cc engine? The PO of the basket case I bought for this project had 26mm carbs on the engine. The main jets were 105's!! I could'nt get it to crank with them in it so I changed to 130's and really haven't run the engine enough to make a call. Thanks, Mark   [/img]
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
