1981 650 Special - hole in the pistion

DMSchuler

I'm looking for advice on replacing the piston in my Nephew's bike.

I can clearly see the hole in the piston after removing the spark plug.

I have not yet pulled the head.

What should I expect, or better what would the experts here recommend? I'd like to fix the bike for him, but want to keep the costs reasonable under control.

Can I simply drain the oil, clean out the pieces, replace the piston, and go?

Or am I looking at more?

I realize that depending on the condition of the cylinder walls once I pull the head that the game might change...

Thanks for any advice!

Doug

xsjohn

Which side has the holded piston............. xsjohn

DMSchuler

left side. closer to the outside if that matters...

xsjohn

That's a carb problem..........these set for a few years and the carbs need a good cleaning.....plus the BS34's were already horribly lean to start with....any reduction in almost no fuel will raise cain with the engine to say the least..... when you get all the trash out of the engine and back and running make sure that side is getting the fuel and no air leakes in the throttle shaft seals or the rubber intakes...... the reason I asked is that the right runs hotter than the left but in your case that didn't pan...at least yet...bet the left was seeing 300 degrees ........... the electronic ignition was not to blame except for being a bit advanced........ need to chase all that aluminum out of the engine and maybe find replacemet cylinder and pistons off ebay that might be good.......well at least thats what I would do being in that situation........... or spend a bunch........

xsjohn

DMSchuler

Thanks xsjohn. I'll look for the pistons and cylinder on ebay. I have a color tune, so I'll set it slightly rich once it's back together.

xsjohn

Keep your eyes open on ebay..............collected a few good things there myself for my future....a lot actually...most are parted long before I would even consider them broke in...... and if not what is fifty bucks......... one set of new rings to begin with maybe...... and still no real guarentee with all the machine work and crap.....just measure it.....afterwards get with me on those BS carbs...and all the rest of the setup......learned a few things there....

xsjohn

mynameismudd

i have a 81 also and blew a hole in my right piston. just bought a set a pistons on ebay from a cat on there here's his addy
stores.shop.ebay.com/m...QQ_armrsZ1
he packed them VERY well and two were only 40** maybe he'll have some or someone else might if not him.
i all so bought rings, gaskets(upper and lower) had my cylinders honed and miked, cam chain, cam chain guide bar and advanced housing unit because i broke mine trying to get the top screw out,had to buy a whole box of part from that guy. so i ordered those also. i might have missed something because i chose to do a complete tear down of everything except the bottom end of the motor. everything has been pretty damn easy. i just put all parts in zip top bags to keep in order.
hope all goes as smooth for you also Smile

BTW xsjohn i need to get with you also about my carbs also. i pm you
when i get to that point if that ok with you Confused

my name is mudd

xsjohn

I'm here..........I can help with the carbs but a hole in the piston...?...all the years with yamaha I saw few of them......like I said earlier with those lean epa carbs it wouldn't take much more leaness especially with the tci advanced like it is.........easy to retard the timing a bit.......I found it runs better too......we are on the pilot jets most of the time until we open the throtte just a bit ....and the log needles don't provide much fuel either coming off the pilots.........I like the custom 46 pilot but lately I have made a 47 ..........just have to be careful not to turn the mix screws much after they get close....like just a tweek...no 1/4 inch turns and all........checked mine and they are with the 47 at about 2 1/4 turns....46's were at 2 1/2 and were cool too....

xsjohn

mynameismudd

would it matter if i'm running the green monster from mike's? i didn't know if that higher kv rating would make a difference on top of running her lean

my name is mudd

xsjohn

Hey the stock coil has lots of volts on the tci bikes........wouldn't think that a few more would do anything but good.......pete might know better that I one that one........but the BS34 are lean ........that I can attest to for sure........the needles I make compensate for the hotter right also.....and come on from the pilots a bunch better that the stockers.....dump the stock 42.5 pilots for double sure....but with a hole in the piston I would look for an air leak especially if on the left which runs 25 or so degrees cooler than the right on a stock tci bike....and the rest of the xs's too.. god I could run 1 exit on mine 11 years ago before I gritted my teeth with all the engine racket fromthe lean ass carbs...... now I just go........... The fricken BS34's were just a gov't epa disasters........but with some work are great carbs.........capable of 55 to the gallon with medium grey plugs which I have proven......... and the gearing on these is way to low making for low throttle at high revs....recipe for disaster on the highway...........oh well.......

xsjohn

mynameismudd

well for starters, would you suggest i get different carbs maybe or how can i get those needles of your. or better yet, we live in the same state. i'll come to you and i pay you to set my carbs to an ideal performance Very Happy

well, let just start with the first two questions

xsjohn

Would be handy to know why the left was so lean.........that situation is usually just the opposite.....right being leaner and hotter at operating temperatures.....were the carbs set up ......with the mix screws exposed and the pilot circuit clean and no air leaks so we could talk straight about this and were the mix screws set half ass correct as best they can be with those tiny pilot jets (3 turns or so for the 42.5 lean pilots) so we can talk about the holed piston..........

Were the throttle shaft seals leaking air......or the carb rubber boots leaking air...or both..... ?....all improtant stuff.......where in NC are you...

mynameismudd

xsjohn wrote:

Would be handy to know why the left was so lean.........that situation is usually just the opposite.....right being leaner and hotter at operating temperatures.....

were the carbs set up
probably not i just got everything going to ride her a week and had not gotten to the carbs

......with the mix screws exposed and the pilot circuit clean and no air leaks so we could talk straight about this and were the mix screws set half ass correct as best they can be with those tiny pilot jets (3 turns or so for the 42.5 lean pilots) so we can talk about the holed piston..........

if you speaking of mine, it is the right side. it was DMSchuler who said his was the left.

probably not i just got everything going to ride her a week and had not gotten to the carbs

i'll get back to you on this when she back up so i can answer these ?'s
properly. at least to where i can trouble shoot these issues with at hand knowledge Wink

xsjohn

Right side Just saw that...........lateness of the hour and all....... ....doesn't supprise me...........get back to me........

46 pilot
custom R/L needles
135 Main jet.....

and retard that timing a bit.......... the .168 thousands I consider max.........start with 1/8"........

DMSchuler

ok gents - started the tear down tonight. Looks like I will need to remove the engine from the frame - is this correct?

any way to pull the head without taking the engine out?

mynameismudd

as tight as the motor is in the frame, i didn't even chance it and mine has been chopped. i would just go ahead and remove it to make it easier on yourself. that way you can put her on the work bench and save your back also Smile

you can look around and find a pattern for a motor stand also
well here's one so you don't have to fish.
www.650motorcycles.com/XSstand.html
here is one from 650motorcycles. any other ?'s just ask Smile

jayel

yes you have to pull the engine on a stocker, damn thing is heavy too, 160lb.? might want to find some help, altho' some people have laid them over on the side on a old tire and then picked up the frame off of it

Retiredgentleman

You don't really need an engine stand. I found that just setting the engine onto a sturdy workbench works quite well. If you remove the sump strainer plate, it makes for the perfect place to support the engine on a 2 X 4 piece of wood. It also makes it very easy to roll the engine forward onto its nose for any work on the bottom of the engine, or when re-installing the cylinders/pistons.

DMSchuler

Finally pulled the engine this morning. I'm a bit concerned about how to proceed. When I drained the oil, there was probably less than 1/2 quart. I'm not sure how far he rode it like this, but I'm guessing somewhere between 5 & 10 miles. The oil that came out feels gritty - I'm guessing that it from the piston...

I found a '79 XS650 with no title that runs - can I simply swap that engine in?

Thanks!
Doug

yamaman

Sure can buddy! Just swap the alternators over so you can keep your
TC Ignition, remove & store the advance rod/points assembly. You might find it easier to swap your carbs & inlet manifolds on to it also.
The rest is pretty much the same I think.....Get all that done in just a few hours....Go for it!

xsjohn

You can bring or send me those BS34's ........ not a biggy for me to get them right......... the 38's won't mount right to your air boxes and would require those funky pods,,,,,,,,,

You will need a rotor puller too..........

xsjohn

mynameismudd

xsjohn wrote:

You can bring or send me those BS34's ........ not a biggy for me to get them right......... the 38's won't mount right to your air boxes and would require those funky pods,,,,,,,,,

xsjohn

hey xsjohn, check your pm, thanks

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