I hope I didn't start this thread prematurely but I just got the OK from my better half to spend a good chunk of our tax return on my big bore project. I've been planning it for a long time and have slowly collected the necessary tooling. Now I can get the last few things I need.
I will be using 87mm flat top pistons from an Isuzu and making my own nodular iron sleeves. The goal isn't to make a screaming race motor. I'm actually shooting to make the same power as a stock engine, but at a much lower rpm.
The first step will be making a fixture and torque plate. Stay tuned...
Still slow going. Waiting for more parts and I have a couple other projects that I need to finish first.
Last night I removed the stock sleeves from the jugs. I had read about the oven trick (heat in oven until the sleeves fall out) but I didn't want to stink up the house and make a bunch of noise with everyone sleeping. Instead, I propped it up on the bench and warmed it up with a heat gun. It only took about ten minutes per hole. Heat until the oil residue starts smoking then one little tap and the sleeve fell right out.
I did mine in a barbecue by mistake. Was trying to dry some heat paint, heated the cylinders in the barby, and when checking found the cylinder had slipped down and was sitting on the grill grate. Sleeves extending well above the gasket surface of the cylinders. I believe the paint cure was for 250 degree and that was the temp I was trying to get too. So any body wanting to remove sleeves on your XS, get out the old barby.
PS: de-grease everything first so you don't ruin the flavor of your barby. HA HA Wife never knew.
Question; My re-phase was via a new center pin and donor crank web for a 270 crank. The 277 crank is just a pull apart and re-align the splines, so no donor parts required, nice. Could the splines be filled in and re-cut on the web to give you the same results as the pin change, but avoid the need for a donor crank and the expensive pin?
What I was meaning was to use the existing crank where the pin is part of one web already and just changing the spline in the opposite web to obtain the desired 270. Either by filling in and re-machining the spline or some kind of adapter spline arrangement.
I'm still not ready to jump into this project but figured I'd post a few more pics just to keep the thread alive.
I found some sleeves that are real close to the size I was going to make. They are "wet" sleeves from an Allis Chalmers tractor. The wall is over 5mm thick! That should alleviate the distortion issues for which big bores are know. Shown below, next to a stock sleeve.
Obviously, they will need to be shortened, and I'll have to work the flange and the OD at the bottom.
Next is a shot of the stock piston next to the Isuzu piston.
The Isuzu piston is a true flat top with no dome or dish. This can actually work when you go this big because the increased swept volume makes up for the lost dome.
The compression height is basically the same as the stock piston. I'll have to deck it a bit to get everything lined up. That's [one of the reasons] why I haven't started on this project yet, I need to get my surfacing grinder up and running first.
To get an idea of what kind of valve reliefs these flat tops will need, I chucked a junk stock piston in the lathe and faced it at the deck height.
The stock valve reliefs are actually quite generous so it would appear that I won't need any relief for the exhaust valves and shallow ones for the intake valves.
A lot of metal will be hogged out of the jugs but the sleeves will not protrude into the cam chain tunnel.
The standard convention is to press iron liners into aluminum cylinders. The cylinders provide the support and the liners provide the wear surface. What I will be doing is more like pressing aluminum cooling fins onto iron cylinders. The iron sleeves are thick enough that they won't depend on the aluminum jugs to keep them round.
Good luck to you in getting the compression any where 8 to 1 with those flat tops. Even a 85mm bore needs a generous amount of dome -16 to 20ccs due to the deep volume of the C/C. For an open chamber like the XS,.100 or + a few will be needed for 5cc reduction if my memory serves me right. On my welded up chamber for a 10cc reduction would require .100 removal. You can remove .060 from the head but not near the exhaust port,must follow the out line of the H/G. Those flat top pistons compression heights fall way short from standard by looking at your pictures. I personally don't believe you can over come this by piston bore volume alone and theoretically throwing some #s out, you might achieve a 6.2 compression but good luck to you!
The biggest problems you'll encounter with bore volumes of this magnitude will of course be over heating as there simply isn't enough meat left after machining to dissipate the heat,unless you plan on welding or machining a billet block with thicker and deeper heat fins and oil leakage based on my conversations with PJ and with his conversations from others who've tried big bores over 83mms.
I've done the math and compression will not be a problem. If I just slapped it together with zero deck height, .030" gasket and stock head it would be about 7.8:1 compression. I can easily take that up to around 8.3:1 by shaving the head or turning a small dome on the piston. The crowns on these pistons are insanely thick so I will likely just turn the pistons and leave the head alone.
r80rt: :)This is a splendid write up, THANK YOU!!!!
Dec 26, 2015 16:54:05 GMT -5
mashermoto: What the what is this shoutbox for? Or should I shout, WHAT THE WHAT IS THIS SHOUTBOX FOR!
May 12, 2016 22:22:21 GMT -5
motormike: Good Day ...just a FYI.. Wild Cat is this Labor Day weekend. Still go'n on. A few 650's still make the scene. Various rides at different skill levels each day.. awards dinner sunday eve. BS in the park'n lot after dinner.
Aug 23, 2016 7:57:01 GMT -5
lsettle: First post in over 6 years!
Aug 28, 2016 19:45:17 GMT -5
kardon: Wow quiet here, where did they all go.
Oct 7, 2016 2:18:13 GMT -5
gggGary: XS650.com LOL
Feb 16, 2017 20:49:02 GMT -5
buell88: Anybody have any idea who built the xs650 tracker used in the Draggin Jeans Ad on Pipeburn?
May 16, 2017 16:24:09 GMT -5
joshua: The regulator/rectifier unit I got from Mikes PMA has closer hole spacing than original. Are we supposed to mill the holes to fit?
Jun 7, 2017 19:25:58 GMT -5
joshua: My bad. I found the bracket they supplied to mount the rectifier/regulator... Uh oh. How is this meant to work? Which way is it meant to mount? Looks like I have to use some spacers or something. Good instructions would be nice.
Jun 7, 2017 22:09:52 GMT -5
craig8johnson: Not sure if this is the right spot or not but oh well...
Jul 11, 2017 18:04:15 GMT -5
craig8johnson: I'm checking the charging system. I'm afraid I might have fried the last battery. With the solid state regulator (after market) what should it be charging at. The book says, I think, 15 volts. I'm hitting 17 when revved. Is that too high?
Jul 11, 2017 18:06:19 GMT -5
gggGary: Yes 17 volts is too high, about 14 volts is max, sounds like you don't have the right regulator or it's wired wrong.
Jul 13, 2017 6:54:33 GMT -5
dean: Just saying Hello, new member who is going to fix up a 79 XS650 that has seen its better days. I will definitely have lots of questions coming up.
Jun 23, 2018 16:45:32 GMT -5
tt650: Trying to breathe life into a 1980 that's been stored (indoors) for 25 yrs. Air filters are dry rotted. Have cleaned carbs but she only runs briefly on choke then stops. Need jet setting info and other ideas that might help her idle and rev.
Jul 3, 2018 19:15:19 GMT -5
trix13: Hey everyone! New to the forum and am fighting those gremlins!! New charging system, ignition switch, coil and fuse box. Resistance is higher than normal on the ignition pick up so I'm trying to find one. No such luck yet.
Aug 16, 2018 8:50:48 GMT -5
trix13: Also, even though all of my connections are clean, I cannot seem to find out why , when at higher rpms, I hit the signals and the rpms pulse with the signals...hahah. same with the brake light. I appreciate all input!!
Aug 16, 2018 8:55:08 GMT -5
bob99: how do I post a question. I am new to the forum
Jun 6, 2019 10:52:10 GMT -5
adlpc: Hello all! Been enjoying your edifying posts and discussions - and as a fan of the XS650 since my early teenage years happy that I now own a 1980 Special which I plan to turn into a vintage half faired racer. Thank you all for being here!
Oct 1, 2019 0:58:56 GMT -5
jimothyj: Hello everyone, I just joined & wish would have known about this site in 2014 when I brought my 1974 TX650A back from the grave. I have spent a good deal of $$ and alot of time on it. Just painted it and working on electrical, I will post pics soon,
Apr 10, 2021 2:14:13 GMT -5
louisvan: trix13 - I had a problem with my 1975 SX650. When I got to highway speeds, the engine lost power. The problem was in the connectors. At a certain vibration and the wind pushing on the wiring loom, the connector lost continuity. A bad crimp to the wire.
May 20, 2021 1:19:09 GMT -5