"extra" oil gallery jets only to the LH side. Why?

[650Skull]

Here is a link to XSJohn and his oil main bearing solution.
http://650rider.com/index.php?name=Forums&file=viewtopic&t=1120&highlight=oil%20restrictor

An interesting comparison on different sized oil holes in the main bearings on different years.

Will not be be held responsible for any waffle you have to sift through to find his info

 

[TwoManyXS1Bs]

gggGary, those conrod mods were for the big end. All I could find on the little end was the cross drilling mod on MMM's site.

Looking at your piston & rod pics in your other thread, my first observations were about the severe scuffing on the front of the piston of the overheated rod. Looks like it may have experienced an overheat seizure there.

That front part of the piston and cylinder area is a punishment zone. During downstroke, the piston is slipping down a freshly oiled cylinder. During upstroke, the piston is moving over a freshly cleaned and scraped cylinder. Hopefully, sufficient oil is splashing thru the oiling holes just below the oil ring to lube the cylinder on this upstroke.

From BDC, to about halfway up, the piston is experiencing extreme acceleration, and the angularity of the conrod causes a forward thrust vector on the cylinder in that zone, up to several hundred pounds at high rpms, skyrocketing even higher at more rpms.

The shorter the conrod, the greater this angle, and the higher this 'sidewall thrust'.

As the piston/cylinder friction increases in this zone, the greater conrod force needed to overcome it, which increases the sidewall drag, requiring even more conrod push, and the whole thing just compounds from there.

That's why most blown engine post-mortems show severe piston-front wear, or cylinder fronts punched-out by the conrod.

Egads, am I rambling again...?

 

[gggGary]

OK thanks 2m, Yeah no way of knowing what all went on in the distant past of this engine as normal the engine was grime encrusted from oil leaks so who knows what if any maintenance had been done. ?This motor was torched out of the frame, cam MIA. Like you have posted, these were sometime use up, throw away, bikes One reason I stay away from 600 class sport bikes. Mostly abused and abandoned by know-nothings. Skull I'll clean and get a couple shots of 75 cranks will be interesting to see.

 

[Gibson]

Hello folks, it is in fact the alternator side that generates the most heat, believe it or not. Many of the manufacturer's of air cooled two stokes from this era learned that timing on alternator cylinder on two stroke multis would not tolerate as much timing advance, and would always be the side that seized first due to this phenomena. Our XS motors, as far as the bearing architecture are sort of built similar to two strokes.

 

[gggGary]

Hello folks, it is in fact the alternator side that generates the most heat, believe it or not. Many of the manufacturer's of air cooled two stokes from this era learned that timing on alternator cylinder on two stroke multis would not tolerate as much timing advance, and would always be the side that seized first due to this phenomena. Our XS motors, as far as the bearing architecture are sort of built similar to two strokes.

That's the conventional wisdom, but XSJohn tested and showed the RH cylinder ran hotter on the XS650, I am not sure if his testing was done over several or many engines. He even went so far as to machine and sell a slightly richer RH jet needle since ~90% of road time is on the needles.

I "believe" I have seen evidence of the sidestand factoring into engine wear pattterns on a couple of engine designs. I observed the Honda twin cam 4s, 80-83 would show cam lobe wear on the RH side, maybe from dry lobes on start up. The low LH side lobes were fine. The Hondas had a RH alternator.

 

[gggGary]

more case pics need to get years on some.

 

[gggGary]

More

 

[gggGary]

Maybe you haven't seen enough yet?







OK I'm done for now. Be glad to have help sorting this a bit!

 

[TwoManyXS1Bs]

*whew*, that's a lotta case pics. Interesting about the variations in the gallery jetting.

And terrifying.

Not just to sort out the differences, but the reverse engineering, the 'whys', and the 'what if I...'.

Makes me wonder, has anyone ever sought-out any of the old Yamaha factory engineers, or workers, to find some 'behind the scenes' info (or coverups and secrets) for the XS's???

 

[gggGary]

I need to order some floats anyways I'll chat up micheal Morse on this see if he knows any thing. Gary hoos might be able to weigh in also? Race builders and all that.

MM makes the comment; if the copper is gone the rod will soon be seeking daylight!

Kinda sorta related; rebuilders bend sportster rods to line up the pins. Someone put three full twists in a sporty rod to show they can take a bit of bending. Sporty's have brass bushings in the rod ends they press in and ream fresh bushings every so often.

 

[Gibson]

Just goes to show, there are good ways to do things, and better ways. It was a learning process for Yamaha. No CAD then. Just good ok seat of the pants engineering. It's all good.

 

[TwoManyXS1Bs]

I'd like to make one of these, to hopefully save some 256 rods.

 

[5twins]

Ummmm, OK, what is it?

 

[TwoManyXS1Bs]

Ummmm, OK, what is it?

.......Whoops! Sorry. Wrong pic. That's a gauge for measuring the small end ID.

Meant to post this, small-end hone:

Friend of mine has a rod honing machine, similar to mrriggs machine, but in bad shape.
Rather than fix it, I'd just rig up a way to use a 22mm sizing hone on 256 rods, cleanup the small end. Then, gauge the hole with some custom gauge dowels, and nickel plate the small end ID back to 22mm.

Just another of 'blue sky' pet projects...

 

[mrriggs]

Friend of mine has a rod honing machine, similar to mrriggs machine, but in bad shape.

Sounds JUST like my machine. Seriously though, all the precision work is done by the mandrel and stones. The machine just spins the mandrel. A clapped out machine will do just as good a job as a fancy new machine as long as the mandrel and stones are true.

Rather than fix it, I'd just rig up a way to use a 22mm sizing hone on 256 rods, cleanup the small end. Then, gauge the hole with some custom gauge dowels, and nickel plate the small end ID back to 22mm.

Just another of 'blue sky' pet projects...

It's a whole lot easier to get a slightly larger wrist pin and hone the rods and pistons to match. I honed my 447 rods to fit Harley wrist pins. An oversize 22mm wrist pin may not be as common but a quick Google search found this possibility. http://www.jepistons.com/Products/868-2250-15-PSC.aspx

I was advised to add 0.0005" to the small end clearance when running steel-on-steel.

 

[mrriggs]

On the subject of the right side running hotter... I put thermocouples under the spark plugs to monitor head temps. Going down the road, the left and right ran at exactly the same temp. When stopped at a light the left side would cool more than the right.

 

[NONclow]

Sounds JUST like my machine. Seriously though, all the precision work is done by the mandrel and stones. The machine just spins the mandrel. A clapped out machine will do just as good a job as a fancy new machine as long as the mandrel and stones are true.

This is my setup....mounted on a vintage Sansui stereo cabinet

 

[NONclow]

Back to the topic at hand.

.....I wonder how many PO's warmed these things up on the sidestand?????.....

 

[TwoManyXS1Bs]

...It's a whole lot easier to get a slightly larger wrist pin and hone the rods and pistons to match. I honed my 447 rods to fit Harley wrist pins. An oversize 22mm wrist pin may not be as common but a quick Google search found this possibility. http://www.jepistons.com/Products/868-2250-15-PSC.aspx

I was advised to add 0.0005" to the small end clearance when running steel-on-steel.

Now, THAT'S definitely worth researching. Thanx for the link.

My understanding of the small end clearance was simply to allow an easy drag-fit assembly/disassembly, since automotive type pressure or heat-shrink fit isn't practical or recommended on 'captured' conrods. More research......

 

[TwoManyXS1Bs]

...This is my setup....mounted on a vintage Sansui stereo cabinet

Youse guyz have all the toys.

Vintage Sansui stereo cabinet?

I wasn't aware that good acoustics was part of the process...