Cut a piece of metal with a taper. Slide it in until it's wedged. Mark that point, pull it out and measure where it contacted. Maybe?
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xs750 build step by tedious step, "build-along" with me
- Thread starter billy icon
- Start date
I installed Mikes 5th gear overdrive, but I also bought the matching pinion gear to go with it. So far it's been a great mod. Would recommend you buy both gears if going this route. Some have had real issues with the 5th gear overdrive, but I carefully measured it prior to installing to make sure it was a well engineered gear with no manufacturing defects.
Edit: should have read the rest of your thread before posting. I was also concerned whether the dogs would mesh properly. Thus why I also purchased the matching pinion gear.
Last edited:
billy icon
test pilot,gunnie pig, and all around experiment
corect me if im wrong but the "other gear" you can by from mikes xs, is 5th gear mainshaft, IT is not he gear that sits nex door to 5th gear overdrive, it does have dogs on it but they do not enter into 5th overdrive, zI belive the reason people buy the second gear is to have the gear teeth that mesh together both be from the "same manufacturer ...
speeking of that I was going to take some close up photos of the two gears meshing , photos from the side to see tooth engagment, bot with the factory 5th and with the mikes 5th overdrive gear..
Ive built a few car manual transmissions before and I belive that the gears actually "swipe" eachother on the mating surface alo more then we think they do, "gear meshing" isnt so much "meshing to gether as it is sliding off one another... ..
and I do question the quality of the "meshing surface on the mikes gear, its very "dull" where as the factory gears are a mirror shine smooth, I was actually thinking about polishing the mikes gear somehow..
billy icon
test pilot,gunnie pig, and all around experiment
some amazing info about cams and valve clearances on xs 650 aw crap that sidnt work
maybe this link will
http://www.smedspeed.co.uk/tech.html#top_anc
these guys are outa britan
XS650 CAMS
The XS650 has relatively recently gone through quite a rebirth, although its popularity in the late 80s and 90s waned, with the interest in vintage Japanese bikes at an all time high, it is only right and proper that the best Japanese twin made should be at the height of this interest.
There are a whole host of improvements available for these bikes and there are many manufacturers worldwide who will provide parts and services to keep these twins alive. I supply a few of them, rephasing is one of the best known current modifications. There is an upgrade for almost every part for the bike that is “evolution”. These bikes, like every commercial enterprise, were built to a price and some of the design reflects this. However, now many have the luxury of an attentive owner who is quite willing to improve the original design by spending money on quality upgrades.
One of the improvements possible, although not one often addressed , is cam shaft replacement. The XS650 camshaft was never a performance item; its design brief would have called for good fuel economy, ease and cheapness of production and reasonable power for an engine of its type. Recently I set up a dial gauge and measured the valve lift, measured against crank rotation. I have done this dozens of times to check what the valve is actually getting lifting, compared to what the cam vendor or manufacturer states.
What I found was quite a revelation to me. I was fully aware that cam design along with everything else has taken huge leaps forward since 1968/9 when these engines were on the drawing board. The cams in an XS650 both early and late styles lift the valve of the seat very slowly.
These are the figures for the inlet valve lift measured at degrees before top dead centre (BTDC)
Inlet valve lift
Degrees BTDC
0.002
93 BTDC
0.004
71 BTDC
0.006
49 BTDC
0.040
11 BTDC
0.050
7 BTDC
Similarly the inlet valve closing after top dead centre ATDC
Inlet valve lift
Degrees ATDC
0.050
43
0.040
47
0.006
77
0.004
95
0.002
122
If the inlet valve tappet clearance is set at 0.002 the overall inlet cam timing event is 93+180+122 = 395 degrees, if the tappet clearance is opened up to just 0.006 then the inlet cam event total is 49+180+77 = 306 degrees.
The late XS650 stock cam holds the valve off its seat for nearly 45 degrees before it actually lifts more than 0.005; this is just wasting power, and compression.
Setting the intake valve clearance at .006" versus .002" means you have lost 89 degrees of the valve opening event. (44 degrees on the intake opening side and 45 degrees on the intake closing side) It won’t lose you any flow or power however, as the valve was only a couple of thousandths of its seat.
The intake valve is just loitering off the valve seat but is still open when it could have opened 44 degrees later, and closed 45 degrees earlier, allowing for greater dynamic compression, and more time for the valve to lose its heat through the valve seat. There is no flow advantage with the slow opening and closing rates that leaves the valves open for 89 degrees a few thousandths off the seat except burned valves, lost mixture and compression.
The early Yamaha XS650 ( XS1, XS2 etc) had tappet clearances of 006" and .012" for the intake and exhaust respectively. It’s one of the reasons the earlier engines perform better, they do have a slightly wilder camshaft (not much) but most of the increase in compression comes from just keeping the valves shut longer .
Setting valve clearances to the LATE stock cam specs just contributes to reversion and lost compression with these antique slow cam lobe opening and closing rates.
The design of the cam echoes the “cooking model” cams of the British bike industry, but as Yamaha engineers had no previous four stroke experience what else could they copy err…. benchmark.
I have checked stock and performance cams from the opening to the closing in thousandths per degree every 10° of crank rotation, just to check cam profiles. Most of the newer design (non symmetrical) cams open the valves faster than they close them, but both rates are very much faster than the old style cam designs of the past. Computer modelling cam profiles helps in this area.
The late XS650 cams set at .002" intake tappet setting is ridiculous. I can’t think of another OHC engine with valves this size that has such small clearances, the camshaft has a run-out of over 0.002 in many cases and setting the tappets to this small clearance will allow the valve to stay open perpetually. It is an effort by Yamaha to reduce engine noise, but this is not the way to do it.
I set all the tappet clearance at the early settings of 0.006 and 0.012. It allows in more oil, and allows for a generous growth in the metal parts, remember….. A loose tappet is a happy tappet.
BACK TO TOP
maybe this link will
http://www.smedspeed.co.uk/tech.html#top_anc
these guys are outa britan
XS650 CAMS
The XS650 has relatively recently gone through quite a rebirth, although its popularity in the late 80s and 90s waned, with the interest in vintage Japanese bikes at an all time high, it is only right and proper that the best Japanese twin made should be at the height of this interest.
There are a whole host of improvements available for these bikes and there are many manufacturers worldwide who will provide parts and services to keep these twins alive. I supply a few of them, rephasing is one of the best known current modifications. There is an upgrade for almost every part for the bike that is “evolution”. These bikes, like every commercial enterprise, were built to a price and some of the design reflects this. However, now many have the luxury of an attentive owner who is quite willing to improve the original design by spending money on quality upgrades.
One of the improvements possible, although not one often addressed , is cam shaft replacement. The XS650 camshaft was never a performance item; its design brief would have called for good fuel economy, ease and cheapness of production and reasonable power for an engine of its type. Recently I set up a dial gauge and measured the valve lift, measured against crank rotation. I have done this dozens of times to check what the valve is actually getting lifting, compared to what the cam vendor or manufacturer states.
What I found was quite a revelation to me. I was fully aware that cam design along with everything else has taken huge leaps forward since 1968/9 when these engines were on the drawing board. The cams in an XS650 both early and late styles lift the valve of the seat very slowly.
These are the figures for the inlet valve lift measured at degrees before top dead centre (BTDC)
Inlet valve lift
Degrees BTDC
0.002
93 BTDC
0.004
71 BTDC
0.006
49 BTDC
0.040
11 BTDC
0.050
7 BTDC
Similarly the inlet valve closing after top dead centre ATDC
Inlet valve lift
Degrees ATDC
0.050
43
0.040
47
0.006
77
0.004
95
0.002
122
If the inlet valve tappet clearance is set at 0.002 the overall inlet cam timing event is 93+180+122 = 395 degrees, if the tappet clearance is opened up to just 0.006 then the inlet cam event total is 49+180+77 = 306 degrees.
The late XS650 stock cam holds the valve off its seat for nearly 45 degrees before it actually lifts more than 0.005; this is just wasting power, and compression.
Setting the intake valve clearance at .006" versus .002" means you have lost 89 degrees of the valve opening event. (44 degrees on the intake opening side and 45 degrees on the intake closing side) It won’t lose you any flow or power however, as the valve was only a couple of thousandths of its seat.
The intake valve is just loitering off the valve seat but is still open when it could have opened 44 degrees later, and closed 45 degrees earlier, allowing for greater dynamic compression, and more time for the valve to lose its heat through the valve seat. There is no flow advantage with the slow opening and closing rates that leaves the valves open for 89 degrees a few thousandths off the seat except burned valves, lost mixture and compression.
The early Yamaha XS650 ( XS1, XS2 etc) had tappet clearances of 006" and .012" for the intake and exhaust respectively. It’s one of the reasons the earlier engines perform better, they do have a slightly wilder camshaft (not much) but most of the increase in compression comes from just keeping the valves shut longer .
Setting valve clearances to the LATE stock cam specs just contributes to reversion and lost compression with these antique slow cam lobe opening and closing rates.
The design of the cam echoes the “cooking model” cams of the British bike industry, but as Yamaha engineers had no previous four stroke experience what else could they copy err…. benchmark.
I have checked stock and performance cams from the opening to the closing in thousandths per degree every 10° of crank rotation, just to check cam profiles. Most of the newer design (non symmetrical) cams open the valves faster than they close them, but both rates are very much faster than the old style cam designs of the past. Computer modelling cam profiles helps in this area.
The late XS650 cams set at .002" intake tappet setting is ridiculous. I can’t think of another OHC engine with valves this size that has such small clearances, the camshaft has a run-out of over 0.002 in many cases and setting the tappets to this small clearance will allow the valve to stay open perpetually. It is an effort by Yamaha to reduce engine noise, but this is not the way to do it.
I set all the tappet clearance at the early settings of 0.006 and 0.012. It allows in more oil, and allows for a generous growth in the metal parts, remember….. A loose tappet is a happy tappet.
BACK TO TOP
billy icon
test pilot,gunnie pig, and all around experiment
check out the above link, further down on the page he discussed the gearbox, and yamaha changerd tooth shape for better meshing in 78,
mikes xs gear is sold for 73 to 84 so hmmmmm what shape tooth did they use, I belive this is why some people have needed the matching 5th from mikes,
so my next post will have photos with all these questions answered and more lol
mikes xs gear is sold for 73 to 84 so hmmmmm what shape tooth did they use, I belive this is why some people have needed the matching 5th from mikes,
so my next post will have photos with all these questions answered and more lol
That's correct. Sorry, been awhile since I built the engine. I just remember buying the two gears to ensure proper meshing of the cogs and gear teeth.
billy icon
test pilot,gunnie pig, and all around experiment
Im working on a post with info on 5th gear overdrive, I have 4 factory 5th gears, all of themm have the lines machined into the ends of the teeth, 3 have 2 lines and 2 have one line, but all look to be the same tooth "shape" I belive I do not have any 74 to 78 5th gears , that has yet to be detirmined, BUT I can say so far none of these 4 factory gears have the same shape tooth as the mikes xs gear, very diferent in tooth shape, now is that because mikes used the 74 to 78 factory tooth desighn, or does mikes have there own "PROprietary" tooth desighn, lol doubt it, either way the mikes xs gear does not mesh well with the factory mainshaft 5th... thats where were at so far kids
billy icon
test pilot,gunnie pig, and all around experiment
I thought I would pause from all the 5th gear stuff for a bit and bore out my cyl. the 83mm boring tool says 70 rpm, so I set to drill to slow.
billy icon
test pilot,gunnie pig, and all around experiment
the crosshatching came out perfect and the bore is just right.
Probably why Mike's "highly recommends" buying their matching gear....
Tell me that this IS just a joke, right? You didn't seriously do a free-handed bore job did you?
If you can bore the cylinder out with that free handed than you are a machine my friend.
billy icon
test pilot,gunnie pig, and all around experiment
billy icon
test pilot,gunnie pig, and all around experiment
oh man, im still crackin up, thank you jim, its been a ruff week, and I needed to have a good laugh ....
and no boys and girls, I didnt Bore it out by hand, I got the cyl back from the machine shop yesterday, it has the perfect piston skirt to cly wall clearance of .0025 and the new rings now have the ring gap of .008 sweetness, i dont have to file the ring gap atol...
and no boys and girls, I didnt Bore it out by hand, I got the cyl back from the machine shop yesterday, it has the perfect piston skirt to cly wall clearance of .0025 and the new rings now have the ring gap of .008 sweetness, i dont have to file the ring gap atol...
billy icon
test pilot,gunnie pig, and all around experiment
i will be returning to 5th gear info soon, but I wanted to share this
ING END GAPS
The Old Skool philosophy of gapping piston rings said the end gaps on second compression rings could be tighter because the number two ring is not exposed to as much heat as the top ring. The current perspective says it’s better to open up the second ring gap 20 to 30 percent so pressure doesn’t buildup between the rings and cause the top ring to lose its seal at high rpm. The result is better compression, better piston cooling and reduced oil consumption.
For XS650 engines running 80mm pistons (750 cc size) a top ring end gap of .004″ per inch of bore diameter is often recommended for stock or performance work.
That translates into a top ring end gap of between .012″ to .013″. But this may vary depending on the power output of the engine.
For oval or track racing, the recommended end gap is somewhat larger (.0045″ per inch of bore diameter). With an 80mm bore, that would be an end gap of .014″ to .015″.
Getting rid of the end gap altogether can also improve sealing, cooling and horsepower. Gapless rings eliminate the gap between the ends of the ring by overlapping slightly. Gapless rings are available in popular sizes with various wear-resistant face and side coatings. Total Seal make excellent rings for this application, but probably only for racing; I ran them on a street Harley for years though.
ING END GAPS
The Old Skool philosophy of gapping piston rings said the end gaps on second compression rings could be tighter because the number two ring is not exposed to as much heat as the top ring. The current perspective says it’s better to open up the second ring gap 20 to 30 percent so pressure doesn’t buildup between the rings and cause the top ring to lose its seal at high rpm. The result is better compression, better piston cooling and reduced oil consumption.
For XS650 engines running 80mm pistons (750 cc size) a top ring end gap of .004″ per inch of bore diameter is often recommended for stock or performance work.
That translates into a top ring end gap of between .012″ to .013″. But this may vary depending on the power output of the engine.
For oval or track racing, the recommended end gap is somewhat larger (.0045″ per inch of bore diameter). With an 80mm bore, that would be an end gap of .014″ to .015″.
Getting rid of the end gap altogether can also improve sealing, cooling and horsepower. Gapless rings eliminate the gap between the ends of the ring by overlapping slightly. Gapless rings are available in popular sizes with various wear-resistant face and side coatings. Total Seal make excellent rings for this application, but probably only for racing; I ran them on a street Harley for years though.
billy icon
test pilot,gunnie pig, and all around experiment
and this,.. for those loosing patience with my build, I believe the assemble will be beginning soo, I want to make some oiling mods to the pistons, and the small end oiling jets for the rods, and such,,, its kind of funny I was just going to assemble this a as a budget engine build, and I have never been on any forums until this one , and I love to teach because you learn even more when you are attempting to teach ( Not saying I know it all)... but the long story short is ....as for me I have found doing this build on a thread has been as much fun as the mechanical part of the build and it has promoted me to give this engine all the bells and whistles, and as the title says (step by tedious step) meaning I want to measure ANY thing than can be, and check ALL tolerances that can be, and then even some that may not normally be considered, .....and with some patience and a little love I will end up with the best version of a 750 I can.... Im not building this engine because I want more power (its nice) but im building it because I love to do this stuff, I love to modify engines, my favorite part is buying a really expensive part and the drilling or grinding on it, (usualy as a bystander looks at me like Im crazy) lol
wanted to share this about timing
WHY A MODIFIED ENGINE REQUIRES TIMING CHANGES
A standard engine has to run acceptably well over a wide range of operating conditions, but still has to deliver good economy and flexibility. Consequently the engine is tuned to give good low down performance and will use conservative ignition timing and fuel settings. It also has to cope with occasional poor quality fuel and changes in altitude changes (not in the UK) that can affect the engines behaviour.
A highly tuned engine generally is not designed to give good performance below 1800-2200 RPM and indeed below this level, the volumetric efficiency of the engine is affected. The more extreme the cam profile, the worse this situation becomes. This means that the effective cylinder filling (volumetric efficiency) at lower RPM could be poorer than with a standard engine. The cylinder filling is affected to such an extent that the effective compression ratio is lower than the static or calculated ratio. To offset this the tick-over or retarded ignition timing should be advanced. The less dense mixture requires more time to burn, hence the change.
The engine speed at which maximum advance is reached also needs to be later for a highly tuned engine, say 3500-3800 RPM. However due to the higher compression that tuned engines use, which increases the speed of the burning fuel air mixture, it needs to have less overall full advance, typically 3-4 less than the specified 38 BTDC of the stock engine.
wanted to share this about timing
WHY A MODIFIED ENGINE REQUIRES TIMING CHANGES
A standard engine has to run acceptably well over a wide range of operating conditions, but still has to deliver good economy and flexibility. Consequently the engine is tuned to give good low down performance and will use conservative ignition timing and fuel settings. It also has to cope with occasional poor quality fuel and changes in altitude changes (not in the UK) that can affect the engines behaviour.
A highly tuned engine generally is not designed to give good performance below 1800-2200 RPM and indeed below this level, the volumetric efficiency of the engine is affected. The more extreme the cam profile, the worse this situation becomes. This means that the effective cylinder filling (volumetric efficiency) at lower RPM could be poorer than with a standard engine. The cylinder filling is affected to such an extent that the effective compression ratio is lower than the static or calculated ratio. To offset this the tick-over or retarded ignition timing should be advanced. The less dense mixture requires more time to burn, hence the change.
The engine speed at which maximum advance is reached also needs to be later for a highly tuned engine, say 3500-3800 RPM. However due to the higher compression that tuned engines use, which increases the speed of the burning fuel air mixture, it needs to have less overall full advance, typically 3-4 less than the specified 38 BTDC of the stock engine.
Perfection takes time; I can say that I am not losing interest in your build. I have been building mine for almost two years now. And does it suck when your waiting for the bike to be running? You bet your bottom dollar it does, but nothing is more satisfying then knowing you were the creator of a unique motorcycle. Sure you could buy a contemporary mass produced motorcycle for around the same price you will spend creating your own, but what is the fun in that. Not only is it more satisfying for yourself, but people notice it more than a common bike they see all the time.
billy icon
test pilot,gunnie pig, and all around experiment
yes yes 
billy icon
test pilot,gunnie pig, and all around experiment
i love wathcing this guy work
